Non-equilibrium carrier dynamics were investigated in epitaxial lateral overgrowth and hydride vapour-phase epitaxially grown GaN layers over wide temperature and excitation ranges by using the time-resolved picosecond FWM technique. The carrier lifetime in samples at 300K increased by 2.8 to 5.1ns in accordance with the decreasing threading dislocation density change from 4 x 107/cm2 to mid-106/cm2 values in hydride vapour-phase epitaxial layers. At below 100K, the hyperbolic shape of the FWM kinetics indicated carrier density dependent radiative lifetimes, which gradually decreased - at lower temperatures - to a few hundred ps. The dominance of bimolecular recombination in hydride vapour-phase epitaxial layers at 10 to 40K was demonstrated by the exposure characteristic of FWM, which had exhibited a sub-linear growth of carrier density with excitation: N  I1/2. Numerical fitting of the set of FWM kinetics for various temperatures confirmed the temperature dependence of the bimolecular recombination coefficient, B  T-1.5, and provided values of 2 x 10-11cm3/s at 300K and 3.2 x 10-9cm3/s at 9K. The measured bipolar diffusion coefficients permitted the determination of carrier diffusion lengths of 0.8 to 1μm at 300K and their 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