Yuankun Zhu

Achieving high mobility ZnO:Al at very high growth rates by dc filtered cathodic arc deposition

Achieving a high growth rate is paramount for making large-area transparent conducting oxide coatings at a low cost. Unfortunately, the quality of thin films grown by most techniques degrades as the growth rate increases. Filtered dc cathodic arc is a lesser known technique which produces a stream of highly ionized plasma, in stark contrast to the neutral atoms produced by standard sputter sources. Ions bring a large amount of potential energy to the growing surface which is in the form of heat, not momentum. By minimizing the distance from cathode to substrate, the high ion flux gives a very high effective growth temperature near the film surface without causing damage from bombardment. The high surface temperature is a direct consequence of the high growth rate and allows for high-quality crystal growth. Using this technique, 500–1300 nm thick and highly transparent ZnO : Al films were grown on glass at rates exceeding 250 nm min −1 while maintaining resistivity below 5 × 10 −4 � cm with electron mobility as high as 60 cm 2 V −1 s −1 . (Some figures in this article are in colour only in the electronic version)

Determining the nonparabolicity factor of the CdO conduction band using indium doping and the Drude theory

Due to their high intrinsic electron mobility, CdO-based materials are gaining interest as transparent conductive oxides. By creating model dielectric functions based on the Drude theory, accurate fits to the measured transmittance and reflectance of CdO and CdO : In thin films were achieved without using a frequency dependent Drude damping parameter. Difference in the model between undoped and In-doped CdO showed that the Burstein–Moss shift is not the only mechanism which improves the transparency in In-doped samples. Comparing the Drude analysis with Hall measurements revealed a nonlinear relationship between the free-electron effective mass and the carrier concentration, an effect which is caused by the nonparabolicity of the CdO conduction band. Analysis of 50 CdO : In thin films grown by pulsed filtered cathodic arc showed the nonparabolicity factor was C = (0.5 ± 0.2) eV−1 and the band-edge effective mass was (0.16 ± 0.05)me. Knowledge of the effective mass allows for optical measurements of carrier mobility, which was less than or equal to the measured Hall mobility in these films due to the large electron mean free path compared with the grain size.

Dopant-induced band filling and bandgap renormalization in CdO:In films

Published in J. Phys D: Appl. Phys. 46 (2013) 195102. http://dx.doi.org/10.1088/0022-3727/46/19/195102 Dopant-induced band filling and bandgap renormalization in CdO:In films Yuankun Zhu 1 , Rueben J. Mendelsberg 2,3 , Jiaqi Zhu 1 , Jiecai Han 1 and Andre Anders 2 Center for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150080, China Plasma Applications Group, Lawrence Berkeley National Laboratory, Berkeley, California, 94720 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, 60439 Email: zhujq@hit.edu.cn (Jiaqi Zhu) Acknowledgment Research was supported by the LDRD Program of Lawrence Berkeley National Laboratory, by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technology, of the U.S. Department of Energy under U.S. Department of Energy Contract No. DE-AC02-05CH11231. Additional support was provided by the National Natural Science Foundation of China (Grant No.51072039 and 51222205), and the Ph.D. Programs Foundation of the Ministry of Education of China (20112302110036). DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California.

Structural, optical, and electrical properties of indium doped cadmium oxide films prepared by pulsed filtered cathodic arc deposition

Indium-doped cadmium oxide (CdO:In) films were prepared on glass and sapphire substrates by pulsed filtered cathodic arc deposition (PFCAD). The effects of substrate temperature, oxygen pressure, and an MgO template layer on film properties were systematically studied. The MgO template layers significantly influence the microstructure and the electrical properties of CdO:In films, but show different effects on glass and sapphire substrates. Under optimized conditions on glass substrates, CdO:In films with thickness of about 125xa0nm showed low resistivity of 5.9xa0×xa010−5xa0Ωcm, mobility of 112xa0cm2/Vs, and transmittance over 80xa0% (including the glass substrate) from 500 to 1500xa0nm. The optical bandgap of the films was found to be in the range of 2.7 to 3.2xa0eV using both the Tauc relation and the derivative of transmittance. The observed widening of the optical bandgap with increasing carrier concentration can be described well only by considering bandgap renormalization effects along with the Burstein–Moss shift for a nonparabolic conduction band.