Silicon nanowires composed of p-n junctions have been grown on 2 × 5 cm glass substrates with a thin layer of indium tin oxide (ITO). These nanowires were grown both directly on ITO utilizing the vapor-solid (VS) method, as well as by vapor-liquid-solid (VLS) method, with a thin layer of gold as a catalyst. Current-voltage analyses show p-n diode characteristics in both cases. When a reverse dc bias was applied, these diodes responded to optical signals incident on the glass surface, showing potential solar-cell application and intriguing possibilities for future optical detection structures. Devices grown via the VS method displayed better electrical properties compared to those produced via the VLS method.