Study on the luminescence mechanism influenced by the inhomogeneous growth of InGaN/GaN multiple quantum wells

Abstract

The luminescence mechanism of inhomogeneous InGaN/GaN multiple quantum wells (MQWs) grown by metal organic chemical vapor deposition (MOCVD) and the way to improve their optical properties are studied. Fluctuations in layer thickness and In content of QWs are found to lead to a blurring of the well/barrier interfaces and a deterioration of MQW’s quality which are checked by measuring transmission electron microscopy and energy dispersive x-ray spectroscopy. Moreover, the temperature-dependent photoluminescence (PL) spectra show that the luminescence homogeneity of MQWs becomes worse as the spectral line width broadens with increasing well thickness. In addition, the theoretical calculation results confirm that the polarization electric field in wider QWs is stronger than that in narrower QWs, and the stronger polarization electric field tilts the energy band and enhances the quantum confinement Stark effect, causing wavelength redshift, which is confirmed by the measurement results of PL mapping. Based on the analysis of inhomogeneity in the MQWs, the thickness of the first QW along the growth direction is especially recommended not to be too thick then it act as a pre-stress modulator to improve the luminescence efficiency of InGaN/GaN MQWs.