Hot electron effects on efficiency degradation in InGaN light emitting diodes and designs to mitigate them

Abstract

Hot electrons and the associated ballistic and quasiballistic transport, heretofore neglected endemically, across the active regions of InGaN light emitting diodes (LEDs) have been incorporated into a first order simple model which explains the experimental observations of electron spillover and the efficiency degradation at high injection levels. The model is in good agreement with experiments wherein an adjustable barrier hot electron stopper, commonly called the electron blocking layer (EBL), is incorporated. The model is also in agreement with experiments wherein the electrons are cooled, eliminating hot electrons, inside a staircase electron injector (SEI) prior to their injection into the active region. Thermionic emission from the active region, even if one uses an uncharacteristically high junction temperature of 1000 K, fails to account for the carrier spillover and the experimental observations in our laboratory in samples with varying EBL barrier heights. The model has been successfully applied to both m-plane (lacking polarization induced electric field) and c-plane (with polarization induced field) InGaN double heterostructure (DH) LEDs with a 6 nm active region featuring a variable barrier hot electron stopper, and a SEI, and the various combinations thereof. The choice of DH LEDs stems from our desire to keep the sample structure simple as well as the model calculations. In this paper, the theoretical and experimental data along with their comparison followed by an insightful discussion are given. The model and the approaches to eliminate carrier spillover proposed here for InGaN LEDs are also applicable to GaN-based laser diodes.