Gallium arsenide based Buried Heterostructure Laser Diodes ... 9091/ ¢  Gallium arsenide

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Transcript of Gallium arsenide based Buried Heterostructure Laser Diodes ... 9091/ ¢  Gallium arsenide

  • Gallium arsenide based Buried Heterostructure Laser Diodes

    with Aluminium-free Semi-Insulating materials Regrowth

    Doctoral Thesis by

    Carlos Angulo Barrios

    Laboratory of Semiconductor Materials Department of Microelectronics and Information Technology

    Royal Institute of Technology Electrum 229, S-164 40 Kista, Sweden

    Stockholm 2002

    SI-GaInP

    n-GaAs substrate

    p-DBR

    n-DBR

    light

    SI-GaInP

  • Cover picture: Schematic cross-section of a buried heterostructure VCSEL incorporating semi-insulating GaInP:Fe as the burying layer. The work on this laser was pointed out as one of the highlights in this field by the magazine Compound Semiconductor, 6(7) Sept./Oct. 2000.

  • To my parents for their never-ending support

  • One shouldn’t work on semiconductors, that is a filthy mess;

    who knows whether they really exist.

    Wolfgang Pauli, 1931

    Well, in that case, one should consider semi-insulating materials as a filthy mess full of traps, which is even worse;

    sometimes they exist, sometimes they don’t.

    The author

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    Carlos Angulo Barrios Gallium arsenide based buried heterostructure semiconductor lasers with aluminium- free semi-insulating materials regrowth.

    Department of Microelectronics and Information Technology, Laboratory of Semiconductor Materials, Royal Institute of Technology, S-164 40 Kista, Sweden

    ISRN KTH/HMA/FR-02/1-SE/TRITA-HMA Report 2002:1/ISSN 1404-0379

    Abstract

    Semiconductor lasers based on gallium arsenide and related materials are widely used in applications such as optical communication systems, sensing, compact disc players, distance measurement, etc. The performance of these lasers can be improved using a buried heterostructure offering lateral carrier and optical confinement. In particular, if the confinement (burying) layer is implemented by epitaxial regrowth of an appropriate aluminium-free semi-insulating (SI) material, passivation of etched surfaces, reduced tendency to oxidation, low capacitance and integration feasibility are additional advantages.

    The major impediment in the fabrication of GaAs/AlGaAs buried- heterostructure lasers is the spontaneous oxidation of aluminium on the etched walls of the structure. Al-oxide acts as a mask and makes the regrowth process extremely challenging. In this work, a HCl gas-based in-situ cleaning technique is employed successfully to remove Al-oxide prior to regrowth of SI-GaInP:Fe and SI-GaAs:Fe around Al-containing laser mesas by Hydride Vapour Phase Epitaxy. Excellent regrowth interfaces, without voids, are obtained, even around AlAs layers. Consequences of using inadequate cleaning treatments are also presented. Regrowth morphology aspects are discussed in terms of different growth mechanisms.

    Time-resolved photoluminescence characterisation indicates a uniform Fe trap distribution throughout the regrown GaInP:Fe. Scanning capacitance microscopy measurements demonstrate the semi-insulating nature of the regrown GaInP:Fe layer. The presence of EL2 defects in regrown GaAs:Fe makes more difficult the interpretation of the characterisation results in the near vicinity of the laser mesa.

    GaAs/AlGaAs buried-heterostructure lasers, both in-plane lasers and vertical- cavity surface-emitting lasers, with GaInP:Fe as burying layer are demonstrated for the first time. The lasers exhibit good performance demonstrating that SI-GaInP:Fe is an appropriate material to be used for this purpose and the suitability of our cleaning and regrowth method for the fabrication of this type of semiconductor lasers. Device characterisation indicates negligible leakage current along the etched mesa sidewalls confirming a smooth regrowth interface. Nevertheless, experimental and simulation results reveal that a significant part of the injected current is lost as leakage through the burying material. This is attributed to double carrier injection into the SI- GaInP:Fe layer. Simulations also predict that the function of GaInP:Fe as current blocking layer should be markedly improved in the case of GaAs-based longer wavelength lasers.

    Index Terms: semiconductor lasers, in-plane lasers, VCSELs, GaAs, GaInP, semi- insulating materials, hydride vapour phase epitaxy, regrowth, buried heterostructure, leakage current, simulation.

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    Preface

    This thesis is a result of the research on the applications of Al-free semi-insulating materials for fabricating GaAs-based buried-heterostructure semiconductor lasers. As a consequence, it deals with the fabrication, performance and analysis of these lasers. Different facets related to the subject of the thesis are: epitaxial growth and cleaning techniques of III-V semiconductor materials, device process technology, materials characterisation, device characterisation and theoretical analysis by computer simulation.

    The thesis is divided into three parts. Part I presents an introduction to the subject, the state-of-the-art, motivation and aims of the work. Part II reviews some of the basics necessary to follow more easily the original work. Part III contains the development of the original work, summary, conclusions and proposals for future research. An appendix illustrates the processing steps of buried heterostructure laser diode fabrication. Reprints of the papers are attached at the end.

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    Acknowledgements

    The realisation of this thesis was possible thanks to the work and efforts of many people and now it is time to thank all of them. First, I would like to thank Prof. Gunnar Landgren, head of the Laboratory of Semiconductor Materials (HMA), for accepting me as a Ph.D. student at KTH.

    The major part of this thesis work was supported by NUTEK, within the framework of ERGO/KOFUMA programme. Actually, this thesis could be considered as the final report of that project. The main characters of this collaboration have been:

    Dr. Sebastian Lourdudoss, called “Doss” by his friends, that is, everybody. Scientist, teacher, poet, family man, and one of the most generous persons I have ever met. He has been my supervisor and friend during these years as a Ph.D. student. His inexhaustible and contagious optimism and enthusiasm gave me the necessary energy during the “hard times”, when the materials we were studying seemed to be “semi- insulting” rather than semi-insulating. “Things work according to one’s own belief”, he told me once. Since then, I become a “believer”. Despite his numerous and growing occupations, he had ALWAYS time for my infinite and disturbing questions. I will be never able to express enough my gratitude to him.

    Dr. Egbert Rodríguez Messmer, my first contact and friend in Sweden. He was my teacher in the lab and revealed me the secrets of the (g)old HVPE reactor. His help and expertise were determinant in the development of this work. It has been a pleasure to work with him. Outside the lab, he also taught me Swedish habits, rules, bureaucracy and other issues that made my incorporation into the “machinery” easier, and introduced to me many interesting and nice people. Since I knew that he was a Real Madrid supporter, I realised that we were going to speak the same language. He also induced me indirectly to run Stockholm Marathon twice and Stockholms Loppet …although I am not sure if I should be grateful for that....

    Martin Holmgren from the former Spectra Precision (now Trimble). He provided IPL structures and mounting and characterisation facilities at SPA. Anita Lövqvist and Dr. Marco Ghisoni from the former Mitel Semiconductors (now Zarlink). Anita provided VCSEL structures and worked very hard on the processing of BH-VCSELs. Christina Carlsson, John Halonen and Prof. Anders Larsson from Chalmers University of Technology. Christina made VCSEL characterisation and John worked on the dry etching of the VCSELs. Andreas Gaarder (excellent pianist and master of wines) and Dr. Saulius Marcinkevicious (expert in Viking stories and Lithuanian basketball) from the Optics department at KTH worked on the TR-PL characterisation. A smooth collaboration with all these people has been extremely beneficial. I am extremely lucky for having worked with such extraordinary group of professionals from industry and academia, and I thank all of them for their help and contribution to this work.

    In addition, other remarkable people not “officially” included in the project have also contributed significantly to this thesis. Christiane Buchgeister and Lena Bäckbom helped me in the clean room during laser processing. I learnt many processing skills from them. Olivier Douhéret (Ph.D. in enthusiasm) and Dr. Srinivasan Anand worked on the SCM measurements. I enjoyed very much discussing scientific and non-scientific topics with Anand. Dr. Renaud Stevens measured high-speed performance of the VCSELs. Dr. Richard Schatz helped me to understand the high frequency modulation results of BH-VCSELs. Dr. Hans

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    Martinsson from Chalmers did electroluminescence measurements on the IPLs. I had also very fruitful discussions with Sebastian Mogg and Dr. Olle Kjebon on semiconductor laser physics.

    I must dedicate a special section to the HVPE group. Dr. David Söderström, a Swede with Latin soul; his passion for dancing salsa is only comparable to his meticulous work procedures. I learnt many things from him. Dr. Denis Jahan, my first officemate; we had interesting discussions a