Tuning the properties of complex transparent conducting oxides: Role of crystal symmetry, chemical composition, and carrier generation

Medvedeva, Julia E.; Hettiarachchi, Chaminda L.

doi:10.1103/physrevb.81.125116

Cited by 88 publications

(129 citation statements)

References 75 publications

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“…These were done based on first principles DFT calculations combined with the particle swarm optimization algorithm as implemented in the CALYPSO code [36,37]. We also particularly calculated the optical absorption spectra of the compounds when doped [38][39][40]. This is an important but often neglected aspect for identifying transparent conductors.…”

Section: Methodsmentioning

confidence: 99%

Sn(II)-Containing Phosphates as Optoelectronic Materials

Zhang

et al. 2016

Chem. Mater.

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We theoretically investigate Sn(II) phosphates as optoelectronic materials using first principles calculations. We focus on known prototype materials SnnP2O5+n (n=2, 3, 4, 5) and a previously unreported compound, SnP2O6 (n=1), which we find using global optimization structure prediction. The electronic structure calculations indicate that these compounds all have large band gaps above 3.2 eV, meaning their transparency to visible light. Several of these compounds show relatively low hole effective masses (∼2-3 m0), comparable the electron masses. This suggests potential bipolar conductivity depending on doping. The dispersive valence band-edges underlying the low hole masses, originate from the anti-bonding hybridization between the Sn 5s orbitals and the phosphate groups. Analysis of structure-property relationships for the metastable structures generated during structure search shows considerable variation in combinations of band gap and carrier effective masses, implying chemical tunability of these properties. The unusual combinations of relatively high band gap, low carrier masses and high chemical stability suggests possible optoelectronic applications of these Sn(II) phosphates, including p-type transparent conductors. Related to this, calculations for doped material indicate low visible light absorption, combined with high plasma frequencies.

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Section: Methodsmentioning

confidence: 99%

Sn(II)-Containing Phosphates as Optoelectronic Materials

Zhang

et al. 2016

Chem. Mater.

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“…The sX-LDA calculated electronic band structures and partial density of states of all single-cation oxides studied in this work have been published earlier [16,17] except for Sc 2 O 3 . The bottom of the conduction band in scandium oxide is governed by the localized Sc d-states, Fig.…”

Section: A Ground State Structuresmentioning

confidence: 99%

“…Recent comparative investigations of main group metal oxides [16,17] have revealed that the fundamental differences in the electronic properties of the conventional TCO hosts (In 2 O 3 , ZnO and CdO) and the light metal oxides (Al 2 O 3 , CaO and MgO) originate from the different energy location of the cation's empty p or d states with respect to the conduction band bottom. In the former oxides, the cation p band is well above its s band which is a prerogative for a good charge transport via a uniform network formed by the spherically symmetric metal s orbitals and the neighboring oxygen p orbitals in degenerately doped materials.…”

Section: A Ground State Structuresmentioning

confidence: 99%

“…Indeed, it was found [17] that the bottom of the conduction band in InGaZnO 4 is governed by the states of all cations despite the fact that the band gaps in the corresponding basis oxides differ significantly (2.9 eV for In 2 O 3 , 3.4 eV for ZnO, and 4.9 eV for Ga 2 O 3 ). Moreover, the electronic properties in a multicomponent oxide may significantly deviate from that expected from the electronic band structures of the single-cation (basis) oxides.…”

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confidence: 99%

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Electronic properties of layered multicomponent wide-band-gap oxides: A combinatorial approach

Murat

Medvedeva

2012

Phys. Rev. B

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The structural, electronic, and optical properties of twelve multicomponent oxides with layered structure, RAMO4, where R 3+ =In or Sc; A 3+ =Al or Ga; and M 2+ =Ca, Cd, Mg, or Zn, are investigated using first-principles density functional approach. The compositional complexity of RAMO4 leads to a wide range of band gap values varying from 2.45 eV for InGaCdO4 to 6.29 eV for ScAlMgO4 as obtained from our self-consistent screened-exchange local density approximation calculations. Strikingly, despite the different band gaps in the oxide constituents, namely, 2-4 eV in CdO, In2O3, or ZnO; 5-6 eV for Ga2O3 or Sc2O3; and 7-9 eV in CaO, MgO, or Al2O3, the bottom of the conduction band in the multicomponent oxides is formed from the s-states of all cations and their neighboring oxygen p-states. We show that the hybrid nature of the conduction band in multicomponent oxides originates from the unusual five-fold atomic coordination of A 3+ and M 2+ cations which enables the interaction between the spatially-spread s-orbitals of adjacent cations via shared oxygen atoms. The effect of the local atomic coordination on the band gap, the electron effective mass, the orbital composition of the conduction band, and the expected (an)isotropic character of the electron transport in layered RAMO4 is thoroughly discussed.

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“…For example, an alternative scheme has been suggested in unconventional TCOs such as Ca 12 Al 14 O 33 , where a defect band crossing the Fermi level was suggested to be the source of conductivity in this very wide band gap material [179]. A recent first-principles investigation by Medvedeva and Hettiarachchi [180] into single-and multi-component TCOs has also identified a number of microscopic properties, such as the overlap of metal s-states with oxygen p-states, oxygen coordination, and the doping with transition metal elements, which could be important to effectively obtain high conductivity material while maintaining optical transparency.…”

Section: Overriding Explanation?mentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

225

180

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Abstract. Despite an extensive research effort for over 60 years, an understanding of the origins of conductivity in wide band-gap transparent conducting oxide (TCO) semiconductors remains elusive. While TCOs have already found widespread use in device applications requiring a transparent contact, there are currently enormous efforts to (i) increase the conductivity of existing materials, (ii) identify suitable alternatives, and (iii) attempt to gain semiconductor-engineering levels of control over their carrier density, essential for the incorporation of TCOs into a new generation of multifunctional transparent electronic devices. These efforts, however, are dependent on a microscopic identification of the defects and impurities leading to the high unintentional carrier densities present in these materials. Here, we review recent developments towards such an understanding. While oxygen vacancies are commonly assumed to be the source of the conductivity, there is increasing evidence that this is not a sufficient mechanism to explain the total measured carrier concentrations. In fact, many studies suggest that oxygen vacancies are deep, rather than shallow, donors, and their abundance in as-grown material is also debated. We discuss other potential contributions to the conductivity in TCOs, including other native defects, their complexes, and in particular hydrogen impurities. Convincing theoretical and experimental evidence is presented for the donor nature of hydrogen across a range of TCO materials, and while its stability and the presence of interstitial and substitutional species are still somewhat open questions, it is one of the leading contenders for unintentional conductivity in TCOs. We also review recent work indicating that the surfaces of TCOs can support very high carrier densities, opposite to the case of conventional semiconductors. In thin-film materials/devices and, in particular, nanostructures, the surface can have a large impact on the total conductivity in TCOs. We discuss models that attempt to explain both the bulk and surface conductivity based on features of the bulk band structure common across the TCOs, and compare these materials to other semiconductors. Finally, we briefly consider transparency in these materials, and its interplay with conductivity. Understanding this interplay, as well as the microscopic contenders for the conductivity of these materials, will prove essential to the future design and control of TCO semiconductors, and their implementation into novel multifunctional devices.

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Tuning the properties of complex transparent conducting oxides: Role of crystal symmetry, chemical composition, and carrier generation

Cited by 88 publications

References 75 publications

Sn(II)-Containing Phosphates as Optoelectronic Materials

Sn(II)-Containing Phosphates as Optoelectronic Materials

Electronic properties of layered multicomponent wide-band-gap oxides: A combinatorial approach

Conductivity in transparent oxide semiconductors

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