| Transparent conductive oxide (TCO) thin films is a kind of semiconductor material with excellent optical and electrical properties, which has been widely used in many fields of photoelectric device, such as flat panel display, solar cells, etc. The very low conductivity of p-CuAlO2 semiconductor compared to n-type TCO limits the potential applications of transparent oxide semiconductor devices for a long time. Therefore, the preparation of p-type TCO materials with excellent properties was research hotspot, and doping was an effective modification methods. In this paper, the rare earth element Eu, Nd, Y and metal elements Mg, Ni doped CuAlO2 powders were prepared by citrate sol-gel method, the ceramics were prepared by uniaxial cold pressed forming and conventional sintering. Differential scanning calorimetry, X-ray diffraction, UV-Vis spectrophotometer, four-probe method, Archimedes method were used to analysis the formation process of CuAl1-xMxO2 powders, phase structure, band gap, conductivity and density of ceramics. The main results are as follows:1). The rare earth elements Eu, Nd, Y were selected as doping elements RE and the rare earth doped CuAlO2 powders were prepared by citrate sol-gel method. The synthesis temperature of CuAl2O4 and CuAl1-xRExO2 (x=0～3%) phase is respectively 750℃ and 1000℃ by CuO, Al2O3, and RE2O3 form by means of decomposition of the dried gel at 300℃.2). During preparation of CuAlO2 powders, as calcine temperature increased, It is more easier to get the pure phase of CuAlO2, reduce the phase of CuO and promote the doping elements to dissolve into CuAlO2. But the CuAlO2 powders decomposes at 1150℃ and the suitable synthesis temperature is 1100℃. The phase structure has not any change when treating time increases from 4h to 8h. Up to 1% Eu, Nd and Y elements could dissolve into the crystal lattice and the samples doped could retain delafossite structure. When the doping content continues to increase, REAlO3 and CuO phases appears and increases.3). The average band gap width of CuAlO2 powder doped by Eu, Nd and Y is 3.52eV,3.58eV and 3.64eV respectively. When doped-Eu, Nd content increases, the width of the band gap gradually decreases to 3.46eV and 3.51eV respectively and then increases. The band gap width of doped-Y sample gradually increases to 3.78eV then decreases to 3.53eV with the doping content increased.4). The rare earth-doped sample presses at 550MPa, sinters at 1100℃ for 4h. The conductivity of ceramic samples doped about 2% by Eu and Y increases to 6.06×10-2S·cm-1 and 7.62×10-2S·cm-1 respectively, and decreases to 5.26×10-2S·cm-1 and 5.15×10-2S·cm-1 respectively when doped about 3%. The conductivity increases to 5.17×10-2·cm-1 when doped by 0.5% Nd, and then decreases with more doping. The density ratio of rare earth-doped samples first increases and then decreases. The conductivity and density ratio of pure CuAlO2 ceramic is 5.52×10-2S·cm-1 and 83.7% respectively.5). Mg and Ni are doped into CuAlO2 lattice by sol-gel. MAl2O4(M=Mg、Ni) phases of spinel structure will appears when the doping content is 5%. When the doping content increased, the width of the band gap gradually decreases from 3.54eV to 3.26eV for doped Mg and from 3.58eV to 3.37eV for doped Ni. The conductivity decreases from 4.50×10-2S·cm-1 to 0.34×10-2S·cm-1 for doped Mg and from 4.81×10-2S·cm-1 to 0.29×10-2S·cm-1 for doped Ni.6). Some research of domestic and overseas about doped-CuAlO2 was compared and analyzed. Doping could obviously improve the conductivity of thin film samples. The conductivity of Zn-doped samples prepared by magnetron sputtering method is relatively high and is 1.24×10-1S·cm-1 when the doping amount is about 0.5%. The conductivity of doped ceramic samples is higher than that of undoped samples, especially for Fe doped. Overall, the conductivity of rare earth-doped sample was higher than that of common metal-doped samples. |
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