Papers by Author: Min Chang Jeong

Abstract: Al-doped ZnO (ZnO:Al) films for transparent electrode applications in dye-sensitized solar cells and thin film solar cells were fabricated and characterized. In order to investigate the effect of crystallinity of the ZnO:Al films to the morphology and optical properties of the etched surface, the ZnO:Al films were deposited with varying substrate temperature by rf magnetron sputtering system and then films’ surface was etched in diluted hydrochloric acid (HCl) solution. Surface morphology of the amorphous ZnO:Al film deposited at room temperature was controllable to have large surface area, but it was not appropriate for transparent electrode layers due to high electrical resistivity. However, the resistivities of the ZnO:Al films deposited at the substrate temperatures of 150 and 300 oC were as low as 1.50×10-3
cm. In addition, the surface morphologies of the films deposited at 150 and 300 oC showed larger surface area for dye-sensitized cells and crater shape for light diffusion through the films, respectively. The surface morphologies and optical properties of the etched ZnO:Al films are attributed to the crystallinity of the as-fabricated films.

Abstract: We present the ferromagnetism and magnetotransport properties in the (Ga,Mn)N epitaxial films with very low Mn concentrations grown by plasma-enhanced molecular beam epitaxy (PEMBE). The (Ga,Mn)N epitaxial films were found to exhibit ferromagnetic ordering with Curie temperature of 700 K. All the films exhibit n-type characteristics. The negative magnetoresistance was observed below 150 K, and found to gradually increase with decreasing temperature. The ferromagnetism in the (Ga,Mn)N is due to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the localized Mn moments mediated by the electron gas.