Influence of low-temperature GaN-Cap layer thickness on the InGaN/GaN multiple quantum well structure and its luminescence

This paper studies the influence of low-temperature GaN-cap (LT-Cap) layer thickness on the InGaN/GaN multiple quantum well (MQW) structure and the related luminescence characteristics. The research results show that the thickness variation of LT-Cap layers seems not to have a substantial impact on the structure of MQWs, i.e., the well layer thickness, but strongly affects the indium composition of well layers. The LT-Cap layer can effectively weaken the decomposition of InGaN, however, the increase in the thickness of the LT-Cap layer will lead to an increase in the polarization effect, resulting in a red shift of the emission peak. Different LT-Cap layers will affect the distribution of the tail states, resulting in an energy shift of carrier emission from the local states. In addition, the thickness variation of LT-Cap layers also affects the luminescence characteristics of MQWs. It is found that as the thickness of the LT-Cap layer increases, the internal quantum efficiency (IQE) of the material gradually decreases, which may be due to the introduction of new non-radiative recombination centers.