Negative Capacitance Analysis of Multi-Quantum-Well Light-Emitting Diodes

To explain the negative capacitance (NC) characteristic of multi-quantum-well (MQW) LEDs, we calculated the continuity equation for a 10-period AlGaInP/GaInP multi-quantum-well (MQW) LED with a mesa size of 90 × 150 μm and build an MQW LED capacitor model. The carrier concentrations and capacitance–voltage characteristics across every quantum well region were analyzed by accounting for carrier spontaneous, Auger, and SRH recombination. In our model, a dynamic carrier lifetime iteration method with an iterative error of less than 1 × 10−14 ns was used to decouple carrier lifetime and electric field variables in the carrier continuity equation, providing a new way to enhance the accuracy of MQW continuous equations. Based on the calculated carrier concentration and lifetime of MQWs, we derived a multilayer epitaxial material LED capacitance equivalent circuit. The theoretical model characterizes the negative capacitance phenomenon at 1.75 V, which is consistent with the actual test results of the sample. Our theoretical analysis indicates that the negative capacitance mainly comes from the carrier recombination in the MQW region. Under low-frequency AC bias conditions, the negative capacitance phenomenon becomes more obvious. This work provides a useful reference for analyzing the capacitance and bandwidth characteristics of LEDs in the fields of display dimming and visible-light communication.