Debye tail mobility enhancement in ZnO:Ga/ZnO structures

David C. Look; E. R. Heller; Y. F. Yao; C. C. Yang

doi:10.1117/12.2217683

15 March 2016 Debye tail mobility enhancement in ZnO:Ga/ZnO structures

David C. Look, E. R. Heller, Y. F. Yao, C. C. Yang

Proceedings Volume 9749, Oxide-based Materials and Devices VII; 974902 (2016) https://doi.org/10.1117/12.2217683
Event: SPIE OPTO, 2016, San Francisco, California, United States

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.

Citation Download Citation

David C. Look, E. R. Heller, Y. F. Yao, and C. C. Yang "Debye tail mobility enhancement in ZnO:Ga/ZnO structures", Proc. SPIE 9749, Oxide-based Materials and Devices VII, 974902 (15 March 2016); https://doi.org/10.1117/12.2217683

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KEYWORDS

Zinc oxide

Interfaces

Epitaxy

Infrared technology

Electromagnetic scattering theory

Thin films

Transmittance

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