Relationship between physical properties and gas purification in GaN grownby metalorganic vapor phase epitaxy

This paper reports on the structural, optical and electrical properties of LP-MOCVD GaN grown on miscut and exactly oriented sapphire substrates as a function of gas purification. SIMS and C-V experiments achieved on GaN laye rs indicate that high purity NH, is a significant source of oxygen contamin ation. Transport studies performed on oxygen-contaminated GaN samples have shown that oxygen acts as a very shallow donor. An activation energy rangin g from 4 to 10 meV is extracted as a function of oxygen concentration. Hall mobilities of unintentionally oxygen-doped GaN samples are comparable to t he data already published in the literature for silicon doped samples over carrier density range: 5 x 10(17)-3 x 10(19) cm(-3) [S. Nakamura et al., Jp n. J. Appl. Phys. 31 (1992) 2283]. Structural and optical GaN properties ar e not degraded by oxygen-contamination. [0 0 2] X-ray rocking curve (omega- scans) widths around 26-80 arcsec are obtained and a strong correlation is observed between low broad band yellow emission and highly oxygen-contamina ted GaN samples. (C) 1998 Elsevier Science B.V. All rights reserved.