| Recently, since the semiconductor materials have unique properties and widelyapplications, it attracted more attention all over the world, and obtained greatdevelopment. InGaZnO (IGZO) is a kind of transparent oxide semiconductor, with ntype conductivity. It gradually drew the attentions of many scientists due to highcarrier mobility, better stability, and relatively simple fabrication processes, etc. Inperiodic table, In, Ga, Zn and other metal cations have the electronic structure:(n-1)d10ns0(n≥5). The conduction band maximum (CBM) were consisted ofunoccupied state in ns-orbital of metal elements for transparent amorphous oxidesemiconductor (TAOS). The s-orbital of cation performed a spherical symmetry, withlarge radius, so that the overlap among the s-orbital forms of the conductive path, andthis will do good to the transportation of electrons. Although many scientists fromdomestic and abroad investigated in the relative theoretical and experimental analysis,still, there are some questions not clear, needs to be solved. There are many methodsto prepare in the IGZO thin films, such as pulsed laser deposition (PLD), plasmaenhanced chemical vapor deposition (PECVD), magnetron sputtering, sol-gel and etc.In the present research, the PLD method was preformed.In this thesis, the research was based on the first principle calculation of IGZO,while the theory and method in the fabrication of IGZO ceramic targets and thin filmsacted as a clue. We did a relatively systematic theoretical analysis and experimentalexaminations. The contents and results of this thesis are as followed:(1) Based on the first principle calculation of ideal ZnO, the band structure,density of state and electron density were calculated out, and by means of introduceoxygen vacancy, we evaluated the effect on the electronic structure of ZnO. TheInGaZnO4in different model was calculated, we analyzed the advantages andcharacters that IGZO should have.The plane wave pseudo potential method was applied in the electron structurecalculation of ideal ZnO and ZnO with oxygen vacancy. We use thePerdew-Burke-Ernzerhof exchange correlation functional (PBE) approach utilizingthe generalized gradient approximation (GGA) scheme. It indicates that ideal ZnO is akind of mix bonds metal oxide, with stronger electrovalent bond and weaker covalentbond. ZnO is a semiconductor with direct bandgap and wide forbidden band. Theideal ZnO was evaluated a bandgap of0.805eV. Because of overrating thecontribution of Zn3d state, the correlation between Zn3d state and O2p state, thetheoretical value of bandgap is lower than the experimental one. Furthermore, webuilt a model of ZnO with oxygen vacancy. The existence of oxygen vacancy makesthe interaction between Zn and O increase, which will induce the Zn3d state and O2p state shifts into lower energy in the valence band, while the Zn4s state shift to lowerenergy too, but the change is relatively small. This will make the bandgap increase.The direct band changed into indirect band, and finally the oxygen vacancy forms thedeep donor state.We built two different single crystalline (sc-) InGaZnO4,line alternated modeland atom alternated model. In describing the relationship between valence state andcore state, we utilized pseudopotential method. The valence electron of In, Ga, Zn andO is4d105s25p1,3d104s24p1,3d104s2and2s22p4, respectively, while the other orbitalelectrons were treated as core electrons. Sc-InGaZnO4is a direct bandgapsemiconductor, and the CBM is manly contributed by s-orbit of metal ionic, especiallyfor the In-s orbit. The Ga and ZnO randomly arrange will not seriously affect thetransportation of charges in the conduction band. We also use the virtual crystalapproximation (VCA) method to calculate the electron structure of sc-InGaZnO4, andthe results have certain rationality.(2) The molecular ratio of In2O3, Ga2O3and ZnO powders were tuned, theIGZO targets with different chemical stoichiometric were prepared by means of solidstate reaction. We did phase analysis, photoluminescence and Raman spectrumdiagnosis to make sure the targets have good quality.The shrinkage in diameter of product IGZO target increased with the In2O3content in the starting material increased. The large shrinkage in diameter shows thewell-reacted process and lower amount of porosity. The X-ray diffraction (XRD) wereutilized to measure the samples, and it indicates that all of the ceramic targets almostdon't contain the starting phase, such as In2O3, Ga2O3and ZnO. That means theprocess of solid state reaction was thorough. The T1target,(Ga2O3)0.1(In2O3)0.1(ZnO)0.8, has InGaZn4O7, InGaZn5O8and InGaZn2O5phase,which was attributed to phase separation and the loss of each elements in hightemperature, etc. With the increase of In2O3content and decrease of ZnO content, themain phase changed from InGaZn2O5phase into rhombohedral InGaZnO4. Whenx≥0.6, the phase can't be recognize by the present JCPDS cards database. Insuccession, Raman spectrum result shows that we can nearly observe the E2H-E2Lvibration mode, which should be obvious in bulk ZnO, also can't find the symbolpeak at about436cm-1 which should be related to Raman active. There were onlyGa-O, In-O and Zn-O vibration mode we could observe. With the increasing In2O3content, while the In2O3content is the main starting material, the further increase willnot affect the vibration mode any more. It indicates that the In2O3will maintainprevious internal structure. The photoluminescence (PL) properties of each target wasexcited by the He-Cd laser, with the wavelength of325nm, the board luminescenceband in350～900nm was the only observation, which is centered at614～639nm. The PL intensity became weak while the content of In2O3increase, and the centerwavelength altered may be attributed to band structure change due oxygen vacancy,but the luminescence mechanism need further investigating.(3) The PLD technique was applied in IGZO thin film preparation. Throughtuning the deposited parameters (e.g. substrate temperature, oxygen partial pressureand etc.), the thin film with different chemical stoichiometric were obtained. Thethickness, crystal structure, surface morphology, proportion of each element, opticaland electrical properties were performed by step profiler, X-ray diffraction (XRD),atomic force microscopy (AFM), Hall-effect measurement and X-ray photoelectronSpectroscopy (XPS), and etc, respectively. The optimized technical parameters wereacquired by means of results evaluation.Using target T1,(Ga2O3)0.1(In2O3)0.1(ZnO)0.8, we produced a series of IGZO thinfilms at the oxygen partial pressure of0.5～44.0Pa under room temperature. ThroughXRD examination, it was confirmed that all the films were amorphous. AFMobservation results indicate that surface root mean square (RMS) roughness valueincreased with oxygen pressure. Although the RMS changes rapidly at lowerdeposition pressure and seems to be saturated at higher deposition pressure. It indicatefrom transmittance spectrum that a number of oxygen vacancies or metallicinterstitials might occupy the bottom of conduction band, leading to a decreasedbandgap. The carrier concentration for the films with the composition of(In2O3)0.1(Ga2O3)0.1(ZnO)0.4deposited at1.0Pa oxygen partial pressure is5.0×1019cm-3, which is almost same as that for our films deposited at0.5Pa oxygen partialpressure being4.3×1019cm-3. Therefore the present XPS results indicated that the In,Ga, Zn elements exist in their oxidized states on the surface of the film, and thenumber of metallic interstitials are negligible in the films. The situation is quitesimilar for the IGZO film fabricated using T8target,(Ga2O3)0.1(In2O3)0.1(ZnO)0.8.We acquired good electronic features at an oxygen pressure of10.0Pa, especially forthe maximum carrier mobility of28.6cm2/(V·s), is higher than the relative literature.The quality is better than our previous work, which contributed to high Zn contentfilms. Controlling In content could sharply increase the carrier concentration andmobility of IGZO thin films. Oxygen vacancies could play an important role indetermining the electrical properties ofthe films.T1target was adopted to grow IGZO film, and oxygen pressure maintained at5.0Pa, while the substrate temperature altered from room temperature (RT) to800°C.The film grown at substrate temperature of200°C has amorphous structure. With thetemperature increased, species could gain higher energy and finally shifted to properposition of crystal site. In visible spectrum range, the transmittance could achieve at90%. In van der Paw configuration, the hall-effect examination shows that theresistivity dropped from3.96×10-3Ω·cm to0.148Ω·cm, when the temperature increased from RT to400°C, furthermore, the carrier concentration and mobility haveaugmentation to some extent. This could be attributed to crystal quality optimization,while the grain size increase will reduce the gain boundary, in order to minimize thescattering and capture mechanism. So the substrate temperature could affect thephysical properties of IGZO thin film.We performed three aspects of research, theoretical calculation on IGZO material,target preparation and thin film fabrication, in order to explore the investigationmethods on different subject. The optimized condition in target preparation and thinfilm fabrication will not only be utilized in daily life and production, but also benefitthe thin film transistor fabrication, even in flat panel display and flexiable display,with short and long term interest.
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