Defect formation near GaN surfaces and interfaces

Abstract

We have used low-energy electron-excited nanoscale-luminescence (LEEN) spectroscopy combined with ultrahigh vacuum (UHV) surface science techniques to probe deep level defect states at GaN free surfaces, metal-GaN contacts and GaN/InGaN quantum well interfaces. Employing energies as low as 100eV and ranging up to 5keV, we have been able to establish the local nature of these states and their spatial variation normal to the interface plane on an incremental 10–20nm scale. Coupled with surface science techniques, these measurements show that a variety of discrete deep levels form deep within the GaN band gap due to (a)native defects, (b)metal-induced bonding, (c)reaction products, and (d), in the case of GaN/InGaN heterostructures, local interface phase changes. These results suggest that deep levels are a common feature at GaN interfaces and hence can play an integral role in charge transfer and the formation of local dipoles at GaN heterostructures.