Model for the thickness dependence of electron concentration in InN films

Cimalla, V.; Lebedev, V.; Morales, F. M.; Goldhahn, R.; Ambacher, O.

doi:10.1063/1.2364666

Cited by 58 publications

(45 citation statements)

References 20 publications

(20 reference statements)

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“…Clearly, oxide interfaces offer potential for the realisation of a variety of novel physical phenomena and conductivities that differ drastically to those in the bulk of the material. In addition to these "designer" interface 2DEGs, we note here that, in the similar material InN, dislocations that are generated at the InN/substrate (or buffer layer) interface have been reported to be a source of n-type conductivity, causing an unintentional increase in electron density approaching the interface [120,[152][153][154]. Given the propensity for donor-like defects and impurities in TCOs, it seems plausible that a similar effect could occur at a latticemismatched TCO/substrate interface.…”

Section: Surface Conductivitymentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

222

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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Section: Surface Conductivitymentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

222

180

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“…2 and Table I). It has been argued in the literature that either dislocations 63,64 or H and O impurities, 16,17,65 are most likely the sources of the unintentional n-type conductivity in as-grown InN. However, usually the edge type dislocations have been considered when no correlation between free electron concentration and the dislocation densities is reported.…”

Section: Microstructurementioning

confidence: 99%

Effect of Mg doping on the structural and free-charge carrier properties of InN films

Xie¹,

Sédrine²,

Schöche³

et al. 2014

Journal of Applied Physics

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We present a comprehensive study of free-charge carrier and structural properties of two sets of InN films grown by molecular beam epitaxy and systematically doped with Mg from 1.0 Â 10 18 cm À3 to 3.9 Â 10 21 cm À3 . The free electron and hole concentration, mobility, and plasmon broadening parameters are determined by infrared spectroscopic ellipsometry. The lattice parameters, microstructure, and surface morphology are determined by high-resolution X-ray diffraction and atomic force microscopy. Consistent results on the free-charge carrier type are found in the two sets of InN films and it is inferred that p-type conductivity could be achieved for 1.0 Â 10 18 cm À3 Շ [Mg] Շ 9.0 Â 10 19 cm À3 . The systematic change of free-charge carrier properties with Mg concentration is discussed in relation to the evolution of extended defect density and growth mode. A comparison between the structural characteristics and free electron concentrations in the films provides insights in the role of extended and point defects for the n-type conductivity in InN. It further allows to suggest pathways for achieving compensated InN material with relatively high electron mobility and low defect densities. The critical values of Mg concentration for which polarity inversion and formation of zinc-blende InN occurred are determined. Finally, the effect of Mg doping on the lattice parameters is established and different contributions to the strain in the films are discussed. V C 2014 AIP Publishing LLC.

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“…There is evidence that dislocations act as donors and may indeed act as junction shunts in these materials as well, providing a plausible explanation for why the depletion region fails to fully isolate the p-type bulk from the n-type surface layer [17,27,[49][50][51][52][53][54][55][56][57].…”

Section: Baars Et Al Use a Parallel Conduction Model In Which The Obmentioning

confidence: 99%

Hole transport and photoluminescence in Mg-doped InN

Miller

Ager

Smith

et al. 2010

Journal of Applied Physics

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Hole conductivity and photoluminescence were studied in Mg-doped InN films grown by molecular beam epitaxy. Because surface electron accumulation interferes with carrier type determination by electrical measurements, the nature of the majority carriers in the bulk of the films was determined using thermopower measurements. Mg concentrations in a "window" from ca. 3 × 10 17 to 1 × 10 19 cm −3 produce hole-conducting, p-type films as evidenced by a positive Seebeck coefficient. This conclusion is supported by electrolyte-based capacitance voltage measurements and by changes in the overall mobility observed by Hall effect, both of which are consistent with a change from surface accumulation on an n-type film to surface inversion on a p-type film. The observed Seebeck coefficients are understood in terms of a parallel conduction model with contributions from surface and bulk regions. In partially compensated films with Mg concentrations below the window region, two peaks are observed in photoluminescence at 672 meV and at 603 meV. They are attributed to band-to-band and band-to-acceptor transitions, respectively, and an acceptor binding energy of ∼70 meV is deduced. In hole-conducting films with Mg concentrations in the window region, no photoluminescence is observed; this is attributed to electron trapping by deep states which are empty for Fermi levels close to the valence band edge. * Corresponding author: JWAger@lbl.gov

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Model for the thickness dependence of electron concentration in InN films

Cited by 58 publications

References 20 publications

Conductivity in transparent oxide semiconductors

Conductivity in transparent oxide semiconductors

Effect of Mg doping on the structural and free-charge carrier properties of InN films

Hole transport and photoluminescence in Mg-doped InN

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