Compressive strain induced enhancement of transverse-electric polarized ultraviolet light emission for AlGaN quantum wells

Abstract

The impact of strain on optical polarization of c-plane Al0.37Ga0.63N/Al0.5Ga0.5N multiple quantum wells (QWs) has been studied by the polarized photoluminescence spectroscopy at room temperature. By adopting multiple alternation cycles of low- and high-temperature growth, the strain state of AlN template can be modulated. With increasing in-plane compressive strain of QWs layers, the polarization degree can be enhanced from 41.5% to 61.9%. Furthermore, the strain dependence of the polarization degree has been confirmed by the numerical simulation based on k.p method, revealing the dominant role of energy level shift and wavefunction overlap. It is found that the relative position of the three valence subbands is responsible for the steep increase of the polarization at smaller strain, while the wavefunction overlap induced by piezo-electric effect modulates the optical polarization at larger strain. These results are of great importance in the design and analysis of AlGaN based ultraviolet light emitting devices.