| ZnO is a direct wide-band gap semiconductor with wurtzite crystal structural. Its wide band gap is 3.37eV at room temperature and exciton binding energy is as large as 60meV, which is much higher than that of ZnSe and GaN. It is an ideal semiconductor material in blue light range and the research in ZnO is named as "low temperature blue project ". Furthermore , it has more potential applications in optoelectronic devides such as gas sensor, photodetectors, surface acoustic wave devices, electroluminescence devices , light emitting diodes and solar cells. ZnO films have been grown by many methods, such as magnetron sputtering, molecular beam epitaxy (MBE), pulsed laser deposition (PLD), spray pyrolysis and metal organic chemical vapor deposition (MOCVD). In this paper, High quality ZnO films were obtained from the c-Al2O3 substrates by MOCVD, which has the right of independence knowledge of ourself. Our works are as follows:(1) High-quality ZnO films were deposited on c-Al2O3 substrates by MOCVD using Diethylzinc (DEZn) and oxygen. The flow rate of high-purity Ar gas (99.999%) , which was applied as the carried gas of DEZn, was 1.25×10-4mol/min and that of O2 gas was 6.0×10-3mol/min.The working pressure of the chamber was kept at 480Pa. Then, ZnO thin films were deposited at the temperature of 580℃.The AFM 3D surface images showed that the surface of ZnO thin films was relatively flat and dense. The resistivity of ZnO thin films was 0.209Ω·cm, and the mobility is 8cm2/V·S, the carrier concentration was –3.73×10-8/cm3. Those indicated that the ZnO thin films was low resistivity and n-type.The XRD spectra of ZnO thin films showed that the (0002) peak was at 2θ=34.48°and the full width at half maximum (FWHM) was 0.184°, According to the Bragg equation, we could obtain the mean grain size (D) was 47.12nm. Raman scattering was performed at room temperature showed that only the A1(LO) and E2(high) modes were observed, which indicated the ZnO thin films had the wurtzite structure. It was found there was a strong ultraviolet near-band-edge emission(NBE) and a week deep level emission(DLE) in the PL spectra at room temperature. The NBE peak was located at 3.28eV, and the intensity ratio of the NBE to DLE was 40:1, which suggested that the ZnO thin film had a high optical quality.(2) Another, the flow rate of DEZn was 6.25×10-5mol/min, the total pressure of the reactor was kept a constant of 180Pa, All the ZnO thin films were at substrate temperature of 610℃ at different flow rate of oxygen, which were 3×10-3mol/min, 8×10-3mol/min and 2×10-2mol/min. Under those conditions, we obtained sample A,B,and C. From the XRD spectrum of the ZnO thin films, the (0002) peaks for sample a, b, and c were at 2θ=34.56°,34.50°, and 34.48°, respectively. But a weak peak at 2θ=47.52°was detected for sample c, which was (102) diffraction peak of ZnO films. With the increase of the flow rate of oxygen, the intensity of (002) diffraction peak decreased for three samples, and the FWHM broadened from 0.20°, 0.26° to 0.30°.This indicated that the crystalline quality degraded from single-oriented crystal to polycrystalline with the increase of the oxygen content. From the AFM 3D images of ZnO films, We could see that the films were deposited in a column-by-column growth process and the mean grain size became smaller when the flow rate of oxygen increased, and the root-mean-square roughness decreased which was 47.16nm, 23.59nm, and 9.04nm for sample a, b and c, respectively. From the PL spectra of ZnO films, with increasing the flow rate of oxygen, the DLE was weakened. It indicated that the DLE might originate from the oxygen vacancies (Vo), whose concentration decreased under oxygen-enriched condition. It could be concluded that the UV emission was more dependent on the stoichiometry than the microstructural quality of the films. (3) Finally, the ZnO films were obtained under those conditions: the flow rate of O2 was kept at 180sccm, the pressure of the reactor was kept at 210Pa, The flow rat...
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