We report the fabrication and characterization of photosensitive heterostructure device using pure and Cu doped ZnO nanorods on n-Si substrate using a low cost hydrothermal technique. Special techniques like Rutherford backscattering spectroscopy and Proton Induced X-ray emission (PIXE) were used to confirm the doping of Cu in ZnO nanorods. The PIXE measurements confirm the absence of any foreign element in parts per million level, except pure Cu doping in ZnO. The compressive stress in (002) peak develops after Cu doping is indicating the successful substitution of Cu +2 ions into Zn +2 lattice sites. The I-V measurement of 5% Cu doped ZnO device shows five orders of magnitude increase in current flow compared to 1% Cu doping.  Under ultraviolet (UV) light exposure further enhancement of the photocurrent in the devices has been observed, which demonstrates the capability of Cu doped ZnO nanorods as a potential UV photodetector.