InGaN MQW Green LEDs Using p-InGaN and p-InGaN/p-GaN Superlattices as p-Type Layers

摘要

High-efficiency "true" green light-emitting diodes (LEDs) (λ～550nm) are one of the key elements in realizing high-brightness RGB-based white-lighting systems. Because the InGaN multiple quantum wells (MQWs) in the active regions of green LEDs contain a high indium alloy composition and a corresponding large lattice mismatch, the QW has a reduced material quality and contains large piezoelectric fields induced by the large strain. The piezoelectric field reduces the overlap of the electron-hole wave functions, and so results in reduced internal quantum efficiency in green LEDs. In addition, other effects can strongly impact InGaN materials with high indium content, e.g., detrimental annealing of the MQW active region during the subsequent growth of the p-type hole injection and contact layers. In this study, the optical and structural characteristics of green LEDs employing p-InGaN and p-InGaN/p-GaN superlattices (SLs) were examined. For the LEDs with a p-In_(0.04)Ga_(0.96)N:Mg layer grown at 840 ℃, only a slight decrease in PL intensity was observed compared to similar structures grown without a p-layer. However, pits are observed for p-In_(0.04)Ga_(0.96)N:Mg layers, which may cause increased reverse current leakage. In order to decrease the reverse leakage current, p-In_xGa_(1-x)N/p-GaN SLs were developed. The hole concentration of the p-In_xGa_(1-x)N/p-GaN SLs is close to that of p-In_(0.04)Ga_(0.96)N, and is much higher than that of p-GaN grown at an acceptably low temperature. In addition, pits disappear in optimized p-In_xGai_(1-x)N/p-GaN SLs. In order to study the structural and optical characteristics of green LEDs with p-In_(0.04)Ga_(0.96)N and p-In_xGa_(1-x)N/p-GaN SL layers, I-V characterization and electroluminescence measurements were performed and the results will be described in detail.