Elucidating negative capacitance in light-emitting diodes using an advanced semiconductor device theory

Abstract

The capacitance characteristics of light emitting diodes (LEDs) are accurately measured using a method based on an alternating-current small signal, together with direct current I-V plot. All measured LEDs display negative capacitance (NC) at large forward bias. By analyzing the dependence of capacitance on both forward bias and frequency, an accurate expression for describing NC was obtained. This expression is in conflict with Shockley’s p-n junction theory, which only describes increasing diffusion capacitance and does not allow NC. Using an advanced p-n junction theory developed by Hess and Laux, the dependence of NC on both voltage and frequency are described quantitatively.