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Self-powered single semiconductor nanowire photodetector

Self-powered photodetectors have been fabricated from a single germanium nanowire (NW) in the metal–semiconductor–metal (MSM) device configuration. The self-powered devices show a high photoresponse (responsivity ∼ 103–105 A W−1) in the wavelength range 300–1100 nm. It has been established from I–V characteristics that asymmetry exists in the Schottky barrier height (SBH) at the two MS contacts. We have used simulation to establish that the asymmetric SBH at the metal contacts in an MSM device is a major cause for the ‘built-in’ axial field that leads to separation of a light generated electron–hole pair in the absence of an applied bias. Thus, even in the absence of external bias, the photogenerated carriers can be separated, which then diffuse to the appropriate electrodes driven by the ‘built-in’ axial field. We also point out the physical origins that can lead to unequal barrier heights in seemingly identical NW/metal junctions in a MSM device.