Low frequency (<102 Hz) electrical characteristics of light-emitting diodes(LEDs) are accurately measured by the self-built-up device.All measured diodes display obvious negative capacitance(NC) at low frequency,and the lower the frequency,the stronger the NC is.At low frequencies,the saturation of the relative-luminescence intensity is observed in the voltage modulation luminescence,and its value decreases with the frequency increase.The comparison of the electrical property with the optical one for LEDs c...