Photovoltaic detection of infrared light in a GaAs/AlGaAs superlattice

We report the observation of photovoltaic infrared photodetection in an n‐type GaAs/AlGaAs superlattice within the optical range 3.6–6.2 μm. A built‐in graded AlGaAs barrier (∼0.2 eV) provides charge polarization in the sample by allowing the optically excited electrons in the second miniband of the superlattice to diffuse over this barrier. The optical polarization of the infrared signal is consistent with the selection rules applicable to the superlattice. The infrared photoresponse results from first‐to‐second miniband as well as shallow donor‐to‐second miniband photoexcitations within the superlattice. Donor‐to‐second miniband photoexcitation is dominant at low temperatures (