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 function of different growth conditions used in MOVPE. Low resistivity p-type GaN is essential e.g. for producing laser diodes with low operating voltages and long lifetimes. We focused on the effects of the Mg flux, growth temperature, growth rate and V/III ratio on the p-type conductivity. By varying the γ = [Mg]/([Mg] + [Ga]) ratio in the range from 0.1 to 0.8% we observed a minimum in the specific resistivity in agreement with other groups. With optimized γ-values we changed the other parameters mentioned above in a range that ensures high quality GaN. The use of Cp2Mg as a doping precursor could entail several difficulties. Therefore we investigated the Mg profiles by SIMS. We observed a linear correlation between the doping delay and the Mg flux. This could be caused by the consumption of Mg by reaction with H2O trace impurities at the tubing walls. The samples with the lowest resistivity realized so far show a specific resistivity of 2 Ωcm with a hole concentration of p = 3 × 1017 cm—3 and a mobility of μ = 10 cm2/Vs.