Defect formation near GaN surfaces and interfaces

We have used low-energy electron-excited nanoscale-luminescence (LEEN) spec troscopy combined with ultrahigh vacuum (UHV) surface science techniques to probe deep level defect states at GaN free surfaces, metal-GaN contacts an d GaN/InGaN quantum well interfaces. Employing energies as low as 100 eV an d ranging up to 5 eV, we have been able to establish the local nature of th ese states and their spatial variation normal to the interface Plane on an incremental 10-20 nm scale. Coupled with surface science techniques, these measurements show that a variety of discrete deep levels form deep within t he GaN band gap due to (a) native defects, (b) metal-induced bonding, (c) r eaction products, and (d), in the case of GaN/InGaN heterostructures, local interface phase changes. These results suggest that deep levels are a comm on feature at GaN interfaces and hence can play an integral role in charge transfer and the formation of local dipoles at GaN heterostructures. (C) 19 99 Elsevier Science B.V. All rights reserved.