| ?-Ga2O3 is an ultrawide bandgap semiconductor with a band gap of about 4.9 e V,transmittance of over 80%in the visible region,a breakdown voltage of 8 MV/cm,and a Baliga's figure of merit of 3444.Due to its advantages such as wide bandgap,high transmittance in the visible region,high-voltage withstanding,and the capacity for carrying high electrical power,?-Ga2O3 has been widely applied in many key fields including solar-blind ultraviolet(SBUV)detectors,electronic power devices,gas sensors,etc.In terms of SBUV detectors,compared with other SBUV materials,such as AlxGa1-xN,diamond,MgxZn1-xO,etc.,?-Ga2O3 has advantages such as the bandgap corresponding to the middle of the SBUV region,good stability,and easy preparation for large-area single crystal,so it has attracted much attention.In recent years,many progresses have been made in the fields of?-Ga2O3,but many aspects could be improved.First,the research on the growth of?-Ga2O3 epitaxial thin films is still immature,and the crystal quality needs to be improved.For modern epitaxy techniques that include a large number of growth parameters,the understanding of the influence of various growth parameters on the film properties is still insufficient,which impedes the improvement of crystal quality.Secondly,in terms of SBUV detectors,the understanding for the influence of various film properties decided by the growth parameters on the performance of?-Ga2O3 epitaxial films needs to be improved,and there is a lack of the study on?-Ga2O3 homoepitaxial films based detectors.For solving the above hot and difficult issues,in this study,we focusing on the growth of?-Ga2O3 epitaxial thin film and the?-Ga2O3 based SBUV detectors,we carried out the following researches:1.We used high-temperature MOCVD to grow?-Ga2O3 heteroepitaxial thin films on sapphire(0001)substrates,with high-purity O2 and TMGa as reaction source.Using the control variable method,we optimized the growth condition of?-Ga2O3films by changing the VI/III ratio,total gas flow,reaction pressure and growth temperature with control variable method.Moreover,we systematically studied the effects of the variations of these four growth parameters on the growth rate,the crystalline properties,the surface morphology and the optical properties of the prepared?-Ga2O3 films.Among them,the competition between the parasitic gas-phase reaction and the epitaxial growth affected the growth rate of the?-Ga2O3film,the increase of the growth temperature brought a significant improvement to the crystal quality of the films,the surface morphology of the films was affected by multiple factors such as the nucleation density at the initial stage of growth,the uniformty of the flow,the violence degree of gas phase reaction,etc.,the optical bandgaps of the thin films were relatively stable,and the luminescence characteristics showed a clear correlation with the crystal quality.2.The?-Ga2O3 heteroepitaxial thin films prepared under different growth conditions were utilized to fabricate the horizontal photoconductor SBUV detectors.The effects of the changes of film properties on the photo-dark current ratio,the external quantum efficiency,the responsivity,and the response speed of SBUV detectors and related physics mechanisms were systematically discussed.The link between the film properties decided by the growth parameters and the detector performance were established.Among them,the crystal quality has the most obvious influence on the detector performance,and the performance of the detectors made of?-Ga2O3 films with different crystal quality ranges followed different changing laws.In addition,the thickness of the films and the surface roughness also influenced the performance of the detectors.3.Using high-temperature MOCVD technology,?-Ga2O3 homoepitaxial thin films were grown on?-Ga2O3(2 01)single crystalline substrates,and the growth temperature was optimized.The properties including the crystalline properties,the morphorlogy,luminescence properties,elemental composition etc.were systematically analyzed.Different from heteroepitaxy under the same range of temprature,with the increase of growth temperature,the crystal quality of the thin film did not continuously improve,but was affected by the uniformity of the flow,showing a trend of first increase and then decrease.The surface morphology and luminescence properties of the thin films were highly consistent with the variation of crystal quality.The FWHM of XRD double-crystal rocking curve for the optimized film is 21.6 arcsec,which is better than 26.3 arcsec for the substrate.4.SBUV detectors with horizontal and vertical structures were fabricated based on homoepitaxial thin films grown on UID(unintended doped)?-Ga2O3 substrates.Under the illumination of 254 nm light,the responsivity and external quantum efficiency of the horizontal structure solar-blind UV detector can respectively reach915.3 A/W and 4.47×105%,and the responsivity and external quantum efficiency of the SBUV detector with vertical structure can respectively reach 44.29 A/W and2.16×104%.5.SBUV detectors Solar-blind UV detectors with horizontal MSM and horizontal SBD structures were prepared based on the homoepitaxial thin films grown on Fe-doped semi-insulating?-Ga2O3 substrates.The characteristics such as photo current,dark current,external quantum efficiency,responsivity,response speed and selectivity of the detector were studied.Under the illumination of 254 nm light,the photo-dark current ratio of the MSM detector can reach 1.17×103,the responsivity and the external quantum efficiency can respectively reach 1.08 A/W and 5.29×102%;the ratio of photo-dark current for the SBD detector The can reach 3.30×102. |
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