GaAs/AlGaAs quantum well photodetectors with a cutoff wavelength at 28 μm

We demonstrate the longest ${\mathrm{(\lambda }}_c$ =28.6 $\mu$ m) far-infrared quantum well photodetectors (QWIPs) based on a bound-to-bound intersubband transition in GaAs/AlGaAs. The responsivity is comparable with that of mid-infrared GaAs/AlGaAs and InGaAs/GaAs QWIPs. A peak responsivity of 0.265 A/W and detectivity of 2.5$\times$ 10${}^9$ cm$\sqrt{\mathrm{Hz}}$ /W at a wavelength of 26.9 $\mu$ m and 4.2 K have been achieved. Based on the temperature dependent dark current and responsivity results, it is expected that similar performance can be obtained at least up to 20 K.