Controllable Fabrication Of Two-dimensional Sb_xSn_1-xSe₂ Alloys And Their Optoelectronic Properties

Since the discovery of graphene,a series of new two-dimensional atomic crystal materials have been manufactured.With their rich structure and excellent properties,these atomic thin-layer two-dimensional materials show great application potential in future new optoelectronic devices.However,graphene cannot effectively shut down its field-effect transistor devices without energy band gap,which greatly limits its application in modern electronic products.However,many two-dimensional materials have been synthesized and reported with graphene-like structure.Due to their unique energy band structure,these materials possess excellent optical and electrical properties,indicating a great application potential in the next generation of electronic devices(such as phototransistors,optical sensors,light-emitting diodes,lasers and high electron mobility transistors).As to a single material mentioned above,its properties always have certain limitations,such as narrow band gap,fixed electrical conductivity,and non-tunability.To further develop the application potential of two-dimensional materials in electronics and optoelectronics,one of the effective measures is to tune the band gap of two-dimensional materials,and indirectly adjust the electronic properties for modern electronic devices based on those semiconductors.By doping heteroatoms into crystal lattice to construct an alloy material,it is expected that the energy band gap and electrical properties of the two-dimensional material can be continuously adjusted.Based on this method,researchers have successfully alloyed in-phase two-dimensional TMDs with high lattice matching,and obtained a series of excellent properties and applications.In fact,alloying two-dimensional TMDs with different phase structures will bring greater freedom to their properties and applications.However,the current researches scarcely focus on such heterogeneous two-dimensional alloy materials,due to the large lattice mismatch of materials with different phase structures,which worsens the synthesization of high-quality,phase-tunable 2D alloys.In recent years,the IVA-VIA group metal tin chalcogenide materials represented by SnSe2 have gotten increasing attention,due to their excellent optical and electrical properties.In particular,its unique 1T phase structure brings new development opportunities for the construction of phase tunable alloys.However,it is still at beginning that the researches on the controllable preparation and properties of such materials are.Therefore,this paper aims to prepare SnSe2 materials for large-scale device application,and conducts systematic and in-depth research from three aspects:material preparation,alloying and physical property control,and device applications.The main research contents of this paper are as follows:1.Controllable preparation of high-quality two-dimensional SnSe2 materials.Using chemical vapor deposition(CVD)growth method,by adjusting growth parameters such as auxiliary agent,growth temperature,precursor weight,flow rate of carrier gas,etc.,a large area,high-quality single crystals SnSe2 film was synthesized on a mica substrate.The field-effect transistor constructed based on thin SnSe2 has a carrier mobility of 0.67 cm2 V-1 s-1 and an on-off ratio of 2.7×103.Under illumination,the grid voltage exhibits a significant modulation effect on the photocurrent.When the bias voltage is 1.0 V,the light responsivity of SnSe2 is about 1.1 × 103 A/W.2.Controllable preparation of phase-adjustable two-dimensional SbxSn1-xSe2 alloy.Considering the innegligible difference of crystal structure between SnSe2 and Sb2Se3 materials,the electrical properties(SnSe2:n-type;Sb2Se3:p-type)and energy band gap(SnSe2:1.73 eV;Sb2Se3:1.21 eV),we adopt CVD growth method,via adjusting the synthetic condition,a series of two-dimensional SbxSn1-xSe2 alloy materials with different compositions are prepared on the mica substrate.By adjusting the alloy material composition,the optical band gap can be continuously adjusted from 1.21 eV to 1.73 eV.Using Raman spectroscopy,X-ray photoelectron spectroscopy andTransmission electron microscopy and other characterization methods,it was confirmed that with the increase of dopant dose,the crystal structure of the two-dimensional SbxSn1-xSe2 semiconductor alloy gradually changed from 1T phase to 1T' phase.The transformation of SbxSn1-xSe2 alloy phase structure has been deeply clarified.3.The electrical and optical properties of the two-dimensional SbxSn1-xSe2 alloy.Based on the high-quality two-dimensional SbxSn1-xSe2 alloy samples prepared above,field effect transistors and photodetectors with different compositions of SbxSn1-xSe2 alloy were designed and constructed.The output characteristic curves of SbxSn1-xSe2 alloy samples with different compositions show a similar ohmic contact between the alloy samples and the electrode.Known from the changing of the transfer characteristic curves corresponding to the composition,the conductivity of the alloy obviously shows the continuous tunability from n-type to bipolar to p-type.In addition,the 1T'-phase two-dimensional SbxSn1-xSe2 alloy device has a high photo responsivity(?1000 mA/W),and the increase of the Sb component decreases the response time of the photodetector.This SbxSn1-xSe2 alloy photodetector with adjustable band gap and electrical properties provides new ideas and feasibility for the construction of multifunctional two-dimensional electronic and optoelectronic devices.