Preparation And Characterization Of Homoepitaxial Gallium Oxide Films And Aluminum-indium Oxide Films

Transparent oxide semiconductors have attracted much attention due to their excellent photoelectric properties,and can be widely used in many fields such as solar cells,flat-panel displays,transparent thin film transistors,light emitting diodes and semiconductor lasers,etc.Recently,the trend of optoelectronics research has turned to short wavelength,which requires the semiconductor thin films are transparent in ultraviolet or deep ultraviolet region.Therefore,new ultraviolet photoelectric materials are necessary to be investigated to meet the rapid demands for ultraviolet photoelectric devices.?-Ga2O3 is a very promising deep ultraviolet photoelectric semiconductor material with a large band gap?-4.9 eV?,high mechanical strength and stable physicochemical property.However,almost all the ?-Ga2O3 thin films are hetero growth,and therefore,the prepared films are mostly amorphous or polycrystalline structures due to the large lattice mismatch between the films and substrates.The structure and properties of these ?-Ga2O3 thin films are always inferior that they cannot meet the demands of practical applications.Until now,few studies about homoepitaxial ?-Ga2O3 films were reported.In order to make the ?-Ga2O3 films practically applied in the field of photoelectric devices,it is necessary to carry out in-depth systematic research on the homoepitaxial growth of ?-Ga2O3 single crystal material.The study of homoepitaxial ?-Ga2O3 as well as the doping ?-Ga2O3 films will lay the foundation for the application of this material in transparent semiconductor photoelectric devices and ultraviolet photoelectric devices.A common problem for the extensively used oxide transparent semiconductor materials is that the band gap width is difficult to adjust.With the continuous development of the material science,new wide band gap semiconductor materials with tunable band gap should be investigated.Both Al2O3 and In₂O₃ are wide band gap transparent oxide materials with band gaps of 8.7 eV and 3.7 eV,respectively.Al2xIn2?1-x?O3 film can be considered as an alloy of Al2O3 and In₂O₃ of which the optical band gap could be modulated from 3.7 to 8.7 eV by controlling the composition of the alloy suitably,which is a promising ultraviolet transparent semiconductor material.Systematically study on the preparation,structure and photoelectric properties of the Al2-xIn2?1-x?O3 film,which not only has important scientific significance for the reseach on the transparent photoelectronic device materials,but alao provides the necessary reference for the applications of this matarial in transparent photoelectronic devices.The content of this dissertation involves three parts.In the first part,homoepitaxial ?-Ga2O3 and the doping ?-Ga2O3 films were prepared on the ?-Ga2O3 single crystal substrates by MOCVD and the structure as well as photoelectric properties of the films was investigated.In the second part,Al2xIn2?1-x?O3 with different contents were prepared on the SiO2 and ?-Al2O3 single crystalline substrates by MOCVD,and the preparation process,growth mechanism,structure and photoelectric properties of the films were systematically studied.In the last part,a new In-Al-Sn-O?IATO?film material was prepared based on the research work in the second part,and the effect of Sn content on the structure and photoelectric properties of the films were studied in detail.The first part of the study is as follows:1.High quality homoepitaxial ?-Ga2O3 films were prepared on the ?-Ga2O3?100?substrates by the MOCVD technology.During the deposition process,the Ga?CH3?3 and high purity oxygen were used as the precursors and the ultra-high purity N2 was used as the carrier gas.The growing temperatures were 600,650 and 700?,respectively.The influences of different growth temperatures on the structure and optical properties of the films were studied.All the prepared films with different deposition temperatures were single crystalline epitaxial films,and the orientation of the films was along ?-Ga2O3[100]direction of the single crystalline substrate.The?-Ga2O3 film grown at 650 ? exhibited the best crystal quality without twinning structures through structural analysis.The average transmittance of the films in the visible and ultraviolet range was about 80%.The optical band gaps of the samples deposited at 600,650 and 700 ? were about 4.72,4.73 and 4.68eV,respectively.2.Based on the above research work,the homoepitaxial ?-Ga2O3 films were injected to n-type doping by using Sn?C2H5?4 as the organometallic source.In order to improve the Sn-doped efficiency,the growth temperature was increased to 700 ?,and the Sn-doping concentration was varied from 1%to 12%?atomic ratio?.The XRD results showed that all the films were homoepitaxially grown along the direction of the ?-Ga2O3 substrate.As the Sn concentration increased,the crystalline quality of the films initially increased and then decreased.The electrical properties analyses revealed the 10%Sn-doped film exhibited the lowest resistivity of about 1.20 × 10-1?· cm,with the carrier concentration of 9.54×1017 cm-3 and the Hall mobility of 12.03 cm2V-1s-1 The doping mechanism and the conductivity mechanism of the films were studied.It was confirmed that the Sn element was an effective n-type dopant for the?-Ga2O3 films and the resistivity of the films could be intentionally tuned by Sn doping.The average transmittances of all the samples in the visible and ultraviolet wavelength ranges were all over 85%and the optical band gaps of the films varied from 4.16 to 4.69 eV.The second part of the study is as follows:1.In₂O₃ films were prepared on the different tangential SiO2 single crystalline substrates at 650? by MOCVD.During the deposition process,the In?CH3?3 was used as the precursor of In,high purity oxygen was used as the oxidant.The XRD results showed that the In₂O₃ films grown on the z-cut SiO2?0001?substrate exhibited the best crystalline quality with single orientation.Therefore,the SiO2?0001?substrate was chosen to epitaxially grow In₂O₃ films with growing temperatures ranging from 570 to 690 ?.According to the structural analysis,the In₂O₃ film grown at 650 ?exhibited the best crystalline quality without domain structures.Furthermore,the in-plane epitaxial relationship between the In₂O₃ films grown on SiO2?0001?substrates could be determined as In₂O₃[110]//SiO2<110>,while the out-plane relationship was In₂O₃?111?//SiO2?0001?.The Hall mobility of the films prepared at different temperatures was in the range of 15.43-27.84 cm2V-1s-1,while the carrier concentration was in the range of 5.03×1019-5.65×1019cm-3 and the resistivity was in the range of 4.24×10-3-4.89×10-3 ?·cm.The prepared films showed good optical transparency,and the average transmittances of all the samples in the visible wavelength range were all over 82%.The film prepared at 650 ? had a minimum optical band gap of 3.68 eV.2.Based on the determination of optimum preparation process for epitaxial In₂O₃ films,Al2xIn2?1-x?O3 films with different Al compositions of x[Al/?Al+In?atomic ratio]were prepared on the SiO2?0001?substrates at 650 ?.During the deposition process,the Al?CH3?3 and In?CH3?3 were used as metallorganic sources,high purity oxygen was used as the oxidant.The effects of different compositions on the structure,optical and electrical properties of the films were investigated.The XRD and HRTEM results indicated a phase transition from bixbyite In₂O₃ with single orientation to amorphous or nanocrystalline structure as the Al content increased.The XPS results confirmed the prepared films were aluminum indium oxide,and the actual values of the Al/?Al+In?atomic ratio for the films were all slightly lower than the experimental enactment values.With the A1 content of x increased from 0.1 to 0.4,the Hall mobility of the films decreased monotonously from 14.62 to 3.89 cm2V-1s-1,the carrier concentration varied in the range of 7.26×1019-3.38×1020 cm-3 and the resistivity varied in the range of 2.15×10-3-2.23 ×10-1?·cm.The average transmittances of all the samples in the visible range exceeded 82%and the optical band gap of the films nearly linearly increased from 3.74 to 5.91 eV with the Al content of x increased from 0 to 0.9.3.The most commonly used ?-Al2O3?0001?was chosen as the substrate material for preparing the Al2xIn2?1-x?O3 film.The MOCVD process conditions were the same as those prepared on the Sio2?0001?substrates.As the Al content increased,the crystalline quality of the films gradually deteriorated with a structural transition from polycrystalline structure of bixbyite In2o3 to amorphous or microcrystalline structure.As the A1 content of x increased from 0.1 to 0.4,the Hall mobility of the films decreased monotonously from 14.63 to 4.6 cm2V-1s-1,the carrier concentration varied in the range of 8.5×1019-2.27×1020 cm-3 and the resistivity varied in the range of 1.52×10-3-1.9×10-1 ?·cm.The temperature dependent Hall measurements were carried out for the Al0.4In1.6O3 arnd Al0.8In1.2O3 films,respectively,and the conduction mechanisms of these two samples were studied.All the samples presented an absorption edge in the ultraviolet region and the average transmittances in the visible range exceeded 83%.The optical band gaps of the films increased monotonously from 3.82 to 5.88 eV as the Al content increased.The third part of the study is as follows:1.Based on the second part about the preparation and research results of Al2xIn2?1-x?O3 films,the Al1.3In0.7O3 film with Al content x=0.65 was chosen as a basis.During the deposition process,the Sn?C2H5?4 was used as the organometallic source.New In-Al-Sn-O?IATO?film materials were respectively prepared on the SiO2?0001?and ?-Al2O3?0001?substrates with the growing temperature of 700 ?.The effects of Sn content on the structural,electrical and optical properties of the prepared films were investigated in detail.1.IATO films were prepared on SiO2?0001?substrates.The structural analysis indicated that the crystalline quality of the films improved as the Sn content increased and the sample with 15%Sn content exhibited the best crystalline quality.The XPS spectra revealed that the prepared film was pure indium aluminum tin oxide and the metal elements were fully oxidized without aggregation.As the Sn content increased from 0 to 18%,the Hall mobility of the films initially increased and then decreased with a maximum value of 15.59 cm2V-1s-1 obtained at 15%Sn content.Correspondingly,the maximIm value of carrier concentration was 2.30×1020 cm-3 and the minimum value of resistivity was 1.5×10-3 ?·cm.The conductivity mechanism of the IATO films with 15%Sn content was studied.The average transmittances for the IATO films in the visible range were over 81%.The optical band gaps of the films decreased continuously from 5.03 to 4.05 eV with the increasing Sn content.The reason for the variations of the electrical properties and optical band gap of the IATO films as a function of Sn contents was analyzed and studied.2.IATO films were prepared on Ca-Al2O3?0001?substrates.The XRD results indicated that the structure of the films varied from amorphous or microcrystalline to well crystalline and then to mixed crystalline as the Sn content increased from 0 to 18%.And the IATO film with Sn content of 15%had the best crystalline quality.The HRTEM results showed that film with 15%Sn content was polycrystalline with fine crystallization quality,high degree of crystallization and few grain boundaries.The electrical properties analyses revealed that the film with 15%Sn content had the highest Hall mobility of 15.47 cm2V-1s-1 with a maximum carrier concentration of 2.1×1020 cm-3 and a lowest resistivity of 2.13×10-3 ?·cm.The average transmittances for the IATO films in the visible range exceeded 80%.The optical band gap of the film with 15%Sn content and the best crystalline quality was about 4.13 eV.