As-grown deep-level defects in n-GaN grown by metal–organic chemical vapor deposition on freestanding GaN

Abstract

Traps of energy levels Ec −0.26 and Ec −0.61 eV have been identified as as-grown traps in n-GaN grown by metal–organic chemical vapor deposition by using deep level transient spectroscopy of the Schottky contacts fabricated by resistive evaporation. The additional traps of Ec −0.13 and Ec −0.65 eV have been observed in samples whose contacts are deposited by electron-beam evaporation. An increase in concentration of the Ec −0.13 and Ec −0.65 eV traps when approaching the interface between the contact and the GaN film supports our argument that these traps are induced by electron-beam irradiation. Conversely, the depth profiles of as-grown traps show different profiles between several samples with increased or uniform distribution in the near surface below 50 nm. Similar profiles are observed in GaN grown on a sapphire substrate. We conclude that the growth process causes these large concentrations of as-grown traps in the near-surface region. It is speculated that the finishing step in the growth process should be an essential issue in the investigation of the surface state of GaN.