| Zinc oxide (ZnO) is a new type of Group Ⅱ-Ⅵ wide band gap semiconductor material, its band gap is 3.37eV and exciton binding energy is 60meV at room temperature. Incorporated the rare earth metal yttrium (Y) into ZnO substrate can widen the material bandgap, improve the light transmittance, decrease the resistivity and enhance the ultraviolet radiation of the film material. Both in home and abroad, the research on YZO film material started early, while the progress is very slow. At present, YZO thin film is still in the laboratory research stage, reports on its business applications has not been reported yet, showing that the structure and optoelectronic properties of YZO films can not meet the needs of practical application. Thus, to find the best conditions for film preparation and to further optimize the properties of the films, will make their applications to be of great significance in the field of solar photovoltaic device and thin film transistor, etc.For Y doped ZnO materials, we have studied two related materials in this paper, namely:Y-doped ZnO (YZO) and yttrium indium (In, Indium) co-doped ZnO (YIZO).1.YIZO transparent conductive thin film.In this paper, we used the R.F. magnetron sputtering method to prepare YZO transparent conductive films on soda lime glass substrates at room temperature. By changing the sputtering time, sputtering power, sputtering pressure and other preparation conditions, the effects of different growth conditions on film structure, morphology, optical and electrical properties were studied. The main contents and conclusions are as follows:(1) The effect of film thickness (sputtering time) on YZO film structure, morphology and optoelectronic properties. The film thickness was 0.98μm, 1.70μm, 2.04μm and 2.52μm, corresponding to sputtering time 30min,40min,50min and 60min, respectively. Through the testing and data analysis on XRD, AFM, UV-visible spectrophotometry and Hall-effect of YZO thin films, we found out that, all films are hexagonal wurtzite structure. With the increasing film thickness increases, the grain size increases; in the visible region, the average film transmittance of YZO thin films was over 80%; The optical bandgap decreases from 3.270eV to 3.225eV; the thin-film resistors first decreased and then increased, reaching the lowest resistivity of 8.13× 10-3Ω·cm as film thickness reaches 1.70μm(2) The effect of sputtering power on YZO film structure and optoelectronic properties. Sputtering power was set as 80W,100W,120W and 140W, respectively. Through the testing and data analysis on XRD, AFM, UV-visible spectrophotometry and Hall-effect of YZO thin films, we found out that, all films are hexagonal wurtzite structure. With the increasing sputtering power, the grain size first increases and then decreases; the band gap increases, which can be explained by Burstein-Moss effect; the film resistance first decreases and then increases, reaching the minimum resistivity of 9.01 ×10-4Ω·cm when the sputtering power was 100W.(3) The effect of sputtering pressure on YZO film structure and optoelectronic properties. Sputtering pressure was set as 1.0 Pa,1.4Pa and 1.8Pa, respectively. Through the testing and data analysis on XRD, AFM, UV-visible spectrophotometry and Hall-effect of YZO thin films, we found out that, all films are hexagonal wurtzite structure. With the increasing sputtering pressure, the FWHM of YZO thin film diffraction peak increases, corresponding to the decreases of grain size, indicates the film crystallization quality deterioration; the film bandgap increases slightly, which can be explained by Burstein-Moss effect; a significant increase was seen in film resistivity, reaching the lowest resistivity of 1.503 × 10-3Ω·cm when the sputtering pressure was 1.0Pa.2. YIZO transparent conductive thin film and TFT.(1) We prepared YIZO transparent conductive thin films through R.F. magnetron sputtering method and investigated the structure, morphology and optical characteristics of YIZO thin film with different film thickness. The research found out that, all the YIZO films prepared at room temperature showed an amorphous structure, the visible region average transmittance of all the films was over 83%. The variation of thickness has little effect on film band gap. The band gap of all the YIZO films is about 4.18eV, which stay almost unchanged with the increasing film thickness.(2) On the basis of the film characteristics study, we used the P-type silicon as the gate electrode, YIZO thin film as active layer and the aluminum medal as source and drain electrodes to prepare the bottom gate-top contact structured YIZO thin film transistor (YIZO TFT). The influence of different active layer thickness on the output and the transfer characteristics of the device were also studied.(3) YIZO thin film transistors are n-channel depletion mode device and all the samples behaved good pinch-off characteristics. With the increasing YIZO active layer thickness, the threshold voltage (Vth) of the device is gradually drift towards the negative voltage direction, the filed effect mobility (μFE) and on/off current ratio (Ion/off) were rapidly reduced, while the subthreshold swing (S.S.) increases, indicated the degraded performance of the device. As a result, we obtained an Ion/off of over 105, an subthreshold swing of 2.20 V/decade, a threshold voltage of -1.0V and a saturation mobility of 0.57 cm2/V·s at the YIZO TFT with the active layer thickness of 20nm. |
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