Hole carrier concentration and photoluminescence in magnesium doped InGaN and GaN grown on sapphire and GaN misoriented substrates

Systematic studies of In(x)Ga(1-x)N layers (0 <= x < 0.13) doped with Mg were performed. Samples were grown by metal organic vapor phase epitaxy. Intermediate Mg doping in the range of 2 x 10(19) cm(-3) was chosen to achieve a maximum hole carrier concentration, p(H) (as measured by Hall effect) of 4 x 10(18) cm(-3) in samples with high x. We confirmed reports on decreasing resistivity in In(x)Ga(1-x)N:Mg epitaxial layers observed with increasing x. This finding is very important for applications. In the performed research we attempted to separate contributions to p(H) increase resulting from increase in In-content and an associated decrease in growth temperature, T(gr) (necessary to obtain high x). For this purpose In-content increase was achieved by means of either (i) lowering the growth temperature (from 1020 to 830 degrees C) or by (ii) varying an intended GaN substrate miscut. We demonstrated that the increase in p(H) in In(x)Ga(1-x)N:Mg is caused by higher In concentration while a drop in T(gr) plays a secondary role. Studies of photoluminescence in the InGaN:Mg layers exhibit band-to-band radiative recombination which has created much controversy. The most important feature of samples grown at temperatures 860 degrees C and below, is a green band observed in InGaN:Mg layers (not in GaN:Mg obtained at the same T(gr)) dominating the whole spectrum at room temperature. Its maximum shifts from 2.5 to 2.2 eV with increasing x up to 0.13. Presence of this band was previously reported for InGaN:Mg. We present arguments that it originates from deep donor level. (C) 2010 American Institute of Physics. [doi:10.1063/1.3466768]