Impurity band in the interfacial region of GaN films grown by hydride vapor phase epitaxy

Using several derivatives of scanning force microscopy with conducting tips, we find direct evidence for the existence of a highly compensated donor impurity band in GaN films near the sapphire substrate interface. Scanning current-voltage and capacitance microscopy measurements both show that the free electron density is much higher in the interfacial region of these films. However, surface contact potential images reveal that the Fermi level …