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The Growth of ZnO Films by Metel-organic Chemical Vapor Deposition (MOCVD) and the Fabrication and Study of ZnO UV Detector

Author: YangXiaoTian
Tutor: DuGuoTong
School: Jilin University
Course: Microelectronics and Solid State Electronics
Keywords: ZnO thin films By MOCVD Tensile strain Photoluminescence spectra of Oxygen atmosphere. Emission energy Nitrogen atmosphere Surface roughness Ultraviolet light-emitting Luminous intensity
CLC: TN304
Type: PhD thesis
Year: 2004
Downloads: 547
Quote: 6
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Abstract


Direct band gap as a wide band gap semiconductor material ZnO Following GaN after another popular research topics of the field of photovoltaic research. The photoelectric properties less affected by defects, plays an important role in today's information age. It can be used for the production of light-emitting display devices, high-frequency filter, light emitting diodes, lasers, high-speed optical switches and other devices, has important applications in both the civilian and military fields. Currently, most of the research on ZnO concentrated on the aspects of the growth of the film material, and its growth method generally includes the following: molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), pulsed laser deposition (PLD), atomic layer epitaxy , sputtering, evaporation, etc.. In this paper, the plasma enhanced MOCVD reactor system ZnO thin films grown on c-sapphire substrate, its relevant characteristics, high-resistivity ZnO films were successfully prepared on the basis of successfully prepared ZnO-based UV detector, characteristics testing and analysis. We have conducted a study on the use of high-quality ZnO film grown by the MOCVD method in the c-Al2O3 substrate and its associated characteristics. X-ray diffraction showed columnar growth of the ZnO film as the c-direction width at half maximum of the diffraction peaks of ZnO (002) 0.28 (ZnO films, analysis shows a certain amount of tensile strain is generated in the growth process. Fluorescent light from the ZnO films at room temperature spectra, we observed high-intensity UV-emitting UV light intensity and the green luminous intensity ratio of 14: 1 was obtained by optical fluorescence spectroscopy the ZnO films bandgap of 3.31eV, indicates that the film has a high optical quality. c-Al2O3 substrate film growth under different conditions on the comparison, first, the growth temperature is optimized, results and analysis showed 5400C when the ZnO film has the best crystallization properties and optical properties. of zinc source temperature affect the growth of ZnO system and X-ray diffraction results show that: the impact of the changes in the temperature of the source of zinc lattice constant of the ZnO films is very small, and that changes in the temperature of the zinc source sample crystal internal tensile stress is small zinc source temperature at -19 (C grown ZnO film has the best crystallization properties, the results of the atomic force microscopy also shows the temperature of the source of zinc in the -19 (C grown ZnO film has a minimum surface roughness the fluorescence spectrum of the sample light ZnO thin films ultraviolet light emission energy is gradually decreased with the decrease of temperature of the zinc source and from -21 (C, the ultraviolet light emission energy begins to rise due to the epitaxial growth of the lattice mismatch among the ZnO film existence of internal tensile strain, so the changes in band gap energy with the structural characteristics of the ZnO thin film (thin film internal tensile strain) related reduction in the energy of the ultraviolet light emitting means inside of the ZnO films tensile strain reduced The analysis shows that in the zinc source temperature reaches -19 (C ~ -21 (C when the thin film growth of the internal tensile strain minimum, and the variation is very small, which proved that the change in temperature of the source of zinc is within a certain range of the growth the influence of the tensile strain of the interior of the film is very small, this with a thin film X-ray diffraction analysis results are consistent -19 (C grown sample of ultraviolet light-emitting and green light emitting intensity ratio of the highest, indicating that the best optical quality. overall sense, the temperature of the zinc source (A) -19 (C grown ZnO film has the best combination of properties. annealing as a method for improving the film quality of the common means, at high temperatures can make the chemical bond of the zinc oxide experienced a stress LT ; WP = 93 gt; release process, to produce lattice reconstruction, thereby effectively improving the quality of the film, we have been systematically studied under different conditions, the influence of the annealing on the film quality of a study the influence of annealing on the ZnO film basic vacuum annealing did not change the resistivity of ZnO thin films, and air annealing and O2 annealing increased resistivity of the films after annealing results, we can draw a deep level transition peaks in the photoluminescence spectra of ZnO films main from the deep level in the conduction band and Zn vacancy between the composite X-ray diffraction results show that annealing improves the crystal quality of the ZnO film annealing atmosphere is not introduced to the other crystal ZnO of ZnO (0 02) diffraction peak strength after annealing is increased about 5 times. oxygen annealing of the sample relative to a stronger ZnO (0 0 2) plane diffraction peak of the sample annealed in nitrogen after annealing XRD FWHM significantly smaller, minimum value of the sample annealed under oxygen. These all show The oxygen annealing respect annealing on the improvement of the quality of the ZnO thin film transistor has a greater influence of the average grain size of the ZnO film is increased after the annealing, this is mainly ZnO particles caused by the thermal annealing of the fusion process. Similarly, the sample annealed in an oxygen atmosphere has a maximum average grain size of 3. photoluminescence spectrum shows: 3.31eV near annealing oxygen atmosphere, the sample an ultraviolet light-emitting intensity of the peak is significantly increased after the annealing. 2.53eV ~ 2.34eV green emission peak intensity at the vicinity of but at the same time after the annealing was significantly enhanced, which means that a single ionized oxygen hole increase UV emitting and green light-emitting intensity ratio of the sharp decline, decreases from 14 to 4, indicate that the deterioration of the optical characteristics of the sample. emission peak intensity in the the 3.31eV near ultraviolet annealing under a nitrogen atmosphere, the sample after annealing under a nitrogen atmosphere, there is a certain enhanced But at the same time in the 2.53eV ~~ 2.34eV at the vicinity of the green emission peak intensity after annealing also significantly enhanced, also deteriorate the optical characteristics of the annealed samples. compares the two results, we found that the sample relative to the annealing under oxygen atmosphere have a higher intensity of ultraviolet light emitting peak of the sample annealed in nitrogen atmosphere, the FWHM of the ultraviolet emission of the former peak is also smaller. UV emission peak of the sample annealed in the oxygen atmosphere occurs the redshift (ultraviolet light emission energy is reduced), under nitrogen annealed samples UV peak position is substantially no change. We believe that for the samples annealed in the oxygen atmosphere, the film growth due to lattice mismatch internal tensile strain, annealing are provided sufficient thermal energy kinds of tensile stress to be released film internal strain is released, the energy will be reduced. near band edge ultraviolet light energy decreases from 3.32eV to 3.30eV sample test of an atomic force microscope display: unannealed sample surface roughness minimum reach 27nm. annealed sample has a surface roughness of 40 nm in the atmosphere of oxygen, and the surface roughness of the sample annealed in nitrogen atmosphere for 52 nm. we analyze changes in the surface morphology of the sample film after annealing is mainly due to oxidation at high temperatures zinc construction chemicals undergo a stress release process generating lattice reconstruction, so that the grain size becomes large and the surface roughness is increased. nitrogen

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