Nonradiative recombination processes in GaN-based semiconductors probed by the transient grating method

Transient grating (TG) method with nanosecond pulsed laser was used to detect the heat released by the nonradiative recombination of carriers and/or excitons in GaN-based semiconductors at room temperature. Obtained TG signal rises immediately within the excitation pulse (few nanosecond) and decayed within few tens nanosecond. This decay profile can be fitted by a single exponential function. By solving the diffusion equation, it was found that the pre-exponential factor and the rate constant obtained from fitting suggest the increase of temperature (DeltaT) originating from the nonradiative recombination and the thermal diffusivity (D-th) in material, respectively. Obtained D-th value (0.41 cm(2) s(-1)) is close to the theoretical value (0.44 cm(2) s(-1)) calculated by the density (rho), heat capacity (C-p), and thermal conductivity (lambda (c)) as D-th = lambda (c)/rhoC(p). The excitation power dependence of DeltaT showed the linear relationship, which is different from the reported case of ZnSe. Such discrepancy can be understood as a difference in capture cross section of carriers and/or excitons to nonradiative recombination centers.