Preparation And Characterization Of Aluminum-indium Oxide Films On MgO Substrates

As the third generation semiconductor materials, transparent oxide materials with wide band gap are always attracting the researchers’keen interest because of their excellent photoelectric properties. Furthermore, these materials show good prospects of the applications in transparent thin film transistor, light-emitting diodes (LEDs), ultravioletdetector, laser, thin film solar cell and etc. There is still an obstacle lying in the oxide semiconductor film materials of extensive use, which is the difficulty to adjust the band gap width of the materials. With the continuous development of transparent optoelectronics and ultraviolet optoelectronic devices, there is a demand for the extending of transparent area of the semiconductor materials to the deep ultraviolet region. In order to satisfy the fast development of the transparent electronic devices and ultraviolet photoelectric devices, it is of great necessary to study the new kind of wide band gap semiconductor materials with the modulation of the band gap. Al2O3 and In2O3 are both transparent oxide materials with direct band gaps of 8.7eV and 3.7eV, respectively. Al2xIn2-2xO3 thin-film material can be regarded as the alloy of Al2O3 and In2O3, whose band gap can be modulated in the range of 3.7～8.7eV by controlling the different component ratios Al and In elements. To obtain Al2xIn2-2xO3 films with good performance as a new type of wide band gap semiconductor materials to meet the fast development of photoelectric devices, it is very necessary to proceed a systematic study on the preparation process, growth mechanism, structural properties and optical-electrical characteristic of the Al2xIn2-2xO3 films. The research work not only has scientific significance, certain perspectiveness and practical application value, but will also provide the necessary reference value for this material in transparent photoelectric devices applications. Compared with molecular beam epitaxy (MBE) and atomic layer deposition (ALD), the metal-organic chemical vapor deposition (MOCVD) method is more suitable for industrial mass production. This dissertation employs MOCVD method for the preparation of thin film materials, putting the research emphasis on the preparation process, growth mechanism, structural properties and optical-electrical characteristic of Al2xIn2-2xO3 film system.This dissertation contains four parts. In the first part, the influences of different substrate materials and growth temperatures on the structural and optical-electrical properties of In2O3 films were studied, and high quality single crystal In2O3 films were prepared successfully. In the second part, Al2O3 films were successfully prepared, and the annealing treatment effect on the structural and optical properties of the films was investigated. Single crystal epitaxial γ-Al2O3 films were obtained. In the third part, on the basis of the first two parts of research, the preparation and characterization of Al2xIn2-2xO3(0.1≤x≤0.9) films have been studied systematically. In the last part, Al-In-Sn-O (AITO) films were prepared and the influence of different Sn contents on the structural, optical and electrical properties of the films has been mainly studied.1. The first part:In2O3 films were tentatively prepared on MgO、SrTiO3、KTaO3 and sapphire substrates by MOCVD. During the preparation process, In(CH3)3 was used as the metallorganic precursor, high purity O2 was used as the oxidant, ultra high purity N2 was used as the carry gas of the system. The influence of deposition temperature on the structural, optical and electrical properties of In2O3 films was investigated. High quality single crystal In2O3 films with the cubic bixbyite structure were epitaxially grown on MgO(110) substrates, and the film deposited at 600℃ exhibited the best crystalline quality. The growth mechanism and microstructure of the film deposited at 600℃ was studied in detail, and the schematic diagram of geometrical epitaxial relationship between the In2O3 film and MgO(110) substrate was given. The epitaxial relationship between the film and substrate was In2O3(110)//MgO(110) with In2O3[001]//MgO[001] and In2O3[110]//MgO[110]. The average transmittance of every sample in the visible wavelength region exceeded 76%, and the optical band gap was in the range of 3.55～3.70 eV. The Hall mobility of the In2O3 films was in the range of 2.593～6.813 cm2V-1s-1. The carrier concentration of the films was in the range of 2.55～7.34×1018 cm-3. And the resistivity was in the range of 3.05～ 3.96×10-1 Ω·cm.2. The second part:Al2O3 films were deposited on MgO(110) and MgO (111) substrates at 700℃ by MOCVD. During the preparation process, Al(CH3)3 was used as the metallorganic precursor, high purity O2 was used as the oxidant, high purity N2 was used as the carry gas. The influence of annealing temperature on the structural and optical properties of Al2O3 films was studied. The annealing temperature was set as 900、1000 and 1100℃. (1) Al2O3 films were deposited on MgO(110) substrates. XRD analysis revealed that Al2O3 films exhibited y-phase structure with a single orientation γ-Al2O3(110) after annealing treatment. And the sample annealed at 1000℃ exhibited the best crystalline quality. The growth mechanism and microstructure of the film annealed at 1000℃ was investigated, and the epitaxial relationship between the γ-Al2O3 film and the substrate was given as y-Al2O3(110)//MgO(110) with γ-Al2O3[001]//MgO[001] and γ-Al2O3[110]//MgO[110]. The average transmittances of samples before and after annealing treatment in the visible wavelength region exceeded 84%, and the optical band gap of the samples were 5.89 eV and 5.81 eV, respectively.(2) The Al2O3 films deposited on MgO(111) substrates exhibited γ-Al2O3(111) phase structure, but they also contained a small thimbleful of a-phase component. XRD analysis revealed that the sample annealed at 1000℃ exhibited the best crystalline quality. The growth mechanism and microstructure of the film annealed at 1000℃ was studied by MFD-XRD and HRTEM measurements. The epitaxial relationship between the film and substrate was given as γ-Al2O3(111)//MgO(111) with γ-Al2O3 [110]//MgO [110] and γ-Al2O3 [011]//MgO [011]. The average transmittances of samples before and after annealing treatment in the visible wavelength region exceeded 83%, and the optical band gap of the samples were 5.83 eV and 5.80 eV, respectively.3. The third part:On the basis of the first two parts about the preparation and characterisation of In2O3 and Al2O3, Al2xIn2-2xO3 (0.1≤x≤0.9) films were grown at different temperatures by MOCVD. During the preparation process, A1(CH3)3 and In(CH3)3 were used as the metallorganic precursors, high purity N2 was used as the carry gas, high purity O2 was used as the oxidant, MgO(100) and MgO(110) wafers were used as the substrate materials. The influence of different compositions on the structural, optical and electrical properties of Al2xIn2-2xO3 films was investigated systematically.(1) Al2xIn2-2xO3 films with different Al content (0.1≤x≤0.9) were deposited on MgO(100) substrates at 600℃, and the structural properties of the films were studied by XRD and HRTEM. The Al2xIn2-2xO3 films with x<0.3 exhibited cubic bixbyite structure with (111) single orientation. While, Al2xIn2-2xO3 films with x≥0.5 exhibited amorphous structure. For the Al2xIn2-2xO3 films with x>0.5 showed high resistance, so only the electrical properties of Al2In2-2xO3 films with x<0.4 were measured. As the Al content increased from x=0.1 to x=0.4, the Hall mobility of the Al2xln2-2xO3 films decreased from 15.2 to 1.0 cm2V-1s-1 monotonously. The carrier concentration of the films was in the range of 1.0～6.2×1019 cm-3. And the resistivity was in the range of 9.2×10-3～8.1×10-2 Ω·cm. The average transmittances of Al2xIn2-2xO3 films with different Al contents in the visible wavelength region exceeded 79%. As the Al content increased from x=0.1 to x=0.9, the optical band gap of the films increased from 3.67eV to 5.38eV.(2) Al2xIn2-2xO3 films with different Al content (0.1≤x≤0.9) were deposited on MgO(110) substrates at 600℃. As the Al content increased, the structure of Al2xIn2-2xO3 films transferred from single crystalline to polycrystalline, and finally to amorphous. The crystallization of the film quality gradually became poor. As the Al content increased from x=0.1 to x=0.4, the Hall mobility of the Al2xIn2-2xO3 films decreased from 12.0 to 1.1 cm2V-1s-1 monotonously. The carrier concentration of the films was in the range of 8.8×1018～6.8×1019 cm-3. And the resistivity was in the range of 1.0～8.3×10-2 Ω·cm. The average transmittances of Al2xIn2-2xO3 films with different Al contents in the visible wavelength region exceeded 80%. As the Al content increased from x=0.1 to x=0.9, the optical band gap of the films could be modulated from 3.65eV to 5.57eV.(3) Al2xIn2-2xO3 films with different Al content (0.1≤x≤0.9) were deposited on MgO(110) substrates at 700℃, and the structural properties and microstructure of the films were studied by XRD and HRTEM. As the Al content increased from x=0.1 to x=0.9, the structure of Al2xIn2-2xO3 films transferred from single crystalline bixbyite In2O3 structure to polycrystalline, and finally to cubic γ-Al2O3 structure. As the Al content increased, the optical band gap of the films could be modulated from 3.65eV to 5.57eV. Compared with that of the films deposited at 600℃, the modulation range of the bang gap was bigger. Furthermore, the variation of the band gap as a function of Al content presented a linear increase relationship, which was easier for the modulation of band gap.4. The last part:On the basis of the third part about the preparation and characterisation of Al2xIn2-2xO3 (0.1≤x≤0.9) films, Al1.3Ino.7O3 film with x=0.65 was chosen as the base material to introduce Stannum element. During the deposition process, Sn(C2Hs)4 was used as the Sn metallorganic precursors. Al-In-Sn-O (AITO) films were prepared on MgO(100) and MgO(110) substrates at 700℃. The influence of Sn content on the structural, optical and electrical properties of AITO films was studied.(1) AITO films were deposited on MgO(100) substrates. As the Sn content increased, the structure properties of AITO films gradually improved. When the Sn content reached 21%, the film exhibited the best crystal quality. As the Sn content increased further to 24%, the film exhibited mixcrystal structure. As the Sn content increased from 0 to 21%, the Hall mobility of the AITO films increased from 1.8 cm2V-1s-1 to 17.5 cm2V-1s-1 monotonously, the carrier concentration of the films increased from 3.9×1019 cm-3 to 3.0×1020 cm’3, and the resistivity decreased from 9.14×10-2 Ω·cm to 1.4×10-2 Ω·cm. As the Sn content increased further to 24%, the Hall mobility and carrier concentration began to decrease, while the the resistivity of the films began to increase. The average transmittances of AITO films with different Sn contents in the visible wavelength region exceeded 78%. As the Sn content increased from 0 to 24%, the optical band gap of the films decreased from 5.42eV to 4.18eV. The band gap of AITO film with Sn content of 21% is 4.45eV. The reason for the variations of the Hall mobility, carrier concentration and resistivity as a function of Sn content was analysed and discussed.(2) AITO films were prepared on MgO(110) substrates. XRD results revealed that as the Sn content increased, the structure of AITO films gradually improved, and the film with Sn content of 21% exhibited the best crystal quality. As the Sn content increased further to 24%, there was no mixcrystal structure detected. HRTEM measurement showed that the AITO film with Sn content of 21% exhibited poly crystalline structure, and the crystalline grain is arranged closely with less grain boundary elements. The Hall mobility of the AITO films increased gradually with the increase of Sn content and got the maximum of 18.5 cm2V-1s-1 at the Sn content of 21%. The corresponding carrier concentration and resistivity of the film were 2.56×1020 cm-3 and 1.32×10-3 Ω·cm, respectively. The average transmittances of AITO films with different Sn contents in the visible wavelength region exceeded 77%. The band gap of AITO film with Sn content of 21% is 4.32eV.