Hydride Vapor Phase Epitaxy Heteroepitaxy Of Metastable Phase ?-Ga₂O₃

As a novel ultra-wide bandgap semiconductor material,gallium oxide?Ga₂O₃?has attracted extensive attention with rapid progress in the field of power electronics and deep-ultraviolet optoelectronics.In previous studies,it has been proved that this material has multiple phases.Except for the stable phase,?-Ga₂O₃,there is still a lack of systematic understanding and application of other metastable phased Ga₂O₃.Among them,ferroelectric?-Ga₂O₃ is expected to be used in functional memory devices and low-power consumption transistors,however the existing reports on the growth and fundamental investigation of this material is still insufficient,which cannot meet the demand of practical device applications.In this study,the hydride vapor phase epitaxy?HVPE?method was used for the heteroepitaxy of Ga₂O₃ on c-plane sapphire substrates,and the optimal growth window of pure phase?-Ga₂O₃was determined through phase engineering.The heteroepitaxial growth mode transition and in-situ doping mechanism have been revealed.The main achievements include:1.Phase engineering and optimal heteroepitaxy of Ga₂O₃ on c-plane sapphire substrate have been performed by means of the HVPE method.X-ray diffraction?XRD?and Raman scattering patterns show that a phase transition from?phase to?phase will occur when the growth temperature exceeds 575?,and 550?is the optimal growth temperature in this experiment to achieve epitaxial growth of?-Ga₂O₃ single crystal.2.The crystal structure of?-Ga₂O₃ has been identified by means of various characterization techniques.According to the cross-section TEM and XRD-?scans,the observed hexagonal symmetric structure is actually composed of three orthogonal lattices of?-Ga₂O₃ rotated 120°to each other,and the lattice mismatch between the epitaxial layer and c-plane sapphire is 5.5%.The epitaxy relations are?010??-Ga₂O₃??101?0?Al₂O₃,and?110??-Ga₂O₃??11?00?Al₂O₃.The screw dislocation density is estimated to be 2.7×10⁹ cm^-2,and the in-plane twist angle is about 0.63°.The transmission spectrum shows that the optical band gap of?-Ga₂O₃ is 4.64 e V.3.The Si in-situ doping?-Ga₂O₃ has been performed by using the Si Cl₄ as Si dopant source during the HVPE epitaxial process.By changing the doping dose,the carrier concentration can be controlled from 4×10¹⁶ cm^-2 to 1×10¹⁹ cm^-2.The reduction of carrier concentration is essential in the epitaxy of the drift layer that is widely used in high power Schottky diode.Combined with the advantages of HVPE technology,the achievement of high-quality ferroelectric?-Ga₂O₃ is expected to deliver novel functionality and expand its diverse applications in solar-blind deep-ultraviolet photodetectors and power electronics.