Non-equilibrium QW populations and internal efficiency of polar and nonpolar III-nitride light emitters

Abstract

III-nitride visible light emitters employ deep QWs and feature strong disparity of electron and hole transport in diode structures. As a result, multi-QW active regions of such devices suffer from inhomogeneous carrier injection, large residual charges of active QWs, and overall active region electrical non-uniformity which unfavorably affects the emitter efficiency. In this work, we show that electron and hole populations of deep optically active III-nitride QWs are highly imbalanced and substantially deviate from thermodynamic equilibrium with corresponding mobile carrier subsystems. Non-equilibrium QW populations are self-consistently determined by carrier injection and light generation processes in active QWs. In turn, QW residual charges impose strong feedback on the active region electrical uniformity. Our selfconsistent modeling of QW radiative characteristics and multi-QW carrier transport in diode structures relates the effects of non-equilibrium QW populations, inhomogeneous QW injection and residual QW charges to the structure internal efficiency. Comparative modeling of polar and nonpolar diodes shows that in both types of structures the nonequilibrium effects tend to decrease the QW operational electron populations; this trend benefits the active region electrical uniformity. For device simulation, we use COMSOL-based Optoelectronic Device Modeling Software (ODMS) developed at Ostendo Technologies Inc.