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/τ)^β] (β<1), where τ is the relaxation time constant and β the decay exponent. The parameters β and τ 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(-(αt)^β)], where β increases from 0.4 to nearly 1 as the excitation intensity decreases from 4×10¹³/(cm²s) to 2.5×10¹¹/(cm²s). A linear relationship is found between the decay parameter associated with the PPC build-up, α, and the excitation intensity N_ph. The average photoionization cross section is 2.8×10^-15/(cm²s) and the average electron decay rate is 4.6×10^-3 s^-1.