Study On Growth Of Ga₂O₃ Film And Device Based On Mist Chemical Vapor Deposition

With the increasing demand for high-frequency,high-power,high-performance power electronic devices and deep ultraviolet optoelectronic devices in the fields of energy,information,and military in modern society,wide band gap semiconductor have become the focus of current research because of their excellent material properties.Among them,the new ultra-wide bandgap semiconductor material Ga₂O₃ has a larger band gap of about 4.5-5.3 e V,compared with the wide band gap semiconductor materials such as gallium nitride（Ga N）and silicon carbide（Si C）.At the same time,the breakdown field strength of Ga₂O₃ is8MV/cm.The Baliga′s figure of merit is usually used as an indicator to characterize the application of semiconductor materials to electronic devices.The Baliga′s figure of merit for Ga₂O₃ is 4 times that of Ga N devices and 10 times that of Si C.This indicates that the conduction loss of Ga₂O₃-based power switches will be is much lower,and more power can be saved in practical applications.In addition,the band gap of Ga₂O₃ is the corresponding cut-off absorption edge is about 250nm,and the ultraviolet light transmittance is over 80%.It is a natural material for the development of"solarblind"ultraviolet detector which does not need to adjust the band gap.At present,the basic research and industrialization of Ga₂O₃materials have shown a significant momentum of accelerated development and the device performance continues to set records.The premise of obtaining high performance devices is to prepare high quality materials.At present,although there are varieties of epitaxial growth technologies can prepare high quality Ga₂O₃ epitaxial thin film materials.However,the high cost of epitaxial equipment and complex process increase the research cost.In order to further develop high quality and low cost Ga₂O₃ thin film epitaxial technology,this paper utilized low cost mist chemical vapor deposition technology to grow Ga₂O₃ films on sapphire,silicon and Ga N substrates.Through a variety of test methods,the crystal quality of the film materials was systematically characterized and the Sn doping of the film was also studied.Moreover,the photodetectors,metal oxide field effect transistors and Schottky barrier diodes were prepared based on the epitaxial film to verify the feasibility of the growth method application in devices.The specific research work and results of this paper are as follows:1.The effects of different growth temperatures on the quality of amorphous Ga O_x films grown on Si/Si O₂ substrates were studied and phototransistors were fabricated.The XRD measuerment shows that the film grown on the p-type silicon（100）/Si O₂ substrate at the growth temperatures of 300-700℃was an amorphous film.The surface roughness of the film grown at 400℃was only 0.385 nm,indicating a uniform and smooth film quality.In order to study the optical properties of epitaxial films,Ga₂O₃ films were grown on transparent quartz glass（Si O₂）under the same conditions.As the growth temperature increases,the absorption edge moved to a longer wavelength region.The corresponding band gap was extracted between 4.7～5.26 e V.Phototransistors with a back-gate structure were fabricated,and the performance of phototransistors based on 400℃,500℃and 600℃grown films were compared.Phototransistor prepared based on the thin film grown at 400℃showed a larger on-state current,the extracted carrier mobility is 0.1 cm²V^-1s^-1.Under 254nm light,the photoresponse current of PT-400 increased by 4 orders of magnitude,the phototransistor responsivity was 2300 A/W,the external quantum efficiency reaches 1.12×10⁶%,and the detection rate is 1.87×10¹⁴ Jones.2.A single crystalα-Ga₂O₃ thin film was epitaxially grown on c-plane sapphire substrate using mist chemical vapor deposition technology.We set up the mist chemical vapor deposition equipment and explored the growth process of Ga₂O₃ thin film.Sinceα-Ga₂O₃belongs to the metastable phase,400℃was selected as the growth temperature,and air,nitrogen and oxygen were used as the carrier gases,respectively.The effect of different carrier gas atmospheres on the quality of Ga₂O₃ epitaxial films was comparatively studied.The XRD scan results showed that only the singleα-Ga₂O₃（0006）diffraction peak appeared at 40.26°in the scanning range of 15-65°,indicating that the film was the single crystal film.At the same time,the half-height width of the rocking curve of Ga₂O₃ epitaxial film with different carrier gas conditions was measured:the FWHM is 88.6 arcsec,86.4 arcsec and 72arcsec,when we used air,nitrogen and oxygen as the carrier gas,respectively.Oxygen as the carrier gas can provide sufficient oxygen source to fully oxidize and decompose the source solution,improve the crystalline quality of the epitaxial film,and obtain a faster growth rate>10nm/min.3.β-Ga₂O₃ films were grown on c-plane sapphire substrates by Mist-CVD method,and the effects of different growth temperatures on the crystalline quality of the films were studied.When the growth temperature is 750℃,Ga₂O₃ films are polycrystalline films dominated byβandαphases.When the growth temperature is in the range of 800-900℃,the XRD scan pattern shows that except for the sapphire substrate diffraction peak,onlyβ-phase（2^—01）,（4^—02）and（6^—03）characteristic peaks are presented.When the growth temperature rised up to1000℃,except for the（2^—01）crystal plane group,two characteristic peaks（110）and（2^—04）appeared,indicating a polycrystallineβ-Ga₂O₃ film.Through the comparison of the rocking curve of the characteristic peaks of（2^—01）,the minimum FWHM of the rocking curve under the growth temperature of 800℃was 0.71°.Based on thisβ-Ga₂O₃ single crystal film,an MSM solar-blind ultraviolet detector was also fabricated,with owning a responsivity of22000A/W,an external quantum efficiency of 1.07×10⁷%,and a detectivity of 1.1×10¹⁶Jones.The device performance has been significantly improved.4.A Sn-doped single crystalβ-Ga₂O₃ film was epitaxially grown on a gallium nitride substrate.The growth temperature was 800℃,and the film was grown preferentially along the（2^—01）crystal plane,The minimum FWHM of the rocking curve of the（2^—01）diffraction peak is 0.6°.High-resolution TEM test results showed that the epitaxial growth relationship was（2^—01）β-Ga₂O₃‖（0002）Ga N.The electrical properties and Ohmic contact of the film under the doping concentration of 10%Sn atomic ratio were also studied.The Hall test at room temperature showed that the carrier concentration of the film is 10¹⁷ cm^-3,and the carrier mobility is 50 cm²V^-1s^-1.An Ohmic electrodes were fabricated and annealed at 500°C for one minute in a N₂atmosphere to obtain a good Ohmic contact,and the resistivity of the Sn-dopedβ-Ga₂O₃ film was 84Ω·cm.The horizontal structure of Schottky diodes and metal oxide field effect transistors based on Sn-dopedβ-Ga₂O₃ thin films were studied.The maximum breakdown voltage of Schottky diodes can reach 2400 V with the characteristic on-resistance is 39.8Ω·cm².The depletion-type metal oxide field effect transistor exhibited good gate control characteristics,with a on-off ratio of 5 orders of magnitude,and the maximum off-state breakdown voltage of 1420 V.