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Proceedings Paper

Debye tail mobility enhancement in ZnO:Ga/ZnO structures
Author(s): David C. Look; E. R. Heller; Y. F. Yao; C. C. Yang
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Paper Abstract

A highly-Ga-doped ZnO (GZO) layer of thickness d grown by molecular-beam epitaxy on an undoped ZnO buffer layer exhibits enhanced mobility μ due to electron diffusion (about 2 nm) from the low-mobility GZO into the high-mobility ZnO. For d = 300 nm, the combined GZO/ZnO structure has Hall mobility μ = 34.2 cm2/V-s, due almost entirely to electrons in the GZO, whereas for d = 50, 25, or 5 nm, μ = 37.0, 43.4, and 64.1 cm2/V-s, respectively, due to the influence of electrons in the ZnO. This observation of an increase of μ with decrease in d is very unusual for thin films of GZO on various substrates. However, Poisson analysis and degenerate scattering theory accurately predict the measured values of μ vs d with no adjustable parameters. For the case d = 5 nm, only 9.7% of the electrons from the GZO diffuse into the ZnO, but those closest to the interface can have μ > 200 cm2/V-s, raising the overall mobility from 34 to 64 cm2/V-s. More complicated structures can produce higher percentages of electrons in the ZnO and thus even higher mobilities. For example, simulation shows that six repeated units of a 1-nm-GZO/2-nm-ZnO structure will have 43% of the electrons in the ZnO and an average mobility of 152 cm2/V-s. This structure has roughly the same conductance as that of a GZO-only layer having the same total thickness (18 nm), but a much lower free-carrier concentration and thus a much higher transmittance in the near IR. This “Debye-tail” technology allows optimization of the conductance/transmittance tradeoff for different applications of transparent conductive oxides.

Paper Details

Date Published: 15 March 2016
Proc. SPIE 9749, Oxide-based Materials and Devices VII, 974902 (15 March 2016); doi: 10.1117/12.2217683
Show Author Affiliations
David C. Look, Wright State Univ. (United States)
Wyle Labs (United States)
Air Force Research Lab. (United States)
E. R. Heller, Air Force Research Lab. (United States)
Y. F. Yao, National Taiwan Univ. (Taiwan)
C. C. Yang, National Taiwan Univ. (Taiwan)

Published in SPIE Proceedings Vol. 9749:
Oxide-based Materials and Devices VII
Ferechteh H. Teherani; David C. Look; David J. Rogers, Editor(s)

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