Non-equilibrium carrier dynamics were investigated in ELO and HVPE grown GaN layers in a wide temperature and excitation range by using the time-resolved ps FWM technique. Carrier lifetime in the samples at 300K increased to 2.8 to 5.1ns in accordance with the decreasing threading dislocation density from 4 x 107/cm2 (ELO) to mid 106/cm2 in HVPE layers. Below 100K, the hyperbolic shape of FWM kinetics indicated carrier density dependent radiative lifetimes, which gradually decreased at lower temperatures to a few hundreds of ps. The dominance of bimolecular recombination in HVPE layers at 10 to 40K was demonstrated by the exposure characteristic of FWM, that has shown a sub-linear growth of carrier density with excitation, N  I1/2. Numerical fitting of the set of FWM kinetics at various T confirmed the temperature dependence of bimolecular recombination coefficient B  T-1.5 and provided its value B = 2 x 10-11cm3/s at 300K and 3.2 x 10-9cm3/s at 9K. The measured bipolar diffusion coefficients allowed determination of carrier diffusion length of 0.8 to 1μm at 300K and its dependence upon dislocation density and temperature.

Contribution of Dislocations to Carrier Recombination and Transport in Highly Excited ELO and HVPE GaN Layers. T.Malinauskas, K.Jarašiūnas, R.Aleksiejunas, D.Gogova, B.Monemar, B.Beaumont, P.Gibart: Physica Status Solidi B, 2006, 243[7], 1426-30