The frequency response of porous silicon electroluminescent devices

Under a constant forward bias, porous silicon light-emitting devices (LEDs) produce stable electroluminescence (EL) that is detectable at applied voltages as low as 5 V and visible in daylight at higher voltages. The recombination dynamics of the EL are studied and correlated to the photoluminescence properties of light-emitting porous silicon (LEPSi). The EL efficiency is related to the LEPSi properties and the device configuration. LEPSi LEDs with an EL efficiency of 0.01% have been achieved. The frequency response of the EL to a modulating ac bias is measured. For metal/LEPSi LEDs, the −3 dB frequency is determined by the carrier transit time which must be larger than the carrier lifetime to achieve efficient EL. For LEPSi pn junction LEDs, the −3 dB frequency is determined only by the carrier lifetime and can be in excess of 200 kHz.