Effect of p-type activation ambient on acceptor levels in Mg-doped GaN

Abstract

The effect of p-type activation ambient on acceptor levels in Mg-doped GaN grown by metalorganic chemical-vapor deposition has been investigated electrically. GaN samples with Mg concentrations of ∼2.7×1019 cm−3 were activated at 700 °C for 5 min in pure O2 and N2 gas ambients, respectively. From room-temperature Hall-effect measurements, the sheet carrier concentration of the O2-annealed sample was ∼2.3×1013 cm−2, a value about three times higher than that of the N2-annealed sample. However, capacitance–voltage, thermal admittance spectroscopy, and current deep-level transient spectroscopy measurements on Schottky diodes fabricated showed no significant difference in Mg acceptor level between them. In addition, secondary ion mass spectrometry and atomic force microscopy measurements revealed that the O2 annealing enhanced the removal of residual H atoms and the formation of Ga-oxide islands with surface roughening, compared to conventional N2 annealing. These results indicate that the O2 anneal induces lowering of the surface resistance via the conductive Ga-oxide phase rather than the enhancement of the p-type doping characteristics in the near surface region.