| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeM |
| Session: | Thin Film Synthesis and Characterization II |
| Presenter: | Dhanya S. Murali, Indian Institute of Technology Madras, India |
| Authors: | D. Murali, Indian Institute of Technology Madras, India M.K. Jain, Indian Institute of Technology Madras, India A. Subrahmanyam, Indian Institute of Technology Madras, India |
| Correspondent: | Click to Email |
Cu2O is an interesting p-type semiconductor; it has high optical absorption coefficient in the visible region and reasonably good electrical properties. It finds application in p-n junction based devices such as solar cells and high mobility p-type thin film transistors 1,4. Among p-type oxides, cuprous oxide (Cu2O) in single crystal form1 is known to have the highest hole mobility ~100 cm2 V-1s-1 at room temperature (300 K). Lee et.al.3 reported a Hall mobility of 62 cm2 V-1s- 1 for Cu2O thin films at room temperature. Sohn et. al. performed vacuum annealing of copper oxide (CuO) thin films on Si substrate in order to obtain Cu2O thin film which possesses Hall mobility of 47.5 cm2 V-1s-1 and good optical properties4.
In the present communication, we report the effect of vacuum annealing (at 623K and 700 K) on polycrystalline copper oxide thin films deposited ( at room temperature 300 K) on a borosilicate glass substrate employing reactive DC magnetron sputtering. Argon and oxygen are the sputter and reactive gases respectively. Pure (99.9%) copper is the target. Deposition pressure is 3.5x10 -3 mbar and the target power density is 1.4 Wcm-2. The films were characterized by X-ray diffraction, Hall effect (with temperature variation in the range 20 K to 300 K) and Raman spectroscopy (excitation wavelength 532 nm and in the temperature range 77 K to 700 K). Optical band gap is evaluated using UV-Vis spectrometer (400 – 1100 nm). The “as prepared” films show CuO phase. At an annealing temperature of 623K (in vacuum at 5x10 -6 mbar), transition to a mixed phase of CuO and Cu2O is observed. Further annealing at 700 K, CuO transforms completely to a cubic Cu2O phase. Sohn et.al.4 reported similar transition at 773 K (CuO prepared on Si substrate by RF sputtering). The optical direct band gap is observed at 2.06-2.51 eV. The reduction of phase CuO to Cu2O is observed to enhance the optical transmittance in the visible region4. The Hall mobility measurements showed that the vacuum annealed Cu2O thin films have high Hall mobility (51cm2 V-1s-1) at 300 K room temperature. High temperature (300 K to 700 K) Raman studies were carried out to confirm the phase by keeping the CuO sample on a hot stage in argon atmosphere, the phase change is observed at 723 K.
References
1 A. Mittiga, E. Salza, F. Sarto, M. Tucci, and R. Vasanthi, Appl. Phys. Lett.88, 163502 (2006)
2 E. Fortin and F. L. Weichman, Can. J. Phys.44, 1551 (1966).
3 Y. S. Lee, M. T. Winkler, S. Cheng Siah, R. Brandt and T. Buonassisi, Appl. Phys. Lett.98, 192115 (2011)
4 Sohn J, Song S. H, Nam D. W, Cho I. T, Cho E. S, Lee J. H and Kwon H. I, Semicond. Sci.Technol. 28, 2815005 (2013).