The forward current-voltage characteristic and forward capacitance-voltage characteristic measurings are the most important methods to study the forward electrical characteristic of GaN light-emitting diodes. We can use the forward alternating current (ac) small signal method to measure the capacitance-voltage charac-teristic of the GaN light-emitting diodes. Some values of GaN light-emitting diodes parameters can be deduced from capacitance-voltage characteristic. The negative capacitance phenomenon of GaN light-emitting diode can be observed by using this method. The negative capacitance phenomenon appears more noticeable when the bias voltage is lager and the frequencies of forward alternating current (ac) small signal are lower. In this paper

we propose that the phenomenon of measured negative capacitance is as the superficial phenomenon

and there no negative capacitance exists in fact. We propose that the p-n junction capacitance of GaN light-emitting diode is equivalent to a variable capacitance in a certain range of forward voltage. By analysis the responds of variable capacitance to the forward alternating current small signal

we find that the variable capacitance for specific parameter can make the current phase of junction capacitance behind the voltage phase of alternating current small signal

lead the variable capacitance behave as a negative capacitance on measu-ring. The behavior of a GaN light-emitting diode can be modeled by the equivalent electrical circuit which has a capacitance with a series resistance. There is an extreme point of apparent capacitance-forward voltage curve when use the equivalent circuit for measurement. We analyze the extreme point with the theoretical model of the variable capacitance for specific parameter. The result of theory analysis tallies with the experiment. That proved the accuracy of this theory model. The research on negative capacitance phenomenon will be valuable for study the electrical characteristics of GaN light-emitting diodes

will be valuable for the knowledge improvement of the characteristic and parameter relevant the p-n junction internal structure of GaN light-emitting diodes.