Photoluminescence from quantum dots in cubic GaN/InGaN/GaN double heterostructures

We have measured photoluminescence spectra of molecular-beam-epitaxy-grown cubic GaN/InxGa1-xN/GaN double heterostructures with x between 0.09 and 0.3 3. We observe a luminescence peak at about 2.3-2.4 eV which is almost indep endent of the InGaN layer composition. High-resolution x-ray diffraction me asurements revealed a pseudomorphic In-rich phase with x=0.56 +/-0.02 embed ded in the InGaN layers. Including strain effects we calculate a gap energy E-g=2.13 eV of this phase. In cubic InGaN, spontaneous polarization and st rain-induced piezoelectric fields are negligible. Therefore, the observed d ifference between the luminescence energy and the gap of the In-rich phase is assumed to be due to the localization of excitons at quantum-dot-like st ructures with a size of about 15 nm. (C) 2001 American Institute of Physics .