Preparation And Optoelectronic Properties Based On Monoelemental Tellurium And Ternary Bismuth Oxyselenide Nanomaterials

Graphene has ultra-high carrier mobility,but the pristine zero band gap character limits its development in the field of low-dimensional optoelectronics.Two-dimensional transition metal dichalcogenides(TMD)possess tunable band gap,but its mobility is limited.Black phosphorus has both high mobility and moderate band gap,while its stability in air is always a challenge.Monoelemental tellurium(Te)nanomaterials and ternary layered bismuth oxyselenide(Bi2O2Se)nanoplates have attracted extensive attention due to their merits of high mobility,high air stability and thickness dependent broadband bandgap modulation..This paper has prepared tellurium nanosheets and nanowires by physical vapor deposition(PVD)and studied their electrical properties.Combined with other two-dimensional materials(WS2,p-InSe,n-InSe)with high light absorptivity,author has fabricated the mixed-dimensional heterostructure and studied their photodetection performance.In addition,Bi2O2Se nanosheets were prepared by chemical vapor deposition under ambient pressure condition,and p-n,n-n heterost:ructures were constructed by transfer method.It was found that they have excellent optical detection performance.The main contents are as follows:(1)Air stable tellurium nanosheets and nano wires are prepared by a simple and scalable physical vapor deposition(PVD)method.The Hall hole mobility of the Hall device with six electrodes based on Te nanosheet reaches 1485 cm2·V-1·s-1 at room temperature and 3500 cm2·V-1·s-1 at low temperature(2 K).This work can arouse researchers' attention to this new two-dimensional Te and open up a new way to explore high-performance nano-micro devices based on PVD growth of p-type Te.(2)The 1D-2D van der Waals(van der Waals)mixed-dimensional heterostructures of one-dimensional Te microwire coated by two-dimensional WS2 nanofilm were prepared by PVA-assisted dry transfer method.The structure have type ? energy band alignment and strong built-in electric field,enabling the device presents photovoltaic effect and a maximum open circuit voltage(Voc)of 0.2 V,which shows excellent self-powered optoelectrical detection ability.Under 635 nm laser illumination,the maximum photoresponsivity,external quantum efficiency and specific detectivity of the self-powered photodetector are 471 mA·W-1,91%and 1.24×1012 Jones,respectively.In addition,benefiting from the large transverse built-in electric field,the dark current is highly suppressed to the scale of 0.1 pA and the light on/off ratio reaches 104 compared with pristine device.The photodetection performance of the device can be further improved under external negative bias voltage.The mixed-dimensional heterostructure of 1D Te-2D WS2 has great potential in high performance photodetectors and photovoltaic devices.(3)1D Te microwire-2D InSe nanosheets with different doping types mixed-dimensional heterostructures(N-N,N-P)were prepared,and their photodetection properties were studied and compared.The raman peaks of the heterostructure are enhanced and photoluminescence spectra are quenched via optical characterization,which are attributed to the strain effect of nanosheet and the type II band alignment.As for electrical property,the rectification ratio of Te wire/p-InSe heterostructure is 20,which is much less than that of Te wire/n-InSe heterostructure(about 252).Under 405 nm light illumination,the maximum photoresponsivity,external quantum efficiency and specific detectivity of Te wire/p-InSe heterojunction devices are 530 mA·W-1,164%and 4.51 ×1011,Jones,respectively.In addtion,the device displays fast photoresponse with reponse time of 25 ms Meanwhile,the maximum photoresponsivity,external quantum efficiency and specific detectivity of Te wire/n-InSe heterojunction photodetectors are 410 mA·W-1,127%and 1.44×1011 Jones,respectively.Photoresponse time ?rise/?decay is 19.4/25.6 ms.In the aspect of polarized light detection,under 635 nm polarized light illumination,the polarization ratios of Te wire/p(n)-InSe mixed-dimensional photodetector are 5.6 and 7.6,respectively.The mixed-dimensional heterojunction photodetectors based on the 1D/2D Te wire/p(n)-InSe provide important references value for the research concerning high-performance photoelectrical detection of P-N and N-N mixed-dimensional heterostructures.(4)Few-layered Bi2O2Se nanosheets were grown by chemical vapor deposition(CVD)at ambient pressure,and the van der Waals p-InSe/Bi2O2Se heterostructure devices were constructed.Due to the built-in electric field and type ? band alignment,the dark current is greatly suppressed to the scale of 10-14 A.Under 405 nm laser illumination and bias voltage of-1 V,the device exhibits an ultra-high light on/off ratio of 105,a high photoresponsivity of 1.86 A·W-1,a fast response speed(response time is only 10 ms),a high external quantum efficiency of 571%and a high specific detectivity of 1.01×1012 Jones,respectively.The structure displays excellent photovoltaic charater with the maximum photoresponsivity,external quantum efficiency and specific detectivity of 130 mA·W-1,39%and 7.51 ×1011 Jones,respectively.In addition,author also fabricated WS2-Bi2O2Se N-N heterostructure and found that the photodetector based on this heterostructure has high photoresponsivity(29.8 A·W-1)and external quantum efficiency(5836%).The heterostructure based on Bi2O2Se nanosheets are expected to be used in high performance optoelectronic and photovoltaic devices in the future.As emerging air stable nano-materials,monoelemental Te and ternary Bi2O2Se with bandgaps of 0.3-1.5 eV possess:ing merits of high mobility and excellent infrared light absorbtion ability have great application prospects in the field of nano-micro optoelectronics.However,aspensts of high off state current,undistinguished swithcing performance,slow response speed and high recombination rate of photogenerated carriers severely limit their applications.The reasonable design of van der Waals heterostructure can compensate drawbacks of pristine material,which effectively suppresses the dark current,improves the photoresponse speed and photodetection performance.In this dissertation,Te sheet(wire)and Bi2O2Se nanosheets were prepared by PVD and CVD,respectively.Consequently,1D/2D mixed dimensional heterostructures,2D/2D heterostructures are fabricated using 2D materials with high light absorbtivity as building blocks and the photodetection properties are investgated.The research results provide guidances and lay foundation for the future application of Te and Bi2O2Se in the field of optoelectronics.