In-polar InN grown by plasma-assisted molecular beam epitaxy

Gallinat, Chad S.; Koblmüller, Gregor; Brown, Jay S.; Bernardis, Sarah; Speck, James S.; Chern, Grace D.; Readinger, Eric D.; Shen, H.; Wraback, Michael

doi:10.1063/1.2234274

Cited by 172 publications

(115 citation statements)

References 22 publications

(17 reference statements)

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“…Hydrogen has also been proposed as a source of conductivity in another novel semiconductor material InN, which is actually similar in many respects to TCOs (see Section 5). In that material, there is currently intense debate over whether hydrogen can be seen as the dominant source of conductivity, whether it is present in sufficient quantities, and whether it remains dominant over native defects over the whole Fermi level range spanned in existing material [113][114][115][116][117][118][119][120][121][122]. Such considerations may be expected to apply to TCO materials as well, and further investigations in this area are still required.…”

Section: Origin Of the Bulk N-type Conductivity?mentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

224

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: Origin Of the Bulk N-type Conductivity?mentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

224

180

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“…[4][5][6] It is well known that continued InN growth decreases both the thin-film conductivity as well as the thin-film dislocation density. [1][2][3]7 Furthermore, it was shown that conductivity and dislocation densities correlate with similar power-law dependencies on the film thickness. 4,8 The density of threading dislocations scales with a power-law dependence on the InN film thickness in the range 300 nm .…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3] InN grown by molecular-beam epitaxy or metalorganic vapor phase deposition techniques is intrinsically n-conductive and the lowest intrinsic electron density reported so far was achieved using molecular-beam epitaxy (MBE) with approximately 10 17 cm -3 . 4 In addition to the intrinsic n-type conductivity an electron accumulation layer is formed on InN thin-film surfaces.…”

Section: Introductionmentioning

confidence: 99%

Optical Hall Effect in Hexagonal InN

Hofmann

Darakchieva

Ḿonemar

et al. 2008

Journal of Elec Materi

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Measurements of the optical Hall effect in naturally doped high-quality wurtzite-structure InN thin films by generalized ellipsometry reveal that both the surface and the interior (bulk) free electron densities decrease with powerlaw dependencies on the film thickness. We discover a significant deviation between the bulk electron and dislocation densities. This difference is attributed here to the existence of surface defects with activation mechanism different from bulk dislocations and identifies the possible origin of the so far persistent natural n-type conductivity in InN. We further quantify the anisotropy of the C-point effective mass.

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“…In addition, a strong electron accumulation occurs at the InN film surfaces 12,13 with a large sheet density in the low-to-mid 10 13 cm À2 range. [12][13][14][15][16][17] Consequently, detecting potential p-type conductivity in the InN bulk using conventional contact-based electrical measurements is not possible, since the surface inversion layer with high electron density conceals the region with free holes. 18 Up to date, only Mg has proven to successfully p-type dope InN, [18][19][20][21] and free holes in InN:Mg films have been experimentally identified by electrolyte capacitance-voltage, 18,22,23 thermopower, [23][24][25] 27 and infrared reflectometry 28 measurements.…”

Section: Introductionmentioning

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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In-polar InN grown by plasma-assisted molecular beam epitaxy

Cited by 172 publications

References 22 publications

Conductivity in transparent oxide semiconductors

Conductivity in transparent oxide semiconductors

Optical Hall Effect in Hexagonal InN

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

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