Contribution of dislocations to carrier recombination and transport in highly excited ELO and HVPE GaN layers

Nonequilibrium carrier dynamics has been investigated in ELO and HVPE grown GaN layers in a wide temperature and excitation range by using the time‐resolved picosecond FWM technique. Carrier lifetime in the samples at 300 K increased up to 2.8–5.1 ns in accordance with the decreasing threading dislocation density from 4 × 107 cm–2 (ELO) to mid 106 cm–2 in HVPE layers. At T < 100 K, 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 10–40 K was demonstrated by the exposure characteristic of FWM, that has shown a sublinear 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 × 10–11 cm3/s at 300 K and 3.2 × 10–9 cm3/s at 9 K. The measured bipolar diffusion coefficients allowed determination of carrier diffusion length of 0.8–1 μm at 300 K and its dependence on dislocation density and temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)