High-quality single-crystalline GaP nanowires were grown by a simple vapour deposition method and their electrical and opto-electric transport properties were studied. Structural studies showed that the GaP nanowires consisted of a core-shell structure with a single-crystalline GaP core and an outer gallium oxide (GaO_x) layer of thickness approx 6 nm. The individual GaP nanowires exhibited n-type field effects with an on/off ratio as high as 10~5 and their carrier mobilities are in the range of about 10-22 cm~2 V~(-1) s~(-1) at room temperature. When the devices were exposed to an ultraviolet (UV) light source, the current in the nanowires increased abruptly to more than 10~3 times, and this was possibly due to carrier generation in the nanowires and de-adsorption of adsorbed O_2~- ions on the GaO_x surface shell. The nanowires also showed good reversible switching actions between the high- and low-resistance states.
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