Effects of alloy disorder on the transport properties of AlxGa1−xN epilayers probed by persistent photoconductivity

Abstract

The effects of alloy fluctuations on the transport properties of AlxGa1−xN alloys (x∼0.35) have been probed through the use of persistent photoconductivity (PPC). In the PPC state, the electron mobility, μe, as a function of electron concentration, n, in a single sample can be obtained under controlled light illumination conditions. It was found that μe is a constant when n is below a critical value nc and it then increases with n at n>nc. This mobility behavior was attributed to the effects of alloy fluctuations in AlxGa1−xN alloys. As a result, the initial PPC buildup kinetics seen in AlxGa1−xN alloys was quite different from those in better understood semiconductor alloys, such as AlGaAs and ZnCdSe, and is a direct consequence of the observed unique dependence of μe on n. From these measurements, the total density of the tail states below the mobility edge in the conduction band was estimated to be 1.46×1017 cm−3 in a Al0.35Ga0.65N sample. The results were compared with those in II–VI semiconductor alloys and their implications on III-nitride device applications were discussed.