Fabrication Of Gallium Oxide Film On Sapphire And Its Photo-electronic Response Research

As a new type of ultra-wide bandgap semiconductor,Ga2O3 has large band gap,high breakdown field strength,and has great development potential in the field of power devices.The β-Ga2O3 film has extremely high chemical and thermal stability,high transparency in the visible light range,and extremely high selectivity for the solar-blind ultraviolet band,which is very suitable for the preparation of ultraviolet photodetectors.In this paper,β-Ga2O3 thin films were grown on sapphire substrates by low pressure chemical vapor deposition technology and UV photodetectors were fabricated.The main research contents are as follows:1.The β-Ga2O3 thin film was successfully grown on the c-plane sapphire substrate by low pressure chemical vapor deposition.The average growth rate of the thin film was between 0.222μm/h and 1.975 μm/h.It has a preferred growth orientation of(201);the bandgap of the βGa2O3 film is 4.73 eV～5.12 eV.The growth of β-Ga2O3 films is controlled by two-dimensional and three-dimensional growth modes.Properly extending the growth time can promote the twodimensional growth,which can improve the surface morphology and crystal structure.2.The growth temperature has a significant effect on the quality of β-Ga2O3 film.The study of films obtained at different temperatures found that with the increase of growth temperature,the average growth rate of the film tends to be saturated,and the surface roughness RMS of the film increases significantly,which is caused by the desorption of adatoms on the film surface.The XRD results show that the increase of growth temperature weakens the(201)preferred growth orientation of β-Ga2O3 films,which is due to the obvious thermal mismatch between the β-Ga2O3 films and the sapphire substrate.Excessive growth temperature will increase the defect density inside the film,which can be seen in the study of β-Ga2O3-based UV photodetectors.When the growth temperature is too high,the photocurrent of the device is significantly reduced.This is due to the influence of the electron scattering effect of internal defects,which makes the anti-interference and photoelectric conversion ability of the detector significantly decrease,and the response speed is significantly slower.The films and devices obtained at a growth temperature of around 950℃ have the best performance.3.The growth temperature was fixed at 950℃.The growth process of β-Ga2O3 film occurs in a low pressure atmosphere.The increase of pressure will change the mean free path of gaseous molecules and atoms,and the probability of gaseous molecules colliding with each other will increase.It is not beneficial to the crystallization of β-Ga2O3 thin films,which is also proved by the test results of ultraviolet photodetectors.The device with a pressure of 1 Torr has the largest photo-dark current ratio and responsivity,and has the fastest response speed.When the oxygen partial pressure is too low,oxygen vacancies are easily formed.When the oxygen partial pressure is too high,the arrangement of oxygen atoms in the β-Ga2O3 film can be destroyed,thereby affecting the crystal structure of the film and making the β-Ga2O3 film transform into polycrystalline.Combined with the test data of the UV photodetector,it can be seen that the dark current of the device is the highest(289nA at 10V bias)when the oxygen flow rate is 5 sccm,which is due to the high oxygen vacancy density inside the film.When the oxygen flow rate is 20 sccm,the photocurrent of the device is the lowest(49.2μA at 10V bias).This indicates that the crystalline quality in the film decreases,and the photoelectric conversion ability of the photodetector becomes weaker.When the O2 flow rate is 7sccm and the N2 flow rate is 50sccm,the photo-dark current ratio of the device is the largest(>104),and the quality of the β-Ga2O3 film is the best.