Dark current reduction of Ge MOS photodetectors by high work function electrodes

A metal/oxide/n-Ge structure has been utilised as a photodetector. The oxide is grown directly on the Ge substrate by liquid phase deposition. We use Al and Pt as the gate electrodes to evaluate the transport mechanism of the MOS detector. At negative gate bias, the dark current of the Al gate detector is composed of the thermal generation of minority carriers in the depletion region and the electron current tunnelling from Al to the conduction band of the rc-type Ge substrate. However, for the Pt gate detector at negative gate bias, the electron tunnelling from Pt to the conduction band of the rc-type Ge is greatly reduced owing to the large work function of Pt (5.65 eV).