Two-dimensional electron gas and persistent photoconductivity in AlxGa1-xN/GaN heterostructures

We present results of electrical and optical measurements in an AlxGa1-xN/G aN heterostructure. The presence of a two-dimensional electron gas at the h igh-quality AlxGa1-xN/GaN heterointerface is confirmed by Shubnikov-de Haas measurement, which shows well-resolved magnetoresistance oscillations star ting in fields below 3 T at 1.3 K. From the temperature dependence of the o scillation amplitude, the obtained effective mass (0.24+/-0.02)m(0) is in e xcellent agreement with the value of cyclotron resonance measurements in tw o-dimensional (2D) systems, but larger than the values of theoretical and e xperimental results in GaN bulk films. We point out that the effective-mass enhancement in 2D systems is due to the effects of band nonparabolicity an d wave-function penetration into the barrier material. The results of photo conductivity measurements reveal that persistent photoconductivity (PPC) do es exist in the AlxGa1-xN/GaN heterostructure, and that the PPC behavior of AlxGa1-xN/GaN heterojunction is quite different from that of the GaN epita xial thin films. A possible mechanism is presented to interpret the observe d PPC effect. [S0163-1829(98)07843-7].