| Transparent conductive oxide (TCO) thin films with good electrical conductivity, and with the properties of high visible light transmittance, therefore was widely used in the field of optoelectronic devices, such as solar cells, flat panel display. The very low conductivity of p-CuAlO2semiconductor by comparison to the n-type TCO limited the potential applications of transparent oxide semiconductor devices. Therefore, the preparation of p-type TCO materials with excellent properties was of great significance. In this paper, pure CuAlO2powders with delafossite structure, doped powders with Cr, Fe, Mg and Ca and their ceramic bulk were prepared by the citric acid complex inorganic sol-gel, adding doped elements, pressing and sintering. Differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, UV-Vis spectrophotometer, tester of semiconductor properties were used to analysis the thermal decomposition of precursor, the composition of the sample structure, morphology, optical properties, conductivity and conductivity mechanism were studied. The main results were as follows:1). The forming temperature of CuAlO2was in between1042and1084℃by thermal analysis of dry gel. Pure CuAlO2phase could be prepared at the calcinaed condition of1100℃for2hour. Average band gap of CuAlO2powders was3.75eV. The particle size distribution was in between50and200nm and the atomic ratio of Cu:Al:O was1.18:1:2.41.2). During preparation of CuAlO2ceramic samples, as compaction pressure increased, the density of samples would improve, the resistivity would reduce and the maximum density of ceramics was4.56g·cm-3, the maximum resistivity of ceramics was37.9Ω·cm. When near room temperature range, the temperature dependence of conductivity was suitable for the Arrhenius behavior, belonged to the thermally activated conduction mechanism, the activation energy was0.288eV. CuAlO2ceramic sample was p-type semiconductor measured by the hot probe method.3). Using sol-gel doping the element of Cr, Fe, Mg and Ca into CuAlO2lattice to replace Al. The samples doped Cr and Fe elements up to7%were still of delafossite structure. However, when the samples doped Mg, Ca elementals, CuO, MgAl2O4and ases would be observed. These indicated that the elements, such as, Cr3+and Fe3+, had the same trivalent, and similar electronegativity and ionic radius as Al3+were ready to locate at the site of Al3+in CuAlO2lattice.4). The CuAlO2prowder doped Cr and Fe, the average band gap width was3.70eV and3.65eV respecrively. When doped-Mg content increased, the width of the band gap gradually decreased from3.70eV to3.11eV. The doping content of Ca was1%, lattice distortion was small due to the Burstein-Moss effect, the band gap width was3.78eV, which was larger than that of pure samples.5). The resistivity of CuAlO2ceramic samples doped Cr was larger than that of undoped samples. However, the resistivity of ceramic samples doped Fe decreased and the resistivity was14.81Ω·cm at the doping amount about7%. Doped Mg and Ca in between1%and7%, the resistivity increased gradually. The doped ceramic samples showed an Arrhenius behavior near room temperature, which indicated that conduction mechanism belonged to thermally activated behavior.6). CuAl0.99-xCrxMg0.01O2(x=1-7%) samles co-doped with Cr and Mg elements were still delafossite structure and the average band gap width was3.60eV, smaller than that of the undoped samples. However, due to the carrier concentration increase, the resisitivity reduced greatly, the minimum resistivity was16.13Ω·cm. Near room temperature, conduction mechanism was the Arrhenius thermal activation model. |
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