Heavily silicon-doped GaN by MOVPE

Abstract

Heavily Si-doped GaN epitaxial layers have been grown at 1050°C on AlN-buffered (0001) sapphire substrates by atmospheric pressure metalorganic vapor phase epitaxy using trimethylgallium, trimethylaluminuim and ammoniac sources. H2 was the carrier gas. The silicon doping characteristics of GaN epilayers have been investigated by varying the silane (SiH4) flow. In order to calibrate the thickness of the buffer layer and the surface flatness of GaN, the growth was monitored in situ by laser reflectometry. Electron concentration between 5×1018 and 2.2×1020cm−3 was obtained with mobility ranging from 200 to 9cm2/Vs. A saturation tendency of electron concentration appears. The comparison between the Hall effect measurements and theoretical calculations of mobility based on a simple model leads to the determination of the compensation ratio of the samples which depends strongly on the SiH4 partial pressure. We attribute the origin of this compensation to the amphoteric behavior of silicon.