We present results of a time-resolved photoluminescence study of the dynamics of photoexcited carriers inAlxGa1−xN/GaNdouble heterostructures (DHs). The carrier dynamics including generation, diffusion, spontaneous recombination, and nonradiative relaxation were studied by examining the time decay of photoluminescence associated with the spontaneous recombination from the samples. The temporal evolution of the luminescence from the GaN active layers of the DH samples was found to be governed by a carrier–diffusion dominated capture process. The determination of the capture time for the carriers drift and diffusion into the GaN active region, in addition to the effective lifetimes of the spontaneous recombination for carriers in the AlGaN cladding layers and the GaN active region, allows an estimation of the diffusion constants for the minority carriers in theAlxGa1−xNcladding layers of the DHs. Our results yield a diffusion constant of2.6 cm2/sforAl0.03Ga0.97Nand1.5 cm2/sforAl0.1Ga0.9Nat 10 K. ©1997 American Institute of Physics.