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Wurtzite-derived ternary I – III – O 2 semiconductors

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ABSTRACT

Ternary zincblende-derived I–III–VI2 chalcogenide and II–IV–V2 pnictide semiconductors have been widely studied and some have been put to practical use. In contrast to the extensive research on these semiconductors, previous studies into ternary I–III–O2 oxide semiconductors with a wurtzite-derived β-NaFeO2 structure are limited. Wurtzite-derived β-LiGaO2 and β-AgGaO2 form alloys with ZnO and the band gap of ZnO can be controlled to include the visible and ultraviolet regions. β-CuGaO2, which has a direct band gap of 1.47 eV, has been proposed for use as a light absorber in thin film solar cells. These ternary oxides may thus allow new applications for oxide semiconductors. However, information about wurtzite-derived ternary I–III–O2 semiconductors is still limited. In this paper we review previous studies on β-LiGaO2, β-AgGaO2 and β-CuGaO2 to determine guiding principles for the development of wurtzite-derived I–III–O2 semiconductors.

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Phase variation in the (1 − x)ZnO–x(LiGaO2)1/2 pseudo-binary system together with the selected area electron diffraction (SAED) of ZnO, Zn2LiGaO4 and β-LiGaO2. The SAED patterns were recorded for the 〈11〉 zone axis of the hexagonal wurtzite structure for ZnO and Zn2LiGaO4 and the 〈01〉 zone axis of orthorhombic β-LiGaO2. The arrows in the SAED of Zn2LiGaO4 indicate superlattice diffractions.
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Figure 2: Phase variation in the (1 − x)ZnO–x(LiGaO2)1/2 pseudo-binary system together with the selected area electron diffraction (SAED) of ZnO, Zn2LiGaO4 and β-LiGaO2. The SAED patterns were recorded for the 〈11〉 zone axis of the hexagonal wurtzite structure for ZnO and Zn2LiGaO4 and the 〈01〉 zone axis of orthorhombic β-LiGaO2. The arrows in the SAED of Zn2LiGaO4 indicate superlattice diffractions.

Mentions: β-LiGaO2, which possesses a band gap of 5.6 eV, is the best-known wurtzite-derived ternary oxide semiconductor. High purity single crystals several inches long can be grown by the Czochralski method and they can be cleaved to form faces that are lattice-matched to ZnO and GaN [30–32]. It has been studied as a substrate material for ZnO and GaN and as an insulating layer for epitaxially grown ZnO-based multilayers [33]. β-LiGaO2 has also been studied as a material for use in nonlinear optics [34–36]. We reported on the band gap engineering of ZnO, which included the UV region, upon alloying with β-LiGaO2 [37, 38]. Figure 2 shows the phase variation in the pseudo-binary alloy system of x(LiGaO2)1/2–(1 − x)ZnO. This was determined by the solid state reaction between ZnO and β-LiGaO2 at 1100 °C. β-LiGaO2 dissolves in ZnO to form wurtzite-related alloys up to x = 0.5. This alloy formation range is much wider than that of the MgO–ZnO system, where the equilibrium solubility limit of MgO in ZnO at 550°–1200 °C is x ∼ 0.15 in xMgO–(1 − x)ZnO [10, 11]. Detailed characterization of the phases reveled that a quaternary wurtzite-derived Zn2LiGaO4 phase is present at x = 0.5 [39]. The Zn2LiGaO4 is clearly distinguished from the wurtzite phase (the space group of P63mc) and the β-LiGaO2 phase (the space group of Pna21) because clear superlattice diffractions appear in its powder x-ray diffraction (XRD) and selected area electron diffraction (SAED; figure 2). Its Raman spectrum was also completely different from that of wurtzite and β-LiGaO2 phases. The cations of Zn2+, Li+ and Ga3+ in Zn2LiGaO4 may have an ordered arrangement similar to the Li2BeSiO4 crystal (the space group of P1n1) [40]; however, the crystal structure has not been determined yet because of its incommensurate nature. Powder XRD, SAED and Raman spectra also elucidated that the phase that appeared in the x(LiGaO2)1/2–(1 − x)ZnO pseudo-binary system varied upon increasing the alloying level as the wurtzite-type phase for 0≤x < 0.2, the Zn2LiGaO4-type phase for 0.2 ≤ x ≤ 0.5 and the β-LiGaO2-type phase for 0.8 ≤ x ≤ 1. The intermediate composition of 0.5 < x < 0.8 is a mixture of the Zn2LiGaO4 and β-LiGaO2 phases.


Wurtzite-derived ternary I – III – O 2 semiconductors
Phase variation in the (1 − x)ZnO–x(LiGaO2)1/2 pseudo-binary system together with the selected area electron diffraction (SAED) of ZnO, Zn2LiGaO4 and β-LiGaO2. The SAED patterns were recorded for the 〈11〉 zone axis of the hexagonal wurtzite structure for ZnO and Zn2LiGaO4 and the 〈01〉 zone axis of orthorhombic β-LiGaO2. The arrows in the SAED of Zn2LiGaO4 indicate superlattice diffractions.
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Related In: Results  -  Collection

License 1 - License 2
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Figure 2: Phase variation in the (1 − x)ZnO–x(LiGaO2)1/2 pseudo-binary system together with the selected area electron diffraction (SAED) of ZnO, Zn2LiGaO4 and β-LiGaO2. The SAED patterns were recorded for the 〈11〉 zone axis of the hexagonal wurtzite structure for ZnO and Zn2LiGaO4 and the 〈01〉 zone axis of orthorhombic β-LiGaO2. The arrows in the SAED of Zn2LiGaO4 indicate superlattice diffractions.
Mentions: β-LiGaO2, which possesses a band gap of 5.6 eV, is the best-known wurtzite-derived ternary oxide semiconductor. High purity single crystals several inches long can be grown by the Czochralski method and they can be cleaved to form faces that are lattice-matched to ZnO and GaN [30–32]. It has been studied as a substrate material for ZnO and GaN and as an insulating layer for epitaxially grown ZnO-based multilayers [33]. β-LiGaO2 has also been studied as a material for use in nonlinear optics [34–36]. We reported on the band gap engineering of ZnO, which included the UV region, upon alloying with β-LiGaO2 [37, 38]. Figure 2 shows the phase variation in the pseudo-binary alloy system of x(LiGaO2)1/2–(1 − x)ZnO. This was determined by the solid state reaction between ZnO and β-LiGaO2 at 1100 °C. β-LiGaO2 dissolves in ZnO to form wurtzite-related alloys up to x = 0.5. This alloy formation range is much wider than that of the MgO–ZnO system, where the equilibrium solubility limit of MgO in ZnO at 550°–1200 °C is x ∼ 0.15 in xMgO–(1 − x)ZnO [10, 11]. Detailed characterization of the phases reveled that a quaternary wurtzite-derived Zn2LiGaO4 phase is present at x = 0.5 [39]. The Zn2LiGaO4 is clearly distinguished from the wurtzite phase (the space group of P63mc) and the β-LiGaO2 phase (the space group of Pna21) because clear superlattice diffractions appear in its powder x-ray diffraction (XRD) and selected area electron diffraction (SAED; figure 2). Its Raman spectrum was also completely different from that of wurtzite and β-LiGaO2 phases. The cations of Zn2+, Li+ and Ga3+ in Zn2LiGaO4 may have an ordered arrangement similar to the Li2BeSiO4 crystal (the space group of P1n1) [40]; however, the crystal structure has not been determined yet because of its incommensurate nature. Powder XRD, SAED and Raman spectra also elucidated that the phase that appeared in the x(LiGaO2)1/2–(1 − x)ZnO pseudo-binary system varied upon increasing the alloying level as the wurtzite-type phase for 0≤x < 0.2, the Zn2LiGaO4-type phase for 0.2 ≤ x ≤ 0.5 and the β-LiGaO2-type phase for 0.8 ≤ x ≤ 1. The intermediate composition of 0.5 < x < 0.8 is a mixture of the Zn2LiGaO4 and β-LiGaO2 phases.

View Article: PubMed Central - PubMed

ABSTRACT

Ternary zincblende-derived I&ndash;III&ndash;VI2 chalcogenide and II&ndash;IV&ndash;V2 pnictide semiconductors have been widely studied and some have been put to practical use. In contrast to the extensive research on these semiconductors, previous studies into ternary I&ndash;III&ndash;O2 oxide semiconductors with a wurtzite-derived &beta;-NaFeO2 structure are limited. Wurtzite-derived &beta;-LiGaO2 and &beta;-AgGaO2 form alloys with ZnO and the band gap of ZnO can be controlled to include the visible and ultraviolet regions. &beta;-CuGaO2, which has a direct band gap of 1.47 eV, has been proposed for use as a light absorber in thin film solar cells. These ternary oxides may thus allow new applications for oxide semiconductors. However, information about wurtzite-derived ternary I&ndash;III&ndash;O2 semiconductors is still limited. In this paper we review previous studies on &beta;-LiGaO2, &beta;-AgGaO2 and &beta;-CuGaO2 to determine guiding principles for the development of wurtzite-derived I&ndash;III&ndash;O2 semiconductors.

No MeSH data available.


Related in: MedlinePlus