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We report on a GaAs/AlxGa1−xAs quantum well intersubband photodetector for the long wavelength infrared region, which operates at zero bias voltage. Detection without bias is achieved by using an asymmetrical barrier structure as well as modulation doping, giving rise to a built-in field across the barrier layers. The maximum of the spectral response is centered at 10 μm with a spectral bandwidth of 1.6 μm and a 77 K peak detectivity of 2.5×109 cm√Hz/W at 0 V.

We report on the intensity dependence of the responsivity in quantum well infrared photodetectors (QWIP). A strong reduction of the responsivity is observed already at small excitation powers for a QWIP with N=4 periods. This nonlinearity is caused by a partial screening of the electric field across the main part of the active region. The intensity dependence is analyzed using a phenomenological approach, which allows us to calculate the nonlinearity from the measured dark current and responsivity. Applying this approach to a background-limited 50 period QWIP, we find that the nonlinearity is already present below 1 mW cm(-2) which is less than the thermal background

We have investigated the temporal response of uncooled photovoltaic quantum well infrared photodetectors (PV QWIP) using 2 ps pulses from a free electron laser. We measured rise and fall times of 8 ps and 63 ps, respectively. We have also determined the temperature dependence of the voltage responsivity and resistance of the sample from 70 K to 300 K. Based on these measurements, we discuss the figures of merit of PV QWIPs in a high-bandwidth 50 ohm environment

We show that the transient intersubband photocurrent in a GaAs/AlGaAs quantum-well infrared photodetector (QWIP) consists of two dynamical components, which are associated, respectively, with the drift motion of photoexcited carriers and with the extra injection current induced by the generated nonequilibrium space charges. The decay time τ of the latter component depends critically on the temperature of the sample and the applied bias voltage. For a temperature of T=22 K, decay times in excess of 15 μs are found. A simple model of the refilling process of the space charges is presented, showing, that the slow component corresponds approximately to the dielectric relaxation time of the structure along the growth direction. While the slow component in the present 8-period structure corresponds to about 50% of the total photocurrent, it is negligible in standard QWIP structures containing 40 or more periods, where ⩾99% of the intersubband photocurrent proceeds on a picosecond time scale.