Kinetics of persistent photoconductivity in GaN grown by MOCVD

Persistent photoconductivity (PPC) in unintentionally doped GaN has been investigated as a function of optical excitation intensity. PPC relaxation behaviors can be well described by a stretched-exponential function I-ppc(t)=I-ppc(0)exp[-(t/tau)(beta)] (beta<1), where tau is the relaxation time constant and beta the decay exponent. The parameters beta and tau. increase as excitation intensity decreases. The photocurrent build-up curves can be described by an equivalent stretched-exponential function I-ppc(t)=I-max[1-exp(-(alphat)(beta))], where beta increases from 0.4 to nearly 1 as the excitation intensity decreases from 4 x 10(13)/(cm(2)s) to 2.5 x 10(11)/(cm(2)s). A linear relationship is found between the decay parameter associated with the PPC build-up, alpha, and the excitation intensity N-ph. The average photoionization cross section is 2.8 x 10(-15)/(cm(2)s) and the average electron decay rate is 4.6 x 10(-3) s(-1).