Electronic structure of Al-doped ZnO transparent conductive thin films studied by x-ray absorption and emission spectroscopies
- Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China)
- Department of Physics, National Sun Yat-sen University, Kaohsiung 804, Taiwan (China)
- National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China)
- Department of Electrical and Computer Engineering, University of Waterloo, Ontario N2L 3G1 (Canada)
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
This study used O K-, Zn L{sub 3}-, Zn K-, and Al K-edges x-ray absorption near-edge structure (XANES) and O K-edge x-ray emission spectroscopy (XES) measurements to investigate the electronic structure of transparent Al-doped ZnO (AZO) thin film conductors. The samples were prepared on glass substrates at a low temperature near 77 K by using a standard RF sputtering method. High-purity Ne (5N) was used as the sputtering gas. The crystallography of AZO thin films gradually transformed from the ZnO wurtize structure to an amorphous structure during sample deposition, which suggests the suitability to grow on flexible substrates, eliminating the severe degradation due to fragmentation by repeated bending. The O K- and Zn L{sub 3}-edges XANES spectra of AZO thin films revealed a decrease in the number of both O 2p and Zn 3d unoccupied states when the pressure of Ne was increased from 5 to 100 mTorr. In contrast, Al K-edges XANES spectra showed that the number of unoccupied states of Al 3p increased in conjunction with the pressure of Ne, indicating an electron transfer from Al to O atoms, and suggesting that Al doping increases the negative effective charge of oxygen ions. XES and XANES spectra of O 2p states at the O K-edge also revealed that Al doping not only raised the conduction-band-minimum, but also increased the valence-band-maximum and the band-gap. The results indicate that the reduction in conductivity of AZO thin films is due to the generation of ionic characters, the increase in band-gap, and the decrease in density of unoccupied states of oxygen.
- OSTI ID:
- 22038774
- Journal Information:
- Journal of Applied Physics, Vol. 110, Issue 10; Other Information: (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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