The Epitaxy And Characterization Of α-Ca₂O₃ Films

With the rapid development of energy,information,national defense,rail transit,electric vehicles and other fields,traditional semiconductor materials cannot be met the new requirements for the performance of power semiconductor devices in modern society.Electronic devices with high voltage,low loss and high power become the development trend of the current semiconductor industry.Ga2O3 is a new wide band-gap semiconductor material.Compared with SiC and GaN,Ga2O3 has larger band gap,higher critical breakdown field strength and higher Baliga value,becoming one of the materials for the preparation of ultra-high voltage electronic power devices in the future.At present,Ga2O3 has become the focus of researchers,and research on Ga2O3 is developing rapidly.In the gallium oxide material family,α-Ga2O3 exhibits more excellent electrical properties,its bandgap is as high as 5.3eV,the breakdown field strength is 10 MV/cm,and the Baliga value of α-Ga2O3 is as high as 6726,20 times that of gallium nitride,and 8 times that of gallium nitride,which has very obvious advantages in the preparation of high-voltage,high-power,and low-loss electronic power devices.Since α-Ga2O3 is a metastable phase,it can only be prepared by heteroepitaxy.At present,the methods used to prepare α-Ga2O3 mainly include Molecular Beam Epitaxy(MBE),Hydride Capor Phase Epitaxy(HVPE),Metal-Organic Chemical Vapor Deposition(MOCVD),Mist Chemical-Vapor Deposition(Mist-CVD)and so on.In this thesis,by building a low-cost Mist-CVD system,the preparation of high-quality α-Ga2O3 epitaxial films was realized on c-plane sapphire substrates.By exploring the growth process,the influence of the position of the sapphire substrate in the growth chamber on the growth rate of α-Ga2O3 epitaxial film is revealed.At the same time,a preliminary exploration of Si-doped α-Ga2O3 epitaxial film was carried out.The main research results are as follows:First,α-Ga2O3 film was obtained on c-plane sapphire substrate by Mist-CVD method,its growth mechanism was studied in depth,and various factors such as Mist-CVD system structure,sapphire substrate position,and growth temperature were reasonably adjusted.In view of the phenomenon that the precursor droplets are easy to evaporate during the transmission process in the growth chamber.By adjusting the installation position of the c-plane sapphire substrate in the growth chamber,the loss of the precursor droplets during the transmission process is reduced,which greatly improves the growth rate of α-Ga2O3 film prepared by Mist-CVD method,the growth rate of α-Ga2O3 epitaxial film can reach 1.45μm/h.Second,by optimizing the growth temperature of the α-Ga2O3 epitaxial film,the crystal phase control was realized.The high-quality and large-size α-Ga2O3 epitaxial film was prepared.Experiments show that too high growth temperature will lead to ε-Ga2O3 in the epitaxial film;too low growth temperature will affect the crystal quality of α-Ga2O3 epitaxial film.In this thesis,540℃ is the optimum growth temperature for the preparation of α-Ga2O3 epitaxial film.The α-Ga2O3 epitaxial film prepared at this temperature has no other crystal phases.Characterized by HRXRD,the rocking curves of the(0006)plane and(10-14)plane have half peak widths of 0.023° and 1.17°,respectively,and the corresponding screw dislocation densities and edge dislocation densities are 2.3 × 106 cm-2 and 3.9 × 1010 cm-2,indicating that the material has a high crystal quality.Third,different Si-doped α-Ga2O3 epitaxial films were prepared with ClSi(CH3)2(CH2)2CN as dopant.With the increase of Si doping concentration,the rocking curves of the(0006)plane of α-Ga2O3 epitaxial film gradually decreases,indicating the crystal quality improves.With the increase of Si doping concentration,the bandgap ofα-Ga2O3 epitaxial film decreases gradually.The element composition and distribution of Si-doped α-Ga2O3 epitaxial film were characterized by EDS and mapping.The distibution of Si,Ga,and O was uniform,which proved that the preparation of uniform Si-doped α-Ga2O3 epitaxial film could be realized by Mist-CVD method.The solar-blind photodetector prepared by Si-doped α-Ga2O3 exhibits good device performance,with a response time of 0.44s,a light-to-dark current ratio of 184,and a responsivity of 2.06 A/W.