Semiconducting p-type MgNiO:Li epitaxial films fabricated by cosputtering method

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2013-07, Vol.31 (4)
• Main Authors: Hun Kwon, Yong, Hyun Chun, Sung, Koun Cho, Hyung
• Format: Article
• Language: English
• Subjects: ALUMINIUM OXIDES; CRYSTAL DEFECTS; DEFORMATION; DEPOSITION; DEPOSITS; DOPED MATERIALS; ELECTRIC CONDUCTIVITY; ENERGY GAP; EPITAXY; EV RANGE 01-10; LAYERS; LITHIUM; MAGNESIUM OXIDES; MAGNETRONS; MATERIALS SCIENCE; NICKEL OXIDES; RADIOWAVE RADIATION; SEMICONDUCTOR MATERIALS; THIN FILMS; X-RAY DIFFRACTION
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.4804172

Li-doped ternary MgxNi1−xO thin films were deposited on (0001) Al2O3 substrates by a radio frequency (RF) magnetron cosputtering method with MgO and NiO:Li targets. The Mg mole fraction and Li content were relatively controlled by changing RF power for the MgO target over a range of 0–300 W, while the NiO:Li target was kept at 150 W. As a result, all films were epitaxially grown on (0001) Al2O3 substrates with the relationship of [ 1 ¯ 1 ¯ 0 ]NiO | | [ 11 1 ¯ 0 ]Al2O3, [ 1 ¯ 1 2 ¯ ]NiO | | [ 2 1 ¯ 1 ¯ 0 ]Al2O3 (in-plane), and [ 1 ¯ 11 ]NiO | | [ 000 1 ¯ ]Al2O3 (out-of-plane), and showed p-type semiconducting properties. Furthermore, from x-ray diffraction patterns, the authors found that MgO was effectively mixed with NiO:Li without structural deformation due to low lattice mismatch (0.8%) between NiO and MgO. However, the excess Li contents degraded the crystallinity of the MgNiO films. The band-gap of films was continuously shifted from 3.66 eV (339 nm) to 4.15 eV (299 nm) by the RF power of the MgO target. A visible transmittance of more than 80% was exhibited at RF powers higher than 200 W. Ultimately, the electrical resistivity of p-type MgNiO films was improved from 7.5 to 673.5 Ωcm, indicating that the Li-doped MgNiO films are good candidates for transparent p-type semiconductors.