Optical and microstructural properties of semi-polar (11-22)InGaN/GaN quantum well structures

In this paper we report on a comparison of the optical properties of a series of semi-polar (11-22)InGaN/GaN multiple quantum well structures with those of a series of polar (0001) control samples. In the semi-polar structures we observe blue-shifts of the quantum well emission, increases of the radiative recombination rates and sharpening of the quantum well excitation spectra; all these changes are compatible with a decrease in the magnitude of the electric field strength with respect to the control samples. However the reduction in the electric field strength does not translate into an improvement in the photoluminescence internal quantum efficiency at room temperature. This failure we attribute to an increased density of non-radiative recombination centres, arising from the larger dislocation density in the (11-22) samples. Using TEM and STEM-HAADF measurements we have also observed gross well width fluctuations in the (11-22) samples which result in broadening of the photoluminescence spectra. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)