Optical and material studies of indium compositional fluctuations in InGaN/GaN quantum well structures

Abstract

Summary form only given. Indium compositional fluctuations in InGaN are crucially important for efficient light emission in such compounds. It was claimed that the quantum-dot-like InGaN aggregations trapped carriers for radiative recombination before they were trapped by defects for nonradiative recombination. This argument explained the efficient light emission in a compound of high defect density. In this paper, we report the results of photoluminescence (PL), stimulated emission (SE), X-ray diffraction, and high-resolution tunneling electron microscopy on InGaN/GaN quantum well structures grown with MOCVD. In material analyses, we observed clear indium aggregation and phase separation structures. With a higher nominal indium content, the indium composition fluctuation becomes more prominent. In optical measurements, we observed the S-shape PL peak variation as a function of temperature. The turning points of the S-shape variation relies on the nominal indium content. Meanwhile, we observed a two-peak feature in the SE spectra. The short- and long-wavelength peaks correspond to the carrier recombination of free-carrier states and localized states.