Gain mechanisms in field-free InGaN layers grown on sapphire and bulk GaN substrate

The gain mechanisms and recombination dynamics of InGaN layers strongly depend on the structural properties of the substrate material. The 4.5 nm and 9.5 nm thick layers were grown by metal organic chemical vapor deposition on two different substrates (sapphire and GaN) with different dislocation densities. Time-resolved photoluminescence spectroscopy at high excitation densities identifies the saturation of nonradiative recombination centers through excited carriers as a major gain mechanism. The prime argument is an unusual nonexponential luminescence decay. This was confirmed by a lower threshold of the optical gain for the structures grown on GaN with lower dislocation densities. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)