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Frequency dependence of negative capacitance in light-emitting devices

In this paper, we present a systematic experimental study of negative capacitance (NC) effect in p-i-n and p-n junctions of light-emitting devices. The focus is the dependence of NC on injected current mixed with a small ac signal (1 kHz - 13 MHz) at variable temperature in forward-biased light-emitting diode (LED) and laser diode (LD). The NC effect is shown by our measurement results to be strong in low frequency region (100 kHz - 1 MHz) and weaker in high frequency one (>; 1 MHz). In addition, the NC in LD changes suddenly at its lasing threshold. These properties of the NC effect, combined with its dependence on temperature, can lead to understanding of impacts of p-n junction capacitance on high frequency modulation in optical communication systems.