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，在1330 nm到1500 nm之间发射的半导体激光器使用电流激光器生长在InP衬底上。然而，由于它们对温度变化不那么敏感，尺寸更大，而且与InP相比更便宜，因此更受欢迎。尽管GaAs更易于使用，但由于衬底晶格常数和激光器有源区的晶格常数不同，最佳性能通常仅限于通信区域之外。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，并允许使用与InP相似的晶格常数的GaAs衬底。变质的砷化镓激光器已经知道了一段时间，但现在开始显示出商业上可行的性能。此外，变质生长还可以用于其他领域的激光，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GaAs激光器设计。由金属有机气相外延生长的一种由3个量子阱组成的有源区的异质结在室温下显示出阈值密度为127 mA/QW的低阈值脉冲激光，在不同注入电流下在288K下连续工作在1300 nm以上(详见MOVPE变质激光器和电信波长的纳米结构工程)。下一步将是更多地了解半导体激光器的结构，因为缺陷、应变和形态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中心(PIADS CDT)合作进行的。CDT是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的任务是解决当前数据存储和传输领域的挑战。这项研究属于PIADS CDT研究主题，即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光谱。将使用计算软件对图像进行分析。总体而言，这些技术将提供纳米级结构的信息，重点是化学成分、缺陷和应变。该项目的目的是研究生长的砷化镓变质样品，并使用这些技术提供原子级的综合分析。然后，这些发现可以与激光的光学性质和生长过程联系起来，以进行优化。反过来，我们希望在1300 nm到1550 nm的范围内提高激光器的性能。

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.