A narrow-band infrared phototransistor is designed and realized based on a double-layer structure. An isolated island formed from the first quantum well (QW) works as a gate, which is capacitively coupled to the remote two-dimensional electron gas (2DEG) layer working as the source/drain channel. Incident radiation excites the intersubband transition within the isolated QW island. Excited electrons tunnel out of the QW causing it to positively charge up. This affects the conductance of the remote 2DEG channel, yielding detectable photosignals. The present detection mechanism makes it possible to design semiconductor infrared detectors with higher sensitivities along with custom designed tunability. The mechanism also holds potentiality of single-photon detection in the infrared region.
This expectation is supported by the additional experimental finding that the amplitude of photosignal increases when another black polyethylene film of is added: The signal does increase despite the total radiation intensity is reduced to about 15%!