Hydrogen in InN: A ubiquitous phenomenon in molecular beam epitaxy grown material

Darakchieva, Vanya; Lorenz, K.; Barradas, N.P.; Alves, E.; Ḿonemar, B.; Schubert, M.; Franco, N.; Hsiao, Ching‐Lien; Chen, Li‐Chyong; Schaff, William J.; Tu, Li‐Wei; Yamaguchi, Tomohiro; Nanishi, Yasushi

doi:10.1063/1.3327333

Cited by 42 publications

(41 citation statements)

References 23 publications

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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

226

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

226

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%

“…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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“…Previously, H concentrations exceeding, although scaling with, the free electron concentrations in c-plane InN films have been also reported. 7,9 Another factor that may affect the incorporation of H in the near surface region is the surface roughness. The values of the rms surface roughness of all InN samples are given in Table II.…”

Section: Resultsmentioning

confidence: 99%

“…Hydrogen is one of the major sources of doping in InN. [2][3][4][5][6][7][8][9][10] Recently, it has been shown that hydrogen is ubiquitous and can be found in significant concentrations in c-plane InN films grown by molecular beam epitaxy (MBE). 2,[5][6][7]9 However, nothing is known about the unintentional incorporation of hydrogen in InN films with surface orientations different from the conventional c-plane.…”

Section: Introductionmentioning

confidence: 99%

Unintentional incorporation of hydrogen in wurtzite InN with different surface orientations

Darakchieva

Lorenz

Xie

et al. 2011

Journal of Applied Physics

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We have studied hydrogen impurities and related structural properties in state-of-the-art wurtzite InN films with polar, nonpolar, and semipolar surface orientations. The effects of thermal annealing and chemical treatment on the incorporation and stability of H are also discussed. The near-surface and bulk hydrogen concentrations in the as-grown films increase when changing the surface orientation from (0001) to (000 1) to (1 101) and to (11 20), which may be associated with a decrease in the grain size and change of the growth mode from 2D to 3D. Thermal annealing at 350 o C in N 2 leads to a reduction of H concentrations and the intrinsic levels of bulk H are found to correlate with the structural quality and defects in the annealed films.

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Hydrogen in InN: A ubiquitous phenomenon in molecular beam epitaxy grown material

Cited by 42 publications

References 23 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

Unintentional incorporation of hydrogen in wurtzite InN with different surface orientations

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