Enhanced Optical Efficiency and Carrier Dynamics in InGaN/GaN Light-Emitting-Diode Structures through Combination of Superlattice- and Prewell-Strain Control Strategy

We explore the effect of combining two distinct strain-engineering multilayer regions (designated as L1 and L2) on the structural quality, carrier dynamics, and device optical efficiency of InGaN/GaN multiple quantum well (MQW)-based light-emitting diode (LED) structures. In S1, L2 consists of a single ultrathin InGaN/GaN layer, whereas in the S2 LED structure, L2 contains several superlattice (SL) pairs beneath the MQWs. The incorporation of superlattices in L2 leads to a significant enhancement in the optical performance in the S2 LED structure relative to S1. A detailed structural analysis indicates that the dimensions of V-pits, including their size, depth, and sidewall thickness, are determined by the configuration of the L2 region. The presence of SLs in S2 promotes a more homogeneous indium distribution within the InGaN quantum wells, whereas S1 exhibits In-rich nanosegregation. In S2, a monotonic decrease in indium content from the bottom to the top of the MQWs adjacent to the V-pits is observed, attributed to the fully pseudomorphic strain regime. Photoluminescence (PL) and time-resolved PL measurements show that S2 achieves an internal quantum efficiency exceeding 85% and exhibits distinct drooping characteristics under high carrier injection. These results indicate that carrier overflow and band-filling effects facilitate the transfer of carriers to higher energy states associated with the V-pit sidewalls, followed by repopulation of the main MQWs occurring through regions with gradually varying indium content, resulting in dominant radiative recombination in S2 at room temperature. Electroluminescence measurements confirm that the S2 LED attains an external quantum efficiency 1.6 times greater and an output power approximately 66% higher than those of S1.