CDT Compound Semiconductor Physics (PhD Progression 1+3)

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The team in Cardiff successful grows epitaxial gallium nitride (GaN) layers on (111) silicon (Si) substrates. This may be one solution to enable integration of light emitting diodes (LEDs) for photonics onto standard Si process technology production lines. Key issues are wafer cracking due to -17% tensile strain of the GaN and the generation of dense misfit dislocation networks due to the misfit and the thermal expansion mismatch between GaN and Si and also the formation of good ohmic electrical contacts for device operation. Various methods to explore and reduce lattice strain will be investigated in this combined electron microscopy and electron spectroscopy study where one key question to answer is whether and to what degree the anneal of the electrical contacts enhances strain relaxation in the GaN layers underneath.Energy-dispersive X-ray spectroscopy (EDX), EDX mapping, electron energy-loss spectroscopy (EELS) with energy-loss near-edge spectroscopy (ELNES) and energy-filtered imaging (EFTEM) will be used in project B to study the local chemistry in cross-section, to measure interdiffusion at the atomic scale and optimise the quality of the electrical contact multilayers that require annealing after deposition.