Preparation Of Ultrathin Transition Metal Carbides And Their Application In Photodetectors

Since the discovery of graphene,two-dimensional?2D?materials have attracted the attention of researchers due to their special structure and characteristics.2D ultra-thin transition metal carbides?TMCs?,as a new member of the 2D material family,have injected new vitality into the application of 2D materials thanks to their 2D structure and excellent physical and chemical properties.For 2D TMCs prepared by exfoliation method,they generally have small lateral size,but good metal conductivity and light transmittance,and their work functions can be adjusted by changing the surface functional groups.The2D ultra-thin TMCs prepared by the chemical vapor deposition?CVD?method generally have a larger size than the TMCs prepared by the exfoliation method.Moreover,the ultra-thin TMCs prepared by the CVD method not only have good electrical conductivity and light transmittance but also have good thermal and environmental stability.The excellent characteristics of TMCs provide new possibilities for the development of high sensitivity and miniaturization of photodetectors in the post-Moore era.Photodetectors are one of the most important and widely used optoelectronic devices in optical information acquisition systems.With the development of photodetectors in the direction of high sensitivity and miniaturization,it is necessary to develop a highly sensitive and miniaturized photodetector.However,research on the photodetector based on 2D TMCs,which are ideal materials for building new-type photodetectors,has rarely been reported.In addition,how to prepare TMCs that are more suitable for application in photodetectors?such as less defects in larger areas?is yet to be further explored.In view of the situation shown above,we conducted the study as described below.1.We prepared a 2D Ti₃C₂T_x by selective etching-assisted liquid exfoliation method and combined it with n-type silicon?n-Si?to construct a Ti₃C₂T_x/n-Si van der Waals Schottky junction photodetector.We studied the effects of Ti₃C₂T_x thickness,annealing treatment and vacuum environment on the properties of Ti₃C₂T_x/n-Si van der Waals heterojunction.We tested and analyzed the photodetection performance of the Ti₃C₂T_x/n-Si photodetector under bias voltage.We prepared self-powered Ti₃C₂T_x/n-Si photodetectors with voltage response and recovery time of 0.84 ms and 1.67 ms,respectively.The Ti₃C₂T_x/n-Si photodetector has a responsivity of 26.95 mA/W and on/off ratio of 10⁵ for a laser with an energy density of 15.17 mW/cm² and a wavelength of 405nm.2.In order to obtain a thin film electrode material which is more favorable for charge transport,we explored the effects of various growth conditions on the synthesis of Mo₂C-Graphene?Mo₂C-Gr?hybrid films synthesized by CVD.After testing the work function of the Mo₂C-Gr hybrid film,we constructed a Mo₂C-Gr/Sb₂S_0.42Se_2.58/TiO₂/FTO two-sided photodetector that can detect the light incident from the two electrodes.We tested and analyzed the photodetection performance of the photodetector at different temperatures and bias voltages,and studied the current response of the photodetector to incident light of different wavelengths and illumination intensities.A photodetector with a responsivity of 35.91 mA/W under self-powered condition for light with a wavelength of650 nm and an energy density of 2.5 mW/cm² was prepared.The voltage response and recovery time of the photodetector are 0.084 ms and 0.100 ms,respectively.3.In order to prepare TMCs which are more suitable for use in photodetectors,we prepared large-area ultra-thin Mo₂C crystals by modified CVD method and discussed the growth mechanism of large-area Mo₂C crystals.Large-area and low-work function Mo₂C was combined with Au to form an asymmetric metal contact structure with large work function difference.The performance of MoS₂-based photodetectors which is driven by asymmetric metal contacts was tested and analyzed.We prepared a Mo₂C/MoS₂/Au photodetector with a responsivity of 10^-1 mA/W to incident light with a wavelength of 600nm and an energy density of 1.78 mW/cm² under self-powered conditions.The current response and recovery time of the photodetector are 23 s and 28 s,respectively.