Title
Electrical transport and Al doping efficiency in nanoscale ZnO films prepared by atomic layer deposition
Author
Wu, Y.
Hermkens, P.M.
van de Loo, B.W.H.
Knoops, H.C.M.
Potts, S.E.
Verheijen, M.A.
Roozeboom, F.
Kessels, W.M.M.
Publication year
2013
Abstract
In this work, the structural, electrical, and optical properties as well as chemical bonding state of Al-doped ZnO films deposited by atomic layer deposition have been investigated to obtain insight into the doping and electrical transport mechanisms in the films. The range in doping levels from 0% to 16.4% Al was accomplished by tuning the ratio of ZnO and Al 2O3 ALD cycles. With X-ray photoelectron spectroscopy depth profiling and transmission electron microscopy, we could distinguish the individual ZnO and AlOx layers in the films. For films with a thickness of 40 nm, the resistivity improved from 9.8 mΩ cm for intrinsic ZnO to an optimum of 2.4 mΩ cm at 6.9 at. % Al. The binding energy of Zn 2p3/2 increased by 0.44 eV from the intrinsic ZnO to the highest Al-doped ZnO. This shift can be ascribed to an increase of the Fermi level. Ex-situ spectroscopic ellipsometry and Fourier transform infrared spectroscopy were used to measure the optical properties from which the carrier concentration and intra-grain mobility were extracted. The results showed that with increasing Al content, the grain boundary mobility increased at first due to an increased Fermi level, and then decreased mainly due to the scattering at AlOx/ZnO interfaces. For the same reasons, the doping efficiency of Al for highly Al-doped ZnO dropped monotonically with increasing Al. Furthermore, a blue shift of the optical band-gap ΔEg up to 0.48 eV was observed, consistent with the shifts of the Fermi level and the binding energy of the Zn 2p3/2 state. © 2013 AIP Publishing LLC.
Subject
Al-doped zno films
Chemical bonding state
Doping efficiency
Doping levels
Electrical transport
Electrical transport mechanisms
Grain-boundary mobility
Nanoscale ZnO
Atomic layer deposition
Binding energy
Deposition
Electric properties
Fermi level
Fourier transform infrared spectroscopy
Grain boundaries
Metallic films
Optical properties
Photoelectrons
Semiconductor doping
Spectroscopic ellipsometry
Transmission electron microscopy
X ray photoelectron spectroscopy
Zinc oxide
Aluminum
High Tech Systems & Materials
Industrial Innovation
Mechatronics, Mechanics & Materials
HOL - Holst TFT - Thin Film Technology
TS - Technical Sciences
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DOI
https://doi.org/10.1063/1.4813136
TNO identifier
476225
ISSN
0021-8979
Source
Journal of Applied Physics, 114 (114)
Document type
article