Ab-initioanalytic calculation of point defects in AlGaN/GaN heterointerfaces.

One of the major challenges for the GaN-based high electron mobility transistors (HEMTs) used as high power devices is to understand the effect of defects, especially on the band alignment. Using ab initio calculation, herein we investigate the variations of band offsets with interfacial structure, defect position, interface states and Al content in AlxGa1-xN/GaN heterostructures (x = 0.063, 0.125, 0.187, 0.250). It was found that N vacancy (VN) and Ga anti-site (GaN) introduce nonlocal interface states and the change of valence band offset (VBO) depends on the defect location. While the interface states induced by Ga vacancy (VGa) and N anti-site (NGa) show strong localization behavior, and their impact on VBO is independent on the defect position. The low symmetry of wurtzite nitride and the lattice mismatch between AlGaN and GaN will generate polarization charge (spontaneous polarization and piezoelectric polarization) at the interface. Along the direction of polarization field, VN and GaN lying in the AlGaN side change the VBO most pronouncedly. These theoretical results provide useful guidance for control of point defects in AlGaN/GaN HEMTs, which have profound impact on the performance and reliability of GaN-based devices.