Impurity contamination of GaN epitaxial films from the sapphire, SiC and ZnO substrates

Likely contamination of GaN films by impurities emanating from Al2O3, SiC and ZnO substrates during growth has been studied by secondary ion mass spectrometry analysis. The highly defective interfacial region allows impurities to incorporate more readily as compared to the equilibrium solubility in a perfect crystal at a given temperature as evidenced by increased impurity levels in that region as detected by SIMS. The SIMS measurements in GaN layers grown on SIC and sapphire showed large amounts of Si and O, respectively, within a region wider than the highly disordered interfacial region pointing to the possibility of impurity diffusion at growth temperatures. The qualitative trend observed is fairly clear and significant. These observations underscores the necessity for developing GaN and/or AIN substrates.