| With the increasing demand for new semiconductor devices with high power and low energy consumption,β-Ga2O3 has gradually become the focus of attention.βGa2O3 not only has the material advantage of ultra-high critical breakdown field strength(8 MV/cm),but also can obtain low-cost large size wafers by melting method.At the same time,the intrinsic absorption longwave limit of β-Ga2O3 material with a band-gap width of 4.9 eV is 254 nm,possessing the capacity of detecting the solar blind ultraviolet region without doping,which avoids the fluctuation of components and phase separation in doped alloy components.As a result,β-Ga2O3 has attracted much attention in the field of high-power devices and ultraviolet detection.At present,the study of β-Ga2O3 is still at the early stage.Many scientific problems in β-Ga2O3 films and devices have greatly limited the development of β-Ga2O3.The heteroepitaxy mechanism and growth mode of β-Ga2O3 thin films are still unclear.The performance of β-Ga2O3 blind UV photodetectors and vertically enhanced β-Ga2O3 field effect transistors need to be improved.In view of these urgent problems,the research content of this paper is as follows:1.The nucleation mechanism of β-Ga2O3 films epitaxial growth on sapphire substrate was studied,and epitaxial 2-inch films with high uniformity were successfully obtained.Firstly,the surface morphology of β-Ga2O3 films grown on sapphire substrate by metal-organic chemical vapor deposition was analyzed by atomic force microscope.And,it was determined that the films follow the island growth at low temperature process,but exhibit smooth two-dimensional surface at high temperature process.Then,the epitaxial lateral growth rates of the films were improved by regulating the growth temperatures,O2 flow rates,and combined with the carrier gas flow rate,a 2-inch sized uniform film with a thickness uniformity less than 2%was successfully obtained.2.The effects of growth parameters on β-Ga2O3 films on sapphire substrate were studied,and the growth mechanism of β-Ga2O3 epitaxial films was explored.High quality β-Ga2O3 thin film was obtained by mis-cut sapphire substrate.Firstly,the optimum growth conditions of β-Ga2O3 films were determined by adjusting growth temperature,O2 flow rate and reaction chamber pressure.At the same time,the β-Ga2O3 domain was analyzed by the arrangement of O atoms in the substrate and epitaxial film,and it was determined that the six-fold rotating twins were the main reason limiting the crystal quality of the film.In addition,the effects of mis-cut directions and mis-cut angles of the substrate on the crystal quality of β-Ga2O3 epitaxial films and the relationship between the step width of the substrates surface and the film growth mode during epitaxial growth were further studied.Finally,high quality β-Ga2O3 films with a full-width half-maximum(FWHM)of 0.55° were obtained on c plane sapphire substrates with mis-cut angles of 6° toward m plane.Moreover,a solar-blind UV detector was fabricated base on the β-Ga2O3 films,and a responsivity of 9.25 A/W under 254 nm illumination was achieved.3.The effect of the surface step on the surface morphology of β-Ga2O3 films grown on p-GaN substrate was studied.In addition,β-Ga2O3/p-GaN PN heterojunction was constructed by in-situ annealing process,and self-powered photodetectors with high response performance at 0 V bias voltage were prepared successfully.Firstly,βGa2O3 thin films were epitaxial grown on p-GaN substrate.By analyzing the epitaxial relationship between the thin films and the substrate,it is confirmed that the six-fold rotating twins and the desorption of Ga2O are the main causes of the triple step morphology on the epitaxial film surface.Secondly,by changing the mis-cut directions and mis-cut angles,step bunching appeared on the p-GaN mis-cut substrate surface was determined to be the direct reason for the deterioration of the surface morphology of the β-Ga2O3 epitaxial film.Finally,β-Ga2O3/p-GaN P-N heterojunction was constructed by in-situ annealing process,and self-powered photodetectors were fabricated successfully.The photodetector has successfully realized ultraviolet detection at 254 nm and 365 nm.The working mechanism of the photodetector was analyzed through the carrier distribution in the depletion region and the energy band diagram of the material.At the same time,with the expansion of the depletion region width by the GaON layer,the photodetector has a responsivity of 2.82 A/W(0.82 A/W)and a response time of 0.066 s/0.036 s(0.036 s/0.073 s)under ultraviolet light at a wavelength of 254 nm(365 nm)without bias voltage,realizing devices with high responsiveness and fast response speed.4.A vertical β-Ga2O3 U-shape trench gate metal-oxide-semiconductor field effect transistor(UMOSFET)devices were prepared by N-ion implantation technique and enhancement operation was realized.Firstly,diode test structure was used to explore the current blocking effect of the current barrier layer(CBL)prepared by different concentrations of N-ions,and the optimal injection conditions were determined.Then,the vertical enhanced β-Ga2O3 UMOSFET was successfully fabricated through the current barrier layer with 5×1018 cm-3(1×1019 cm-3)concentration of N ion.The current density of the device was up to 702.3 A/cm2(374.9 A/cm2)and the breakdown voltage was 455 V(534 V).All of the properties are the highest reported values in CBLβ-Ga2O3 field effect transistors.Finally,the influence of U-shaped groove side wall morphology on device performance was studied,and the best direction of channel current was determined. |
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