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The fabrication of an ultraviolet photodiode employing a single ZnO tetrapod nanocrystal is reported. We have attached two tungsten leads and one platinum lead to three of the arms of the tetrapod. By measuring the transport properties between each pair of leads we show that the tungsten contacts are ohmic and the platinum contacts are rectifying. Photoresponse measurements were carried out with above and below band gap illumination. We observe a much larger ultraviolet photoresponse for the rectifying Pt-ZnO-W junction than the linear W-ZnO-W junction. We conclude that the enhanced photoresponse of our rectifying junction results from a photoinduced reduction of the Schottky barrier height at the Pt-ZnO interface.