Research On The Growth,Pahse Transition And Physical Property Modulation Of Doped Gallium Oxide Epitaxial Thin Film

Gallium oxide(Ga2O3),an ultra-wide bandgap semiconductor material with direct bandgap,has a great application prospect in power electronic devices,such as solar blind photodetectors,field effect transistors,light-emitting diodes,information storage,gas-sensitive sensors,transparent conductive electrodes and other fields.Among the five polymorphs of Ga2O3(?,?,?,? and ?),the ? phase is the most common,stable and widely studied.However,the monoclinic structure of?-Ga2O3 makes it difficult to improve the epitaxial quality on the mainstream substrate,and its intrinsic n-type conductivity also limits its development in power devices to some extent.Therefore,exploring the application potential in different fields of other metastable phases,as well as realizing phase controlled growth of high-quality epitaxial thin films,is a critical path for the further development of Ga2O3 materials.Doping process is an effective application technology to regulate lattice stress,induce structural phase transition,improve crystal quality and optimize physical properties.In this paper,Fe,Mn or Mg doped Ga2O3 epitaxial thin films were prepared by laser molecular beam epitaxy technology or metal organic chemical vapor deposition technology under different growth conditions.The effects of doping concentration,substrate temperature,chamber pressure and annealing process on the crystalline quality,phase transition process and basic physical properties of Ga2O3 epitaxial thin films are systematically investigated.And we have provided reliable theoretical and experimental basis for the application prospects in different fields of Ga2O3 epitaxial thin films with different crystal phases.The main research results are as follows:(1)By using laser molecular beam epitaxy technology,and by adjusting the Fe doping concentration,substrate temperature and growth oxygen pressure,the phase-controlled growth of ?-Ga2O3 and ?-Ga2O3 epitaxial thin films on sapphire substrate was achieved successfully.We reported for the first time that how to use X-ray diffraction pole figure measurement to effectively,low cost and nondestructively distinguish?-Ga2O3 and ?-Ga2O3 phases.By regulating the concentraion of vacancy defects and crystalline quality of thin films through Fe doping,the semi-insulating properties of Ga2O3 thin films were successfully improved.Most high quality epitaxial thin films could maintain a nA-level current at 150 V external bias.The application potential in dilute magnetic semiconductor of Fe doped ?-Ga2O3 material was proved by first-principles calculation and experimental data.The saturation magnetic moment value of 5.73 ?B/Fe at room temperature was observed in the ?-Ga2O3:Fe thin film with the doping concentration of 9.62 at%,which was ahead of most of the current literature reports.(2)The ?-(Ga1-xMnx)2O3 thin films with different Mn doping concentrations were prepared on sapphire substrate by using the laser molecular beam epitaxy technology.The crystalline quality,room temperature ferromagnetism and the solar blind optoelectronic detection performance of the thin films all increased first and then decreased with the further increase of doping concentration.The results showed that when x=0.04,the thin film had the maximum saturation magnetization.When the external magnetic field was parallel&perpendicular to the sample surface,the saturation magnetic moments were 1.54&0.35?B/Mn,showing obvious magnetic anisotropy.At the same time,the solar blind photodetector based on this ?-(Ga0.96Mn0.04)2O3 thin film had the lowest dark current,the highest light to dark ratio and the shortest response time.Its excellent physical properties were mainly due to the optimization of Mn doping on the crystal structure,band gap and carriers of thin film.(3)The effects of growth temperature,deposition chamber pressure and post annealing on the crystal structure,crystalline quality and physical properties of ?-Ga2O3 thin films were investigated.An infinitesimal Mg doped ?-Ga2O3 thin film was further grown on the obtained ?-Ga2O3 epitaxial thin film.And its basic physical properties were thoroughly studied.When the external bias was 5 V,the dark current of the schottky type Au/?-Ga2O3/Au solar blind photodetector,based on unintentional doped high quality ?-Ga2O3 epitaxial thin film,was only 19.7 pA.And the inhibition ratios of R250 nm/R280 nm and R250 nm/R400 nm were 4.2×102 and 1.3×104,respectively,showing excellent wavelength selectivity.While under the illumination intensities of 40&5 ?W/cm2,the light to dark ratios could reach 1.82×104&6.03×102,respectively,indicating a good detection capability for weak light source signals,and has determined the promising application prospect of ?-Ga2O3 epitaxial thin film in solar blind photodetectors.