A "Janus" double sided mid-IR photodetector based on a MIM architecture

We present a mid-IR (lambda similar to 8.3 mu m) quantum well infrared photodetector (QWIP) fabricated on a mid-IR transparent substrate, allowing photodetection 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 nanostructured metal-insulator-metal cavity and hosted on a mid-IR transparent ZnSe substrate. Metallic stripes are symmetrically patterned by e-beam lithography on both sides of the active region. The detector spectral coverage spans from lambda similar to 7.15 to lambda similar to 8.7 mu m by changing the stripe width L-from L = 1.0 to L = 1.3 mu m-thus frequency-tuning the optical cavity mode. Both micro-FTIR passive optical characterizations and photocurrent measurements of the two-port system are carried out. They reveal a similar spectral response for the two detector ports with an experimentally measured T-BLIP of similar to 200 K.