Improved crystalline quality of GaN by substrate ion beam pretreatment

Abstract

The use of a buffer layer and nitridation are the most common methods employed to reduce defects in GaN epilayers grown on a sapphire substrate by metal organic chemical vapor deposition (MOCVD). Ion beam pretreatment of a substrate was carried out for further reduction of strain and dislocation in the GaN epilayer. The ion dose was set at 1 x 10(16) cm(-2); the ion energies were 800 eV and 55 keV. The 800 eV ion beam was a reactive (N-2(+)) ion beam (RIB) and the 55 keV N+ ion beam was from a normal ion implanter (N+ implantation). Both ion beam pretreatments resulted in the formation of a disordered amorphous phase on the substrate surface. Obviously, the thickness of the amorphous phase increased with the ion beam energy, However, the phase formed by the 800 eV ion beam was AlON, whereas the phase formed by the 55 keV ion beam was AlN. A Raman shift clearly showed that the strain in the GaN epilayer was decreased by the ion beam pretreatment of the sapphire substrate. Defect density in the GaN was reduced up to 50% by the ion beam pretreatment. The present results show that sapphire (0001) substrate ion beam pretreatment can be used to improve the properties of GaN epilayers grown by MOCVD.