Deep defects in InGaN LEDs: modeling the impact on the electrical characteristics

Deep defects have a fundamental role in determining the electro-optical characteristics and in the efficiency of InGaN light-emitting diodes (LEDs). However, modeling their effect on the electrical characteristics of the LED is not straightforward. In this paper we analyze the impact of the defects on the electrical characteristics of LEDs: we analyze three single-quantum-well (SQW) InGaN/GaN LED wafers, which differ in the density of defects. Through steady-state photocapacitance (SSPC) and light-capacitance-voltage measurements, the energy levels of these deep defects and their concentrations have been estimated. By means of a simulation campaign, we show that these defects have a fundamental impact on the current voltage characteristic of LEDs, especially in the sub turn-on region. The model adopted takes into consideration trap assisted tunneling as the main mechanism responsible for current leakage in forward bias. For the first time, we use in simulations the defect parameters (concentration, energy) extracted from SSPC. In this way, we can reproduce with great accuracy the current-voltage characteristics of InGaN LEDs in a wide current range (from pA to mA). In addition, based on SSPC measurements, we demonstrate that the defect density in the active region scales with the QW thickness. This supports the hypothesis that defects are incorporated in In-containing layers, consistently with recent publications.