Phase-controlled Growth And Physical Properties Of In₂Se₃ Compounds

Indium selenide?chemical formula:In₂Se₃?is an important group III-VI direct bandgap layered semiconductor material.Five main crystal phases have been found,namely:?,?,?,?,and?.Indium selenide thin film materials have been widely used in solar cells,photoelectric detection,phase change memory,etc.Because the indium selenide film phase is easy to transition with the temperature change during the growth process,the growth of single crystal indium selenide film becomes relatively difficult.The traditional preparation techniques include:magnetron sputtering method,source co-evaporation method,chemical bath deposition method,solid phase reaction method,metal organic chemical vapor deposition method,electrodeposition method,sol-gel method.However,these methods are difficult to grow high-quality single crystal thin films.At present,it has been reported that the thin film growth technology that can prepare all five main crystal phases of In₂Se₃ is molecular beam epitaxy,but many basic problems of molecular beam epitaxy method for growing In₂Se₃ have not been fully studied.On the other hand,due to the low-quality of the In₂Se₃ thin film prepared by the existing methods,it has restricted the indepth study of the intrinsic physical properties of In₂Se₃,which has further affected the application of In₂Se₃.Therefore,this paper will focus on the growth of indium selenide thin film by molecular beam epitaxy and its basic physical characterization.The work includes:?1?In₂Se₃ single crystal thin films were prepared on H-Si?111?substrates,beveled 4°H-Si?111?and molybdenum-fluoride phlogopite substrates.The preparation process and growth kinetics of indium selenide film were systematically studied.It provides a reference for the study of epitaxial growth of single crystal indium selenide film and the study of heterojunction band.First,the effects of growth beam conditions?in terms of beam equivalent pressure?on the resulting film were investigated through experiments.Within a certain temperature range,it is found that when the beam ratio of Se:In is about15:1-20:1,it tends to obtain a single crystal thin film with a stoichiometric ratio of In₂Se₃.When the beam ratio of Se:In is less than 15,the film is InSe.And when the Se:In beam ratio is greater than 20,the stoichiometric ratio In6Se7 or In₂Se₃-In₆Se₇ continuous binary solid solution film can be obtained.The relationship between the phase structure of the epitaxial thin film conforming to the stoichiometric ratio In₂Se₃ under 15:1-20:1optimized beam current ratio and growth temperature were further studied.It is concluded that the?-In₂Se₃ film can be obtained with the growth temperature in the range of 100?-150?,?-In₂Se₃ in 200?-250?,and?-In₂Se₃ in 300?-350?.?2?The physical properties of the prepared indium selenide films were studied.A series of thin film samples of different thicknesses were grown using molecular beam epitaxy systems.And the surface morphology and crystal structure of the?-In₂Se₃ thin films obtained by scanning tunneling microscope?STM?,scanning electron microscope?SEM?,reflective high energy electron diffractometer?RHEED?,high resolution X-ray diffractometer?HRXRD?,and Raman spectrometer.The structure characteristics of?-In₂Se₃ thin film were accurately determined.The atomic force microscope?AFM?was used to study the ferroelectric properties of the?-In₂Se₃ thin film.The vibration analysis of the?-In₂Se₃ thin film was carried out by Raman spectroscopy.The optical energy band of the?-In₂Se₃ thin film was inferred to be 1.94eV by photoluminescence spectroscopy.In addition,the?-In₂Se₃ film with thickness of 200nm was studied for light transmittance,and found that for light with a wavelength in the range of 0.5?m-2.5?m,when the wavelength is 1?m,the transmittance is 60%,and at 1.5?m,the transmission rate is as high as 90%.Electrical tests on the?-In₂Se₃ thin film indicate that the film resistivity is on the order of 10⁴?cm,and under simulated solar lighting conditions,the film resistivity is on the order of 10³?cm.The photoelectric switch ratio of?-In₂Se₃ thin film device under daylight conditions is greater than 10.Further photoelectric response test showed that the photocurrent density of the optimized?-In₂Se₃ thin film was 3.15mA/cm².