Preparation and properties of CuCr1 − xFexO2 thin films prepared by chemical solution deposition with two-step annealing
Introduction
Transparent conducting oxides (TCOs) have attracted much attention in recent years. They are widely used in flat panel displays, touch panels, light-emitting diodes, low-e glass, defroster glass, and solar cells [1]. In general, most of the known TCOs, such as indium-doped tin oxide and aluminum or gallium-doped zinc oxide, are n-type materials. The fabrication of a p–n junction is the most fundamental step in developing electronic devices such as transparent diodes, transistors, UV-LEDs, and photovoltaic cells [2], [3]. n-Type transparent semiconductors with conductivity as high as 103 S cm− 1 are well developed and applied in certain fields [4]. However, p-type transparent semiconductors are very difficult to fabricate due to the strong localization of the upper part of the valence band to oxide ions [5]. Kawazoe et al. [5] reported a p-type transparent semiconductor film with relatively high conductivity (about 0.39 × 10−1 S cm− 1).
Materials with the A+ 1B+ 3O2 delafossite structure, or compounds derived from the mineral CuCrO2, are quite interesting because they can be stabilized with A and B cations, with A+ 1 representing monovalent cations such as Cu and Ag, and B+ 3 representing trivalent cations such as Fe [6], Y [7], Co [8] and Cr [9], [10], [11]. The ABO2 delafossite structure can be stacked in BO2 layers made of edge-sharing MO6 octahedrons linked by planes of A+ 1 cations arranged in a triangular network. Each A+ 1 cation is linearly coordinated by two O− anions belonging to the upper and lower MO2 layers.
To date, most delafossite films have been fabricated with high vacuum-based and expensive technologies such as pulsed laser deposition (PLD) [12], sputtering [13], electron beam evaporation [14], and chemical vapor deposition [15]. But little information has been published on the chemical solution deposition (CSD) of p-type delafossite thin films [16], [17], [18], [19], [20].
The Cu ion in a delafossite structure is Cu (І); however, the typical wet chemical-derived Cu ion is Cu (ІІ), which will react with B site ions such as Al and Cr to form stable spinel-type AB2O4 [18], [21].
According to the isobaric phase diagram of the bulk Cu2O–Cr2O3–CuO ternary system reported by Jacob et al. [22], CuO and Cr2O3 favorably react to form spinel-type CuCr2O4 at 700 °C, and pure delafossite-type CuCrO2 is converted from spinel-type CuCr2O4 with residual CuO above 1000 °C. The chemical formulas are given in Formulas (1), (2):Cr2O3 + 2CuO → CuCr2O4 + CuOCuCr2O4 + CuO → 2CuCrO2 + 1/2O2.
According to Formula (2), the reduced ambient helps the formation of the CuCrO2 phase thermodynamically. Chiu et al. prepared CuCrO2:Mg thin films by chemical solution deposition with annealing in nitrogen at 700 °C [16].
For TCOs to have good conducting and optical properties, it is necessary to lower the resistivity by adding a suitable dopant and thereby increasing the concentration of carriers in the film. Moreover, the introduction of Fe may provide control of the magnetism, so such TCOs are a likely class of materials for dilute magnetic semiconductors (DMSs). DMSs have attracted a lot of interest because of their unique magnetic, magneto-optical, and magneto-electrical effects [23], [24].
In this work, the CuCrO2 and CuCrO2:Fe films were prepared by chemical solution method. Films deposited on non-alkali glass were annealed in a two-step process using forming gas and nitrogen gas to obtain pure delafossite-type CuCrO2:Fe thin films after annealing at 600 °C. The influences of Fe content on the structure and the morphological, electrical, optical, and magnetic properties of the thin films are reported.
Section snippets
Experimental
Copper acetate [Cu(CH3COO)2·H2O], chromium acetate [Cr3(OH)2(CH3COO)7], iron nitrate [Fe(NO3)3·9H2O], and ethanolamine were dissolved in 2-methoxyethanol to obtain 0.2 M dark-blue precursor solution. The precursor solution was then stirred at room temperature for 24 h to obtain a well-mixed precursor solution without unwanted precipitates.
CuCr1 − xFexO2 thin films (x = 0, 0.03, 0.05, 0.10 and 0.15) were grown on non-alkali glass substrates by chemical solution method. The films were spin coated in
XRD analysis
The two-step annealing process consisted of a forming gas annealing step at 400 °C to reduce Cu (ІІ) ion to Cu (І), followed by a nitrogen gas annealing step to form CuCrO2:Fe and improve its crystallinity. Fig. 1 presents the X-ray diffraction patterns of 15 wt.% Fe-doped of CuCrO2 thin films prepared with the two-step annealing method as a function of the sintering temperature. The peaks obviously belong to 3R-CuCrO2 (JCPDF card no. 39-0247) (0 0 6), (0 1 2), (1 0 4), (0 1 8) and (1 1 0). The
Conclusions
Fe-doped CuCrO2 wide gap thin films were prepared by chemical solution deposition with a two-step annealing method. According to the XRD results, delafossite-type CuCrO2 structures were obtained by two-step annealing at 400 °C in 10% forming gas ambient, followed by an increase to sintering temperature in nitrogen atmosphere. The optical properties of thin films decreased when temperature or Fe concentration was increased. The electrical properties of the thin films were lower at 600 °C. The
Acknowledgments
The authors wish to thank Prof. Thomas C.-K. Yang and his student Yue-Lin Yang for their kindly assistance with the measurement of atomic force microscopy and Prof. Chien-Ming Lei's recommendation for magnetic properties.
References (37)
- et al.
Discovery-based design of transparent conducting oxide films
Thin Solid Films
(2007) - et al.
Fabrication of transparent CuCrO2:Mg/ZnO p–n junctions prepared by pulsed laser deposition on glass substrate
Vacuum
(2008) - et al.
Characterization of delafossite-type CuCoO2 prepared by ion exchange
J. Alloys Compd.
(2010) - et al.
Preparation of CuAlO2 and CuCrO2 thin films by sol–gel processing
Thin Solid Films
(2009) - et al.
Preparation of transparent Cu2Y2O5 thin films by RF magnetron sputtering
Appl. Surf. Sci.
(2015) - et al.
Optical and electrical properties of p-type transparent conducting CuAlO2 thin film
Thin Solid Films
(2007) - et al.
Preparation of p-type conductive transparent CuCrO2:Mg thin films by chemical solution deposition with two-step annealing
Ceram. Int.
(2012) - et al.
Formation and characterization of p-type semiconductor CuCrO2 thin films prepared by a sol–gel method
Ceram. Int.
(2015) - et al.
Properties of copper–aluminum oxide films prepared by solution methods
Thin Solid Films
(2002) - et al.
Nanoscaled ceramic powders prepared by laser ablation
Mater. Sci. Eng. B
(2002)
Ni doped ZnO thin films for diluted magnetic semiconductor materials
Curr. Appl. Phys.
Magnetic, electrical and optical properties of p-type Fe-doped CuCrO2 semiconductor thin films
J. Alloys Compd.
Preparation of delafossite-type CuCrO2 films by sol–gel method
J. Alloys Compd.
Electron energy loss spectra from polycrystalline Cr and Cr2O3 before and after surface reduction by Ar+ bombardment
Appl. Surf. Sci.
Investigation of Fe/Al interface as a function of annealing temperature using XPS
Appl. Surf. Sci.
Analysis of XPS spectra of Fe2 + and Fe3 + ions in oxide materials
Appl. Surf. Sci.
a. Ben Salah, Metal transition doping effect on the structural and physical properties of delafossite-type oxide CuCrO2
J. Alloys Compd.
Current injection emission from a transparent p–n junction composed of p-SrCu2O2/n-ZnO
Appl. Phys. Lett.
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