Controllable Synthesis And Photodetection Performance Of Two-dimensional Group ?-? Semiconductors

As an important component of two-dimensional layered materials(2DLMs),the two-dimensional(2D)group IV metal chalcogenides(GIVMCs)have drawn much attention recently due to their earth-abundant,low-cost,and environmentally friendly characteristics,thus catering well to the sustainable electronics and optoelectronics applications.However,2D GIVMCs remain great challenge compared to transition metal dichalcogenides,which have been studied relatively mature.After a comprehensive review on reaserch development of 2D GIVMCs family,this dissertation will present our work on this field including controllable growth,high performance photodetectors,and improvement of performance through designing device structures.Firstly,this thesis demonstrates that we employ SnI2 and Se powders via CVD method to obtain ultrathin SnSe2 nanosheets with thickness of?1.5 nm and lateral size of?40 ?m.Then,Raman and TEM characeterizations have been employed to identify the high-quality and single-crystalline structure of the as-sysnthesized SnSe2 nanosheets.What's more,high performance photodetector based on high-quality SnSe2 nanosheet has been fabricated,and studied systematically.Secondly,we describe that large-size ultrathin single-crystalline SnS2 nanosheets with average size up to 100 ?m were synthesized via an improved CVD method by applying the low melting point SnI2 as the Sn precursor.Then phototransistor based SnS2 nanosheet has been constructed with SiO2 as bottom gate so that we can modulate the photodetection via applying gate.Thirdly,we present that SnS nanosheet/nanobelt arrays have been sysnthesized employing Au as catalysts through PVD method.Then we fabricate photodetector based on ultrathin SnS nanobelt with Ti electrodes.Because the work function of Ti(?4.33 eV)is larger than the electron affinity of SnS(?3.9 eV),Schottky contacts are formed between SnS and Ti resulting in fast response.Forthly,we present the construction of heterostructure realizing effective separation of electron hole pair so as to improve the photoelectric response of the device.Firstly,CVD method is used to synthesize single MoS2 triangles,and SnSe2 nanosheets are synthesized using MoS2 triangles as templates.Then aberration-corrected high resolution transmission electron microscopy is employed to identify the crystal phases of SnSe2/MoS2 heterostructures,found that both of SnSe2 and MoS2 are belong to 2H-type.Theoretial calculations demonstrates that SnSe2/MoS2 belong to type-? heterostructure,which promoting electron-hole pairs separation and have been verified by Raman,PL,and XPS characterizations.The photoresponse of SnSe2/MoS2 heterostructure is two orders of magnitude higher than that of MoS2.Fifthly,high performance photo transistor based on p-WSe2/n-SnS2 heterostructure has been fabricated on BN.The p-n heterostructure has been fabricated by mechanical transfer.In order to avoiding the charge impurities and adsorbates at the interface we have employed BN between the SiO2/Si substrate and device.The fabricated p-WSe2/n-SnS2 heterostructure shows abousolute rectifying characteristics and the channel is dominated by holes.What is more,The fabricated p-WSe2/n-SnS2 heterostructure shows excellent photodetection performance.At last,we summarize our work in chapter six,and list some plans for future investigation.