Improvement of efficiency droop in resonance tunnelling LEDs

A resonance tunnelling LED structure having a high efficiency, low droop and negligible wavelength shift with current is reported in this study. The LED structure contains a thick InGaN bottom spacer between an n-GaN contact layer and a multiple quantum well (MQW) active region, and a thin InGaN top spacer between the MQW and an AlGaN electron blocking layer (EBL). The observed high efficiency and negligible wavelength shift with applied current are attributed to the thick InGaN bottom spacer that nucleates V-pits and acts as a strain control layer for the MQW. The thick InGaN layer also provides an electron reservoir for efficient electron tunnelling injection into the MQW and reduces the electropotential difference between the n-emitter and the p-emitter, to suppress current leakage at high driving current and reduce droop. The top InGaN spacer was designed to act as a magnesium back-diffusion barrier and strain relief layer from EBL so as to obtain high efficiency.