Effects of post-deposition heat treatment on the microstructure and properties of Al-doped ZnO thin films prepared by aqueous phase deposition

Pin Chuan Yao, Shih Tse Hang, Menq-Jiun Wu, Wen Tse Hsiao

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

In this study, transparent conducting aluminum-doped ZnO thin films (AZO) were deposited on glass substrates by a water-based liquid phase deposition method. The results show that by employing a two-step post-deposition heat treatment, the preferential orientation of ZnO (002) appeared as soon as the polycrystalline films were formed. Under a reducing atmosphere, the crystallinity of the films was effectively improved. Furthermore, the reducing atmosphere was also beneficial for the removal of the residual stress of the prepared films and the c-axis lattice constant was less stretched as compared to those under an inert atmosphere at identical T p. Both the atomic force micrograph and scanning electron micrograph clearly exhibited that the heat treatment induced considerable grain growth. The X-ray photoelectron spectrum revealed that the heat treatment atmosphere had little impact on the bonding state of zinc and that the reducing atmosphere was favorable for the non-stoichiometric alumina, which in turn, resulted in more oxygen vacancies and led to improvement in electrical conductivity. The ratio of chemisorbed oxygen declined substantially when applying the reducing atmosphere. Accordingly, hydrogen was helpful for the reduction of chemisorbed oxygen onto AZO films. Generally, the electrical resistivity declined linearly with T p. A minimum resistivity of 9.90 × 10 - 3 Ω•cm was obtained with a doping concentration of Al/Zn = 2.25 at.% at T p = 700 °C. The largest mean free path of the carriers was 1.2 Å, which was much smaller than the observed grain sizes of the AZO films. Accordingly, the grain boundary scattering was not the detrimental scattering mechanism. In contrast, the scattering within the grains was responsible for the low mobility. An increase in optical transparency with the heat treatment temperature was observed due to the compact and smooth topography with larger grains, among which, less porous structures were formed at elevated temperature.

Original languageEnglish
Pages (from-to)2846-2854
Number of pages9
JournalThin Solid Films
Volume520
Issue number7
DOIs
Publication statusPublished - 2012 Jan 31

Fingerprint

heat treatment
Heat treatment
atmospheres
Thin films
microstructure
Microstructure
thin films
Scattering
electrical resistivity
oxygen
scattering
Oxygen
inert atmosphere
Aluminum Oxide
Oxygen vacancies
Photoelectrons
Aluminum
Grain growth
mean free path
Transparency

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

Cite this

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title = "Effects of post-deposition heat treatment on the microstructure and properties of Al-doped ZnO thin films prepared by aqueous phase deposition",
abstract = "In this study, transparent conducting aluminum-doped ZnO thin films (AZO) were deposited on glass substrates by a water-based liquid phase deposition method. The results show that by employing a two-step post-deposition heat treatment, the preferential orientation of ZnO (002) appeared as soon as the polycrystalline films were formed. Under a reducing atmosphere, the crystallinity of the films was effectively improved. Furthermore, the reducing atmosphere was also beneficial for the removal of the residual stress of the prepared films and the c-axis lattice constant was less stretched as compared to those under an inert atmosphere at identical T p. Both the atomic force micrograph and scanning electron micrograph clearly exhibited that the heat treatment induced considerable grain growth. The X-ray photoelectron spectrum revealed that the heat treatment atmosphere had little impact on the bonding state of zinc and that the reducing atmosphere was favorable for the non-stoichiometric alumina, which in turn, resulted in more oxygen vacancies and led to improvement in electrical conductivity. The ratio of chemisorbed oxygen declined substantially when applying the reducing atmosphere. Accordingly, hydrogen was helpful for the reduction of chemisorbed oxygen onto AZO films. Generally, the electrical resistivity declined linearly with T p. A minimum resistivity of 9.90 × 10 - 3 Ω•cm was obtained with a doping concentration of Al/Zn = 2.25 at.{\%} at T p = 700 °C. The largest mean free path of the carriers was 1.2 {\AA}, which was much smaller than the observed grain sizes of the AZO films. Accordingly, the grain boundary scattering was not the detrimental scattering mechanism. In contrast, the scattering within the grains was responsible for the low mobility. An increase in optical transparency with the heat treatment temperature was observed due to the compact and smooth topography with larger grains, among which, less porous structures were formed at elevated temperature.",
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Effects of post-deposition heat treatment on the microstructure and properties of Al-doped ZnO thin films prepared by aqueous phase deposition. / Yao, Pin Chuan; Hang, Shih Tse; Wu, Menq-Jiun; Hsiao, Wen Tse.

In: Thin Solid Films, Vol. 520, No. 7, 31.01.2012, p. 2846-2854.

Research output: Contribution to journalArticle

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T1 - Effects of post-deposition heat treatment on the microstructure and properties of Al-doped ZnO thin films prepared by aqueous phase deposition

AU - Yao, Pin Chuan

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AU - Hsiao, Wen Tse

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N2 - In this study, transparent conducting aluminum-doped ZnO thin films (AZO) were deposited on glass substrates by a water-based liquid phase deposition method. The results show that by employing a two-step post-deposition heat treatment, the preferential orientation of ZnO (002) appeared as soon as the polycrystalline films were formed. Under a reducing atmosphere, the crystallinity of the films was effectively improved. Furthermore, the reducing atmosphere was also beneficial for the removal of the residual stress of the prepared films and the c-axis lattice constant was less stretched as compared to those under an inert atmosphere at identical T p. Both the atomic force micrograph and scanning electron micrograph clearly exhibited that the heat treatment induced considerable grain growth. The X-ray photoelectron spectrum revealed that the heat treatment atmosphere had little impact on the bonding state of zinc and that the reducing atmosphere was favorable for the non-stoichiometric alumina, which in turn, resulted in more oxygen vacancies and led to improvement in electrical conductivity. The ratio of chemisorbed oxygen declined substantially when applying the reducing atmosphere. Accordingly, hydrogen was helpful for the reduction of chemisorbed oxygen onto AZO films. Generally, the electrical resistivity declined linearly with T p. A minimum resistivity of 9.90 × 10 - 3 Ω•cm was obtained with a doping concentration of Al/Zn = 2.25 at.% at T p = 700 °C. The largest mean free path of the carriers was 1.2 Å, which was much smaller than the observed grain sizes of the AZO films. Accordingly, the grain boundary scattering was not the detrimental scattering mechanism. In contrast, the scattering within the grains was responsible for the low mobility. An increase in optical transparency with the heat treatment temperature was observed due to the compact and smooth topography with larger grains, among which, less porous structures were formed at elevated temperature.

AB - In this study, transparent conducting aluminum-doped ZnO thin films (AZO) were deposited on glass substrates by a water-based liquid phase deposition method. The results show that by employing a two-step post-deposition heat treatment, the preferential orientation of ZnO (002) appeared as soon as the polycrystalline films were formed. Under a reducing atmosphere, the crystallinity of the films was effectively improved. Furthermore, the reducing atmosphere was also beneficial for the removal of the residual stress of the prepared films and the c-axis lattice constant was less stretched as compared to those under an inert atmosphere at identical T p. Both the atomic force micrograph and scanning electron micrograph clearly exhibited that the heat treatment induced considerable grain growth. The X-ray photoelectron spectrum revealed that the heat treatment atmosphere had little impact on the bonding state of zinc and that the reducing atmosphere was favorable for the non-stoichiometric alumina, which in turn, resulted in more oxygen vacancies and led to improvement in electrical conductivity. The ratio of chemisorbed oxygen declined substantially when applying the reducing atmosphere. Accordingly, hydrogen was helpful for the reduction of chemisorbed oxygen onto AZO films. Generally, the electrical resistivity declined linearly with T p. A minimum resistivity of 9.90 × 10 - 3 Ω•cm was obtained with a doping concentration of Al/Zn = 2.25 at.% at T p = 700 °C. The largest mean free path of the carriers was 1.2 Å, which was much smaller than the observed grain sizes of the AZO films. Accordingly, the grain boundary scattering was not the detrimental scattering mechanism. In contrast, the scattering within the grains was responsible for the low mobility. An increase in optical transparency with the heat treatment temperature was observed due to the compact and smooth topography with larger grains, among which, less porous structures were formed at elevated temperature.

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