Enhanced NIR photo response of ZnO-silicon nanowire array photodetector

Photodetectors, composed of a single semiconductor such as Si, Ge, GaAs or InGaAs, are widely used in many fields and their photo-response is determined by the bandgap, thus defining the spectral region of their photoresponse. Heterojunction photodetectors have recently received much attention as a powerful platform to obtain better absorption and efficiency due to bandgap engineering. Si is preferred for constructing photodetectors due to its amenability for large scale production resulting in cost efficiency, less noise and integration potential; however, its detection capability is not highly effective in the near-infrared region of 700-1000 nm and declines abruptly over 1100 nm due to its bandgap limitations. Here, we demonstrate high-performance photodetectors based on shaped ZnO/silicon nanowire structures. Nanostructures such as nanowires can enhance performance by increasing the probability of light absorption. Spin coating was used to add a thin film of ZnO over the top-down fabricated silicon nanowire array. The thickness of the deposited ZnO was about 300 nm, although it lacked uniformity. The fabricated photodiodes show higher photocurrent and responsivity over those devices without the ZnO film. Reflectance measurements indicate that the ZnO film reduces the surface reflectance of silicon, allowing more light to enter the nanowire photodiode, thus increasing the photogenerated electron-hole pairs.