Efficient double-side detection in the mid-IR using a QWIP MIM architecture on a transparent substrate

We present a mid-IR ($\lambda \approx$ 8.3 μm) quantum well infrared photodetector (QWIP) fabricated on a transparent substrate, allowing photo detection with illumination from either the front surface or through the substrate. The device is based on a 400 nm-thick GaAs/AlGaAs semiconductor QWIP heterostructure enclosed in a metal-insulator-metal (MIM) optical cavity. For two different excitation configurations - backside illumination through the substrate and frontside direct illumination - we present passive optical characterizations (reflectivity and transmissivity), electric transport measurements and photocurrent generation, showing similar broadband spectral response for the two detector ports and an experimental $T_{\text{blip}}$ of $\approx$ 200K.