| The third generation of semiconductor materials SiC and GaN have been widely used in high power devices due to there have the large band gap,high breakdown field and high thermal conductivity.In comparison,?-Ga2O3 semiconductor material with larger bandgap,low on-resistance and higher breakdown strength,is considered to be one of the ideal preparation of power devices.In this paper,?-Ga2O3 thin films were grown on sapphire and Ga2O3 bulk substrates by PLD.The influence of temperature and oxygen pressure on the properties of?-Ga2O3 thin films were systematically investigated.In addition,we fabricated the Ga2O3 photodetectors and the electrical characteristics of the devices are investigated.The results obtained are shown as follow:First,Sn-doped Ga2O3 films were prepared by PLD mounting Ga2O3 target with fractions of SnO2 of 0.01 wt.%.The influence of oxygen pressure and temperature on the properties of the Sn-doped thin films were investigated.The XRD results show that the epitaxial films grow along the?201?direction.According to the results of AFM test,the surface morphology of the films can be improved by changing the oxygen pressure and temperature.Through the analysis of the optical properties of the thin films,it is found that the change of the oxygen pressure and the temperature not only affects the refractive index of the films,but also the bandgap of thin films is decreased.Second,the target with different SnO2 compositions will also affect the quality of Sn-doped Ga2O3 films.The change of the oxygen pressure of the Sn component increases the XRD peak of the sample,and when the oxygen partial pressure rises to 0.05 mbar,the epitaxial film becomes a polycrystalline thin film.The AFM test results show that the increase in the Sn component in the target makes the surface of the deposited films more flat.Similarly,changing the growth conditions of the samples can be used to obtain epitaxial films with different optical properties.Third,the performance of the photodetector is related to the temperature when the samples are grown.The increase of temperature helped to obtain a larger photocurrent and photocurrent versus dark current ratio.The Sn-doped Ga2O3 films at 700°C achieve the biggest photocurrent.At a Voltage of 20 V and a Plight of 50?W/cm2,the photodetector achieves a high ratio of photocurrent to dark current above 68.A peak responsivity 0.00118A/W is achieved at wavelength of 249 nm indicates that the direct Eg of Sn-doped Ga2O3films on sapphire is 4.78 eV.Fourth,the effect of oxygen pressure on the quality of the films was studied by homogeneously epitaxially growing Ga2O3 films under different oxygen pressures.The XRD and AFM results show that the epitaxial films are homogeneously grown on the Ga2O3 substrate.However,the crystallinity of the epitaxial films are not as good as bulk substrate,and its surface morphology is obviously worse,and it has a rough surface appearance.With the increase of the oxygen pressure,the FWHM of the rocking curve increases from 198 arcsec to 360 arcsec,indicating the crystallinity of the epitaxial films deteriorates.The surface morphology of the epitaxial films have a significant relationship with the oxygen pressure.The higher the oxygen pressure is,the more smooth the surface of the film is.Last,Sn-doped Ga2O3 thin film was epitaxially deposited on Ga2O3 bulk substrate at temperature of 650°C and an oxygen pressure of 0.01 mbar.The XRD results showed that the epitaxial film has a crystal quality close to single crystal substrate.We compare the AFM results before and after the growth.Although the films were not grown in a two dimensional mode,the surface was very flat.It has been found that Ti/Au has a good ohmic contact with Ga2O3 films after rapid annealing.The Sn-doped Ga2O3 thin film is of the n-type conductivity with a Hall mobility of 6.23 cm2/V?s and a carrier concentration of6.74?1019 cm-3. |
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