CDT Compound Semiconductor Physics (PhD Progression 1+3)

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Many modern applications (e.g. LiDAR, free space communications) require the rapid, accurate detection of weak optical signals. Internal gain within the detector can help to improve sensitivity to these signals, but if electrons and holes both cause gain in a device then a feedback loop will limit performance. Using bismuth alloying to engineer valence band structure has recently led to unprecedented improvements in APD performance by preventing holes from attaining the energy levels necessary to cause impact ionisation. While these results are promising, the technique needs to be applied to current state-of-the-art APD materials to produce game-changing devices. This project will explore the molecular beam epitaxy (MBE) growth of InAlAsBi APDs on InP. The growth of dilute bismide semiconductors is challenging, with material properties sensitively depending on a great number of parameters. Throughout the project, the student will explore the MBE growth of InAlAsBi, pursue material characterisation through photoluminescence, XRD, Nomarski microscopy and externally contracted techniques such as SIMS and TEM. They will then grow and fabricate a series of devices based on InAlAsBi and conduct detailed opto-electronic characterisation. By the end of the project, the student will understand dilute bismide APDs from growth to avalanching properties.