불순물이 첨가된 ZnO 박막의 구조적 및 전기적 특성에 관한 연구
(A) Study on the structural and electrial properties of impurity-doped ZnO thin films
박막 ZnO ZnO박막 전기공학;
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Zinc oxide (ZnO) films were prepared from a solution containing zinc acetate by ultrasonic spray pyrolysis. Silicon wafers coated with SiO_(2), 7059 corning glasses and r-plane sapphires were used as substrates. Al, Cu, In, Pt atoms were doped into the films. The crystallinity, surface morphology and composition of the films were studied using the x-ray diffraction method (XRD), scanning electron microscopy (SEM) and Rutherford back scattering spectrometry (RBS), respectively. The influences of the zinc acetate concentration in the solution and substrate temperature on the crystallinity of the films were studied. The films on the SiO_(2)/Si substrate that were grown at the substrate temperature of 400-500℃ from the 0.03 mol/ℓ solution showed a highly (002) preferred orientation with very smooth surface. The resistivities of the films were around 10Ωcm. Vapor oxidation increased the resistivity by a factor of 10^(4). Strongly (110) oriented ZnO films were obtained in the r-plane sapphires at a substrate temperature of 300℃. The resistivity was increased to above 3 x 10^(6)Ωcm with Cu doping and vapor oxidation. Transparent conductive films such as ITO, TO:F have been widely studied for their applications as transparent electrodes, window materials in display, solar cells and various optoelectronic devices. However, the ITO has problems such as expensive raw materials and low thermal stability which causes increasing in resistivity by post processes. Especially, the unstability of ITO in a hydrogen plasma makes it difficult to be compatible with amorphous silicon. In the case of TO:F films, the process temperature is too high to use glasses as substrates. Thus recently, many studies have been concentrated on replacing ITO or TO:F with ZnO:Al films. In this study, we modified conventional ultrasonic spray system to lower the processing temperature for preparing ZnO:Al films. The optimal deposition conditions were obtained by studying on the structural and electrical properties of films as a function of Al concentration and substrate temperature. The concentration of zinc acetate in the methanol was 0.03 and 0.06 mol/ℓ, which produced the ZnO:Al films with a deposition rate of 50-100 A˚/min. Al was doped by incoporating AlCl in zinc acetate solution. Slide glasses were used as substrates. The substrate temperature varied from 180℃ to 260℃. Rapid increase in grain size of ZnO:Al films were observed by doping Al. Doped Al raised the concentration of electron in the limit of 1 x 10^(20)cm^(-3). The mobility of the ZnO films doped with 3.0 wt% Al increased to 35 ㎠/Vsec. The optical transmittance at 550 nm was more than 80% which is high enough to be practical application. The optical band gap was around 3.3 eV. There were no evidence in blue shift. We prepared ZnO:Al films (resistivity:5 x 10^(-3)Ωcm, transmittance : 85 % at 550 nm) successfully with laboratory-made apparatus. The optimal substrate temperature and Al concentration for the transparent conductive films were 230℃ and 1.4-3.0 wt%. Zinc oxide (ZnO) films deposited on indium (In) films were post-annealed in a rapid thermal annealing (RTA) system. The ZnO/In films were RTA-treated in air or a vacuum ambient. The crystallographic properties and surface morphologies of the films were studied before and after the RTA by XRD and SEM, respectively. The resistivity variation of the films with RTA temperature and time was measured by the 4-point probe method. Auger electron spectroscopy (AES) was carried out to figure out the redistribution of indium atoms in the ZnO films. The resistivity of the ZnO/In films decreased to 2 x 10^(-3)Ωcm by diffusion of the In. The In diffusion into the ZnO films roughened the surface of the ZnO films. The results of depth profile by AES showed a hump of In atoms around ZnO/In interface after the RTA at 800℃. The effects of temperature, time and ambient during the RTA on the structural and electrical properties of the ZnO/In films were discussed. Pt-doped zinc oxide (ZnO:Pt) films were deposited by ultrasonic spray pyrolysis. Resistivity variation with Pt concentration was measured. The Pt distribution in ZnO:Pt films was studied through AES. The ZnO:Pt films were annealed in the ambient of air, water vapor and ozone, respectively. The variation in crystallographic properties and surface morphologies with respect to the annealing condition was observed by XRD and SEM. The resistivity variation of the films with the annealing condition was measured. Finally, atomic force microscopy (AFM) measurements were carried out to study the effects of the annealing on the roughness of ZnO:Pt films.