Tunable hybrid photodetectors with superhigh responsivity.

For practical applications, increasing the photosensitivity, response speed, and selectivity of UV photodetectors is a prerequisite. Many research studies on Si-based photodiodes, the most common devices for UV detection, have been conducted to improve their photosensitivity. The calculated photoresponsivities of these devices were typically less than 10 A W . Although these studies showed an improved performance, the devices exhibited some inherent limitations: the requirement for filters to block out visible and infrared photons, and the degradation of devices when exposed to UV light with energies much higher than the semiconductor bandgap. With the obvious advantages of a room-temperature wide bandgap (Eg1⁄4 3.37 eV), low cost, and ease of manufacturing, zinc oxide (ZnO) is emerging as one of the most important materials for many applications in nanooptoelectronics, nanogenerators, field-effect transistors (FETs), sensors, and so forth. In particular, ZnO nanomaterials have recently been extensively investigated by several groups for UV photodetection applications. For example, Soci et al. reported ZnO nanowire photodetectors with a large photocurrent increase by several orders of magnitude upon UV illumination at a low light intensity. Lao et al. successfully demonstrated the huge enhancement of the UV response of ZnO nanobelt sensors by close to five orders of magnitude after surface functionalization with a polymer that shows a high UV absorption ability. Zhang et al. fabricated ZnO tetrapodbased sensors to distinguish false response and increase