Modulating The Optoelectronic Properties Of Two-Dimensional Semiconductor Material Indium Selenide

In recent years,two-dimensional semiconductor materials represented by graphene and transition metal chalcogenides(TMDCs)have attracted attention from researchers due to their excellent properties such as atomic level thickness,high mobility and adjustable bandgap.However,the zero bandgap of graphene and the low mobility of TMDCs have become the biggest obstacle to the application of this kind of material in the field of photodetection.Indium selenide(InSe),as a member of the two-dimensional material family,has excellent optical and electrical properties.At room temperature,its intrinsic mobility is as high as10³cm²V^-1s^-1and the bandgap transits from 2.11e V to 1.26e V with the increasing of the number of layers,which has great application potential in photoelectric detection especially in the near-infrared detection.However,it was found that the interface has a great influence on InSe optoelectronic devices during the research process.For example,the InSe film itself easily reacts with molecules such as oxygen and water in the air,causing degradation of device stability;substrate defects,impurities and surface defect states and other factors will form a large amount of scattering,which limits the mobility,switching ratio and other characteristics of the device;the electrode leads to a serious fermi pinning effect due to a large number of defects introduced in the evaporation process,which greatly hinders the transfer between charge and the separation of photogenerated carriers.Hence,adjusting the InSe device from the interface is an important means to achieve high performance photodetection.In this paper,InSe optoelectronic devices are regulated from three aspects:organic molecular doping,indium film coating and heterostructure construction,which improve the mobility and photoresponsivity of the device.The specific content is as follows:1.Realizing the regulation of InSe ophotoelectric device performance by organic molecular doping.First,by comparing the mobility and switching ratio of the devices on the Si O₂/Si substrate and the BN substrate,it is proved that the device performance on the BN substrate is more excellent and the device mobility has increased from 20cm²V^-1s^-1to326cm²V^-1s^-1and the switching ratio has also increased by an order of magnitude;Then,the InSe-BN device was doped with different concentrations by F₄TCNQ molecules,which is found that as the concentration increases,the response gradually increases.When the concentration reaches 0.5M,the photocurrents at 447nm reaches 495.6n A and at 940nm64.272n A.Finally,by comparing the absorption spectrum and band structure,the main mechanism of photocurrent enhancement is analyzed,that is,the band bending at the interface causes a large number of electrons in the InSe to be captured by organic molecules,resulting in charge transfer.2.Studying the effect of indium film on the performance of indium selenide optoelectronic devices.First,characterizing and comparing the surface morphology of indium films of different thicknesses and their effects on the optical and optoelectronic properties of InSe,the device mobility achieves a 29 times increase from 12.3cm²V^-1s^-1to 359cm²V^-1s^-1,which obtaines indium films with a thickness of 20nm without changing the optical contrast of InSe.Then,by covering 20nm indium films on the surface of the InSe-BN device,the responsivity at 940nm wavelength is greatly improved from 7×10^-3m AW^-1to 3.5×10^-1m AW^-1.Finally,through the comparison of work function and barrier height,it is believed that the main reason for the improvement of device performance is that the difference in work function causes the InSe energy band to bend downward,which makes the electrons accumulate at the interface and the surface charge under illumination will continuously transfer from indium to InSe,thereby intensifying the recombination and separation rate of photogenerated carriers and improving the photoelectric performance.3.Regulating the performance of InSe optoelectronic devices by constructing different types of heterostructures.First,the InSe array structure with a channel width of 2um was prepared by photolithography technology and some areas were selectively covered with indium film to construct an n-n⁺type optoelectronic device,which realizes the self-driving detection of photocurrent under 0V bias voltage;Then,F₄TCNQ molecules are used to selectively dope the InSe device on the surface of BN to construct an n-n^-type photoelectric device based on molecular doping,it is found that as the doping concentration increases,the mobility and dark current of the device have been improved.When the concentration reaches0.5M,the mobility increases from 0.87cm²V^-1s^-1to 350cm²V^-1s^-1and the dark current reduces from 10^-7to 10^-9.Finally,through the systematic comparison of the responsivity of the two types of heterostructures,the analysis shows that the n-n^-type structure not only enhances the photodetection ability due to the partial wrapping of the BN,but also effectively shields the interference from the external environment,thereby enhancing its stability and making it more suitable for high performance optoelectronic devices.