Adulteration Study Of P-type Transparent Conducting Oxide CuAlO₂

Based upon the theory of"the chemical modulation of the valence band", CuAlO₂ thin films with delafossion structure were firstly prepared as a p-type transparent conducting oxide (TCO) by Kawazoe in 1997. CuAlO₂ thin films have attracted much attention since they were found to be p-type TCOs. However, the preparation of CuAlO₂ thin films with excellent properties always is a very difficult case. So far several growth methods have been investigated for the deposition of CuAlO₂ thin films including pulse laser deposition (PLD), magnetron sputtering, chemical vapor deposition and so on.In this paper, to prepare the CuAlO₂ thin films with excellent properties, fabrication procession of high-quality CuAlO₂ ceramics targets were explored firstly. Ceramics targets of CuAl_1-xM_xO₂(M=Mg , Ca, x=0, 0.0025, 0.005, 0.01, 0.015 and 0.02)was synthesized by heating a stoichiometric mixture of Cu₂O, Al₂O₃, MgO and CaO powder at different temperature for different time. XRD, SEM and four-probe were used to characterize crystallization microstructure and electrical properties. XRD results show that all diffraction peaks can be attributed to CuAlO₂ for un-doped CuAlO₂ ceramics targets and there is a small amount of phase of CuO for M-doped CuAlO₂ ceramics targets (M=Mg , Ca). SEM results show that the higher temperature is, the bigger crystalline grain is. Four-probe results show the electrical conductivity un-doped CuAlO₂ ceramics targets at 16 degree centigrade is about 9.87×10-3S/cm and the electrical conductivity M-doped CuAlO₂ ceramics targets (M=Mg , Ca) at 16 degree centigrade increases first and then reduces with the content of M and the maximum conductivity of Mg, Ca doped is 2.34×10^-2S/cm , 2.016×10^-2S/cm with x=0.01, respectively.In view of virtue of PLD, CuAlO₂ thin films were deposited on (00l) sapphire substrates by PLD using CuAlO₂ ceramics as targets synthesized by the conventional solid-state reaction. XRD, SEM and four-probe were used to characterize crystalline phases, microstructure and cross-section, optical properties and electrical properties of CuAlO₂ thin films. XRD results show that CuAlO₂ thin films are polycrystalline and principal diffraction peaks can be identified as diffraction peaks of CuAlO₂ . SEM results show surfaces morphology of CuAlO₂ thin films are uniform and dense and the films are tightly attached to substrates. The optical transmission spectra results show the average optical transmittance in visible region are more than 75% for the films deposited at different conditions. The results of the electrical properties indicate that substrate temperature and oxygen pressure sorely influence the conductivity of CuAlO₂ thin films. The higher substrate temperature and the lower oxygen pressure are propitious to improve the conductivity of CuAlO₂ thin films.