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

摘要

Systematic studies of In_xGa_(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 × 1019 cm~(-3) was chosen to achieve a maximum hole carrier concentration, p_H (as measured by Hall effect) of 4 × 10~(18) cm~(-3) in samples with high x. We confirmed reports on decreasing resistivity in In_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 pH 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 ℃) or by (ii) varying an intended GaN substrate miscut. We demonstrated that the increase in p_H in In_xGa_(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 ℃ 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.