Donor defect profiles in pseudomorphic AlGaN layers, grown onto GaN, were calculated while taking account of the effects of a strain polarization field upon the defect formation energy. Under certain conditions, the defect concentration could be increased by more than an order of magnitude. These large concentrations, combined with the band-bending effects of the piezoelectric field, made charge transfer from the AlGaN barrier to the GaN well extremely efficient; thus resulting in a 2-dimensional electron gas of very high density and low mobility.

L.Hsu, W.Walukiewicz: Applied Physics Letters, 1998, 73[3], 339-41