Identification of point defects in GaN materials and their impact on device performance

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The project proposes to extend the electrical characterisation techniques used for smaller gap materials by the Manchester group for decades to measure the electrical properties of defects in wide band gap semiconductors. The most important wide gap materials at the present time are GaN and InGaN. They are used to make low energy LED lighting and highpower transistors. Today's generation of these devices does not function as well as would seem possible from the properties of the materials and at the present time functionality and performance is limited. This is due, at least in part, to the presence of point defects in the component materials and devices. Eg, In LEDs so called Shockley-Reed-Hall recombination due to gap states is still a significant efficiency loss mechanism. The student will use deep level transient spectroscopy and photoluminescence techniques to identify the nature of the point defects in these materials and how they impact on real LED and transistor devices. Particular defects and impurities will be introduced, either by the industrial collaborator during growth or by using eg implantation or irradiation. The resulting defect energy levels will be then characterised using the techniques described, and the impact of device performance assessed. The nitride materials are still their infancy as semiconductors, they contain high levels of point defects, vacancies, interstitials and impurities such as carbon. The electronic behaviour of these defects is almost completely unknown. What is known is that real world devices show undesirable properties such as current collapse in transistors and anomalous efficiency droop in LEDs. These effects are believed to be due to defect states, but as of today there is no definitive demonstration of what defect is responsible. This project represents a tremendous opportunity to perform world class, high impact, research in this area.