Study On The Growth Of ?-Ga₂O₃ Film And Its Heterojunction Band Structure

Wide-gap semiconductors are the third-generation semiconductor materials following Si-based and GaAs-based semiconductors,represented by GaN and SiC.This type of material has a large bandgap,high breakdown electric field,fast saturated electron drift velocity,large thermal conductivity,low dielectric constant,strong radiation resistance,and good chemical stability,which is very suitable for the development of anti-radiation,high-frequency,high-power and high-density integrated semiconductor devices.Compared with SiC and GaN,Ga2O3 has a bandgap of about 4.9 eV,and its corresponding absorption wavelength is 253 nm.It is an ideal material that can work in the solar-blind spectral region;its critical breakdown electric field is as high as 8 MV/cm,which is suitable for making high-voltage,high-power field electronic devices;and due to the increase in electric field breakdown resistance,Ga2O3-based power electronic devices can achieve low heat loss by reducing on-resistance.Since Ga2O3 material devices are mainly for high-power,high-voltage applications,and have higher requirements for crystal quality,correspondingly,most studies on Ga2O3 devices use ?-Ga2O3 single crystals.At present,the preparation of its materials and devices is still in its infancy.The factors that restrict Ga2O3 devices,especially MOSFET devices,include larger device series resistance and lower electron mobility.To give full play to the ultra-wide bandgap of Ga2O3,it is necessary to continue to optimize and improve the quality,device structure,and process flow of single crystal and epitaxy.Ga2O3 includes five phases:?,?,?,?,and ?,among which ?-Ga2O3 is a stable phase,? and ? are metastable phases,and ? and ? phases are poor in stability.The ? phase is a monoclinic crystal system,and there are fewer heterogeneous substrates available.Therefore,Ga2O3 is not suitable for heteroepitaxy;both ? and ? phase have hexagonal symmetry,so it is suitable to use a substrate with hexagonal symmetry Mass epitaxy,such as sapphire or silicon(111)surface substrate.At present,epitaxial Ga2O3 thin film mainly adopts sapphire substrate,which is conducive to the realization of large-size and low-cost preparation of Ga2O3 thin film.On sapphire and other substrates with hexagonal symmetry,the formation of ?-Ga2O3 films can generally be observed using metal organic chemical vapor deposition(MOCVD).Due to the spontaneous polarization effect in ?-Ga2O3,learning from the experience of the formation of 2DEG in AlGaN/GaN,a high-mobility two-dimensional electron gas can be formed in the ?-Ga2O3-based heterojunction to solve the problem of low mobility of Ga2O3 materials.In addition,?-Ga2O3 has the ferroelectric property of reversible spontaneous polarization,which can more drastically change the 2DEG density through polarization reversal.In this article,the main research results are as follows:(1)Preparation of ? phase gallium oxide film by MOCVD heteroepitaxy.By providing triethyl gallium(TEGa)and oxygen as reaction materials to the MOCVD device,and adjusting the growth pressure and temperature,gallium oxide heterojunctions with different crystal phases can be epitaxially grown on substrates such as SiC.Combined with the crystal structure characterized by X-ray diffraction spectroscopy(XRD),the best conditions for growing ?-Ga2O3/SiC heterojunction can be obtained.The growth temperature is 470?,the pressure is 25 torr,the flow rate of the reaction gas is 300 sccm of TEGa,and 6000 sccm of oxygen.(2)Characterization of film characteristics.Characterize gallium oxide films under different growth conditions,and use optical microscope,XRD,ultraviolet-visible absorption spectroscopy,X-ray photoelectron spectroscopy(XPS)and other characterization methods to analyze the morphology and crystal structure of gallium oxide films,Characterization of band structure and component composition.From the optical bandgap obtained by measuring the ultraviolet-visible absorption spectrum and the atomic binding energy data obtained by measuring XPS,the band alignment of the ?-gallium oxide heterojunction can be calculated.The optical bandgaps of SiC and Ga2O3 are 3.29 eV and 4.80 eV,respectively.The valence band offset of the SiC/Ga2O3 heterojunction is ?EV=0.61 eV,and the conduction band offset?EC=0.9 eV,which shows a type I band alignment.(3)Research on device volt-ampere characteristics.Studying the volt-ampere characteristics of the device is also an important means to obtain information about the energy band structure of the heterojunction.At the same time,because of the absorption characteristics of the gallium oxide device in the solar blind ultraviolet region,it has a good photodetector application prospect,so the photoelectric performance of the thin film was preliminary tested.Combining the existing semiconductor heterojunction conduction model,the calculated heterojunction barrier height VD=0.983 eV.The test results of the optical and electrical properties of the film show that the device still has room for improvement in the field of photoelectric detection.