A heterojunction metal-semiconductor-metal photodetector

A novel metal-semiconductor-metal photodetector is demonstrated in which a heterojunction is formed of doped Al/sub 0.24/Ga/sub 0.76/As 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 Al/sub 0.24/Ga/sub 0.76/As 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.