Amphoteric behavior of impurities in GaN film grown on Si substrate

Hall measurement presented that an unintentionally doped uniform and crack-free GaN film grown on n-type (111)-oriented Si substrate with high temperature-grown relatively thin AlN single and multiple buffer layer shows p-type conductivity. The position of valence band maximum at the surface of the film measured by the synchrotron radiation photoemission spectroscopy is below Fermi level at 1.09 eV due to band bending at the surface, which is indicative for the p-type nature of the grown film. The n-channel metal-oxide-semiconductor field effect transistor (MOSFET) fabricated on the GaN layer exhibited normally-off mode operation. This cannot be achieved if the GaN layer is not p-type. It is believed that the spatial coordination of auto-doped Si atoms, out-diffused from the substrate, or carbon complexes from metal-organic (MO) precursor favorably occupy the substitutional nitrogen site of the GaN film when the film is under tensile strain during the growth, which clearly explains that the p-type conduction is originated from the stress dependent amphoteric nature of Si atom and/or carbon complex in GaN.