Study On The Growth Of Ga₂O₃ Films And Fabrication Of Ga₂O₃-based UV-photodetector

Ga₂O₃ is a wide direct bandgap oxide semiconductor with band gap of 4.5⁴.9eV.Ga₂O₃ has five kinds of crystal structures and ?-Ga₂O₃ is the common structure.Ga₂O₃ has the excellent chemical and heat stability,so that it has potentials of being used in solar-blind ultra-violet photodetectors,transparent conductive oxide films,oxide sensors and LEDs.In this paper,?-Ga₂O₃ films were grown and optimized on c-plane sapphire substrate by MOCVD.Furthermore,the samples were annealed in the conditions of vacuum,Nitrogen,Oxygen under different temperature and time separately.The crystal and optical properties of as-deposited and annealed ?-Ga₂O₃ films were measured and analyzed.After that,the as-deposited and annealed ?-Ga₂O₃ films were fabricated into UV solar-bind photodetectors,and the electrical properties were measured and analyzed.1.?-Ga₂O₃ films were grown on the sapphire substrate with a thin homogenous buffer layer and the influences of buffer layer on ?-Ga₂O₃ films were studied.The crystal quality of ?-Ga₂O₃ films were optimized by changing the growth temperature.In the XRD patterns,the ?-Ga₂O₃ film grown without buffer exhibited amorphous,and it converted to polycrystalline gradually with the rising temperature.But the samples with buffer exhibited single-phase which preferred orientation of)012?.The?012?plane of ?-Ga₂O₃ was parallel to?0001?plane of sapphire substrate.By calculation and analysis of the lattice constants,it showed that ?-Ga₂O₃ lattice suffer tensile strain in?012?plane and compressive strain at ]012[ direction which was perpendicular to the plane of?012(.The transmittance of ?-Ga₂O₃ reached 75% in the UV region,which was smaller than 85%⁹0% in visible region with a calculated optical bandgap of 4.73 eV.In the SEM image,the thickness of ?-Ga₂O₃ film was about 850 nm,and the surface exhibited smooth plane and small-size crystal grains.2.The ?-Ga₂O₃ films were annealed under different conditions and the effects of anneal on the crystal and optical properties were analyzed.The results turned out that the crystal and optical properties could get better after annealed in oxygen conditions than that in vacuum and nitrogen conditions.With the increase of annealing temperature and time,the residual stress in ?-Ga₂O₃ films turned to be released gradually with the degeneration of crystal quality.The films were found transformed from monocrystal to polycrystalline.Furthermore,the surface roughness of ?-Ga₂O₃ films decreased and the transmittance increased with the increment of annealing temperature and time.3.The solar-bind ultra-violet photodetector was fabricated and the electrical properties were measured.The light current and dark current of the photodetector were measured in the light of 254 nm UV light source with luminous power of 80 ?W/cm2.The responsibility of these photodetectors was also calculated.The properties of photodetector made of as-deposited film was compared with that made of the annealed films.The photodetector made of as-deposited film exhibited the better photoelectric property than that made of the annealed films.Its light-dark current ratio almost reaches three orders of magnitude,and responsibility is in the neighborhood of 1.35A/W.