Excitonic structure and spatially indirect recombination in MOCVD-grown GaN/Al(x)Ga(1-x)N heterostructures

Recombination paths in GaN/Al(x)Ga(1-x)N (x<0 18) heterostructures on sapphire were studied by temperature and excitation power density dependent photoluminescence. Free and bound AlGaN excitons are identified. A spatially indirect, below band gap emission line shows a strong red shift with increasing Al content. The data provide evidence, that this red shift is caused by a piezoelectric field which forms a two-dimensional electron gas at the GaN/AlGaN interface.