Spectroscopic Understanding of Structural and Electrical Property Variations in Dopant-Free ZnO Films

doi:10.1016/j.jmst.2016.10.009

Abstract

Abstract:

Physical property variation in dopant-free ZnO films was investigated. Film annealing under various environments (O₂, in-Air, N₂ and vacuum) resulted in better crystallinity than in the as-grown film. In particular, the film annealed under the N₂ environment showed better crystallinity and electrical properties than films annealed in other environments. Based on spectroscopic analysis, we found a correlation between physical (structural, electrical) and chemical properties: The crystallinity of ZnO films is closely related to Zn-O bonding, whereas carrier concentration is associated with V_O (oxygen vacancy).

Key words: ZnO films, Annealing, Oxygen vacancies, Environmental stability

Kim Hyegyeong, Kim JiWoong, Lee Dooyong, Lee Won-Jae, Bae Jong-Seong, Lee Jaekwang, Park Sungkyun. Spectroscopic Understanding of Structural and Electrical Property Variations in Dopant-Free ZnO Films[J]. J. Mater. Sci. Technol., 2017, 33(6): 523-526.

Figures/Tables 7

Fig. 1. (a) XRD profile of the as-grown and post-annealed ZnO films grown on Al2O3(0001) at room temperature. The vertical dotted line indicates the reference ZnO(002) peak position (2θ = 34.42°). The inset shows the full range of XRD pattern of the films. (b) ω-rocking curves of the ZnO films grown on Al2O3(0001) at room temperature. The vertical dotted line indicates the half of the reference ZnO(002) peak position.

Table 1 As-grown and post-annealing environment-dependent structural properties of ZnO films

Annealing environment	2θ₍₀₀₂₎ (°)	FWHM₍₀₀₂₎ (°)	FWHM of ω-Rocking (°)	Stress (GPa)
Vacuum	34.39	0.25	1.16	-0.46
N₂	34.36	0.22	0.84	-0.74
In-Air	34.45	0.25	1.14	0.34
O₂	34.40	0.23	0.98	-0.32
As-grown	34.11	0.25	2.08	-3.85

Fig. 2. Post-annealing environment-dependent (a) carrier concentration and (b) conductivity of ZnO films grown on Al2O3(0001) at room temperature.

Table 2 Post-annealing environment-dependent electrical properties of ZnO films

Annealing environment	Concentration (cm^-3)	Mobility (cm²/(V s))	Conductivity (1/(Ω cm))
Vacuum	-1.37 × 10¹⁷	1.39	3.05 × 10^-2
N₂	-9.11 × 10¹⁸	15.10	22.00
In-Air	-3.13 × 10¹⁸	7.87	3.94
O₂	-2.17 × 10¹⁶	0.32	3.12 × 10^-4

Fig. 3. Core-level XPS spectra of O 1s of as-grown and post-annealed ZnO films grown on Al2O3(0001). The vertical dotted lines indicate the reference of O 1s binding energy associated with loosely bound oxygen (532.40 eV), VO (531.25 eV) and Zn-O (530.15 eV)[21-24].

Table 3 Deconvoluted peak area ratio of O 1s spectra of as-grown and post-annealed ZnO films

Annealing environment	Binding energy
Annealing environment	Loosely bound O₂ (532.05 ± 0.18) eV	V_O (531.13 ± 0.13) eV	Zn-O (530.19 ± 0.30) eV
Vacuum	44.59%	16.35%	39.06%
N₂	36.42%	19.93%	43.65%
In-Air	41.99%	18.56%	39.45%
O₂	48.50%	10.99%	40.51%
As-grown	50.23%	11.67%	38.10%

Fig. 4. (a) Correlation between FWHM of ω-rocking and the fraction of ZnO bonding and (b) correlation between electron concentration and the fraction of VO.

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