Preparation And Photoelectric Properties Of 2D GaS_xTe_1-x Nanomaterials

The two-dimensional layered structural materials have attracted worldwide attention due to its unique optical and electrical properties.In particularly,the transition metal sulfides have been investigated extensively due to its graphene-like single layer structure.And more importantly,some of the transition metal sulfide with rich content in the earth are semiconductors with broad bandgap.By far,two-dimensional atomic crystal semiconductor nanomaterial is widely used to fabricated various optoelectronic devices,such as optical transistor,photo-detector and solar cell.However,one of the important factors limiting the spectral response characteristics and responsiveness of these optoelectronic devices is the bandgap engineering of the semiconductor.Therefore,the richness and change of bandgap can greatly improve the performance of these devices.In order to obtain continuous and tunable bandgap semiconductor nanostructures,some methods have been found to be useful to adjust their bandgap such as the plane of epitaxial growth,quantum size effect,temperature effect.However,compared with these methods,alloying materials with different bandgaps is the most practical way.Therefore,it is an important subject to synthesize the 2D transition metal sulfide semiconductor nanostructures with tunable compositions.This dissertation mainly studies the bandgap regulation based on the two-dimensional gallium chalcogenide.Firstly,we synthesized the nanostructure of alloy materials GaSxTe1-x by chemical vapor method(CVD)and realized continuous tunable band gap.Then we studied the Raman mapping of GaS nanosheet with different thickness.The spatial inhomogenity of Raman scattering enhancement was observed by Raman imaging.Lastly,we studied the photoelectric current of devices based on GaS nanosheets with different thickness.The main research results are summarized as follows:(1)We synthesized the GaSxTe1-x(x=0.3～1)with high purity(99.999%)of GaS and GaTe powder by chemical vapor deposition.The scanning electron microscope(SEM),EDS energy spectrum characterization proves that the material we obtain is not a mixture of GaS and GaTe.PL characterization showed continuous tunable spectrum on a single substrate along a certain direction.We collected the PL spectrum from the side near the source to the other side far from the source.It is found that a continuous tunable spectrum within a certain range when x=0.3～0.7.While the PL spectrum is relatively single when x=0.8～0.9.(2)The CVD synthesized GaS nanosheets were selected for further characterization.After transferred these samples to silicon wafers,the Raman mapping of GaS with different thickness show enhanced Raman scattering at the edge of the nanosheet.We proved that the spatial inhomogeneity of Raman scattering arise from the thickness of GaS,the photon energy and the polarization direction of excitation light source.The performance of this spatial inhomogeneity may be applied to light sensing and optical switching devices.(3)We fabricated two terminal devices by using different thickness of GaS nanosheets as channel material.The photocurrent we tested shows that the thicker GaS nanosheet has weak electrical conductivity but good light response under the wavelength of 455 nm.In contrast,the thinner GaS nanosheet has a high current under the dark field and not obvious light response.