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4 Feb 2008

Volume 92, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 053301 (2008); http://dx.doi.org/10.1063/1.2838457 (3 pages)

Michael S. Arnold, Gregory J. McGraw, Stephen R. Forrest, and Richard R. Lunt
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Proposal of mechanics of liquid crystals and development of liquid crystalline microactuators

Shigeomi Chono and Tomohiro Tsuji

Appl. Phys. Lett. 92, 051905 (2008); http://dx.doi.org/10.1063/1.2840673 (3 pages) | Cited 4 times

Online Publication Date: 5 February 2008

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We propose a research field “mechanics of liquid crystals,” in which liquid crystals are studied from a mechanical viewpoint. The unsteady behaviors of a liquid crystal between parallel plates under an electric field are investigated. The imposition of the electric field on the liquid crystal induces flows, whose profile and magnitude strongly depend on the twist angle of the director at the plates. A visualization experiment confirms the generation of flows. The mechanism of such generation can be explained by considering that the rotation of molecules generated by the imposition of the electric field induces a local velocity gradient.
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83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)

Tunable energy transfer efficiency based on the composite of mixed CdSe quantum dots and elastomeric film

C. W. Chen, C. H. Wang, Y. F. Chen, C. W. Lai, and P. T. Chou

Appl. Phys. Lett. 92, 051906 (2008); http://dx.doi.org/10.1063/1.2841047 (3 pages) | Cited 4 times

Online Publication Date: 5 February 2008

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We demonstrate a facile and general approach to investigate the dependence of energy transfer on the separation distance between proximal mixed-size quantum dots. Without varying the mixed concentrations, the tunable energy transfer efficiency is achieved based on the composite of mixed quantum dots and elastomeric film by utilizing the inherent nature of the flexibility of elastomeric film. To demonstrate our working principle, the composite of mixed-size CdSe quantum dots and poly-dimethylsiloxane has been studied. The results clearly show that the energy transfer process between proximal quantum dots follows the Förster resonance energy transfer, in which the dependence of the transfer efficiency E as a function of the donor-acceptor distance R obeys E = 1/[1+(R/R0)6].
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78.67.Hc Quantum dots
78.66.Qn Polymers; organic compounds
78.55.Et II-VI semiconductors
78.55.Kz Solid organic materials

In situ observation of gas reemission and blister rupture during helium implantation in silicon

Klaus Wittmaack

Appl. Phys. Lett. 92, 051907 (2008); http://dx.doi.org/10.1063/1.2839601 (3 pages) | Cited 3 times

Online Publication Date: 5 February 2008

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Gas phase ionization mass spectrometry is shown to provide means for exploring the processes that control the retention of 10 keV He+ implanted in Si at 45°. Blistering, observed in situ, was preceded by a long period of bombardment (70% of the critical fluence for blistering) during which implanted He was released at a rather high rate ( ∼ 33% of the incident He flux). Assisted by the stress due to the growing bubbles, bombardment induced detrapping allows a large fraction of the implanted He atoms to migrate to the nearby surface and escape into vacuum.
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61.72.U- Doping and impurity implantation
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Localized and free exciton spin relaxation dynamics in GaInNAs/GaAs quantum well

S. L. Lu, L. F. Bian, M. Uesugi, H. Nosho, A. Tackeuchi, and Z. C. Niu

Appl. Phys. Lett. 92, 051908 (2008); http://dx.doi.org/10.1063/1.2841041 (3 pages) | Cited 2 times

Online Publication Date: 6 February 2008

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We have investigated the exciton spin relaxation in a GaInNAs/GaAs quantum well. The recombination from free and localized excitons is resolved on the basis of an analysis of the photoluminescence characteristics. The free exciton spin relaxation time is measured to be 192 ps at 10 K, while the localized exciton spin relaxation time is one order of magnitude longer than that of the free exciton. The dependence of the free exciton spin relaxation time on the temperature above 50 K suggests that both the D’yakonov–Perel’ and the Elliot–Yafet effects dominate the spin relaxation process. The temperature independence below 50 K is considered to be due to the spin exchange interaction. The ultralong spin relaxation time of the localized excitons is explained to be due to the influence of nonradiative deep centers.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Defect reduction by epitaxial lateral overgrowth of nanorods in ZnO/(0001) sapphire films

D. Cherns and Y. Sun

Appl. Phys. Lett. 92, 051909 (2008); http://dx.doi.org/10.1063/1.2841707 (3 pages) | Cited 5 times

Online Publication Date: 7 February 2008

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It is shown that epitaxial ZnO/(0001) sapphire films grown by pulsed laser deposition have defect-free Zn-polar nanorods protruding from a continuous O-polar underlayer containing high densities of threading dislocations (TDs). By continuing the ZnO growth hydrothermally, the nanorods grew laterally over the O-polar layer. TDs in the underlayer were thereby blocked and only formed in the overlayer when nanorods coalesced. This epitaxial lateral overgrowth produced continuous Zn-polar films with TD densities reduced to 1×109/cm2 from 7×1010/cm2 in the underlayer. It is noted that the same growth mode can be achieved in GaN/(0001) sapphire films.
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81.15.Fg Pulsed laser ablation deposition
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Catalytic effect of mixed Zr–Fe additives on the hydrogen desorption kinetics of MgH2

Nicola Bazzanella, Riccardo Checchetto, and Antonio Miotello

Appl. Phys. Lett. 92, 051910 (2008); http://dx.doi.org/10.1063/1.2840180 (3 pages) | Cited 5 times

Online Publication Date: 7 February 2008

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Mg films containing Fe–Zr mixed additives were prepared by rf sputtering and their hydrogen sorption kinetic was studied by Sievert technique. We observed that mixed Fe–Zr additives improve the H2 desorption kinetics better than singly Fe or Zr. X-ray diffraction analysis evidences that mixed additives optimize the Fe distribution that forms smaller clusters than in Mg sample with single Fe catalyst. The presence of mixed additives, with Fe having larger diffusivity than Zr, contributes to maintain the atomic Zr dispersion in the Mg matrix, thus, favoring the presence of a greater number of nucleation sites for MgH2 to Mg transformation.
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68.43.Nr Desorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Blue-light emission from GaN/Al0.5Ga0.5N quantum dots

T. Huault, J. Brault, F. Natali, B. Damilano, D. Lefebvre, L. Nguyen, M. Leroux, and J. Massies

Appl. Phys. Lett. 92, 051911 (2008); http://dx.doi.org/10.1063/1.2841825 (3 pages) | Cited 12 times

Online Publication Date: 7 February 2008

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The growth by molecular beam epitaxy and the optical properties of GaN/Al0.5Ga0.5N quantum dots on (0001) sapphire substrates are reported. The quantum dots are spontaneously formed via a two dimensional to three dimensional transition upon growth interruption. Photoluminescence over the blue range (435–470 nm) is obtained at room temperature by varying the GaN nominal thickness. A weak temperature dependence of the integrated photoluminescence intensity between low temperature and room temperature is observed indicating strong carrier localization in the quantum dots.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Anomalous two-photon generation of excitons in CuCl pellets

J. I. Jang, M. A. Anderson, J. B. Ketterson, and R. P. H. Chang

Appl. Phys. Lett. 92, 051912 (2008); http://dx.doi.org/10.1063/1.2841043 (3 pages) | Cited 3 times

Online Publication Date: 7 February 2008

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We report on an anomalous excitation of excitonic matter in pressed CuCl pellets. In these random materials, we find that excitons are initially created for an excitation energy in the range of 1892–2843 meV, which is far below the bandgap of this semiconductor. The excitation-power dependence from the population dynamics of excitonic matter strongly indicates an unusual two-photon generation of ground-state excitons. Considering this off-resonance effect, excitons are probably generated from a continuum of impurity-induced levels excited by two-photon pumping.
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71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Broad forbidden bands in parallel-coupled locally resonant ultrasonic metamaterials

Y. Cheng, J. Y. Xu, and X. J. Liu

Appl. Phys. Lett. 92, 051913 (2008); http://dx.doi.org/10.1063/1.2839401 (3 pages) | Cited 12 times

Online Publication Date: 8 February 2008

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The authors demonstrate that a class of ultrasonic metamaterial, which is composed of subwavelength resonant units built up by parallel-coupled Helmholtz resonators with identical resonant frequency, possesses broad locally resonant forbidden bands. The bandwidths are strongly dependent on the number of resonators in each unit. The broadening of bands is ascribed to the change of effective acoustic impendence. The coupling effects on the wave vector and negative dynamic modulus are discussed. Numerical simulations by finite element method further confirm the theoretical results.
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62.65.+k Acoustical properties of solids
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Mechanical stress impact on thin Pd1−xFex film thermodynamic properties

Stefan Wagner and Astrid Pundt

Appl. Phys. Lett. 92, 051914 (2008); http://dx.doi.org/10.1063/1.2841636 (3 pages) | Cited 8 times

Online Publication Date: 8 February 2008

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Thermodynamic properties of thin films deviate strongly from those of bulk. The deviations are reported to originate from microstructure and from mechanical stress, whereas the contribution of both is unknown in particular. Focussing on the mechanical stress contribution and by using Pd1−xFex–H as a model system, it is shown that mechanical stress strongly changes phase transition pressures. The measured loading pressures shift up to 400 mbars in contrast to 18 mbars for bulk. These shifts relate to the film bonding to the substrate and can be affected by film detachment.
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68.60.Bs Mechanical and acoustical properties
65.40.G- Other thermodynamical quantities
64.70.kd Metals and alloys
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Ohmic conduction of sub-10 nm P-doped silicon nanowires at cryogenic temperatures

F. J. Rueß, A. P. Micolich, W. Pok, K. E. J. Goh, A. R. Hamilton, and M. Y. Simmons

Appl. Phys. Lett. 92, 052101 (2008); http://dx.doi.org/10.1063/1.2840182 (3 pages) | Cited 2 times

Online Publication Date: 4 February 2008

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We investigate the conduction properties of an embedded, highly phosphorus-doped nanowire with a width of 8 nm lithographically defined by scanning tunneling microscope based patterning of a hydrogen-terminated Si(100):H surface. Four terminal I-V measurements show that ohmic conduction is maintained within the investigated temperature range from 35 K down to 1.3 K. A prominent resistance increase is observed below ∼ 4 K which is attributed to a crossover into the strong localization regime. The low temperature conductance follows a one-dimensional variable range hopping model accompanied by positive magnetoresistance which dominates over weak localization effects at low temperature.
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73.63.Nm Quantum wires
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Ee Mobility edges; hopping transport
73.21.Hb Quantum wires

Experimental evidence of ballistic transport in cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field-effect transistors

K. H. Cho, K. H. Yeo, Y. Y. Yeoh, S. D. Suk, M. Li, J. M. Lee, M.-S. Kim, D.-W. Kim, D. Park, B. H. Hong, Y. C. Jung, and S. W. Hwang

Appl. Phys. Lett. 92, 052102 (2008); http://dx.doi.org/10.1063/1.2840187 (3 pages) | Cited 19 times

Online Publication Date: 4 February 2008

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We have investigated the electrical characteristics of cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field effect-transistors with 4 nm radius and the gate length ranging from 22 to 408 nm. We observed strong transconductance overshoot in the linear source-drain bias regime in the devices with channel length shorter than 46 nm. The mean free path estimated from the slope of the zero-field one dimensional ballistic resistance measured as a function of device length was almost the same as this length.
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85.30.Tv Field effect devices

Comparison of electron and hole charge-discharge dynamics in germanium nanocrystal flash memories

Imran B. Akca, Aykutlu Dâna, Atilla Aydinli, and Rasit Turan

Appl. Phys. Lett. 92, 052103 (2008); http://dx.doi.org/10.1063/1.2835455 (3 pages) | Cited 7 times

Online Publication Date: 4 February 2008

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Electron and hole charge and discharge dynamics are studied on plasma enhanced chemical vapor deposition grown metal-oxide-silicon germanium nanocrystal flash memory devices. Electron and hole charge and discharge currents are observed to differ significantly and depend on annealing conditions chosen for the formation of nanocrystals. At low annealing temperatures, holes are seen to charge slower but to escape faster than electrons. They discharge slower than electrons when annealing temperatures are raised. The results suggest that discharge currents are dominated by the interface layer acting as a quantum well for holes and by direct tunneling for elec-trons.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices
85.40.Sz Deposition technology
85.35.-p Nanoelectronic devices

Negative differential conductance in two-dimensional electron grids

W. Pan, S. K. Lyo, J. L. Reno, J. A. Simmons, D. Li, and S. R. J. Brueck

Appl. Phys. Lett. 92, 052104 (2008); http://dx.doi.org/10.1063/1.2840996 (3 pages) | Cited 7 times

Online Publication Date: 5 February 2008

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Negative differential conductance has been observed in grid-shaped surface superlattices, realized in a high mobility two-dimensional electron system. The current-voltage characteristics vary with the modulation strength, indicating that the two-dimensional electronic transport properties can be manipulated in a controllable way. Theoretical modeling yields reasonable agreement with the experimental data.
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68.65.Cd Superlattices

Photoinduced insulator-to-metal transition in ZnO/Mg0.15Zn0.85O heterostructures

A. Tsukazaki, A. Ohtomo, M. Nakano, and M. Kawasaki

Appl. Phys. Lett. 92, 052105 (2008); http://dx.doi.org/10.1063/1.2841044 (3 pages) | Cited 5 times

Online Publication Date: 6 February 2008

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We report on the persistent photoconductivity accompanied with a steep insulator-to-metal transition at low temperatures in ZnO/Mg0.15Zn0.85O heterostructures. The photoexcited electrons were confined in the ZnO adjacent to the Mg0.15Zn0.85O to form a two-dimensional electron gas (2DEG). The electron density was controlled either by the power or number of ultraviolet laser pulses (266 nm wavelength) irradiated to the sample. The 2DEG exhibits Shubnikov-de Haas oscillation in magnetoresistance, whose oscillation periods coincide with the electron density evaluated by Hall effect measurements.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.40.+w Photoconduction and photovoltaic effects
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.82.Fk Semiconductors

Stability of p-type conductivity in nitrogen-doped ZnO thin film

Z. Y. Xiao, Y. C. Liu, R. Mu, D. X. Zhao, and J. Y. Zhang

Appl. Phys. Lett. 92, 052106 (2008); http://dx.doi.org/10.1063/1.2838330 (3 pages) | Cited 26 times

Online Publication Date: 6 February 2008

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The behavior of p-type conductivity in nitrogen-doped ZnO prepared by thermal oxidation of zinc oxynitride thin film was investigated. The sample exhibited a stable p-type characteristic in the darkness over a 1 yr period after deposition. However, when the p-type sample was irradiated by 2.72 eV photons, it underwent a classic-mixed conductivity transition from p type to n type. An anomalously thermal equilibrium process was observed. It took 24 h for the persisted n type photoconductivity to fade away in the dark and transit back to original p type. A local potential fluctuation model was used to explain the transient electrical behavior.
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73.61.Ga II-VI semiconductors
72.60.+g Mixed conductivity and conductivity transitions
73.50.Pz Photoconduction and photovoltaic effects

Effect of rubbed polyimide layer on the field-effect mobility in pentacene thin-film transistors

Seok-Ju Kang, Yong-Young Noh, Kang-Jun Baeg, Jieun Ghim, Jeong-Ho Park, Dong-Yu Kim, Jong Soo Kim, Jong Hwan Park, and Kilwon Cho

Appl. Phys. Lett. 92, 052107 (2008); http://dx.doi.org/10.1063/1.2830694 (3 pages) | Cited 14 times

Online Publication Date: 7 February 2008

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We investigated preferentially oriented pentacene grains on rubbed polyimide (PI) layers under various conditions, such as substrate temperature and cumulative rubbing number. In case of pentacene thin films deposited on rubbed PI at room temperature (RT), compared to unrubbed, the field-effect mobilities were improved by two- to threefold in contrast to the cases of elevated temperature. From the results of crystalline in-plane orientation and thin-film versus bulk-phase ratio, we proposed that pentacence crystalline orientation on a rubbed PI layer could be more favorable at RT, whereas the heating energy might weaken the interaction energy between pentacene molecules and aligned PI layer.
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85.30.Tv Field effect devices

The effects of the ZnTe capping layer thickness on the optical and electronic properties in CdTe/ZnTe quantum dots

H. S. Lee, H. L. Park, and T. W. Kim

Appl. Phys. Lett. 92, 052108 (2008); http://dx.doi.org/10.1063/1.2841711 (3 pages) | Cited 8 times

Online Publication Date: 8 February 2008

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Photoluminescence spectra showed that the excitonic peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band (E1-HH1) in the CdTe/ZnTe quantum dots (QDs) was shifted to a higher energy with increasing thickness of the ZnTe cap layer. The intensity of the excitonic peak related to the E1-HH1 transition for the CdTe/ZnTe QDs increased with increasing thickness of the ZnTe cap layer. The activation energy of the electrons confined in the CdTe/ZnTe QDs increased with increasing thickness of the ZnTe cap layer.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
73.21.La Quantum dots

Thermally stable amorphous (AlMoNbSiTaTiVZr)50N50 nitride film as diffusion barrier in copper metallization

Ming-Hung Tsai, Chun-Wen Wang, Chia-Han Lai, Jien-Wei Yeh, and Jon-Yiew Gan

Appl. Phys. Lett. 92, 052109 (2008); http://dx.doi.org/10.1063/1.2841810 (3 pages) | Cited 19 times

Online Publication Date: 8 February 2008

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Results on copper metallization diffusion barriers using high-entropy alloy (HEA) nitride are reported. The HEA nitride (AlMoNbSiTaTiVZr)50N50 is amorphous in the as-deposited state and remains its noncrystallinity up to a high temperature of 850 °C. To evaluate its diffusion barrier characteristics, Cu/(AlMoNbSiTaTiVZr)50N50/Si test structures were prepared and annealed under 750–900 °C for 30 min. The results show that the current nitride prevents the reaction between Cu and Si before its failure at 900 °C. The outstanding barrier performance and high thermal stability of amorphous structure are suggested to originate from multiprincipal-element effects.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Suppression of the critical current of a balanced superconducting quantum interference device

Antti Kemppinen, Antti J. Manninen, Mikko Möttönen, Juha J. Vartiainen, Joonas T. Peltonen, and Jukka P. Pekola

Appl. Phys. Lett. 92, 052110 (2008); http://dx.doi.org/10.1063/1.2842413 (3 pages) | Cited 4 times

Online Publication Date: 8 February 2008

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We present an experimental study of the magnetic flux dependence of the critical current of a balanced superconducting quantum interference device (SQUID) with three Josephson junctions in parallel. Unlike for ordinary direct current (dc) SQUIDs, the suppression of the critical current does not depend on the exact parameters of the Josephson junctions. The suppression is essentially limited only by the inductances of the SQUID loops. We demonstrate a critical current suppression ratio of higher than 300 in a balanced SQUID with a maximum critical current 30 nA.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
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Modification of the spin state in Sm0.52Sr0.48MnO3 by external magnetic field

P. Sarkar and P. Mandal

Appl. Phys. Lett. 92, 052501 (2008); http://dx.doi.org/10.1063/1.2840184 (3 pages) | Cited 11 times

Online Publication Date: 4 February 2008

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The effect of applied magnetic field (H) on the magnetic properties of Sm0.52Sr0.48MnO3 single crystal in the paramagnetic (PM) state has been investigated. We observe a field induced steplike jump in magnetization (M) above TC (110 K). The temperature and magnetic field dependence of susceptibility reveal that the PM phase of this system is quite complicated due to the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions. The nature of magnetic interaction changes abruptly from AFM to FM at around 3.5 T, above which M ceases the steplike jump.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.20.Ck Nonmetals
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials

Remanence enhancement in nanoscaled electrodeposited FePt films

K. Leistner, H. Schlörb, J. Thomas, L. Schultz, and S. Fähler

Appl. Phys. Lett. 92, 052502 (2008); http://dx.doi.org/10.1063/1.2836944 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2008

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L10 FePt films with a small grain size of around 13 nm have been prepared by electrodeposition and postannealing at a low annealing temperature of 400 °C. A high remanence of up to 0.9 T is achieved due to remanence enhancement by exchange coupling between the nanosized grains. Coercivity increases with longer annealing time as the L10 order becomes more complete. The resulting maximum energy product reaches a high value of 70 kJ/m3 after annealing for 120 min, exceeding the maximum energy products so far obtained in electrodeposited hard magnetic films.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Pq Electrodeposition, electroplating
68.55.-a Thin film structure and morphology

First-principles prediction of enhanced magnetic anisotropy in FeCo alloys

Dangxin Wu, Qiming Zhang, J. Ping Liu, Dingwang Yuan, and Ruqian Wu

Appl. Phys. Lett. 92, 052503 (2008); http://dx.doi.org/10.1063/1.2840721 (3 pages) | Cited 6 times

Online Publication Date: 4 February 2008

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The structural, electronic, and magnetic properties of FeCo alloys were studied by first-principles calculations. It has been found that the alloys prefer chemically noncubic geometries in a wide composition range. This produces appreciable uniaxial magnetic anisotropy, which facilitates interphase magnetic interaction and enhances the overall magnetization in exchange-coupled nanocomposite systems. Large magnetostrictive coefficients provide another venue for manipulations of magnetic anisotropy energies.
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75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction

Nanocrystalline iron nitride films with perpendicular magnetic anisotropy

Ajay Gupta, Ranu Dubey, W. Leitenberger, and U. Pietsch

Appl. Phys. Lett. 92, 052504 (2008); http://dx.doi.org/10.1063/1.2840185 (3 pages) | Cited 4 times

Online Publication Date: 4 February 2008

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Nanocrystalline α-iron nitride films have been prepared using reactive ion-beam sputtering. Films develop significant perpendicualr magnetic anisotropy (PMA) with increasing thickness. A comparison of x-ray diffraction patterns taken with scattering vectors in the film plane and out of the film plane provides a clear evidence for development of compressive strain in the film plane with thickness. Thermal annealing results in relaxation of the strain, which correlates very well with the relaxation of PMA. This suggests that the observed PMA is a consequence of the breaking of the symmetry of the crystal structure due to the compressive strain.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Cd Deposition by sputtering
68.55.at Other materials
68.60.Bs Mechanical and acoustical properties

Theoretical evidence of a superconducting transition in doped silicon and germanium driven by a variation of chemical composition

K. Kádas, L. Vitos, and R. Ahuja

Appl. Phys. Lett. 92, 052505 (2008); http://dx.doi.org/10.1063/1.2840696 (3 pages) | Cited 3 times

Online Publication Date: 5 February 2008

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We present the first theoretical evidence of chemical composition driven superconductivity in acceptor-doped silicon and germanium, using density functional theory. We examine the concentration dependence of Tc in B-doped Si and Ge and predict that B-doped Ge is a superconductor with a slightly higher Tc than B-doped Si. We show that there is a critical concentration above which B-doped Si and Ge become superconducting and estimate it to be ∼ 2.6% in Si:B and ∼ 2.2% in Ge:B. Considering the Al-doped Si and Ge, we point out the decisive role of the chemical element in the hole-doping scenario.
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74.62.Dh Effects of crystal defects, doping and substitution
74.70.-b Superconducting materials other than cuprates
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