摘要
近年来,二维二硒化铂(PtSe_(2))由于其独特的性质,在锁模激光器、光电探测器、太阳能电池等领域均表现出巨大的应用潜力,引起了科研人员的广泛兴趣。本实验使用化学气相沉积法,在蓝宝石衬底上生长出不同层数的PtSe_(2)薄膜。使用原子力显微镜和拉曼光谱仪对样品的表面形貌和拉曼振动模式进行研究。吸收光谱表明,PtSe_(2)具有随着层数增加而减小的带隙。使用椭圆偏振光谱仪对样品的光学常数进行表征,结果表明,PtSe_(2)的光学常数与厚度有明显的相关性。使用变温椭偏光谱仪分析温度对PtSe_(2)光学常数的影响,并得到不同波长下的热光系数。本实验结果可以为基于PtSe_(2)的光电器件的设计和优化提供参考。
Objective Recently,two-dimensional materials,particularly transition metal sulfides,have attracted broad attention in the field of optoelectronics because of their unique properties.Platinum diselenide(PtSe_(2))is a new type of transition metal sulfide material with unique features,such as adjustable bandgap and high carrier mobility,that has excellent potential for saturable absorbers,photodetectors,and photovoltaic cells.It is necessary to study the variation of PtSe_(2)optical properties with the number of layers,which is essential for designing and optimizing related devices.Moreover,it is also valuable to study the change in the refractive index of PtSe_(2)films with temperature in practical applications.In this work,PtSe_(2)films with two,four,and six layers were grown on sapphire substrates using the chemical vapor deposition method.The optical properties of PtSe_(2)with different thicknesses,including optical bandgap,refractive index,extinction coefficient,dielectric function,and thermooptical coefficient,were investigated using the spectrophotometer and spectroscopic ellipsometry.This work can guide the design and optimization of PtSe_(2)-based optical modulation devices.Methods The synthesis method of PtSe_(2)films used in this work is the three-zone temperature-controlled chemical vapor deposition method(Fig.1).PtSe_(2)films with two,four,and six layers were grown on sapphire substrates by controlling the growth time.The thickness and surface morphology of the samples were confirmed using atomic force microscopy.The Raman vibration patterns of samples with different layer numbers were investigated using Raman spectroscopy.The samples\absorption spectrum was obtained using the spectrophotometer,and the optical bandgap of the samples was obtained using the Tauc formula.The optical constants and dielectric functions of PtSe_(2)with different layer numbers were obtained using spectroscopic ellipsometry.Three Tauc-Lorentz oscillators were used to describe the dielectric function of the PtSe_(2)films during the analysis of elliptical polarization spectra.In addition,we studied the refractive index and extinction coefficient of PtSe_(2)with increasing temperature using spectroscopic ellipsometry and a high-temperature thermal bench.The thermo-optical coefficients of four-layer and six-layer PtSe_(2)films were calculated.Results and Discussions The prepared PtSe_(2)films have good homogeneity and the transmittance decreases as the number of layers increases(Fig.2).Raman spectra show that PtSe_(2)has three main Raman vibrational modes,and the Egand A1g modes are red-shifted as the number of layers increases(Fig.3).This phenomenon can be attributed to the increase in interlayer coupling.The absorption spectra and Tauc formula calculations show that the optical absorption increases and the bandgap decrease as the number of sample layers increases(Fig.4).The bandgaps of the two-layer,four-layer,and six-layer PtSe_(2)films are 1,0.85,and 0.73eV,respectively.The spectroscopic ellipsometry spectrum of PtSe_(2)was modeled using three Tauc-Lorentz oscillators,and the optimum fitting parameters were obtained(Table 1).By fitting the ellipsometric parameters of the PtSe_(2)films,the optical constants of the samples with different layers,including the refractive index,extinction coefficient,and the real and imaginary parts of the dielectric function,were obtained(Fig.6).The results show that the optical constants of PtSe_(2)films are significantly correlated with both wavelength and thickness.In the wavelength range of 300-700nm,the refractive index of PtSe_(2)films increases with wavelength until it reaches a certain wavelength and then starts to decrease slowly.This transition wavelength is also red-shifted with the increase in the number of layers.This may be related to the increase in the interlayer coupling as the number of layers increases.Alternatively,as the number of layers increases,the peak position of the imaginary part of the dielectric function is also red-shifted,indicating that the electron leap energy between the conduction and valence bands is decreasing.In addition,the variation of the refractive index and extinction coefficient of PtSe_(2)with temperature was obtained from variabletemperature spectroscopic ellipsometry measurements(Fig.7).The thermo-optical coefficient of PtSe_(2)as a function of wavelength was obtained(Fig.8).As shown in Fig.8,the thermo-optical coefficient is around the zero-axis between the wavelength of 400-500 nm,indicating that the refractive index of PtSe_(2)hardly changes with temperature in this band and has good thermo-optical stability.In contrast,the thermo-optical coefficient is negative within the wavelength of 500-800nm,indicating that the refractive index decreases with an increase in temperature.It may be related to the semi-metallic properties exhibited in multilayer PtSe_(2)films.Therefore,PtSe_(2)films are more suitable for application within optoelectronic devices operating in the wavelength range of 400-500nm.Conclusions Continuous PtSe_(2)films with two,four,and six layers were grown using chemical vapor deposition.Raman spectra indicated the existence of interlayer coupling in the samples.The bandgap,refractive index,extinction coefficient,and the dielectric function of the samples were characterized using the spectrophotometer and spectroscopic ellipsometry,and the results showed that the bandgap and optical constants of PtSe_(2)were significantly correlated with the thickness.The effect of temperature on the optical constants of PtSe_(2)was analyzed using variable temperature ellipsometric spectroscopy,and the thermo-optical coefficients at different wavelengths were obtained.The result shows that the thermo-optical coefficient is near the zero-axis between the wavelength of 400-500nm.In contrast,the thermal-optical coefficient is negative in the wavelength range of 500-800nm,which may be related to the semi-metallic nature of PtSe_(2)multilayer films.This research can guide the design and optimization of PtSe_(2)-based light modulation devices.
作者
魏铭洋
连洁
姜清芬
张裕
王宸琳
王月明
许镇
Wei Mingyang;Lian Jie;Jiang Qingfen;Zhang Yu;Wang Chenlin;Wang Yueming;Xu Zhen(School of Information Science and Engineering,Shandong Provincial Key Laboratory of Laser Technology and Application,Shandong University,Qingdao,Shandong 266235,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2021年第12期172-181,共10页
Chinese Journal of Lasers
基金
国家自然科学基金(12074214)
国家重点基础研究发展计划(2015CB921003)
山东省重点研发计划(2017GGX201008)。
关键词
材料
光学性质
二维材料
椭圆偏振
光学常数
热光系数
materials
optical property
two-dimensional materials
ellipsometry
optical constants
thermo-optical coefficient
