Bottom-up assembly of metallic germanium

Scappucci, Giordano; Klesse, Wolfgang M.; Yeoh, L. A.; Carter, Damien J.; Warschkow, Oliver; Marks, Nigel A.; Jaeger, David L.; Capellini, Giovanni; Simmons, M. Y.; Hamilton, A. R.

doi:10.1038/srep12948

Cited by 22 publications

(17 citation statements)

References 28 publications

(39 reference statements)

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“…have proposed a MBE based bottom-up approach to produce n -type metallic Ge layers with electrically active carrier concentrations as high as 1.9 × 10 20 cm −3 and 0.9 × 10 20 cm −3 in the bi-layer and multi-layer sample, respectively1920. The recent progress in the n -type doping in Ge is summarized in Fig.…”

Section: Resultsmentioning

confidence: 99%

Ultra-doped n-type germanium thin films for sensing in the mid-infrared

Prucnal

Liu

Voelskow

et al. 2016

Sci Rep

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A key milestone for the next generation of high-performance multifunctional microelectronic devices is the monolithic integration of high-mobility materials with Si technology. The use of Ge instead of Si as a basic material in nanoelectronics would need homogeneous p- and n-type doping with high carrier densities. Here we use ion implantation followed by rear side flash-lamp annealing (r-FLA) for the fabrication of heavily doped n-type Ge with high mobility. This approach, in contrast to conventional annealing procedures, leads to the full recrystallization of Ge films and high P activation. In this way single crystalline Ge thin films free of defects with maximum attained carrier concentrations of 2.20 ± 0.11 × 1020 cm−3 and carrier mobilities above 260 cm2/(V·s) were obtained. The obtained ultra-doped Ge films display a room-temperature plasma frequency above 1,850 cm−1, which enables to exploit the plasmonic properties of Ge for sensing in the mid-infrared spectral range.

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Section: Resultsmentioning

confidence: 99%

Ultra-doped n-type germanium thin films for sensing in the mid-infrared

Prucnal

Liu

Voelskow

et al. 2016

Sci Rep

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“…The Ge films are obtained by the molecular beam epitaxy in a bottom up approach, where nearly-identical twodimensional phosphorus doped layers are repeatedly stacked at short distances in the third, vertical dimension. Previous studies based on the anisotropic quantum interference electrical measurements, atom probe tomography, and density functional theory 23 have shown that the multi-layered doped region can be interpreted as a 3D volume of precisely defined thickness h where electrons coming from the 2D donorcontaining layers can freely move, thus realizing a 3D metallic conductor with the homogenous electron density n e .…”

Section: à3mentioning

confidence: 99%

Mapping the electromagnetic field confinement in the gap of germanium nanoantennas with plasma wavelength of 4.5 micrometers

Calandrini

Venanzi

Appugliese

et al. 2016

Applied Physics Letters

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We study plasmonic nanoantennas for molecular sensing in the mid-infrared made of heavily doped germanium, epitaxially grown with a bottom-up doping process and featuring free carrier density in excess of 1020 cm−3. The dielectric function of the 250 nm thick germanium film is determined, and bow-tie antennas are designed, fabricated, and embedded in a polymer. By using a near-field photoexpansion mapping technique at λ = 5.8 μm, we demonstrate the existence in the antenna gap of an electromagnetic energy density hotspot of diameter below 100 nm and confinement volume 105 times smaller than λ3

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“…Basic theory of solid-state solutions tells us that active dopants are those that substitute to Ge in a lattice position, while donor atoms that occupy interstitial sites or phase-separate into clusters are usually inactivated. It is well known that at high doping levels other effects take place, among them dopant-dimer formation 32 , increase of the dislocation density and clustering of dopants around crystal defects 33 . All these effects contribute to the decrease of N A /[P ].…”

Section: Growth Of Heavily Doped Filmsmentioning

confidence: 99%

Tunability of the dielectric function of heavily doped germanium thin films for mid-infrared plasmonics

et al. 2016

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Heavily-doped semiconductor films are very promising for application in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate heavily n-type doped germanium epilayers grown on different substrates, in-situ doped in the 10 17 to 10 19 cm −3 range, by infrared spectroscopy, first principle calculations, pump-probe spectroscopy and dc transport measurements to determine the relation between plasma edge and carrier density and to quantify mid-infrared plasmon losses. We demonstrate that the unscreened plasma frequency can be tuned in the 400 -4800 cm −1 range and that the average electron scattering rate, dominated by scattering with optical phonons and charged impurities, increases almost linearly with frequency. We also found weak dependence of losses and tunability on the crystal defect density, on the inactivated dopant density and on the temperature down to 10 K. In films where the plasma was optically activated by pumping in the near-infrared, we found weak but significant dependence of relaxation times on the static doping level of the film. Our results suggest that plasmon decay times in the several-picosecond range can be obtained in ntype germanium thin films grown on silicon substrates hence allowing for underdamped mid-infrared plasma oscillations at room temperature.The recent push towards applications of spectroscopy for chemical and biological sensing in the mid-infrared (mid-IR)1-8 has prompted the need for conducting thin films displaying values of the complex dielectric functionǫ(ω) = ǫ ′ (ω) + iǫ ′′ (ω) that can be tailored to meet the needs of novel electromagnetic designs exploiting the concepts of metamaterials, transformation optics and plasmonics 9 . In the design of metamaterials, where subwavelength sized conducting elements are embedded in dielectric matrices, if the values of ǫ ′ of the metal and the dielectric are of the same order, but have opposite sign, the geometric filling fractions of the metal and dielectric can be readily tuned to achieve subwavelengthresolution focusing of radiation 10 . Such requirement is met by silver for wavelengths λ around 400 nm. The same condition cannot be achieved in the IR range by using elemental metals, however, because metals possess an extremely high negative value of ǫ ′ not equaled, in

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Bottom-up assembly of metallic germanium

Cited by 22 publications

References 28 publications

Ultra-doped n-type germanium thin films for sensing in the mid-infrared

Ultra-doped n-type germanium thin films for sensing in the mid-infrared

Mapping the electromagnetic field confinement in the gap of germanium nanoantennas with plasma wavelength of 4.5 micrometers

Tunability of the dielectric function of heavily doped germanium thin films for mid-infrared plasmonics

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