Study of photoluminescence and absorption in phase-separation InGaN films

InGaN/GaN layers have been grown under low pressure by metal-organic vapor phase epitaxy on sapphire substrate. X-ray diffraction (XRD), photoluminescence, and optical absorption measurements have been performed to study the radiative recombination mechanisms in the samples. The In composition was determined by XRD measurement using Vegard's law. With increasing In composition, a red shift of absorption edge and a broad Urbach tail in absorption spectra were observed. The InN inclusions in InGaN played a key role in long-wavelength absorption. There existed large Stokes shifts in all thick InGaN layers with different In compositions. The intensities of low-energy emissions were enhanced compared to those of high-energy ones with increasing In composition. We attributed low-energy emissions to deep levels and high-energy emissions to In-rich quantum dots.