Synthesis And Photoelectric Characterization Of Two-dimensional Germanium Selenide

Germanium selenide monolayer is a novel two-dimensional material with wide band gap and complex band structure.It is a kind of direct band gap semiconductor material with excellent photoelectric properties.It has a bright future in the field of optoelectronics.At present,there is still a lack of basic experimental research on GeSe from less layer to monolayer.The main challenge is to develop the technology to control the preparation of monolayer films.We demonstrated the preparation of GeSe monolayer on SiO2/Si substrate by mechanical stripping and laser thinning.The morphology,Raman and fluorescence spectra of the GeSe monolayer were studied.Atomic force microscope data showed that average thickness of the bottom layers was thinned to≈1.5nm as the thinning laser power density is increased to 9.6 ×104W/cm2,the average thickness of the thinned bottom layers is close to the calculated monolayer thickness of GeSe.Thickness dependence of Raman spectra of GeSe was performed.It was found that the monolayer GeSe has eight continuous fluorescence peaks at～589nm,655nm,737nm,830nm,1034nm,1178nm,1314nm,and 1456nm.According to the first principle calculation,the band structure of several photoluminescence spectra peaks was explained,and some of the spectral peaks were consistent with the band gap values obtained by the theoretical calculation.The first principle method is used to calculate the band structure of multilayer to GeSe monolayer.In combination with the photoluminescence of GeSe materials,the results showed that the band gap of GeSe is changed into a direct band gap when the number of layers from the fourth layer to the third layer.In this paper,the effects of annealing on the fluorescence properties of the GeSe monolayer were investigated,the GeSe monolayer prepared by using the mechanical stripping method and laser thinning technology.The effect of thermal treatment and annealing under different temperatures from 100℃ to 250℃ on the photoluminescence spectroscopy of the GeSe monolayer is reported.Under the same measuring conditions,the photoluminescence intensity of A exciton and B exciton is increased twice when the annealing temperature is 200℃,while the increasing of the photoluminescence intensity of C exciton reaches～84%.At the same time,the vacuum annealing treatment does not affect the position of A exciton,B exciton and C exciton peaks.The fluorescence quantum efficiency of single layer GeSe can be improved by annealing treatment,it is a potential two-dimensional material in the field of nanoelectronics and optics in the future.We also studied the current-voltage and photoresponse characteristics of bulk and monolayer GeSe devices,it is to be noted that compared with the dark condition,photocurrent under 8mW/cm2 of illumination have been increased for 8.2 times and 27.2 times for the pristine and monolayer devices,respectively.Therefore,the photosensitivity of monolayer device is 3.3 times higher than that of bulk device.Time-dependent photoresponse characteristics is measured subsequently at the same conditions as the pristine NS counterparts.Similarly,as the thickness decreased to monolayer,photocurent decreased accordingly.However,the monolayer device shows a similar quick rising edge as the pristine NS device but a much quicker of falling edge,indicating high-performance photoresponse applications of GeSe monolayer.