Dissertations / Theses on the topic 'AlGaInAs'

This thesis investigates different material systems and processing technology for high temperature compatible laser diodes used in volume applications within the 1.3-μm telecom wavelength window. Laser diodes built from such materials are much desired in order to eleminate the need for active temperature control needed in current systems, which significantly increases both complexity, size and cost. The structures were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) and the evaluation of materials was performed using different characterization methods such as High-Resolution X-Ray Diffraction (HR-XRD), Photoluminescence (PL), Time-Resolved Photoluminescence (TR-PL). Fabrication and evaluation of Fabry-Perot lasers with different geometries was used to check the material quality and temperature performance. A novel in-situ etching technique was developed for the use i future more advanced, buried hetrostructure lasers. The first studied materials system was AlGaInAsP/InGaAsP/InP. To handle a 5-element material with the precision required, modelling of the materials and heterostructure properties was performed. The addition of Al to the InGaAsP barrier allows better electron confinement with little change in valence band properties. The optimum aluminium content was found to be about 12%. Although the effect of Al could be identified, it was not sufficient with T0 of only 90 K only up to 60 °C. A second materials system InGaP/InAsP/ InP initially looked quite promising from a materials and quantum well design point of view but encountered severe problems with the device integration and further work was discontinued. The main effort was therefore was devoted to a third materials system: AlGaInAs/AlGaInAs/InP. This material system is not unknown but has hitherto not found a widespread application for fibre optic applications. In this work, the MOCVD growth of 1.3 μ;m quantum well laser structures was optimized and ridge waveguide laser devices with excellent temperature performance was fabricated (T0 = 97 K at 85 °C). A ridge waveguide laser was identified as suitable structure since it requires only a single epitaxial growth, thus avoiding the main problem of oxidation of Al based buried structures. The dynamic performance was excellent up to 110 °C and the device fabrication is highly reliable (lifetime >7000 h). This high yield uncooled ridge Fabry-Perot laser process has now been transferred to production and is applied in short length 10 Gb/s multimode links. In order to further improve the usefulness of the Al-containing materials in even higher performance devices needed in future applications developments towards fully buried heterostructure device geometry were also pursued. To overcome difficulty of oxidation of Al containing layers at the mesa walls an in-situ etching technique was implemented. Different chemistry approaches were investigated and the first results of lasers devices were reported.
QC 20100930

The rise of photonic integration makes optical code division multiple access (OCDMA) worth revisiting due to its promising role in future all-optical networks. OCDMA has the potential to exploit the surplus bandwidth of optical fibres and to carry over to the optical domain the benefits seen CDMA radio communication systems, such as the effective sharing of the spectrum for multiple network subscribers, and resistance to jamming and eavesdropping. One of the major requirements for the deployment of OCDMA in networks is integration. This thesis presents a research study of integrated OCDMA systems using the AlGaInAs/InP semiconductor material system. This material is considered due to its useful intrinsic properties such as thermal stability, strong electron confinement, and low threshold, making it suitable for fabricating optoelectronic devices. Two bespoke OCDMA systems are considered for integration: coherent temporal phase coding (TPC), and incoherent wavelength-hopping time-spreading (WHTS) OCDMA systems. TPC systems are excellent for high speed communications due to their static en/decoding enabling features. In this research, a 2×2 asymmetric Mach Zehnder interferometer (AMZI) is used to generate a 2-bit phase code, allowing multiplexing for up to four users. A semiconductor mode-locked ring laser is also embedded in the circuit, and using a synchronous mode-locking method, adequate signal en/decoding is achieved. WHTS systems on the other hand fully exploit the spectral and temporal space available in networks by assigning each user with a unique wavelength-time hop sequence for en/decoding data signals. Here, a mode-locked laser array is used with intracavity distributed Bragg reflectors (DBRs) for spectrally tuning each laser, and a 4:1 multimode interference coupler is used to combine the laser signals into a single channel for amplification, modulation and transmission. The integrated system is fully characterised and synchronisation experiments are performed to show the potential for its use in high speed multi-user networks. Mode-locked lasers play an important role in many OCDMA implementations due to their wide spectrum and discrete temporal properties, which can be easily exploited during data en/decoding. Various mode-locked laser devices have been studied during this research with additional embedded components such as intracavity DBRs and phase controllers for precise tuning of the wavelength and pulse repetition frequency. However, the noisy nature of passively operating mode-locked lasers make them prone to high jitter, which can result in high bit error rates. Synchronisation schemes are thereby explored in order to temporally stabilise the pulse oscillations to make them suitable for use in long haul transmission systems. This includes synchronous and hybrid mode-locking, as well as a passive technique using an optical fibre loop to provide phase feedback, which is shown to promote ultralow RF linewidths in mode-locked lasers.

In this thesis, monolithically integrated photonic devices for next generation optical telecommunications networks were investigated, namely semiconductor modelocked ring lasers and Mach-Zehnder interferometers operating at 1550 nm. Fabricated on the aluminium quaternary, the 2.3mm long passively mode-locked ring devices produced 1 ps pulses at a repetition rate of around 36GHz. It was found that the symmetrically placed dual saturable absorber configuration lead to the largest area of stable mode-locking, agreeing well with theoretical predictions in the literature. Optical harmonic injection mode-locking was found to improve the pulse timing stability, with a reduction in the radio frequency 3 dB linewidth from 1.4MHz down to 108 kHz, indicating a vast improvement in timing jitter. The sputtered SiO2 quantum-well intermixing technique allowed for the realisation of both symmetric and asymmetric arm length Mach-Zehnder interferometers, which were demonstrated as an electro-optic switch, tunable wavelength filter and optical code division multiple access encoder/decoder. The work concluded with the monolithic integration of a mode-locked ring laser and asymmetric Mach-Zehnder interferometer to demonstrate a simple, yet effective, photonic integrated circuit.

Ces materiaux quaternaires algainas et les ternaires limites gainas et alinas sont elabores par epitaxie par jets moleculaires sur substrat de phosphure d'indium. Les diffusions sont realisees en utilisant la technique de la boite semi-fermee et elles sont caracterisees par profilometre electrochimique (polaron) et par sonde ionique (sims). On etudie experimentalement le mecanisme de diffusion du zinc dans gainas et on determine un mecanisme intersticiel-substitutionnel. Ensuite on expose l'utilisation de la diffusion dans le procede de fabrication des transistors bipolaires a heterojonction

Nous avons effectue, sur des superreseaux gainas/algainas accordes en maille avec des substrats inp, des mesures de photoluminescence, photocourant, photocourant-voltage et photoluminescence-excitation. Nous avons mis en evidence les echelles de wannier-stark relatives aux etats 1s et 2s de l'exciton lourd, permettant ainsi une determination precise de son rydberg, ainsi que les echelles relatives au trou leger et a l'etat excite du trou lourd. Cette derniere transition est permise par le champ electrique qui brise la symetrie miroir du potentiel du superreseau. Les mesures de photoluminescence ont mis en evidence, a basse temperature, le piegeage des excitons sur les rugosites d'interface avec une energie moyenne de 3,1 mev. La photoluminescence a mis en evidence deux autres caracteristiques. D'une part des fluctuations de l'energie de la transition optique fondamentale ; cet effet est important et peut etre represente par une distribution gaussienne avec un ecart type de 6 mev. D'autre part des variations importantes de rendement radiatif avec la temperature et la longueur d'onde d'excitation ; cet effet a ete rapproche d'une propriete generalement admise des atomes d'aluminium d'induire des centres de recombinaison non radiative. En conclusion les superreseaux etudies, malgre la complexite des alliages qui les constituent (alliage ternaire dans les puits, quaternaire dans les barrieres), presentent des structures electroniques fines

Le développement des réseaux d'accès multi-longueur d'onde à 10 Gb/s fait apparaître un besoin pour des composants achromatiques bas-coûts. L'utilisation d'un modulateur électro-absorbant intégré avec un amplificateur optique à semiconducteurs est une solution qui permet de répondre à la fois aux critères de débits, gain d'insertion, achromacité, athermalité et insensibilité à la polarisation. Le modulateur amplifié fonctionne dans un schéma réflectif et ne nécessite donc qu'une seule fibre optique.
L'épitaxie sélective en phase vapeur est utilisée afin d'intégrer monolithiquement le modulateur et l'amplificateur. La technique permet une variation spatiale et locale des épaisseurs des couches épitaxiéees au voisinage d'un masque diélectrique sélectif. Le
matériau définissant la zone active consiste en un empilement de puits quantiques à base de matériaux AlGaInAs. Les épaisseurs et les compositions définissant l'empilement sont déterminées afin d'obtenir l'insensibilité à la polarisation et d'appliquer un décalage
spectral entre le modulateur et l'amplificateur. Ce dernier point optimise le gain d'insertion du composant intégré puisque la position spectrale du pic de gain est décalée dans la zone de modulation. L'analyse et l'interprétation des spectres en réflexion du modulateur amplifié démontrent l'intérêt de ce décalage spectral. Le comportement dynamique à haut débit montre des pénalités négligeables sur la puissance reçue en fonction de la longueur d'onde et de la température. Les résultats obtenus illustrent l'intérêt du composant pour les réseaux d'accès passifs mais aussi pour d'autres applications à plus haut débit.

Ce travail s'articule suivant deux axes : - l'étude des propriétés de transport des électrons dans le canal du transistor, pour laquelle a été développée une méthode originale de mesure d'effet hall différentiel sur biseau. Cette étude a conduit a l'emploi de couches tampons en algainas pour séparer le canal du substrat inp semi-isolant. - la réalisation de transistors à effet de champ utilisant un contact de grille métal semi-conducteur. L'obtention de très faibles courants de fuite nécessite l'emploi d'une barrière en alinas entre la grille métallique et le canal en gainas. Les transistors a transconductance élevée (200 ms/mm pour une longueur de grille de 1 mu m) présentent des fréquences de coupures élevées (206 hz)
GainAs Field Effect Transistors: improvements of the transistor behaviour with AIGalnAs/GalnAs heterojunctions. This work includes two parts:-a study of the electron transport properties in the FET channel: for that purpose, an original differential Hall method has been developed. This study led to the incorporation of AIGalnAs buffer layers in order to avoid the proximity of the semi-insulating inP substrate. - the fabrication of field effect transistors using a metal semiconductor gate contact. Ln order to obtain very low gate leakage currents, a thin AllnAs barrier layer has been added in between the gate metal and the GainAs channel layer. High transconductances - 200 mS/mm for 1 micron gate length - have been measured. Moreover, MAG cutoff frequency above 35 Ghz were obtained

L'objet de ce travail est la conception et la realisation de photodiodes a avalanche a multi-puits quantiques a eclairage lateral pour les telecommunications optiques. Ces photodiodes permettent d'obtenir des produits gain-bande eleves et d'envisager la realisation de photorecepteurs tres sensibles et fonctionnant a 20 gbit/s. Les couches sont epitaxiees par jets moleculaires. Les epaisseurs de la couche d'absorption et d'avalanche ont ete definies par la resolution des equations de courants dans les differentes zones. Les resultats ont abouti a des produits gain-bande simules situes entre 130 ghz et 170 ghz. La zone de transition, permettant la repartition des champs electriques dans les zones d'avalanche et d'absorption, a ete definie en resolvant l'equation de poisson. L'etude du champ electrique et de la capacite a permis de determiner une zone de transition graduelle non dopee, intercalee entre deux fines zones dopees p. L'optimisation des couches de confinement est necessaire pour realiser des structures multimodes a forte sensibilite. Les calculs des modes guides et de la sensibilite (autour de 0,9 a/w) ont abouti a des structures dissymetriques, simplifiant ainsi les etapes technologiques. La methode modale a ete validee par des calculs de puissance propagee (bpm) et par des calculs des modes guides en complexe, mettant en evidence l'influence des metallisations de contact sur la dependance de la sensibilite a la polarisation. Les differentes etapes technologiques ont ete mises au point, en particulier les etapes de gravure. Le nitrure de passivation sert egalement de couche anti-reflet. La technologie developpee est simple, reproductible et permet une caracterisation des composants directement sur tranche. Les composants realises ont donne des performances a l'etat de l'art. Les mesures de bruit ont permis de determiner des gains allant jusqu'a 30 et des facteurs d'exces de bruit inferieurs a 4 pour m=10. Les frequences de coupure, superieures a 20 ghz, conduisent a des produits gain-bande superieurs a 165 ghz. Les sensibilites de 10 a/w mesurees prouvent, pour la premiere fois, la faisabilite de photodiodes a avalanche sensibles et rapides. Ces caracteristiques, etablissant un nouvel etat de l'art dans le domaine, font de ces photodiodes d'excellentes candidates pour la photoreception a 20 gbit/s.

Le développement des réseaux optiques et l’augmentation des interconnexions à courtes distances, amènent un besoin croissant en transmetteurs émettant à 1,3 µm, performants, peu énergivores et fabriqués à bas coût.Ainsi, l’intégration photonique monolithique, qui vise à juxtaposer plusieurs fonctions optiques dans un même circuit, est une solution. L’épitaxie sélective en phase vapeur aux organo-métalliques est une technique prometteuse pour cela. Elle permet, en une seule étape de croissance, de définir les structures des différents composants unitaires constituant le circuit intégré photonique. Il est nécessaire d’avoir un outil de simulation qui permet de modéliser la croissance sélective. Auparavant la modélisation proposée ne prenait en compte que des phénomènes de diffusion en phase vapeur et négligeait les phénomènes de surface. Une modélisation plus précise a été développée, fondée sur la relaxation de l’interface. En parallèle, nous avons conçu sept différentes structures actives, à base de multi-puits quantiques en matériaux AlGaInAs pour des composants DML et EML émettant à 1.3 µm. Nous avons fait des mesures de laser à contacts larges et des mesures d’absorption en photo-courant, pour sélectionner la meilleure structure.Une étude expérimentale de la croissance, à partir de microscopie électronique en transmission et de micro-diffraction aux rayons X, a permis de réaliser l’épitaxie sélective de la structure sélectionnée. Les composants fabriqués ont des performances à l’état de l’art avec une bande passante de 12,5 GHz pour un DML de 250 µm ainsi qu’un diagramme de l’œil ouvert à 32 Gbit/s avec un taux d’extinction dynamique de 10 dB, pour en EML
The development of passive optical networks and the increase of short-reach connections make an increasing need for efficient, energy-friendly and low-cost transmitters emitting at 1.3 µm.To this end, monolithic photonic integration, which aims to embed several optical functions into the same circuit, is a solution. Selective area growth (SAG) by metal-organic vapor-phase-epitaxy (MOVPE) seems to be an attractive technique to achieve this integration. This approach allows defining, in a single epitaxial step, the structures of the different unitary photonic functions constituting the photonic integrated circuit. One issue of this technique is the growth modeling, necessary to predict the material distribution. Previously, the model was only taking into account vapor phase diffusion phenomena, neglecting surface phenomena. Consequently a more accurate approach was developed, based on interface relaxation.Simultaneously, we designed seven different active structures, all based on AlGaInAs multi-quantum wells, in order to optimize the DML and EML devices emitting at 1.3µm . We performed wide area laser and photocurrent absorption measurements to select the best trade-off design for devices fabrication.In order to perform accurate SAG of the selected structure, experimental study has been done to optimize the growth using transmission electronic microscopy and X-ray micro-diffraction. Devices have been processed and exhibit state of the art performances. A bandwidth of 12.5 GHz was demonstrated for a 250 µm long DML and 32 Gbit/s open eye diagram with a 10 dB dynamic extinction ratio has been shown, on a EML with a 100 µm long EAM

L'objectif de cette thèse, réalisée dans le cadre du contrat européen Senshy, était la réalisation de diodes laser émettant dans le moyen infrarouge (de 3,0 à 3,4 µm). Ces diodes sont destinées à intégrer des détecteurs et des systèmes d'analyse de gaz basés sur le principe de la spectroscopie d'absorption (TDLAS) pour la détection des alcanes (méthane, éthane, propane) et des alcènes (acétylène). Les structures à puits quantiques de type I ont été réalisées par épitaxie par jets moléculaires sur GaSb.Bien qu'ayant d'excellentes performances dans la gamme 2,0-3,0 µm, les lasers GaInAsSb/AlGaAsSb montrent rapidement leurs limites en franchissant la frontière des 3 µm (la longueur d'onde la plus haute atteinte avec un tel composant est de 3,04 µm en continu à 20°C). Cette situation était d'autant plus regrettable que plusieurs gaz ont leurs raies d'absorption au-delà de 3 µm : le méthane par exemple a un pic d'absorption à 3,26 µm 40 fois plus fort que celui à 2,31 µm. En remplaçant le quaternaire AlGaAsSb par le quinaire AlGaInAsSb, nous avons montré que l'on pouvait améliorer l'efficacité quantique interne et avons obtenu des densités de courant de seuil à 2,6, 3,0 et 3,3 µm qui pouvaient être comparées favorablement aux précédents records à ces longueurs d'onde (respectivement, 142 A/cm², 255 A/cm² et 827 A/cm²).Les diodes laser DFB fabriquées à partir des structures epitaxiées ont permis d'atteindre l'émission laser à température ambiante en continu à 3,06 µm avec un caratère mono-fréquence (SMSR supérieur à 30 dB) et un courant de seuil de 54 mA. À 3,3 µm, les diodes DFB fonctionnent en continu jusqu'à 18°C avec un SMSR > 30dB et un courant de seuil de 140 mA. Finalement, ces diodes ont été intégrées dans un système d'analyse de gaz et ont permis d'atteindre une limite de concentration du méthane de 100 ppbv soit 17 fois moins que la concentration du méthane dans l'air ambiant
The objective of this thesis, conducted as part of the European contract Senshy, was the realization of laser diodes emitting in the mid-infrared range (from 3.0 to 3.4 µm). These devices are to be integrated into detectors and gas analysis systems based on the principle of absorption spectroscopy (TDLAS). for the detection of alkanes (methane, ethane, propane) and of alkenes (acetylene). The quantum well type-I structures were made by molecular epitaxy on GaSb. Despite having excellent performance in the 2 to 3 µm range, GaInAsSb/AlGaAsSb quantum well lasers rapidly show their limits when crossing the 3 µm barrier (the highest wavelength reached with such a device was 3.04 µm under cw operation at 20°C). This situation was all the more regrettable because several gases have their strongest absorption lines in the 3 to 4 µm range: methane, for example, has a peak of absorption at 3.26 µm overhanging a weaker peak at 2.31 µm by a factor 40. By replacing the quaternary AlGaAsSb by the quinary AlGaInAsSb, we have shown that the internal efficiency could be improved and we have obtained threshold current densities at 2.6 , 3.0 and 3,3 µm that could be favourably compared to the previous records at these wavelengths (respectively, 142 A/cm², 255 A/cm² and 827 A/cm²).DFB laser diodes made from the epitaxial structures were operated at room temperature in the continuous wave regime at 3.06 µm with a single-frequency emission (SMSR greater than 30dB) and a threshold current of 54 mA. At 3.3 µm, DFB devices were operated in cw up to 18 ° C with a SMSR > 30 dB and a current threshold of 140 mA. Eventually, these devices were integrated into a gas analysis system and allowed to reach a concentration limit of 100 ppbv of methane, i.e. 17 times less than the concentration of methane in the air

This thesis describes the development of a monolithic dual-wavelength laser based on an InP/AlGaInP quantum dot (QD) laser structure. Each wavelength is sourced from the same active region and can be operated simultaneously or independently, with light being emitted from a common aperture. The inhomogeneity of the QD material provides a wide distribution of energies, resulting in a broad and relatively flat-topped gain spectrum, which is ideal for sourcing multiple wavelengths. Measurements of optical absorption, gain and laser threshold current densities were used to characterise the optical properties of InP/AlGaInP QDs and ascertain a suitable structure from which to fabricate the dual-wavelength source. A growth temperature of 710 °C resulted in the lowest threshold current densities, and the incorporation of tensile strain into the upper confining layers was found to reduce the temperature dependence. Optical gain measurements were used to assess how state-filling and temperature govern the gain-peak wavelength. For a fixed gain at low injection the wavelength dependence follows that of the band gap (≈ 0.17 nm/K), but at higher levels of injection it becomes relatively temperature-insensitive. A minima in wavelength sensitivity corresponded to a net gain of ≈ 28 cm-1. Edge-emitting lasers with a wavelength temperature dependence as low as 0.03 nm/K were demonstrated for temperatures up to 107 °C (380 K). An Ar-Cl2 based inductively-coupled plasma (ICP) etch process, suitable for fabricating sub-micron features, was developed to create the necessary device architecture. Using the effects of state-filling and spectrally preferential feedback, coupled-cavity ridgewaveguide lasers with unequal length sections were used to generate two wavelengths, with separations up to 61.5 ± 0.2 nm. Time resolved spectra were used to demonstrate dual-mode operation, where both wavelengths were observed to emit simultaneously. This is a promising result as it suggests that this device could potentially be used as a compact terahertz source

Optical characterisation of InP/AlGaInP quantum dot laser structures, involving laser threshold and wavelength, optical modal gain and absorption spectra, and radiative efficiency are presented. The samples were grown by MOVPE in Sheffield University on (100) 10 off and (211)B GaAs substrates, and consist of 5 layers of self-assembled InP dots, with each layer grown on Alo.3Gao.7InP and placed in a GaInP quantum well. A record low threshold current density of 290A/cm2 at a wavelength of 740nm for a 1.6 mm-long device with uncoated facets is obtained from one of the sample grown on (100) 10 off substrate at 690 C. This sample has an internal optical mode loss of 4 1 cm"1 and an internal quantum spontaneous emission efficiency of 30% for current densities corresponding to the threshold. The ground state modal gain is shown to saturate at 17cm"1 at room temperature, which is about lA of the full population inversion limit, and the saturation level increases with decreasing temperature. A sample grown at a lower temperature of 650 C has higher optical mode loss (7.5 1 cm"1) and quantum efficiency under 15%. A sample grown on (211)B substrate exhibits optical transitions at higher photon energies, consistent with smaller dot sizes. The thesis also presents an analysis of the segmented contact technique used to measure gain and absorption spectra, determining criteria for the excitation and detection geometries required to ensure accurate measurement. It is shown that the collection angle and device nearfield should be limited so that rays that intercept the stripe edges are not collected. If this is not satisfied, the measurement underestimates the modal gain. An exponential variation of the measured ASE upon stripe length cannot be taken as evidence for a correct collection geometry.

The aim of this thesis is to understand and optimise the optoelectronic properties of InP quantum dot laser diodes which operate in the range around 730nm required for various application such as the photodynamic therapy. The properties of wafers with two barrier widths, 8 and 6nm, each grown at different temperatures, 690, 710, 730 and 750T, and consisting of 5 layers of dots forms from different quantity of deposited material, 2, 2.5 and 3ML, are described and investigated. The laser and multisection devices of these structures are used to determine threshold current density, lasing wavelength, modal absorption, modal gain and spontaneous emission spectra. The modal absorption spectra show three different dot size distributions, small, large and very large dots. Their variation with growth temperature results in a blue shift accompanied by an increasing number of states while the variation with quantity of deposited material shows only an increase to the number of states. The lasing wavelength variation with growth temperature covers a range between 715–745nm. The threshold current density as a function of temperature for 2000/m long laser devices grown at temperature of 750°C exhibits a distinctive dependence on the operating temperature and becomes less pronounced when the growth temperature reduces. This is explained in terms of the carrier distributions in the quantum dot and quantum well states without invoking an effect from Auger recombination. The optimisation of threshold current density can be reached by using structures with higher barrier width grown at low temperature and deposited with high quantity of quantum dot material to minimise both the affect of the very large dot, which contain a number of defects associated with them, and carrier leakage from quantum dot to quantum well states. This reduces the room temperature threshold current density to ISO A/cm 2 for 2mm long lasers with uncoated facets.

This thesis describes work undertaken to understand the physics of dry-etching AlGaInP/GaAs laser structures in Cl-based plasmas to develop a process that allows the fabrication of high-aspect-ratio, sub-micron features. The effects of the main process parameters on the etch rate, selectivity and post-etch surface roughness were studied to understand how the interactions between the semiconductor materials and the plasma gives rise to different sidewall geometries. The behaviour of the two types of material in the presence of a Cl-based plasma was found to be very different due to the production of InCb when etching the AlGaInP layers which is absent when etching GaAs. This product is involatile and rate limiting in Cl-rich plasmas. Effective removal of the inhibiting InCb was shown to be necessary to selectively etch the AlGaInP layers anisotropically at a reasonably high etching rate. A narrow range of plasma conditions satisfied these requirements. These conditions provided the thermal- and ion-assisted desorption of the InCh such that the removal rate matches the formation rate. In contrast, GaAs was shown to etch anisotropically under a much wider range of conditions as the mechanism for anisotropic etching does not require an inhibitor. With an optimized set of etch parameters, etching of high-aspect-ratio, sub-micron features in AlGaInP/GaAs laser structures was demonstrated. Despite the difference in etch mechanisms of GaAs and AlGaInP and the use of a 2-step process, at the same Ar fraction vertical sidewall features were achieved in both materials when etching sub-micron gratings. Under conditions that provide smooth vertical sidewalls the etch rate was shown to be aspect-ratio dependent due to the depletion of neutral species at the base of the feature. A range of 1-D gratings were etched with lattice constants as short as 200 nm and aspect ratios as high as 20:1. To the best of my knowledge these are the deepest vertically etched structures on this scale in AlGaInP/GaAs. Using this process, a range of devices including laser cavities defined by dry-etched facets and Distributed Bragg Reflectors and an integrated emitter/detector device were fabricated to demonstrate the quality of the etch process.

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Objective: To analyze the healing activity AlGaInP laser in induced skin wounds in rats wistar. Materials and Methods: This is an experimental study, pre-clinical trial conducted in the room at the Center for Research and Toxic-pharmacological approaches. Were used for the experiment 54 Wistar rats divided into 3 groups of 18 animals and divided into 3 groups of 6 animals. The animals were weighed, tricotomiados anesthetized and then subjected to a surgical incision in the dorsal-neck of all animals using a punch of 1 cm (diameter). After 24 hours of surgery, we used the laser diode Aluminum Indium Gallium Phosphorus - AlGaInP (IBRAMED - Laserpulse) with a continuous power of 30 mW and wavelength (ʎ) of 660 nm for the treatment groups L3 and L6 (3 and 6J/cm2 + saline (0.9%) respectively and for the control group (CG) received only saline (0.9%). The animals (n = 6) for each group were euthanized at 5, 10 and 15th days after injury. The samples were embedded in paraffin, stained with hematoxylin-eosin and picrossírius. We observed the daily appearance of the wound during the healing process and noted in individual spreadsheet, by the same examiner. Data from histological evaluation were converted in quantitative variables by assigning scores: absent (0), mild (1-25%), moderate (25-50%) and severe (above 50%). For morphometric analysis, we used the program Image J. The count of the number of blood vessels was used for point counting planimetry. For analysis of collagen was used picrossírius staining and polarized light to scan images. The data were treated statistically by analysis of variance (ANOVA) and post-Tukey test. For the non - parametric variables we used the Kruskal - Wallis test. The significance level was set at (p<0.05). Results: There was a statistically significant difference in the contraction of the wound edge in L3 group compared to GC and L6 on the 10th day of the injury, indicating that the laser energy density 3J/cm2 acted positively in the healing process. During the histological assessment, we observed reduction of bleeding (p=0.007) L3 group compared to control and to the number of polymorphonuclear (p=0.045) treated groups L3 and L6 compared to control. Also on the 10th day there was also an increase in collagen content (p=0.003) L3 and L6 in the groups compared to control. On the 15th day was observed a significant increase in collagen content (p=0.034) of the L6 in the control group. Conclusion: The wound healing activity AlGaInP laser was evidenced by increased angiogenesis, decreasing inflammation and stimulation of fibroplasia. Thus it is assumed that the laser used in the study contributed positively tested in both phases (inflammatory and proliferative) to accelerate the healing process and also that the energy densities of three proposals 6J/cm2 and responded to the type of treatment proposed in this study.
Objetivo: Analisar a atividade cicatrizante do laser AlGaInP em feridas cutâneas induzidas em ratos wistar. Materiais e Métodos: Trata-se de um estudo experimental, pré-clínico, realizado na sala de experimentação do Núcleo de Estudos e Pesquisas Tóxico-farmacológicas. Foram utilizados para o experimento 54 ratos fêmeas linhagem Wistar distribuídos em 3 grupos de 18 animais e subdivididos em 3 grupos de 6 animais. Os animais foram pesados, tricotomiados, anestesiados e posteriormente submetidos a uma incisão cirúrgica em região dorso-cervical de todos os animais utilizando um punch de 1cm (diâmetro). Após 24 horas da cirurgia utilizou-se o laser diodo Alumínio Gálio Índio Fósforo - AlGaInP ( IBRAMED Laserpulse) com uma potência contínua de 30 mW e comprimento de onda (ʎ) de 660 nm para o tratamento dos grupos L3 e L6 (3 e 6J/cm2 + solução fisiológica (0,9%) respectivamente e para o grupo controle (GC) utilizou-se apenas solução fisiológica (0,9%). Os animais (n=6) de cada grupo foram eutanasiados no 5, 10 e 15° dias após a lesão. As amostras obtidas foram emblocadas em parafina, coradas com hematoxilina-eosina e picrossírius. Foi observado diariamente o aspecto da ferida durante o processo de cicatrização e anotado em planilha individual, sempre pelo mesmo examinador. Os dados da avaliação histológica obtidos foram transformados em variáveis quantitativas, pela atribuição de escore: ausente (0), discreto (1 a 25%), moderado (25 a 50%) e acentuado (acima de 50%). Para análise morfométrica, utilizou-se o programa Image J. A contagem do número de vasos sanguíneos utilizou-se a planimetria por contagem de pontos. Para análise do colágeno utilizou-se coloração picrossírius e luz polarizada para digitalizar as imagens. Os dados foram tratados estatisticamente pela análise de variância (ANOVA) e pós-teste de Tukey. Para as variáveis não paramétricas utilizou-se o teste Kruskal Wallis. O nível de significância foi fixado em p< 0,05. Resultados: Observou-se uma diferença estatística significativa na contração da borda da ferida no grupo L3 em relação aos grupos GC e L6 no 10º dia da lesão, indicando que o Laser na densidade de energia 3J/cm2 atuou de forma positiva no processo de cicatrização. Durante a avaliação histológica, observou-se diminuição da hemorragia (p=0,007) do grupo L3 em relação ao controle e também no número de polimorfonucleares (p=0,045) dos grupos tratados L3 e L6 em relação ao controle. Ainda no 10°dia observou-se também um aumento no conteúdo de colágeno (p=0,003) nos grupos L3 e L6 em relação ao controle. No 15° dia foi observado um aumento significativo no conteúdo de colágeno (p=0,034) do grupo L6 em relação ao grupo controle. Conclusão: A atividade cicatrizante do laser AlGaInP foi evidenciada pelo aumento da angiogênese, diminuição da inflamação e estímulo da fibroplasia. Dessa forma admite-se que o laser utilizado no estudo contribuiu de forma positiva em ambas as fases testadas (inflamatória e proliferativa) para acelerar o processo de cicatrização e também que as densidades de energia propostas 3 e 6 J/cm2 responderam ao tipo de tratamento proposto neste estudo.

博士
國立清華大學
電子工程研究所
91
1.3 and 1.55 μm semiconductor laser are most popular for the application in subscriber networks and optical interconnection systems. 1.3 μm-based semiconductor lasers have lower dispersion but higher attenuation compared to that of 1.55 μm-based semiconductor lasers. Besides, one of the most troublesome components in present laser modules is a thermoelectric cooler, which both makes the modules expensive and complicated but also may degrade its long-term reliability. In order to overcome these problems, 1.3 μm high power and without thermoelectric cooler AlGaInAs with high conduction band offset than conventional GaInAsP are used as light source in optical interconnection systems. The higher conduction band offset can alleviate the Auger recombination that will affect the performance of long wavelength laser diode so that increase the light output power. In this thesis, we first investigate the 1.3 μm AlGaInAs/AlGaInAs strain compensated multiple-quantum well. The compress strain wells which have several merits in optical and reduction of threshold current and compensated by tensile barriers to increase the well number. The threshold current density and differential quantum efficiency for the as-cleaved BA LDs with a 900 μm cavity length are 400 A/cm2 and 22%, respectively. We also calculate the internal quantum efficiency, internal optical loss, and threshold gain as 54.1%, 6.5cm-1, and 45 cm-1. The characteristic temperature of 75 K between 20 and 80 ℃, and the longitudinal mode oscillation has a red-shift rate of 0.5 nm/℃ under 25 ℃ and 60 mA. Graded index separate confinement heterostructure (GRINSCH) has superior optical confinement and smooth electric field intensity distribution than that of step (or abrupt) structure. Besides, to tailor the electric field intensity distribution in the abrupt junction between InGaAs and InP, we introduce a thin graded composition (GC) GaInAsP layer between InGaAs and InP. With the GC GaInAsP layer, the 3μm-ridge-stripe LDs without facet coating under the CW operation exhibit a lower threshold current of 14 mA, a lower resistance of 7.8 Ω, a higher differential quantum efficiency of 47.46%, a higher characteristic temperature of 79 K in the range from 20 to 80 ℃and 42 K in 80 to 100 ℃, and a red-shift rate of 0.43 nm/℃, which are better than those of the LDs without the GC GaInAsP layer. The differential gain for LDs with GC GaInAsP layer is about 8.45x10-16 cm2 for 300-μm cavity length and decreases to 4.68x10-16 cm2 for 900 μm. The relaxation oscillation frequency is about 9.2 GHz under the 80 mA driving current at 20℃. With neglecting the effect of damping factor and couple loss, the calculated 3-dB frequency width can reach to 14.26 GHz under the 80 mA driving current at 20℃. More recently, modulation doping in the barriers will serve several merits such as lower transparency carrier density and higher optical gain. The BA LDs with this optimum concentration of 5 x 1018 cm-3 in the doped barriers exhibit the threshold current density, internal quantum efficiency, internal optical loss, threshold gain (for the cavity length of 300 μm), and transparency current density of 215 A/cm2, 61.7%, 7.5 cm-1, 47.5 cm-1, and 71 A/cm2, respectively, which are much better than those of the LDs with undoped and other doping concentrations in the barriers. In addition, the ridge-stripe LDs without facet coating have a lower threshold current of 12.5 mA, an enhanced differential quantum efficiency of 52.3%, a characteristic temperature of 85 K in the temperature range from 20 to 80 ℃, and a red-shift rate of 0.38 nm/℃ under the CW operation. The relaxation oscillation frequency with driving current of 80 mA under 20 ℃ is about 9.9 GHz. Without consideration to damping factor and couple loss, the calculated 3-dB bandwidth is about 15.34 GHz. InAsP/InP/InGaP MQW has higher conduction band offset than that of GaInAsP MQW. In this thesis, InAsP/InP/InGaP with n-type doping laser diode is also investigated. The optimum doping concentration is 1x1018 cm-3 in the Si-doped barrier and InP intermediate layer. The threshold current density can be reduced to 0.8 kA/cm2 for 900-μm-cavity length for these optimum thickness and doping concentration. In addition, the LDs exhibit an enhanced differential quantum efficiency of 25% and an internal quantum efficiency of 31%. The internal optical loss can be also lowered to 19.01 cm-1. The threshold gain will be reduced to 43.07 cm-1 compared to 44.1 cm-1 for the LDs with undoped active region.

博士
國立清華大學
材料科學工程學系
87
In this dissertation, we report the development of high performance 1.3- and 1.5-mm laser diode arrays which are shown to present the possibility of suitable applications in the next generation of computing and switching systems. The growth of the AlGaInAs epitaxyer lattice matched to InP using low-pressure organometallic vapor phase epitaxy (LP-OMVPE) technique was investigated first. The effects of the growth conditions on the crystal quality and the laser structure on the device performance were studied. Based on these well-established results, the high uniform 12-element 1.5 and 1.3-mm ridge-waveguide AlGaInAs/InP laser diode arrays were fabricated with excellent device performance. The devices exhibited a highly reliable and uniform characteristics, and good performance of laser element in low threshold current, high characteristic temperature, low slope efficiency drop, high temperature operation, low crosstalk, and large modulation bandwidth. In order to improve the laser diode arrays performance, the effects of high-reflectivity facet coating on 1.3 and 1.5-mm AlGaInAs/InP lasers were also evaluated. System results, such as increasing maximum operation temperature, increasing characteristic temperature, decreasing threshold current and decreasing slope-efficiency drop by increasing the facet reflectivity, were present. On the other hand, the aluminum-contained lasers have a concern problem for the degradation of active region by aluminum oxidation. We took a reliability tests including the screening test and accelerated aging based on the technical advisory of Bellcore''s TA-NWT-000893 to estimate life time of these AlGaInAs/InP lasers. The median life will exceed 249 years for the lasers operating at 10mW and 250C. On the other hand, we also developed the multiple wavelengths GaInAsP/InP laser arrays by selective area organometallic vapor phase epitaxy technique. The lasing wavelength, threshold current and slope efficiency can be tuned by the variation geometry of SiO2 mask. Since wide band-gap energy can be simply controlled in one epitaxial growth step, it is possible to monolithically integrate two different devices on same wafer.

博士
國立交通大學
電子物理系所
97
The author demonstrates the investigation of novel solid-state laser technologies with AlGaInAs semiconductor materials. A periodic AlGaInAs quantum well / barrier based on Fe-doped InP substrate can be a semiconductor gain chip and a semiconductor saturable absorber. In addition to the introduction and the future work, the main text were divided into three chapter. In chapter two, AlGaInAs saturable absorber with a periodic QW/barrier structure that can be used to achieve an efficient high-peak-power and high average- power passively 1.06 and 1.34μm Q-switched lasers. In chapter three, AlGaInAs QWs grown on the Fe-doped InP substrate was designed to be a saturable absorber for self-starting continuous-mode-locked Nd:YVO4 laser at 1342 nm. In addition to be a saturable absorber, the periodic quantum well / barrier structure also can be a gain medium in solid-state laser. We demonstrated an AlGaInAs QW/barrier structure grown on an Fe-doped InP transparent substrate was developed to be a gain medium in a room-temperature high-peak-power nanosecond laser at 1.36 and 1.57μm for optical communication and eye-safe applications.

碩士
國立交通大學
光電工程研究所
86
we present the fabrication results of the 1.5um complex-coupled distributed feedback lasers (DFB lasers ) with a InGaAs loss grating and strained A1GaInAs multi-quantum well (MQW) active region. The device with coupling coefficient of 30 cm-1 has a CW threshold current of 19mA and a output power of 29mW. Stable single mode emission was demonstrated with a side mode suppression ratio of up to 44dB at 5mW output power. It has been found that the presence of loss-coupling strength can eliminate the mode degenercy effectively.

碩士
國立交通大學
電子物理系所
100
1.52μm near eye-safe wavelength regime is widely used in laser range finder and optical communication, for laser range finder in order to achieve high speed scanning and measurement long distance object, the high-repetition-rate and high-peak-power eye- safe laser is very important for applications. In this thesis, we used optically-pumped semiconductor laser to produced 1.52μm eye-safe laser, semiconductor laser output performance are susceptible to thermal effect, the thermal effect are more significant when pumping power and pumping repetition rate increasing therefore remove heat are very important issue. We used diamond heat spreader to enhance the heat removal We work to studied how to perfect bonding diamond heat spreader with semiconductor gain medium. The experiment results used diamond heat spreader can improve laser performance at high-repetition-rate.

碩士
國立彰化師範大學
光電科技研究所
93
The 1.3- and 1.55-um semiconductor lasers are important for application in optical interconnection and long-distance optical fiber communications because they provide the lowest dispersion and loss in silica fiber respectively. Although the traditional InGaAsP/InP strained multiple quantum-well lasers have been studied for a long time and applied in many areas, they still suffer from problems of relatively high temperature dependence. Therefore, it does not retain low temperature sensitivity of threshold current and high slope efficiency in the absence of a thermoelectric cooler when the InGaAsP/InP laser systems are operated at elevated temperatures. In recent years, there are two novel material systems utilized to fabricate the 1.3- and 1.55-um semiconductor lasers. One of the new material systems is AlGaInAs/InP and the other is InGaAsN/GaAs. Both the AlGaInAs/InP and InGaAsN/GaAs lasers show better performance and lower temperature dependence than the conventional InGaAsP/InP lasers, enabling uncooled continuous-wave operation at high ambient temperatures. In this work, I present a complete study for the AlGaInAs material system. Moreover, the InGaAsN and InGaAsP (InAsP) material systems are also systematically analyzed at the same time. In chapter 1, I first introduce the optical properties and physical parameters of the three material systems, InGaAsP (InAsP), AlGaInAs, and InGaAsN, which are utilized to fabricate the 1.3-um semiconductor lasers. Then, the development status of these material systems are also reviewed and described. In chapter 2, the material gain performances and spontaneous emission rates of these 1.3-um semiconductor material systems, obtained from real devices fabricated by different researchers, are systematically analyzed and compared. Furthermore, the effect of design of active region on optical properties of each material system is also investigated in this chapter. In chapter 3, optical properties of a 1.3-um AlGaInAs/InP laser structure with an electron stopper layer are studied numerically with the Lastip simulation program developed by Crosslight Inc. On the other hand, the effect of strain compensating barrier layers on the laser performance of InGaAsN/GaAs laser system is also investigated in detail. Finally, in chapter 4, based on the preceding simulation results and analyses, I make a brief summary and provide the optimized designs of laser structures for 1.3-um AlGaInAs and InGaAsN material systems. It is my hope that the researches in this thesis may be helpful to the researchers and crystal growers.

Die vorliegende Arbeit beschreibt die Charakterisierung von Halbleiter-Quantenpunkten (QP) in unterschiedlichen Materialsystemen. Die hier dargelegten Untersuchungen wurden mit verschiedenen Methoden der optischen Spektroskopie durchgeführt. Zu Beginn der Arbeit werden theoretische Grundlagen von QP hinsichtlich ihrer elektronischen Struktur und statistischen Eigenschaften erläutert. Darüber hinaus wird näher auf die Physik von Solarzellen eingegangen, in dem die relevanten Gleichungen für die Beschreibung des Ladungsträgertransportes hergeleitet und diskutiert werden. Darauf folgend werden die experimentelle Methoden erklärt, welche zur Charakterisierung der jeweiligen Proben dienten. Besonderes Augenmerk wird auf die Methode zur Messung des Zwei-Photonen-Absorptionsprozesses gelegt. Der Abschnitt der experimentell gewonnenen Ergebnisse beginnt mit Untersuchungen an einzelnen, spektral isolierten InP QP, welche mit ultralangsamen Wachstumsraten hergestellt wurden. Aufgrund der sehr geringen Flächendichte konnten grundlegende physikalische Eigenschaften von QP ohne zusätzliche laterale Strukturierungen studiert werden. Mittels Messungen in Abhängigkeit der Anregungsleistung und Detektion in Abhängigkeit der Polarisation konnten die verschiedenen Lumineszenzlinien eines QP-Spektrums den jeweiligen exzitonischen Zuständen zugeordnet werden. Zusätzlich wurden die QP in einem externen Magnetfeld in Faraday-Konfiguration untersucht. Abschließend durchgeführte Autokorrelationsmessungen erlaubten die Untersuchung der zeitlichen Statistik der QP-Photonen. Es konnte die Emission einzelner Photonen nachgewiesen werden. Anschließend folgen spektroskopische Untersuchungen von InP QP, welche mittels sequentiellen Wachstums hergestellt wurden. Anhand von Messungen in Abhängigkeit der Anregungsleistung und bestätigt durch zeitaufgelöste Messungen am QP-Ensemble wurde eine bimodale QP-Verteilung mit Typ-I und Typ-II Bandverlauf bestimmt. Zusätzlich konnten an einzelnen, spektral isolierten QP verschiedene Exziton-Zustände identifiziert werden, bevor abschließend Autokorrelationsmessungen die Emission einzelner Photonen demonstrierten. Zur Steigerung der Auskoppeleffizienz der Photonen wurden InP QP in Mikrosäulenresonatoren, bestehend aus zwei Bragg-Spiegeln mit einer dazwischenliegenden GaInP Kavität, eingebettet. Anfangs wurde die Emission der Kavitätsmode von Strukturen mit unterschiedlichen lateralen Durchmessern charakterisiert. Mittels Temperaturverstimmung konnte die Energie eines einzelnen QP-Exzitons in Resonanz mit der Resonatormode gebracht werden. Im Regime der schwachen Wechselwirkung wurde eine signifikante Überhöhung der Lumineszenzintensität aufgrund des Purcell-Effektes gemessen. Zusätzlich wurde im Regime der schwachen Kopplung die Emission einzelner Photonen anhand von Korrelationsmessungen nachgewiesen. Im zweiten Schritt wurden die QP-Mikrosäulenresonatorstrukturen elektrisch angeregt. Nach einer grundlegenden Charakterisierung konnte auch hier mittels Temperaturverstimmung die Energie der Resonatormode mit der eines Exziton in Resonanz gebracht werden. Im Regime der schwachen Wechselwirkung stieg die Intensität der Lumineszenz aufgrund des Purcell-Effekts signifikant an. Zum Abschluss bestätigen Korrelationsmessungen den Nachweis der Emission einzelner Photonen. In Kapitel 6 werden die Eigenschaften von InGaN QP genauer analysiert. Nitrid-Verbindungshalbleiter kristallieren vorzugsweise stabil in der Wurtzit-Kristallstruktur. Polare Kristallebenen mit fehlender Spiegelsymmetrie führen zu starken piezoelektrischen Feldern. Dies hat eine Lumineszenz mit ausgeprägter linearer Polarisation zur Folge hat. Diese Eigenschaft wurde mittels statistischen Untersuchungen näher betrachtet. Zusätzlich erlaubten Messungen in Abhängigkeit der Anregungsleistung die verschiedenen Exziton-Zustände eines QP zu identifizieren. Zudem wurde die Emission einzelner Photonen durch InGaN QP demonstriert, erstmals sogar bis zu einer Temperatur von 50 K. Im abschliessenden Kapitel wird eine mögliche Anwendung von QP präsentiert, bei der Eigenschaften in Bauteilen gezielt ausgenutzt werden, um die Bandbreite der Photonenabsorption zu erhöhen. Das Konzept der Zwischenband-Solarzellen verspricht auch Photonen mit einer Energie kleiner der Bandlücke des umgebenden Materials aufnehmen zu können und somit den spektralen Absorptionsbereich zu erweitern. Für eine systematische Untersuchung wurden verschiedene Proben mit integrierten AlGaInAs QP hergestellt. Anhand der Strom-Spannungs-Kennlinien der jeweiligen Proben im Dunkeln und unter Beleuchtung konnten wichtige Solarzellenparameter bestimmt werden. Spektrale Messungen liefern Informationen über die externe Quanteneffizienz der Proben. Entscheidend für den experimentellen Nachweis des Funktionsprinzips der Zwischenband-Solarzellen ist die Messung der Zwei-Photonen-Absorption für zwei Photonen mit jeweils kleineren Energien als der Bandlücke des umgebenden Materials
This thesis describes the characterization of semiconductor quantum dots (QDs) in different material systems with potential applications as single photon emitters or intermediate band solar cells. All investigations were carried out by means of optical spectroscopy methods. First, the theoretical background regarding the physics of QDs with respect to their electronic structure and their associated statistical properties are presented. Especially peculiarities of photon statistics of light are explained. Moreover, a closer look at the physics of solar cells and the respective carrier transport is given. Then experimental methods, which were used to characterize the QD-samples, are briefly explained. First, the components and techniques of optical spectroscopy for the study of individual, isolated QDs are described. Second, different experimental technologies for the characterization of solar cells are discussed. The method for measuring the two-photon-absorption process is explained in detail. The section of experimental results begins with studies of individual and spectrally isolated InP QD. Due to the low surface density of one QD per μm2, it is possible to study the physical properties of individual QDs optically without additional lateral sample structuring. Based on power and polarization dependent measurements, various luminescence peaks of a single QD were associated with different exciton states. In addition, the QDs were tested subject to an external magnetic field in a Faraday configuration. Finally, the temporal photon statistics of a single QD was tested using autocorrelation measurement. Afterwards, InP QDs manufactured by cyclic material deposition with growth interruptions were investigated by means of PL spectroscopy. Based on excitation power and time-resolved measurements on the QD ensemble, a bimodal QD distribution of type-I and type-II band alignment was observed. In addition, different exciton states were identified on spectrally isolated single QDs. Finally, the emission of single photons has been demonstrated using autocorrelation measurements. For a more efficient diffraction-limited output coupling of photons, the InP QDs grown by cyclic material deposition were embedded in micropillar resonator structures and investigated by means of spectroscopy. First, structures with different diameters were characterized by photoluminescence spectroscopy. Second, the energy of a single QD exciton and the energy of the cavity were tuned into resonance by changing the temperature. In the regime of weak coupling a luminescence enhancement due to the Purcell Effect was observed. Finally, also in the regime of weak coupling, the emission of single photons has been demonstrated by autocorrelation measurements. In terms of applications, electrical operations are desirable. Therefore, the Bragg mirrors of the micropillar resonator were doped for an efficient current injection and electrical contacts were deposited. After basic electrical characterization, the regime of weak coupling of a single QD exciton and the cavity resulting in a luminescence enhancement were demonstrated by the Purcell effect. Finally, the emission of single photons based on autocorrelation measurements is shown. In this chapter, the luminescence properties of single InGaN QD were investigated. Based on the wurtzite crystal structure of nitrite-compound semiconductors strong piezoelectric fields occur that lead to strongly linearly polarized luminescence. Several QDs were investigated and statistical studies were performed. Excitation power depending measurements allows one to identify the different exciton states of a single QD. In addition, the emission of single photons of InGaN QDs up to a temperature of 50 K was demonstrated for the first time. In the final chapter, an application of QDs in solar cells is presented to specifically exploit the unique properties of QDs in optical devices. The concept of the intermediate band solar cell utilizes the energy position of the QD ground state to absorb photons with energy smaller than the host materials bandgap. This enables an enhancement of the spectral absorption range to longer wavelengths. For systematic studies various samples with AlGaInAs QDs were fabricated. The current voltage characteristics of the samples were tested in the dark and under illumination and the respective solar cell parameters were evaluated. Additionally, based on spectral measurements, the external quantum efficiencies of the samples were determined. Furthermore, the measurement of two sub-bandgap-photon absorption demonstrates the operation principle of an intermediate band solar cell. Finally, band structure calculations are shown, which describe the results qualitatively and which also hint to future sample designs

博士
國立交通大學
電子物理系所
101
Recently, the semiconductor multiple-quantum-wells (MQWs) structure is extensively used in the semiconductor lasers owing to the characteristics like versatile emission wavelength, lower laser threshold and excellent performance under room temperature operation. It is also applied as a promising saturable absorber in the diode-pumped passively Q-switched solid-state laser. Compared to the doped crystal saturable absorber, the MQWs absorber has lower non-saturable loss and allows the shorter cavity length. According to these characteristics, the MQWs structure has the potential to be designed simultaneously as a saturable absorber and an active medium in the intra-cavity pumped solid-state lasers. Besides, the many-body effect of the high density electron-hole plasma (EHP) under this quasi-2D confinement structure is also an interesting issue. Therefore, the contents of this dissertation are organized to be three parts. At the first part we investigate the many-body effect of the high density EHP in the quasi-2D confined MQWs structure. The room temperature spontaneous emission of the renormalized bandgap is observed under the designation of high confinement energy and periodically aligned gain structure. The temperature dependent luminescence features such as photoluminescence (PL) spectrum and the integrated PL intensity are discussed and the threshold excitation intensity of the luminescence of renormalized band-edge is shown to be exponentially increased with increasing temperature. As a result we have confirmed that the periodically aligned MQWs structure is beneficial to the observation of room temperature many-body state emission In the second part, an AlGaInAs MQWs structure is designed to be the gain chip of a high repetition rate and high peak power 1220 nm optically-pumped semiconductor laser (OPSL). By using an Yb-doped master oscillator fiber amplifier as the pump source, the output performance could be optimized with the free controlled pump conditions such as pump repetition rates and pulse durations. Then the same pump laser is used to excite the high repetition rate and high peak power AlGaInAs MQW OPSL at the communication and eye-safe spectral region of 1520 nm. By capillary bonding the highly transparent and thermal conductive single crystal diamond heat spreader to the gain chip, the thermal roll-over effect was eased at high average pump power under high repetition rate operation. The optimized repetition rate was raised from 30 to 200 kHz and the maximum average output power was scaled to be 4.7 times higher. When operated at as high as 500 kHz, the maximum average power of 2.32 W and peak power of 170 W were obtained. At the end of this dissertation an AlGaInAs MQW structure is used simultaneously as the saturable absorber (SA) and wavelength-converted component in the Nd:GdVO4 laser. It is fabricated to accommodate the pump level of 1064 nm and the emission level of 1530 nm in the quantum well region. The upper state is served as the nonlinear saturable absorption device at 1064 nm and the lower state is served as the active medium at 1530 nm with additional couple-cavity in the Nd:GdVO4 laser. This configuration combines the advantages of the self-Q-switched lasers, pulse-pumped solid state lasers and the semiconductor MQW structures. Because there is no need of additional electronic drivers for passively Q-switches and the shorter action lengths of the MQWs compared to the bulk crystal SAs and nonlinear crystals, the device configuration could be simplified and cavity length is shortened, respectively. According to these characteristics and the capillary bonding technique in second part, this laser system has potential to be served as a low cost, simple and monolithic passively Q-switched microchip laser with broad achievable spectral range.

碩士
崑山科技大學
電子工程研究所
95
The Ⅲ-Ⅴcompound solar cells can get high efficiency as a result of structure of tandem and we also call tandem solar cell, it compose of different band–gap compound semiconductor and it absorb spectrum of solar , respectively . it compose of top cell . bottom cell and substrate in the two layer structure of tandem . By the three layers , it compose of top cell . middle cell . bottom cell and substrate . Structure of tandem can supply efficiency from each cell , so it can get high efficiency . Material of top cell usually compose of GaInP , in this paper , we use AlGaInP to substitute for GaInP and we optimize the epitaxy and process conditions of AlInGaP top cell in order to get max efficiency .

碩士
國立高雄應用科技大學
電子與資訊工程研究所碩士班
93
Recently, high-brightness LEDs have been applied to traffic signs and lighting equipment, because they have the advantages of low power consumption, low cost, and long life in comparison to the traditional lighting devices. Hence, the improvement of LED’s performance that includes life time and brightness of the device is very important. In this work, the reliability tests for 620nm-AlGaInP LEDs with difference sizes and circumstances were studied. Our results show that three passivation mechanisms affect device reliability, that are: (1) surface passivation of LED caused by the epoxy coverage, (2) hydrogen passivation from bulk, and (3) hydrogen passivation caused by diffusion from epoxy coverage. Here, the surface passivation has the quickest characteristic time, and, however, the hydrogen passivation caused by epoxy coverage requires the longest time, especially as the device with a large area operated under the environment temperature of 85℃. The characteristic times were extracted by use of curve fitting method. Furthermore, our results show that the bevel corners to the top capping layer can effectively reduce the critical angle loss and relax the stress at the interface between semiconductor and epoxy.

Laser Diodes (LD) have numerous applications for industry, military, medicine and communications. The first visible LD was invented in 1962 by Nick Holonyak, emitted at 710 nm (red). In 1990s, Shuji Nakamura invented the blue and green Light Emitting Diodes (LED) and later LDs. The production of LDs emitting between 532- 632 nm has been severely lagging behind the rest of the visible spectrum. Yellow and orange LDs are still not accessible due to the lack of successfully grown material with high optical efficiency. AlGaInP is the quaternary compound semiconductor used to grow green to red LEDs and red LDs. At a material composition that is supposed to lase below 630 nm, the optical efficiency becomes low due to the oxygen-related defects associated with high Al content. The quantum well intermixing (QWI) is a post-growth process that is applied to laser structure to tune the wavelength of laser. Until now, there are limited reports on successful intermixing of InGaP/InAlGaP laser structures while maintaining the crystal quality. In this work, we introduced a novel intermixing process that utilizes the high strain induced by the dielectric film during annealing to initiate the intermixing. We deposited SiO2 capping by plasma-enhanced chemical vapor deposition (PECVD) onto the InGaP/InAlGaP laser structure emitting at 635 nm, and then annealed the structure up to 950 Celsius for different periods of time, resulting in an astonishing 100 nm blueshift. This blueshift allowed us to produce an unprecedented shorter wavelength orange lasers emitting at 608 nm. For low degree of intermixing, we have noticed an increase in the intensity of the photoluminescence (PL) signal. The improvement in the PL signal was translated to a reduction in threshold current. We implemented the technique on an LED structure with Al-rich QWs emitting at 590 nm. Significant increase in the PL intensity (20 folds) was observed. By analyzing the improved structure, we observed reduction in oxygen contamination. This may represent a solution to the oxygen-related defect. The thesis opens the door for major steps forward in GaInP/AlGaInP structures for manufacturing efficient optoelectronic devices in the green, yellow and orange visible range.

碩士
長庚大學
光電工程研究所
94
There are two generally and accurately method to measure junction temperature. These two methods are called emission peak wavelength shift method and diode forward-voltage method. The defect of these methods is that the junction temperature measurements are strongly depend on the device structures above the substrate. The influence of structures induced deviation and incommodity when measured junction temperature. This work discussed with using photoluminescence spectra of GaAs substrate excited by active layer. According to Varshni equation and the red shift of spectra, we have a new method of measuring junction temperature. The results of new method were consisting with emission peak wavelength shift method, and because the substrate PL spectra shift depend directly on temperature unaffected by the structures. On the other hand, by reaching the circular pattern for p-contact, the unevenness of temperature distribution and current crowding effect in high power AlGaInP LED when the operation current increase.

碩士
國立中興大學
精密工程學系所
105
In this thesis, the manufacturing processes of FCLED；9 mil×6 mil are discussed. The current spreading ability of different shapes of n-GaAs is analyzed by SpecLED and the real chip is manufactured. The real chip and simulation both proved that the current spreading ability can be improved by etching n-GaAs. The mirror is changed from AuGe to Ag which has higher reflectivity than AuGe in order to improve the output power. The ohmic contact of p-electrode can be accomplished by AuBe/GaP, but the annealing temperature would make bonding glue produce bubbles. In this thesis, Au/Cr/ITO is deposited on p-GaP to accomplished ohmic contact. Mesa etching process is accomplished by wet etching and etching solution is Bromine-methanol solution which provides high etch selectivity of epilayer and ITO. The dry etching process with ICP(Inductively Coupled Plasma) do not have high etch selectivity of epilayer and ITO, so it can not control etch depth. In this thesis, FCLEDs with three types of n-GaAs area including 100%、17.7%、9.8% are discussed. FCLEDs with17.7% n-GaAs area have lower current density compared with FCLEDs with 9.8% n-GaAs area and have lower n-GaAs area which can absorb output power compared with FCLEDs with 100% n-GaAs area. With the same 17.7% n-GaAs area, two types of arrangement of n-GaAs including 9 circles with a diameter of 20 um and 25 circles with a diameter of 16 um are discussed. The result of SpecLED simulation shows that arrangement of n-GaAs of 9 circles has better current spreading ability than 25 circles. While the injection current is 5 mA, the output power of FCLED with 100% n-GaAs area is 2.08 mW. The output power of FCLED with17.7% n-GaAs area and 9 circles n-GaAs arrangement is 2.20 mW. The output power of FCLED with Ag mirror and 17.7% n-GaAs area 9 circles n-GaA pattern is 2.38 mW and is 2.69 mW after packaged. The FCLED output power can be improved from 2.08 mW to 2.69 mW and WPE can be improved from 22.1% to 28.0% by n-GaAs etching and changing mirror.

碩士
國立交通大學
材料科學與工程系所
96
In this thesis, the AlGaInP epi layer was successfully transferred from GaAs to diamond substrate by wafer bonding technology at first. Then the light-extraction efficiency was also increased by metal mirror reflector. The results of the experiments showed that the saturation current of diamond-light emitting diodes (LEDs) was increased. Therefore, the issue of joule-heat effect was solved by using diamond substrates because of the better heat conduction diamond substrates have. This allows the diamond-substrate LED with mirror system to operate a current up to 350 mA and a peak luminous intensity of 1849 mcd. The improvement of the light-extraction efficiency was due to the surface roughening and metal reflector. As the light driven by multi-quantum well passed through the boundary of air and LED, the rougher surface can decreased the probability of the total reflection. Therefore, the light-extraction efficiency was improved. A structure with p-roughed AlGaInP LED on GaAs substrate was fabricated by wet etching. The luminous intensity of LED was enhanced 57.4% at an injection current of 20 mA after wet etching 1 minute. A structure with p-roughed AlGaInP LED on silicon substrate was fabricated by wet etching, mirror system and wafer-bonding. The luminous intensity of LED with 3µm wet etching pattern was enhanced 53.5% at an injection current of 20 mA. Moreover, the forward voltage was decreased slightly because the augmentation of contact area. A structure with double-roughed AlGaInP LED on silicon substrate was fabricated by wet etching, mirror system, wafer-bonding and ICP dry etching. The luminous intensity was decreased after ICP dry etching. We do not know the reason exactly right now. Moreover, the forward voltage was increased because the debasement of current spreading and damage to the epi layer.

碩士
國立中興大學
精密工程研究所
93
In the study, the surface of AlGaInP light emitting diodes were roughened by dry and wet etching methods. Textured surface can increase the emitting area and allow more lights to escape from the surface of LEDs. It will enhance the light intensity and output power. In the dry etching process, polystyrene spheres were used to as natural mask. Polystyrene spheres were coated on the surface of AlGaInP LEDs in a randomly close-packed array. The surface of LEDs was roughened by ICP employing the mixture of Cl2 and Ar gases. After roughing, the light intensity and the outpower of LEDs are increased by 25% and 12% respectively at an operation current of 20mA for light-emitting diode chip of 12 mil size. In the wet etching process, the surface was roughened by the mixture of HF, HNO3, CH3COOH and ICH2COOH solution. The light intensity of LEDs is increased by 15% at an operation current of 20mA for light-emitting diode chip of 12 mil size.

碩士
國立成功大學
電機工程研究所
85
In the thesis, we present the dynamic equivalent circuit model of the quantum well visible InGaAlP laser diodes. First, we measure the static characteristics of gain-guided and index-guided laser diodes such as L-I curve, I-V curve, spectrum, and far-field pattern. We use different cavity length to obtain ηint (internal quantum efficiency), αint (internal loss), J0 (transparency current), and β (differential gain coefficient). >From L-I curve at different temperature, the T0 (characteristic temperature) is decided. Second, network analyzer is used to get the frequency response data. Finally, by fitting the L-I curve and frequency response, we can get the parameters of our model.

碩士
國立高雄海洋科技大學
微電子工程研究所
102
This study is to fabricate AlGaInP light-emitting diodes (LEDs) with multiple quantum well by metal organic chemical vapor deposition (MOCVD).The work was divided into two parts: (1) We use ethylenediamine tetraacetic acid (EDTA) to etch the surface of LEDs for 20, 30, 40 sec, respectively. The deviation of surface roughness, light spectrum, forward voltage and light output power (LOP) of the LED were evaluated. The result indicates that the as etched LED for 40 sec has a better light output power with an improvement of 116.57%. (2) A transparent conductive layer (TCL) of aluminum zinc oxide (AZO) was sputtered on the LEDs. A chip of 2 mm × 2 mm was prepared as the samples and annealed at 300 and 450℃, respectively. Under a inject current at 75 mA, The light output power of the sample with TCL annealed at 300℃ increases by 65% and that annealed at 450℃ increases by 11.62 %. These show that good quality of the TCL AZO films provides the current spreading, and results in a significant increases in the emission area with a higher external quantum efficiency.