Negative Terminal Capacitance of Light Emitting Diodes at Alternating Current (AC) Biases

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Measurement of obvious negative capacitance (NC) at large forward bias of light-emitting diodes (LEDs), using an alternating current (AC) small signal, together with direct current (DC) <formula formulatype="inline"> <tex Notation="TeX">$I-V$</tex></formula> plot, has shown that the NC grows exponentially with the forward applied voltage. The experimental results are unexpected and are in conflict with Shockley's p-n junction theory which only includes increasing diffusion capacitance and certainly no negative capacitance. The experiment also shows that the ideal factor of LEDs is about 4, which far exceeds the traditional theory value. However, these results support the comprehensive p-n junction theory presented by Hess. Using the framework of his theory, the NC could be interpreted distinctly. </para>