【作者】 何波；

【导师】 刘兴钊；

【作者基本信息】 电子科技大学 ， 电子信息材料与元器件， 2018， 硕士

【摘要】 近几十年来,随着半导体技术的发展,传统以及新型半导体材料越来越受到重视。作为一种传统的窄带隙半导体,PbSe属于直接带隙,常温下禁带宽度为0.27 eV,常被应用于红外探测。由于其载流子迁移率较低,硒化铅在红外探测领域的应用大多是基于对PbSe薄膜的后期敏化处理,以达到好的探测性能。石墨烯是一种新型的二维半导体材料,有很多奇特的性能,如极高的载流子迁移率、零带隙等,被广泛应用于光学、传感等领域。近年来又有不少研究者将其应用于红外探测领域,但是由于其单层结构只有较小的光吸收率（约2.3%）。将石墨烯优异的电学特性和PbSe对光的敏感性两者结合起来,优势互补,形成新型的异质结结构,实现光生电子空穴对的有效分离,将有助于它们在红外探测领域的广泛应用。本文采用分子束外延法（MBE）制备了PbSe薄膜,并制备了石墨烯/PbSe异质结,对该异质结的红外光敏特性作了初步探索,并在此基础上,用化学浴沉积法（CBD）制备了PbSe薄膜,来进一步探索石墨烯/PbSe复合材料对红外光敏的特性。我们探索了两种工艺的最优工艺参数,并对PbSe薄膜的结构、形貌、成分、光学等特性进行了表征。表征结果表明,MBE外延制备PbSe的优化参数为:PbSe源温度为600℃,Se源温度为160℃,基底加热200℃。在此工艺条件下,PbSe沿（200）面取向生长,薄膜样品表面均为PbSe化合态,无杂质氧化物（如SeO₄等）,且表现出富Pb状态。用CBD法制备PbSe薄膜时,我们发现温度很大程度上会影响薄膜的质量,温度越低,膜的结晶质量越差,且PbSe沿晶面（111）取向生长。XPS分析显示,各温度条件下沉积的PbSe薄膜均为富Pb状态,随着生长温度升高Se原子含量也随着升高。SEM扫描结果显示,与CBD法相比,MBE外延制备的PbSe薄膜表面更平整,且晶粒尺寸更小、更均匀。红外透射谱结果表明,MBE外延法制得的PbSe薄膜的光学带隙为0.38 eV,表明PbSe对红外光谱响应。此外,我们还初步表征了石墨烯的材料特性。Raman谱显示,石墨烯特征峰强度之比I_G/I_2D=0.45,且无D峰,与单层石墨烯的特征符合,表明转移所得石墨烯缺陷少、质量高,适合异质结的制作。为表征石墨烯的电学特性,我们将湿法转移所得的石墨烯制成了石墨烯晶体管,据转移特性曲线算得石墨烯的迁移率（空穴）μ_hole=839.5 cm²/（V·s）。在对PbSe薄膜材料以及石墨烯研究的基础上,我们用MBE外延PbSe薄膜制备了背栅型石墨烯/PbSe异质结光敏晶体管（宽长比W/L=10μm/100μm,PbSe面积50μm×50μm）,测试结果表明,该异质结器件具有良好的红外光敏特性（光照波长1050 nm）,光生电流ΔI最大值为8μA,对应的响应度R最大值为420 AW^-1,表现出栅压可控的特性,这有助于其在弱光探测领域的应用。能带模型分析认为,器件响应度表现出栅压可控的原因是PbSe光敏层中的光生空穴转移至石墨烯中,导致当V_gs<V_Dirac时,I_ill>I_dark（空穴积累）;当V_gs>V_Dirac时,I_ill<I_dark（从PbSe转移到石墨烯的空穴与石墨烯中的电子复合）。更多还原

【Abstract】 In recent decades,with the development of semiconductor technology,traditional and new semiconductor materials have received increasingly attention.As a traditional narrow-gap semiconductor,PbSe is a direct bandgap material,and its bandgap is 0.27 eV at room temperature,and it is often used in infrared（IR）detection.Due to its low carrier mobility,the application of lead selenide in the field of infrared detection is mostly based on the post-sensitization treatment of PbSe thin films to achieve good performance.Graphene is a new type of two-dimensional semiconductor material.It has many unique properties,such as extremely high carrier mobility,zero band gap,etc.It is widely used in optics,sensing and other fields.In recent years,many researchers have applied it to the infrared detection field,but due to its single-layer structure,there is only a small light absorption rate（about 2.3%）.Combining the excellent electrical properties of graphene with the sensitivity of PbSe to IR,forming a new type of heterojunction structure,with complementary advantages,and separating the photogenerated electron-hole pairs,will contribute to their wide application in the field of infrared detection.In this paper,PbSe thin films were prepared by molecular beam epitaxy（MBE）and graphene/PbSe heterojunctions were prepared.The infrared photosensitivity of the heterojunctions was preliminary explored,and on this basis,the chemical bath deposition（CBD）method was used to prepare PbSe thin films to further explore the infrared photosensitivity characteristics of the graphene/PbSe heterojunction interface.We explored the optimum process parameters for both processes and characterized the structure,morphology,composition,and optical properties of PbSe thin films.The characterization results showed that the optimal parameters for the epitaxial preparation of PbSe by MBE are:PbSe source temperature is 600°C,Se source temperature is 160°C,and substrate temperature is 200°C.Under this process condition,PbSe grows along the（200）plane orientation.The surface of the thin film sample is all PbSe-combined,and there is no impurity oxide（such as SeO4,etc.）,and it shows a Pb-rich state.When the PbSe thin film was prepared by the CBD method,we found that the temperature largely affected the quality of the thin film.The lower the temperature,the worse the crystalline quality of the film,and the PbSe grows along the（111）orientation of the crystal plane.XPS analysis showed that the PbSe films deposited under various temperature conditions were all Pb-rich,and the Se atom content also increased with the increase of the growth temperature.The SEM scan results showed that the surface of PbSe films prepared by MBE epitaxy was smoother than the CBD method,and the grain size was smaller and more uniform.The infrared transmission spectrum results showed that the optical bandwidth of the PbSe film prepared by MBE method is 0.38 eV,indicating that PbSe responds to the infrared spectrum.In addition,we also characterized the graphene’s material properties.Raman spectrum showed that the ratio of the peaks’intensity of graphene(I_G/I_2D)is 0.45,and there is no D peak,which consistent with the characteristics of monolayer graphene.These results indicat that graphene made by CVD method has fewer defects,which is suitable for the production of heterojunctions.In order to characterize the electrical properties of graphene,field effect transistor based on graphene was fabricated.The mobility of graphene（hole）calculated from the transfer characteristic curve was 839.5 cm²/（V·s）.Based on the study of PbSe thin film materials and graphene,we used MBE epitaxial PbSe thin film to prepare a back gate type graphene/PbSe heterojunction phototransistor（W/L=10μm/100μm,PbSe area 50μm×50μm）.Results showed that the device has good infrared photosensitivity（the light wavelength is 1050 nm）,and the maximum photocurrent is 8μA,and the corresponding maximum responsivity is 420 AW^-1.The device showed controllable characteristics of the gate voltage,which contributes to its application in the field of low-light detection.The energy band model analysis believes that the device’s variable responsivity is caused by the transfer of photo-generated holes in the PbSe layer to graphene,which could be controlled by gate voltage.When the V_gs is lower than the V_Dirac,the I_ill is bigger than the I_dark（hole accumulation）,and when the V_gs is higher than the V_Dirac,the I_ill is smaller than the I_dark（holes transferred from PbSe to graphene recombine with electrons in graphene）.更多还原