Preparation Of GaSe Flakes And Their Applicaitons For Surface Raman Enhancement And Field Electron Device

Gallium Selenide, as a member of ?-? chalcogenides, has a unique structure with four layer Se-Ga-Ga-Se. The bandgap of GaSe increases gradually with decreasing the layer number, and it changes from the direct bandgap to indirect one when the thickness of the flake is less than 7 layers. Owing to its unique electronic structure, GaSe has an amount of wide applications for optoelectronic, nonlinear optics and terahertz devices.By virtue of the atomic flat and nonpolar surface, the GaSe flakes can also be used as an ideal materials for studying the chemical mechanism of surface Raman enhancement. In addition, the potentially high carrier mobility in the GaSe flake makes it a good candidate for the field effect transistor. To this end, we pay our attention in this dissertation to prepare the GaSe flake and investigate their properties of surface Raman enhancement and field transport. The dissertation contains four chapters and corresponding contents outlined as follow:In chapter one, we briefly introduced the development history, common synthetic methods, structure, properties and potential applications of GaSe. Then we give an outline of the fundamental and trends of SERS and FET. At last, we presented the background and motivations of our study.In chapter two, we mainly introduced the SERS of the GaSe surface. In order to research the surface Raman enhancement effect, we used the GaSe flakes prepared by mechanical exfoliation as the substrate for measuring the Raman signal of the molecules. According to Raman characterization, it was found that the Raman signal of the detected molecules on the monolayer GaSe showed the strongest intensity, and the enhancement effect decreases with increasing the thickness of GaSe flakes.Combined with the observation of the "first layer effect" on the Raman enhancement for the CuPc molecules and the significant quenching effect of GaSe after CuPc coating, we attributed the Raman enhancement on GaSe to the chemical mechanism arising from the charge transfer between molecules and GaSe.In chapter three, we concentrated on the improvement of mobility of GaSe flakes. We used the shadow mask method to prepare GaSe FET to study its transport properties. According to the electronic band structure of GaSe and the work function of different metals, we used palladium as the electrodes to reduce the contact resistance of metal-semiconductor interface and improve the electrical properties of GaSe FET. Then through annealled the device, the residual tape impurities by mechanical exfoliation can be effectively eliminated and the contact between electrodes and GaSe can be improved. It is also found that the GaSe FET stored in air becomes degradation but the performance can be recovered partly by the annealing. We also tried using PMMA / Si02 as the substrate to suppress the interfacial scattering to improve the carrier mobility.In chapter four, the challenges and the development tendency for the future researches of GaSe were proposed.