Mechanism of Indium Redistribution and Thermal Degradation in InGaN/(In)GaN Quantum Wells of Vertical Cavity Surface Emitting Lasers

The redistribution and segregation behavior of indium atoms in InGaN multiple quantum wells (MQWs) have been observed during the thermal annealing process in a vertical cavity surface emitting laser (VCSEL) structure. The migration of indium atoms may lead to a thermal degradation of InGaN/(In)GaN MQWs, resulting in the decomposition of InGaN QW and quantum barrier (QB) layers as well as the broadening of QW layers. Photoluminescence (PL) mapping measurements indicate that indium aggregation occurs in QWs without protection, which will cause the inhomogeneous luminescence of the MQW and decrease the laser optical performance. Temperature-dependent and excitation power-dependent PL spectra were employed to examine the presence of nonradiative recombination centers in deep localized states formed by indium aggregation, which also deteriorate the luminescence performance. Furthermore, a protective structure containing an InGaN or GaN sacrifice layer is proposed to suppress thermal degradation and improve the luminescence performance.