A heterojunction metal-semiconductor-metal photodetector

A novel metal-semiconductor-metal photodetector is demonstrated in which a heterojunction is formed of doped Al0.24Ga0.76As layer on GaAs. The new device shows improved rectifying characteristics since the Schottky metal contacts a two-dimensional electron gas, The triangular quantum well that is formed at the hetero-interface due to doping of Al0.24Ga0.76As improves collection of optically generated electrons, The AlGaAs window also reduces reflection of light from air and eliminates GaAs surface recombination centers. The fabricated devices show up to a factor of four higher photocurrent and an order of magnitude less dark current than a conventional MSM. They also show smaller reach-through voltages consistent with the expected metal to two-dimensional gas contact properties.