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

The effects of alloy fluctuations on the transport properties of AlxGa1-xN alloys (x similar to 0.35) have been probed through the use of persistent p hotoconductivity (PPC). In the PPC state, the electron mobility, mu(e), as a function of electron concentration, n, in a single sample can be obtained under controlled light illumination conditions. It was found that mu(e) is a constant when n is below a critical value n(c) and it then increases wit h n at n > n(c). This mobility behavior was attributed to the effects of al loy 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 mu(e) on n. From these me asurements, the total density of the tail states below the mobility edge in the conduction band was estimated to be 1.46 x 10(17) cm(-3) in a Al0.35Ga 0.65N sample. The results were compared with those in II-VI semiconductor a lloys and their implications on III-nitride device applications were discus sed. (C) 2000 American Institute of Physics. [S0003-6951(00)02513-4].