Effect of indium incorporation on optical and structural properties of m-plane InGaN/GaN MQW on LiAlO 2 substrates

Abstract

We report about the optical and structural characterization of m-plane InGaN/GaN multiple quantum well (MQW) structures. All samples were grown on 2-inch LiAlO 2 substrates in AIXTRON MOVPE reactors. By lowering the MQW growth temperature, an increase of an indium fraction from 5% to 30% is achieved. High-resolution X-ray diffraction (HRXRD) reciprocal space mapping reveals fully strained growth of the quantum wells. The photoluminescence (PL) peak full width half maximum (FWHM) values increase from ∼130 to ∼240 meV at room temperature when the indium fraction rises from 10% to 30% . Also, PL peaks show good wavelength stability for indium contents up to 10% when the excitation intensity is varied by two orders of magnitude. However, at 20% indium and above, a clear excitation intensity-induced peak shift of around 50 meV is detected which is likely caused by indium segregation. Cross-section transmission electron microscopy (TEM) hints at indium fluctuation near extended defects. We conclude that an improved growth process for nonpolar InGaN/GaN MQW is necessary to achieve high-performance long-wavelength light-emitting devices.