MOVPE growth and characterization of Mg-doped GaN

Mg-doping of GaN films has been investigated as a function of growth rate, reactor pressure and N to Ga flow ratio (V/III ratio). The nominal doping level, determined by the Mg to Ga flow ratio, was kept constant. Secondary-ion-mass-spectroscopy (SIMS) measurements indicate that more Mg is incorporated at low pressure; the incorporation efficiency is independent of the other variables. The electrical properties of the films grown at atmospheric pressure appear independent of growth rate and V/III ratio, displaying an average hole concentration of 7.4 x 10(17) cm(-3) and mobility of 9.3 cm(2)/V s. However, films grown at a reduced pressure of 76 Torr exhibit a strong dependence on V/III ratio; the conductivity is observed to improve by an order of magnitude when the V/III ratio is raised by a factor of four. We observe a simultaneous increase in hole concentration and mobility in these films suggesting that a high degree of compensation, probably due to nitrogen vacancies, is present in the films grown at low V/III ratios. Finally, room-temperature photoluminescence (PL) measurements were performed on the samples. The PL spectra are dominated by a broad peak at 2.8 eV; the peak intensity is found to increase with increasing V/III ratio. (C) 1998 Elsevier Science B.V. All rights reserved.