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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.

No MeSH data available.


Schematic illustration of the chemical bond between an oxide ion and a monovalent silver or copper ion in (a) β-AgGaO2 and (b) β-CuGaO2.
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Figure 5: Schematic illustration of the chemical bond between an oxide ion and a monovalent silver or copper ion in (a) β-AgGaO2 and (b) β-CuGaO2.

Mentions: For I–III–O2 semiconductors with a delafossite structure, materials containing monovalent copper such as α-CuAlO2, α-CuGaO2, and α-CuInO2 exist in addition to materials containing monovalent silver [56, 57]. However, wurtzite-derived I–III–O2 materials with a β-NaFeO2 structure that contain monovalent copper had not been reported before we began to study the synthesis of β-CuGaO2. Figure 5 shows a schematic illustration of formation of the chemical bond between an oxide ion and a monovalent silver or copper ion with an (n − 1)d10ns0 electronic configuration. The top of the VB is formed by the Ag 4d or Cu 3d states and the O 2p states. Both the O 2p and the Ag 4d or Cu 3d orbitals are fully occupied by electron pairs assuming that the O2−, Ag+ or Cu+ ions and the resulting antibonding level forms the highest occupied level, i.e., the Ag 4d or Cu 3d significantly contributes to the VBM of the materials [58]. Taking the higher energy of the Cu 3d atomic orbitals rather than the Ag 4d atomic orbitals into account [59], the VBM for the wurtzite-derived I–III–O2 materials containing the monovalent copper should be higher than that of the materials that contain monovalent silver. This leads to a narrower band gap for the material that contains copper rather than silver when the trivalent cation species are the same. In fact, a comparison between the delafossite α-AgGaO2 and α-CuGaO2 semiconductors indicates that the band gap of α-CuGaO2 is smaller than that of α-AgGaO2 [48, 60, 61]. Consequently, wurtzite-derived β-CuGaO2 is expected to have a band gap narrower than that of β-AgGaO2 and the energy range covered by the wurtzite and its derived oxide semiconductors will expand into the near-infrared region.


Wurtzite-derived ternary I – III – O 2 semiconductors
Schematic illustration of the chemical bond between an oxide ion and a monovalent silver or copper ion in (a) β-AgGaO2 and (b) β-CuGaO2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036475&req=5

Figure 5: Schematic illustration of the chemical bond between an oxide ion and a monovalent silver or copper ion in (a) β-AgGaO2 and (b) β-CuGaO2.
Mentions: For I–III–O2 semiconductors with a delafossite structure, materials containing monovalent copper such as α-CuAlO2, α-CuGaO2, and α-CuInO2 exist in addition to materials containing monovalent silver [56, 57]. However, wurtzite-derived I–III–O2 materials with a β-NaFeO2 structure that contain monovalent copper had not been reported before we began to study the synthesis of β-CuGaO2. Figure 5 shows a schematic illustration of formation of the chemical bond between an oxide ion and a monovalent silver or copper ion with an (n − 1)d10ns0 electronic configuration. The top of the VB is formed by the Ag 4d or Cu 3d states and the O 2p states. Both the O 2p and the Ag 4d or Cu 3d orbitals are fully occupied by electron pairs assuming that the O2−, Ag+ or Cu+ ions and the resulting antibonding level forms the highest occupied level, i.e., the Ag 4d or Cu 3d significantly contributes to the VBM of the materials [58]. Taking the higher energy of the Cu 3d atomic orbitals rather than the Ag 4d atomic orbitals into account [59], the VBM for the wurtzite-derived I–III–O2 materials containing the monovalent copper should be higher than that of the materials that contain monovalent silver. This leads to a narrower band gap for the material that contains copper rather than silver when the trivalent cation species are the same. In fact, a comparison between the delafossite α-AgGaO2 and α-CuGaO2 semiconductors indicates that the band gap of α-CuGaO2 is smaller than that of α-AgGaO2 [48, 60, 61]. Consequently, wurtzite-derived β-CuGaO2 is expected to have a band gap narrower than that of β-AgGaO2 and the energy range covered by the wurtzite and its derived oxide semiconductors will expand into the near-infrared region.

View Article: PubMed Central - PubMed

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.

No MeSH data available.