Picosecond response of steady-state photovoltaic effect in an asymmetrical graded semiconductor superlattice structure

A steady-state photovoltaic effect of picosecond response speed has been observed in an asymmetrical graded InAlGaAs superlattice structure with a responsivity of ∼0.3 V/W and a saturation photovoltage of ∼0.3 V. For 10 devices of varying sizes ranging from 51 to 502 μm in diameter, the measured full width at half-maximum of the impulse response to a 1.6-ps laser pulse varies only twofold from 29 to 58 ps. The intrinsic rise time of each device is less than 10 ps. Steady-state photovoltage signals were observed in all the devices when excited with 100-ps–2-μs laser pulses. No dc bias voltage is needed.