Polarization‐induced surface band bendings of GaN films studied by synchrotron radiation photoemission spectroscopy

The change in the surface band bandings of GaN films with crystal polarity and strain was investigated using synchrotron radiation photoemission spectroscopy. The Ga‐face GaN sample showed larger surface band bending than the N‐face one by 1.4 eV due to spontaneous polarization‐induced sheet charges at the surface, resulting in a higher Schottky barrier height of a Pt contact. For both n‐type and p‐type GaN, the shift of the surface Fermi level with longitudinal tensile strain (∼4 × 10−3) is negligible, while that with compressive strain (∼3 × 10−3) is significant. This could be attributable to combined effects of piezoelectric polarization‐induced sheet charges and the change of bandgap energy with the strains near the surface region. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)