(Invited) Shallow Donor Impurities in GaN

Abstract

Significant advances have been achieved during the last three decades in heteroepitaxial, homoepitaxial, and bulk growth of nitride semiconductors. Despite this remarkable progress, the full realization of the functionality of this material system is often limited by the presence of pervasive residual impurities inherent to the high-temperature growth process, and/or by the presence of lattice point and extended defects. A number of important fundamental aspects of these properties must be understood and controlled in order to realize optimum device performance.We review here on a systematic investigation, employing a combination of defect-sensitive techniques, carried out on freestanding HVPE-GaN films to identify the chemical nature of the shallow donors. High-resolution, variable temperature PL experiments were performed in the spectral region associated with recombination processes involving the ground and excited states of the neutral donor bound excitons and their two-electron-satellites in GaN substrates and homoepitaxial films. High-sensitivity SIMS and high-resolution FTIR measurements unambiguously identify Si and O shallow donors with ground state binding energies of 30.18 meV and 33.20 meV, respectively. These binding energies are in excellent agreement with values obtained by the analyses of the two-electron-satellite PL spectra considering the participation of ground and excited state donor bound excitons. High-resolution PL studies of homoepitaxial GaN films confirm the SIMS and the FTIR impurity identifications. These results were conveniently employed to verify the incorporation and activation of shallow donors in high crystalline quality GaN substrates.This work supported by the Office of Naval Research