Preparetion And Properties Of P-Type Transparent Oxides Semiconductor With Delafossite Structure

Transparent oxides semiconductor (TOS), which possess both high conductivity and high transparency, were extensively used in the fields of electrodes for information displays, solar cells and electrochromic windows. However, the coexistence of high conductivity and transparency has so far been achieved only in n-type semiconductors. Lacking of p-type TOS with a fair performance has limited their applications. Obtaining a p-type TOS with both high conductivity and high transparency is urgency in scientific research. Based upon the theory named the chemical modulation of the valence band, we selected delafossite structure oxides: CuAlO₂, CuCrO₂, CuNdO₂ and AgAlO₂ as the main subject investigated. Considering issues about the present developing state of TOS thin film and the superiority of sputtering in the industrialization, the dissertation is aimed at fabricating high-quality p-type TOS thin film on quartz glass using radio frequency (rf) magnetron sputtering, the main research processes achieved have been summed up as following:1. Cu²⁺ and Fe³⁺ doped CuAlO₂ thin films were prepared by rf magnetron sputtering. It is observed that the film presents the excellent preferred (001) orientation after annealed at 1173K. The optical band gap analyses suggested that the Cu or Fe atoms occupying the Al sites of the delafossite structure provided the CuAlO₂ with an impurity energy level in the energy gap, the average transmittance of CuAl_1-xCu_xO₂ films and CuAl_1-xFe_xO₂ films are around 60～80% and 60～70% in visible light region. The band gap increase from 3.30eV to 3.73 and 3.67eV, respectively, which might be related with the Burstein–Moss effect. The highest conductivity reaches 0.0122 S cm^-1 and 0.0110 S cm^-1 for CuAl_0.94Cu_0.06O₂ film and CuAl_0.85Fe_0.15O₂ film, and the reciprocal temperature dependence of electrical conductivity agrees well with the Arrhenius relationship in the range of 300～200K for all samples, it indicates that the electrical conductivity is ascribe to thermal activation.2. CuCrO₂ thin film is reported as one of the highest conductivity in delafossite structure oxides, but the transparency is very low. CuCrO₂ films were deposited using rf magnetron sputtering, the average transmittance increase with the increase of anneal temperature. The average transmittance reaches 70% when annealed at 1223K, however, the conductivity decreased from 0.079 S cm^-1 to 0.005 S cm-1 with the increase in annealing temperature. SEM images show that the reason for conductivity decrease is mainly due to the cracking on the surface. While improved the deposition temperature, both the conductivity and transparency raised.3. N doped CuCrO₂ thin film have been prepared successful by sputtering under the mix ambience of N2O and Ar. N concentration is detected by XPS to 18.4 at.% for the film with 30% N2O specific flux, indicating that acceptor impurities N is doped into CuCrO₂ thin films indeed. The optimal film doped shows the maximal conductivity of 17.85 S cm^-1 and the maximal hole concentration of 1.38×10²⁰ cm^-3, which are decreased and increased two order of magnitude comparing to the undoped CuCrO₂ thin film, respectively. The transmittance of N doped CuCrO₂ thin film is 50～70% in the visible light range. The p-type conduction was confirmed by the positive Hall coefficient and Seebeck coefficient.4. Polycrystalline CuNdO₂ and AgAlO₂ powders were synthesized by the conventional solid-state reaction method and the cation exchange method. The absorption spectrum was detected by UV-Vis spectrophotometer. The band gap is estimated to be 3.14eV and 3.10eV for CuNdO₂ and AgAlO₂ powders, respectively, which testified these materials are candidates for TOS.