Tailoring the resonance wavelength and loss of Ga doped ZnO thin
film with high
carrier concentration
Chaoting Zhu, Jia Li, Ye Yang, Weijie Song
Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences,
Ningbo 315201 P. R. China
Email:
As a family member of ZnO based transparent conductive films (TCF), Ga-ZnO (GZO)
thin film exhibits its specific characteristics such as high carrier concentration, low
temperature fabrication and comparable optoelectrical properties. The high carrier
concentration make it possible to be a promising low-loss plasmonic material operating at
telecommunication wavelengths.
In our group, GZO thin films are deposited on glass substrates by radio frequency
magnetron sputtering. The effects of Ga
2
O
3
content in the target and substrate temperature on
the electrical, structural and optical properties of GZO films are investigated. GZO thin film
with the highest carrier concentration of 7.0 × 10
20
cm
−3
was obtained at a Ga
2
O
3
content of 5
wt% in the target under room temperature deposition. With increasing deposition temperature,
the lowest electrical resistivity of 3.8 × 10
−4
Ω·cm was acquired at a deposition temperature
of 200 °C. The values of plasmonic resonances wavelength could be changed from 1.35 to
2.39 μm by adjusting the carrier concentration. Material absorption losses in these GZO films
are 10 times lower than that of conventional Ag films at telecommunication wavelengths.
To further improve the carrier concentration as well as electrical properties, we introduce a
Zn-aided defect control technique followed by a post-rapid thermal annealing (RTA) process,
which causes a dramatic improvement in carrier concentration due to elimination of
Zn-vacancy defects. Among the samples with varied Zn thickness, 8 nm Zn/100 nm GZO thin
film exhibits the highest carrier concentration of 1.02×10
21
cm
-3
and the lowest resistivity of
4.0×10
-4
Ω·cm. Higher electronic concentration shifts the zero-crossover of the real
permittivity below 1.3 µm, which confirms the metal-like optical properties in the
near-infrared (NIR) range. Optical losses in these annealed Zn/GZO films are four times
smaller than conventional Ag films in the NIR. The average transmittances of all the annealed
GZO thin films were above 84% in the visible range. The GZO ultrathin film deposited by
this method is a promising low-loss alternative material to conventional metals for plasmonic
devices operating in the NIR.
References:
1. C. T. Zhu, J. Li, Y. Yang, P. J. Lan, J. H. Huang, Y. H. Lu, R. Q. Tan, N. Dai, W. J. Song.
Thin Solid Films 605 (2016) 95-101.
2. C. T. Zhu, J. Li, Y. Yang, P. J. Lan, J. H. Huang, Y. H. Lu, R. Q. Tan, N. Dai, W. J. Song.
Phys. Status Solidi A 212 (2015) 1713-1718.
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