Preparation And Properties Of Gallium Oxide Thin Films

Gallium oxide(Ga₂O₃)is a kind of oxide semiconductor material with ultra wide direct band gap(band gap is about 4.5-4.9 eV).It has excellent properties,especially in physical and chemical aspects,with high stability,and it also has excellent performance in optoelectronics.These characteristics make gallium oxide(Ga₂O₃)have a good future in high frequency,high mobility,high power devices and other fields.Gallium oxide(Ga₂O₃)thin films were deposited on silicon and glass substrates by magnetron sputtering.In this paper,the influence of magnetron sputtering parameters on the properties of Ga₂O₃ thin films is studied,so as to study how to improve the quality of Ga₂O₃ thin films and obtain high quality Ga₂O₃ thin films.The main research work of this paper is as follows:(1)Gallium oxide(Ga₂O₃)thin films were deposited on silicon(Si)and glass substrates by magnetron sputtering.The effects of substrate temperature,sputtering power and sputtering pressure on the properties of Ga₂O₃ thin films were investigated.The effects of substrate temperature,sputtering power and sputtering pressure on the crystal structure,surface morphology and optical properties of Ga₂O₃ thin films were analyzed.Scanning electron microscopy(SEM),X-ray diffraction(XRD),ultraviolet spectrophotometer(UV VIS)and atomic force microscopy(AFM)were used to characterize the surface morphology,crystal structure,grain size and optical properties of the films(2)The average grain size of Ga₂O₃ films is about 11 nm,13 nm,16 nm,25 nm and 41 nm at 200?,300 ?,400 ?,500? and 600?.The average grain size of Ga₂O₃ films increases with the increase of sputtering temperature.This is mainly due to the fact that with the increase of substrate temperature,the sputtered atoms can obtain more energy on the substrate,have strong mobility,and the grain size grown from single core is larger.At the same time,the high bombardment energy leads to the increase of substrate temperature during the deposition process.Both of these two factors contribute to the nucleation and growth of target atoms.At 200?,300?,400?,500? and 600?,the thickness of gallium oxide film is about 215 nm,243 nm,338 nm,534 nm and 565 nm.When the substrate temperature changes from 200? to 600?,it is found that the thickness increases gradually and sharply at 500?.This indicates that the deposition rate increases with the increase of substrate temperature.When the substrate temperature is 500?,the peak value of 2 ? The angle is 69.06°,It corresponds to the(223)plane of silica.Except for the diffraction peaks corresponding to SiO₂,no other diffraction peaks were observed.This shows that the growth of gallium oxide film on silicon substrate is amorphous structure.(3)The effect of magnetron sputtering power parameters on the properties of Ga₂O₃ thin films was studied.Scanning electron microscope(SEM)observation shows that the surface morphology of gallium oxide(Ga₂O₃)film is composed of tiny grain.With the increase of sputtering power,the degree of crystallization and grain size of the film increase gradually.This may be because with the increase of sputtering power,the number of atoms bombarded on the gallium oxide target increases,and the kinetic energy increases.Under its bombardment,the increase of substrate surface temperature makes the atoms or clusters deposited on the substrate surface easier to migrate and form nuclei.The more nucleation on the substrate surface,the more grains grow.The higher the substrate temperature,the greater the grain growth,The denser the grains,the fewer the grain boundaries.Therefore,with the increase of sputtering power,the grain size of Ga₂O₃ films increases gradually.Therefore,with the increase of sputtering power,the grain size increases gradually.By observing the X-ray diffraction(XRD)patterns of Ga₂O₃ films prepared by magnetron sputtering at substrate temperature of 600?and sputtering power of 200W,it can be seen that when the substrate temperature is 600? and the sputtering power is 200W,the two peaks in the XRD patterns correspond to two peaks 69.09°?69.30°,respectively,This corresponds to the(223)and(204)faces of silica.In addition,no other diffraction peaks corresponding to the gallium oxide film are observed in the figure,which indicates that the gallium oxide film grown on the silicon substrate is amorphous structure.(4)The effect of argon pressure parameters on the properties of Ga₂O₃ thin films deposited on glass substrates by magnetron sputtering was studied.The average transmittance of all samples in the visible region(400-800 nm)decreases with the increase of pressure.The average transmittance of samples at different pressures of 15 Pa,25 Pa and 35 Pa is 70%,50%and 45%,respectively,This shows that the sample has high visible transparency,and the change of the average transmittance of the film may be related to the thickness of the film.With the increase of argon pressure,more ionized argon atoms make more target atoms sputtered out,and more target atoms reach the substrate,which makes the thickness of the film increase and the average transmittance of the film decrease.It is found that with the increase of argon pressure,the absorption edge of the sample shifts red at different pressures of 15 Pa 25 Pa and 35 Pa.This may be because with the increase of argon pressure,the number of ionized argon atoms per unit time increases,the number of target atoms bombarded by argon ions increases,and the number of target atoms arriving on the substrate per unit time increases,which leads to the increase of film growth rate,the decrease of film band tail state,the narrowing of film band gap,and the red shift of absorption edge.In addition,high argon pressure leads to more uneven distribution of grains on the surface of the films,which may lead to red shift of the absorption edge.The diffraction peaks of gallium oxide thin films grown on glass substrates are a combination of a series of irregular peaks in size and shape.The intensity of the diffraction peaks decreases with the increase of the diffraction angle,with a slight repetition.When the pressure is 15Pa,25Pa and 35Pa,the influence of pressure change on the diffraction peak is very small.It can be seen that the growth of gallium oxide film on glass substrate is amorphous.