Preparation And Study Of β-Ga₂O₃ Nanostructured Films By Thermal Oxidation Method

Ga₂O₃ is a new kind of semiconductor material with wide band gap.Its intrinsic absorption limit is in the solar blind ultraviolet band range because of its ultra-wide band gap.In addition,Ga₂O₃ has a theoretical breakdown field strength of 8 MV/cm and high thermal and chemical stability,which has great potential in semiconductor power devices and solar blind UV photodetectors.β-Ga₂O₃ is the most stable phase among the many phases of Ga₂O₃ ,which is also the most widely used.The band gap of β-Ga₂O₃ is about 4.2～4.9 eV.At present,the reported structural morphology of β-Ga₂O₃ materials can be roughly divided into three categories:bulk materials,thin film materials,and nanomaterials.Compared with the former two,the nanomaterials accumulate less stress during the growth process,which can effectively reduce the defect density and improve the crystal quality.In addition,the nanostructure has a large specific surface area and a high surface state density,which has unique advantages in the field of photoelectric detection and gas sensing.In recent years,synthesis and properties of β-Ga₂O₃ nanostructures have been studied in many aspects.However,the preparation method mostly uses precious metals（Pt,Au,etc.）as catalysts,which has a high cost and is easy to introduce other unintentional impurities.In addition,there is a lack of systematic research on the microstructure and crystal quality optimization of β-Ga₂O₃ nanostructure.In order to solve these problems,β-Ga₂O₃ nanostructured thin films were prepared by a catalyst-free thermal oxidation method in this paper.The performance differences of β-Ga₂O₃ with different morphologies were studied,and the experimental conditions were optimized on three aspects of oxygen flow,oxidation temperature.The main work contents are as follows:1.The preparation and characterization methods of β-Ga₂O₃ nanostructured thin films were introduced in this article.Through comparative analysis,the main experimental method is determined to be the hot oxidation method based on the rapid tube annealing furnace.The combination of rapid annealing process and material preparation has the advantages of simple operation and low cost.Theβ-Ga₂O₃ nanostructured films were characterized by SEM,XRD,Raman spectroscopy,PL spectroscopy,and optical microscope.2.In view of the high cost of preparing β-Ga₂O₃ nanostructures caused by using precious metals as catalysts,a high temperature annealing of Ga-containing substrates and in-situ growth of high-quality β-Ga₂O₃ nanostructured thin films were proposed by using a catalyst free thermal oxidation method.Nanowires,nanoislands,and β-Ga₂O₃ nanoparticles were prepared,respectively.The crystal structure and optical properties of β-Ga₂O₃ with three different morphologies were analyzed in detail,and the growth mechanism of β-Ga₂O₃ nanostructures was described.In addition,β-Ga₂O₃ blocks with nanostructured surfaces were obtained during the experiment.The samples were characterized at different oxidation times,and the reasons for the formation of β-Ga₂O₃ blocks during the oxidation process were discussed.3.Considering the lack of systematic studies on the microstructure of β-Ga₂O₃ nanostructures and the optimization and control of crystal quality,the effects of oxygen flow rate,oxidation temperature and process pressure on the β-Ga₂O₃ nanostructured films were studied by using the catalyst free thermal oxidation process with（100）crystal surface Ga As as the substrate.The oxygen flow rate has a great effect on the surface morphology of β-Ga₂O₃ .The high oxygen atmosphere promotes the growth of nanocrystalline grains in multiple directions,forming β-Ga₂O₃ nanoisland morphology.Oxidation temperature has a great effect on the crystallization characteristics of β-Ga₂O₃ ,and the samples prepared at different temperatures have different crystal orientations.The change of process pressure leads to the change of oxygen partial pressure and molecular mean free path in the reaction chamber,which has a certain influence on the crystal mass and reaction rate of the material.By comparing the characteristics of β-Ga₂O₃ nanostructured films under different technological conditions,the optimum oxygen flow rate,oxidation temperature and process pressure were obtained,and the quality of β-Ga₂O₃ nanostructured films was optimized.