Electrical and Optical Enhancement Properties of Metal/Semimetal Nanostructures for Metal Oxide UV Photodetectors

UV photodetectors have been investigated for various commercial and military applications, such as secure space-to-space communications, pollution monitoring, water sterilization, flame sensing, and early missile plume detection [1]. To date, epitaxially grown or bulk wide bandgap semiconductors such as GaN, AlN, AlGaN, C (diamond), and SiC have been used for ultraviolet detection [2–12]. Fabrication of devices from these materials is often expensive with intricate processes. Also organic semiconductor materials are an attractive alternative [13, 14], though they lack the carrier mobility of inorganic semiconductors. Metal oxide semiconductor nanomaterials have the advantages of low processing cost, ease of fabrication, a large surface-to-volume ratio with carrier and photon confinement, and amenability to surface functionalization for hybrid inorganic–organic configurations. Furthermore, the unique combination of the carrier transport mechanism and oxygen adsorption/desorption processes on the nanostructures surface leads to a high internal gain. However, they also lead to slow transient response with response time on the order of seconds. Significant enhancement of photodetector performance can be enabled by layers of metal/semimetal nanostructures. The trade-off between sensitivity and time response may be significantly reduced with careful design of metallic nanostructures relative to metal oxide active regions. The primary mechanisms for enhancement include surface plasmon resonance and carrier transfer to highly conductive materials. Details of the fundamental concepts, parameters of influence, and comparisons of enhanced devices are presented.