| The history of semiconductor research and development has been driven by the exploration of new materials with different bandgap energies,from Ge and Si to III-V(GaAs,InGaAs,In P,etc.),to broadband gap materials such as SiC and GaN.This is simply because band gaps determine most of the basic optical and electrical properties of semiconductors,leading to specific applications that utilize the strength of each material.In the past decade,gallium oxide(Ga2O3)has been recognized as a new type of wide bandgap semiconductor,and its material properties and device processing technology are being intensively studied and developed in recent years.The revival of Ga2O3 research has also stimulated a new semiconductor field called "ultra-wide bandgap semiconductors",which corresponds to materials classified by bandgap energies greater than 3.4 eV for SiC and GaN.According to the current social trend that efficient switching devices are becoming increasingly important for our sustainable energy economy,unipolar Ga2O3 power switching devices have a particular prospect and demand.In this paper,metal organic chemical vapor deposition(MOCVD)was used to prepare epitaxial Ga2O3 thin films on sapphire substrates,and characterization equipment such as X-ray diffraction(XRD)and atomic force microscopy(AFM)were used for testing and analysis.During the experimental process,the effects of different combinations of conditions and factors on the growth rate and crystallinity of Ga2O3 thin films,their interaction relationships,and mechanisms were studied;Among the combination conditions involved in all experiments,explore the changing trend of the relationship between different conditions and factors on growth speed and crystallinity,and select the most suitable combination of conditions for growth of each crystal phase.The experimental results are as follows:1.Using the MOCVD method,(201)β-Ga2O3 thin film was prepared on(0001)sapphire single crystal substrate,tested by XRD and AFM scanning.The test results show that at a temperature angle β-Ga2O3 thin film has the best crystallinity and is grown on a 530℃ sapphire substrateε-Ga2O3 thin film has the best crystallinity.The conclusion has also been confirmed again by AFM scaning,and it is found that growth on sapphire substrates at 900℃ and 530℃.β and ε-Ga2O3 thin films exhibit excellent uniformity,with thickness root mean square differences as low as 1.028 and 0.963 nm.2.The thin films grown by MOCVD were further measured by UVVis and ellipsometer.The experimental results show that as the temperature increases from 600 ℃ to 900 ℃,the absorption peak wavelength of gallium oxide thin films gradually approaches 190 nm,while the band gap continues to increase,with a maximum value of 5.04 eV.The film thickness grown under suitable conditions is relatively uniform,regardless of the average thickness of 31 pieces 2-inch films grown at different locations on a single chip or during the same deposition process.Through two parts of experiments,this paper explores the mechanism of controlling epitaxial Ga2O3 thin films,and concludes that epitaxial Ga2O3 thin films on the substrate have the highest crystal quality at temperatures of 900℃ and 530℃;At the same time,the growth regulation of thin films deposited on the substrate by other factors(pressure,oxygen admission rate,and Ga source)was explored,and the possible mechanisms were discussed.Finally,a summary of all the experiments was made,and a binary phase diagram for the growth of gallium oxide thin films using the MOCVD method was prepared,providing experimental support for subsequent work. |
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