Molecular beam epitaxial growth of terahertz quantum cascade lasers

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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.