Preparation, Modification And Self-Powered Properties Research Of Silicon Nanowire Arrays As A Visible And Near-Infrared Photodetector

The one-dimensional (1D) silicon nanowire (SiNW) array has the advantages of high sensitivity, low energy consumption and fast response speed due to their low reflectance and large surface-to-volume ratio for increasing the collection efficiency of photons and low dimension of the effective conductive channel to shorten the transit time of carriers. Recently,1D SiNW arrays are promising candidate structures for the fabrication of high performance optoelectronic device.The highly ordered n-SiNW array was prepared through an Ag-assisted chemical etching method. There were two different methods to fabricate the photodetectors. Firstly, the n-SiNWs array was covered with pattern Au by thermal evaporation method. And then the Au/n-SiNWs Schottky photodiode (SPD) was formed. Second, the n-SiNWs array surface was coated by a nanoscale copper oxide (CuO) layer using liquid drops reaction designed by myself. And then the p-CuO/n-SiNWs junction was formed. The two light detectors are studied to response the near-infrared light (405nm,532nm and1064nm).Otherwise, the p-CuO/n-SiNWs devices were annealed with different temperature in order to study the effects of annealing temperature to the properties of the device.The main work and conclusion of this paper are as follows:(I) Arrays of vertical silicon nanowires were fabricated from a commercial Si wafer [n-type,(111)-oriented,0.01Ω·cm] by an Ag-assisted electroless etching method. The cross section of SiNWs array is observed by scanning electron microscope (SEM) and the length of the SiNWs are obtained. As a result of the experient, the deposition time of the silicon in the deposition directly affect the length and the surface topography of the etching silicon nanowires.(Ⅱ) A new broadband self-powered photodetector was fabricated by coating an n-SiNW array with a layer of p-CuO nanoflakes through a new simple solution synthesis method. The samples were annealing treated at the temperature of350℃,450℃,550℃,700℃and800℃for3hours. The samples were analyzed by SEM, TEM and XRD. After the annealing treatment, the CuO nanoflakes changed into the spherical particals. As the annealing temperature increasing, the CuO on the SiNWs was gradually faded.(III) The two different array structure photodetectors were fabricated and tested. Firstly, self-powered visible and near-infrared photodetector based on Au/silicon nanowires array Schottky photodiode (SPD) was fabricated. The as-fabricated SPD exhibited excellent rectification characteristics with a rectification ratio up to584within±1V in the dark and significant photovoltaic (PV) effects under visible and near-infrared light illuminations. Photodetection analysis revealed that the SPD was highly sensitive to illumination of405nm,532nm and1064nm with good stability, reproducibility and high response speed at zero bias voltage. Meanwhile, the SPD could provide a rapid binary-response of positive current to negative current switch upon illumination at a small forward bias. The current work demonstrates that the self-powered Au/silicon nanowires SPD would have a bright application prospect in self-powered optoelectronic systems. Secondly, a new broadband self-powered photodetector was fabricated by coating n-SiNWs array with a layer of p-CuO nanoflakes via a new simple solution synthesis method. The p-n heterojunction exhibits an excellent rectification characteristic in the dark and a distinctive photovoltaic behavior under broadband light illumination. Photoresponse at zero bias voltage shows that this self-powered photodetector is high sensitive to visible and near-infrared light illumination with excellent stability and reproducibility. An ultrafast response rise/recovery time of60μs and80μs was first represented for CuO based nano-photodetectors. Meanwhile, the broadband photodetector can provide a rapid binary-response with changing current from positive to negative upon illumination at a small bias. The binary-response arose from the photovoltaic behavior and the low turn on voltage of the CuO/SiNWs device. These properties make the CuO/SiNWs broadband photodetector suitable for nanoscale applications that require high response speed and self-sufficient functionality.(Ⅳ) The photoresponse of the detectors which were treated with different annealing temperatures to VIS (405nm,532nm) and NIR (1064nm) were investigated. The results showed that as the treating temperature increased the open-circuit voltage and the photocurrent were all shown to decrease.