IDEALITY FACTOR IN InGaN/GaN MULTIPLE QUANTUM WELL LIGHT-EMITTING DIODES WITH NONUNIFORM CURRENT SPREADING

Abstract

In this research we demonstrate that a high p-n junction ideality factor (β) in multiple quantum well InGaN-based light-emitting diodes grown on sapphire substrate may be connected to the current crowding effect. This effect is due to the localization of the current flow routes in some regions of a multilayer LED structure whose position are difficult to predict a priori. In lateral structures the current crowding forms regions of high current density in the vicinity of the contacts, resulting in a reduction of the effectively emitting area and the local overheating of the emitting structure. Numerous efforts have been made to identify the effect of the current crowding on the InGaN-based light-emitting diodes performance. Following this tendency, we show that high nonuniformity of current flow can lead to the increasing of the “apparent” ideality factor. This result shows that the ideality factor is not uniquely determined by carrier recombination and transport mechanism in the space charge region as it is predicted by classical one-dimensional theory of p-n junction. The experimental investigation of InGaN blue (λ=460 nm) light-emitting diodes with two different contact geometries confirm that the ideality factor increase from 2.2 (current spreading geometry) up to 3.6 (current crowding geometry). These findings reveal that the ideality factor obtained from I-V measurements in light-emitting diodes employing lateral injection can not be considered as a pure internal parameter of the p-n junction. This the current crowding affected modification of the ideality factor occurs mostly in the intermediate range of current where the space charge region dominates in the light-emitting diodes performance and erroneously could be treated as the change of carrier transport mechanism and carrier recombination nature.