The influence of growth conditions on the electrical properties of magnesium-doped GaN grown by MOVPE

We report on the electrical properties of magnesium-doped p-type GaN as a f unction of different growth conditions used in MOVPE. Low resistivity p-typ e GaN is essential e.g. for producing laser diodes with low operating volta ges and long lifetimes. We focused on the effects of the Mg flux, growth te mperature, growth rate and V/III ratio on the p-type conductivity By varyin g the gamma = [Mg]/([Mg] + [Ga]) ratio in the range from 0.1 to 0.8% we obs erved a minimum in the specific resistivity in agreement with other groups. With optimized gamma-values we changed the other parameters mentioned abov e in a range that ensures high quality GaN. The use of Cp2Mg as a doping pr ecursor could entail several difficulties. Therefore we investigated the Mg profiles by SIMS. We observed a linear correlation between the doping dela y and the Mg flux. This could be caused by thr consumption of Mg by reactio n with H2O trace impurities at the tubing walls. The samples with the lowes t resistivity realized so far show a specific resistivity of 2 Omega cm wit h a hole concentration of p = 3 x 10(17) cm(-3) and a mobility of mu = 10 c m(2)/Vs.