Molecular beam epitaxial growth of terahertz quantum cascade lasers

本项目将集中在分子束外延(MBE)生长的GaAsAlGaAs太赫兹频率(THz)量子级联激光器(QCL)。尽管这种高功率太赫兹光源将带来许多应用，从高带宽通信和卫星传感到制造业的无损检测，但目前所有太赫兹QCL都需要在低温下运行，这限制了它们的开发。该项目将通过与国际合作伙伴和行业合作，展示具有高输出功率的Peltier冷却THz QCL操作，以及有史以来第一个室温THz QCL，从而使THz技术的接受度发生阶段性变化。在该项目中，候选人将成为通过分子束外延生长半导体结构的专家，并在器件建模、器件制造以及激光器的电气和光学特性方面获得丰富的经验。他们将使用分子束外延技术来生长太赫兹QCL，每个QCL都有1000多个单独的层，以原子单层的精度进行图案化。他们将对不同的异质结构设计进行系统的比较，包括研究势垒高度和掺杂对性能的影响，以及优化生长条件，如衬底温度和III/V通量比。该项目将以使用原位通量测量和光学测温以及非原位X射线衍射等技术的详细生长特征为基础。这将确保不同晶圆生长之间的长期重现性。所有材料都将在该大学新的布拉格材料研究中心的纳米技术洁净室中加工成激光，然后在该学院的太赫兹实验室进行电学和光学测试。结果将与模拟结果进行比较，以优化工作在2太赫兹和5太赫兹之间的激光器的性能。

This project will focus on the molecular beam epitaxial (MBE) growth of GaAs-AlGaAs terahertz-frequency (THz) quantum cascade lasers (QCLs). Despite the many applications that would benefit from such a high-power THz source, ranging from high bandwidth communications and satellite sensing through to non-destructive testing in the manufacturing sector, currently all THz QCLs need to operate at cryogenic temperatures, which limits their exploitation. The project will make a step change in the take-up of THz technologies, working in collaboration with international partners and industry, by demonstrating Peltier-cooled THz QCL operation with high output powers, and the first-ever room temperature THz QCL. During the project, the candidate will become an expert in the growth of semiconductor structures by MBE, as well as gaining extensive experience in device modelling, device fabrication, and electrical and optical characterisation of lasers. They will use MBE techniques to grow THz QCLs, each of which has more than 1000 separate layers, patterned with atomic monolayer precision. They will perform systematic comparisons between different heterostructure designs, including investigating the effect of barrier height and doping on performance, as well as optimising the growth conditions such as substrate temperature, and III/V flux ratios. The project will be underpinned by detailed growth characterisation using techniques such as in situ flux measurements and optical pyrometry, as well as ex situ X-ray diffraction. This will ensure long-term reproducibility between different wafer growths. All material will be processed into lasers using the nanotechnology cleanroom in the University's new Bragg Centre for Materials Research before being testing electrically and optically in the School's terahertz laboratories. Results will be compared with simulations to enable optimisation of performance of lasers operating between 2 THz and 5 THz.