Electronic Defect States Observed by Cathodoluminescence Spectroscopy at GaN/Sapphire Interfaces

Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used to probe the spatial distribution and energies of electronic defects near GaN/Al2O3 interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy imaging, CLS and CL imaging show systematic variations in defect emissions with a wide range of HVPE GaN/sapphire electronic properties. Highly degenerate interface regions give rise to above bandgap emissions due to band filling and free electron recombination. Besides the common donor and acceptor bound exciton, CLS and CL images also reveal emissions due to excitons bound to stacking faults and cubic phase GaN.