We report optical scanning measurements on photocurrent in individual Si nanowire field effect transistors (SiNW FETs). We observe increases in the conductance of more than 2 orders of magnitude and a large conductance polarization anisotropy of 0.8, making our SiNW FETs a polarization-sensitive, high-resolution light detector. In addition, scanning images of photocurrent at various biases reveal the local energy-band profile especially near the electrode contacts. The magnitude and polarity of the photocurrent vary depending on the gate bias, a behavior that can be explained using band flattening and a Schottky-barrier-type change. This technique is a powerful tool for studying photosensitive nanoscale devices.
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