Carrier-Induced Defect Saturation in Green InGaN LEDs: A Potential Phenomena to Enhance Efficiency at Higher Wavelength Regime

Non-radiative defects play a deterministic role in regulating the performance of LEDs. Yet, defect saturation in LEDs is relatively unexplored in the literature. Here, we establish the theoretical background of carrier-induced defect saturation from the band structure of quantum well (QW)-based InGaN LEDs after solving Poisson and Schrödinger's equations self-consistently. Time dynamics of defect saturation are demonstrated through solving a set of coupled differential rate equations iteratively, considering carrier transitions between different energy levels in the QW region. They indicate an increasing degree of defect saturation with higher carrier injection at steady state. Capacitance versus voltage (CV) measurements on fabricated InGaN MQW LEDs, conducted at low frequencies clearly demonstrate the considerable effect of defect saturation at higher bias. We propose a correction term in the typical RC circuit model for LEDs, considering defect saturation, and solved it analytically to explain the frequency-dependent CV characteristics. Analytical calculation of CV response, based on the modified RC model, shows a fairly satisfactory matching with the experimental data at different frequencies. Also, the frequency dependence of negative capacitance at a higher bias regime is explained through the conductance versus voltage (GV) characteristics.