Transmission electron microscopy study of defects in GaN/(111)Si epitaxial layers with annealed metallisation contacts

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.

Conventional electron diffraction contrast (EDC), high-resolution lattice imaging (HREM), and annular dark-field (ADF) scanning transmission electron microscopy (STEM) will be used in project A to image dislocation lines and measure their density in plan-view (top-down) geometry, and to determine the dislocation types and image their cores in cross-sectional geometry.