The Study Of Silicon Micro/Nano Structures Heterojunction Based Photoelectric Devices

Silicon based optoelectronic devices are expected to form building blocks in chip integration and optically controlled gas sensor for its compatibility with modern microelectronic technology and relatively low cost. The light absorption ability and surface area of silicon can be improved effectively by introducing micro-(nano-)structure on the surface. In this dissertation, the formation of graphene/micro-pyramid textured silicon and ZnO nanorod (NR) array/black silicon heterojunction were studied, and their photoelectric properties and gas sensitivity were explored. The main results are as follows:1. Micro-pyramid textured silicon array was prepared by alkaline etching. The size of micro-pyramid can be controlled by tuning the concentration of etching solution.Absorption spectra and optical simulations showed that the absorption ability and surface photocurrent density of the Si micro-pyramid increased with the decrease of micro-pyramid size.2. Graphene/micro-pyramid textured silicon heterojunction exhibits obvious rectification characteristic, with a rectification ratio as high as 1.5 × 104, and its ideality factor could be deduced to be 1.66. In addition, the heterojunction is very sensitive to near infrared light (850nm), and its on-off ratio can reach 104. It is capable of monitoring fast-switching frequency optical signal (-2000 Hz), with a fast response speed (?r=96 ?s, ?f=160 ?s).3. Black silicon was fabricated by Ag ion assisted etching of micro-pyramid textured Si. The absorption of black silicon increased by 73% compared to planar silicon. ZnO NR array, which is hexagonal wurtzite structure, was synthesized on black silicon surface via low-temperature hydrothermal method. The diameter of ZnO NR can be controlled (from 100 nm to 300 nm) by changing the proportion of methenamine and zinc nitrate hexahydrate in the growth solution.4. The surface area of ZnO NR array/black silicon heterojunction increased significantly for the porous morphology of black silicon and nanometer size of ZnO NR. The rectification ratio of heterojunction is 20, and its ideality factor could be deduced to be 15.13. When illuminated by ultraviolet light, its rise time and fall time of the heterojunction is 34 ms and 18 ms, respectively. The heterojunction is sensitive to volatile gases even at room temperature.