利用射頻濺鍍法於c面氧化鋁基板上成長純相CuAlO2薄膜及其特性分析

Abstract

In this thesis, we investigate the development of phase-pure CuAlO2 film. CuAlO2 films were deposited on the c-plane sapphire substrates by radio-frequency (RF) magnetron sputtering using a CuAlO2 ceramic target at different deposition temperatures. The as-deposited films were found to be amorphous regardless of the deposition temperatures. After annealing at 1050 °C in air, only the film deposited at 700 °C showed the crystalline CuAlO2 structure but with a small amount of CuAl2O4 impurity. During post-annealing, Al in the sapphire substrate reacted with the as-deposited Cu–Al–O film so the whole film contained excess of Al, leading to the formation of CuAl2O4. To suppress CuAl2O4, a layer of 100 nm Cu2O film was deposited between the Cu–Al–O film and sapphire. In the annealing process, Cu2O reacted with sapphire to form CuAlO2 so the ratio of Cu to Al of the whole film was maintained, and a phase-pure CuAlO2 film without impurity was fabricated. After the successful fabrication of phase-pure CuAlO2 film, the film was characterized, focusing on the crystal structure, electric and optical properties, and the surface morphology. In XRD, the film shows a highly preferred c-oriented structure. The electric conductivity of the phase-pure CuAlO2 thin film at room temperature is 1.01 S cm-1, which is almost two orders of magnitude better than that of the film with CuAl2O4 impurity. The p-type conduction was also confirmed by using the hot probe and Hall effect method. In the optical properties, the phase-pure CuAlO2 film is reasonably transparent in the visible region. The direct band gap fitted by the Tauc plot was found to be 3.3 eV. In the photoluminescence measurement, a near-band-edge (NBE) emission occurred at 3.27 eV was also found. The surface morphology was investigated by using FESEM and AFM. The specular surface of the as-deposited film was lost and the roughness increased after post-annealing. The surface morphology of phase-pure CuAlO2 film consists of stacked hexagonal facets with parallel edges, suggesting that the film may be grown epitaxially. Finally, we try to find out whether the film was grown epitaxially or not by using the phi-scan measurement. The detail procedures of the phi-scan measurement performed by using the Bede D3 diffraction system were reported. We use a tricky method to exceed the hardware limit of the instrument. The film was confirmed to be grown epitaxially in the phi-scan measurement. We also found that 2H-CuAlO2, the relatively rare prototype of CuAlO2, coexisted in the epitaxial films in addition to 3R-CuAlO2