Growth And Annealing Study Of Gallium Oxide Films On Sapphire Substrates

Ga2O3is one of the new semiconductor materials with5kinds of crystal structures which are α, β, ε,δ and y, respectively. Among these crystal structures, β-Ga2O3is the most common which belongs to monoclinic. β-Ga2O3is a kind of direct band gap oxide semiconductor materials with a band gap of4.5-4.9eV, it also has good chemical and thermal stability, thus it has become one of the research hot spots in the field of oxide semiconductor materials. β-Ga2O3could be widely applied to solar blind detectors, deep ultraviolet transparent conductive thin films, gas sensors and thin film transistors. It is crucial to obtain high quality films of β-Ga2O3, so that it could be used in fields which have been stated before. There are many methods can be used to fabricate β-Ga2O3films, including high temperature spray pyrolysis, magnetron sputtering, pulsed laser deposition, electron beam evaporation and mental organic chemical vapor deposition, etc. Compared with other methods, MOCVD has its unique advantages in fabricating high quality semiconductor films.On this background, in this paper, β-Ga2O3films were grown on c-plane sapphire substrates by MOCVD, post heat-treatment was taken under different atmosphere for different times at different temperatures. Crystal structure and optical properties of β-Ga2O3films as-deposited and post-annealed were characterized and analyzed. The research could be divided into two parts as following:1. Crystal and optical properties of β-Ga2O3films as-deposited were studied. The XRD patterns show that the as-deposited sample is single-phase β-Ga2O3films with excellent preferred orientation of (201), and the (201) plane of β-Ga2O3is parallel to (0001) plane of sapphire substrates. The lattice constants of β-Ga2O3were calculated as a=1.185nm, b=0.308nm, c=0.531nm and β=111.7°, which indicates that the β-Ga2O3lattice gets tensile strain in (201) plane while gets compressive strain at [201] direction which is perpendicular to the plane of (201). The transmittance of as-deposited β-Ga2O3films is over90%in the visible regions and more than75%in UV regions with a calculated optical band gap of4.93eV.2. The effects of different annealing conditions on crystal and optical properties of β-Ga2O3films were studied. With the increase of annealing time and annealing temperature, the residual stress of β-Ga2O3films are released gradually along with a increasing of defect density and degeneration of crystalline quality. The surface roughness of the β-Ga2O3films decreased after a slightly increasing with the increase of the annealing time and annealing temperature as shown by the SEM images. The transmittance of the β-Ga2O3films changed with the changing of annealing conditions, influenced by the surface roughness and crystalline quality. The optical band gap of the β-Ga2O3decreased from4.94eV to4.79eV, which indicates that the films were more likely to transform to single crystal films after annealing.