Investigating GaAs metamorphic lasers

电信是社会的重要组成部分，数据传输的方式之一是通过光纤发送光脉冲。通常，半导体激光器发射在1330nm和1500nm之间的区域，与目前的激光器生长在InP衬底。然而，GaAs衬底是首选，因为它们对温度变化不太敏感，与InP相比，尺寸更大，价格更便宜。虽然GaAs更有利于使用，但由于衬底的晶格常数和激光器的有源区域之间的差异，其最佳性能通常限制在通信区域之外。克服这一问题的一种方法是通过在GaAs上生长晶格不匹配的InGaAs晶格缓冲层来创建具有选定晶格常数的虚拟衬底。这一过程被称为变质生长，并允许使用晶格常数与InP相似的GaAs衬底。变质砷化镓激光器已经为人所知有一段时间了，但现在才开始显示出商业上可行的性能。此外，变质生长还可用于其他领域的激光器，如医疗和环境监测。最近，位于科克的廷德尔国家研究所的纳米结构外延和物理小组开发了一种新的变质砷化镓激光器设计。通过金属有机气相外延生长，一个具有3个量子阱有源区的异质结构在室温下表现出低阈值脉冲激光，阈值密度电流为127mA / QW，在不同注入电流下在288K下连续波工作超过1300nm（详细信息请参见MOVPE变质激光器和电信波长纳米结构工程）。下一阶段将是进一步了解半导体激光器的结构，因为诸如缺陷、应变和形貌等特性会影响激光器的性能。该项目是与EPSRC光子集成和高级数据存储博士培训中心（PIADS CDT）联合进行的。包括贝尔法斯特女王大学和廷德尔国家研究所在内的多个学术和工业组织之间的合作，CDT的职责是解决当前数据存储和传输领域的挑战。本研究属于PIADS CDT研究主题：在恶劣环境下工作的超可靠半导体激光器和原子尺度分析技术。该项目将使用电子显微镜技术，如透射电子显微镜、扫描电子显微镜和能量色散电子能谱。计算机软件将用于分析图像。总的来说，这些技术将提供纳米尺度结构的信息，重点是化学成分、缺陷和应变。本项目的目的是研究生长的砷化镓变质样品，并利用该技术在原子尺度上提供全面的分析。这些发现可以与激光的光学特性和优化的生长过程联系起来。反过来，我们希望在1300nm到1550nm范围内提高激光性能。

Telecommunication is an important part of society and one of the ways data is transmitted is by sending light pulses down an optical fibre. Typically, semiconductor lasers emitting in the region between 1330nm and 1500nm are used with the current lasers being grown on InP substrates. However, GaAs substrates are preferred as they are less sensitive to temperature changes, available in larger sizes and cheaper in comparison to InP. Although GaAs is more favourable to use, optimal performance is usually limited to outside the telecommunication region due to differences between the lattice constants of the substrate and active region of the laser. One way to overcome this is to create a virtual substrate with a chosen lattice constant by growing a lattice mismatched InGaAs lattice buffer layer onto GaAs. This procedure is known as metamorphic growth and allows GaAs substrates to be used with lattice constants that are similar to InP. Metamorphic GaAs lasers have been known for a while but are now starting to show performances which are commercially viable. Furthermore, metamorphic growth could also be used for lasers in other fields such as medical and environmental monitoring.Recently, the Epitaxy and Physics of Nanostructures group at the Tyndall National Institute in Cork developed a novel metamorphic GaAs laser design. Grown by metalorganic vapour phase epitaxy, one heterostructure with active region of 3 quantum wells showed low threshold pulsed lasing with threshold density current of 127mA per QW at room temperature and continuous wave operation over 1300nm at 288K under various injection currents (further details in MOVPE metamorphic lasers and nanostructure engineering at telecom wavelengths). The next stage would be to find out more about the structure of the semiconductor laser as properties such as defects, strain and morphology can influence the performance of the laser.This project is being conducted in conjunction with the EPSRC Photonic Integration and Advanced Data Storage Centre for Doctoral Training, PIADS CDT. A collaboration between multiple academic and industrial organisations including Queen's University Belfast and Tyndall National Institute, the CDT's remit is to solve current challenges in the field of data storage and transmission. This research falls into the PIADS CDT research theme of Ultra-reliable semiconductor lasers operating in hostile environments and atomic scale analysis techniques.The project will use electron microscopy techniques such as Transmission Electron Microscopy, Scanning Electron Microscopy and Energy Dispersive electron spectroscopy. Computational software will be used to analyse the images. Overall, these techniques will provide information on the structures at the nanoscale, with the focus on chemical composition, defects and strain.The aim of this project is to investigate the GaAs metamorphic samples grown and use the techniques to provide a comprehensive analysis at the atomic scale. The findings can then be linked to the optical properties of the laser and the growth procedure for optimisation. In turn, we hope to improve the laser performance in the range of 1300nm to 1550nm.