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8 Oct 2012

Volume 101, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 153501 (2012); http://dx.doi.org/10.1063/1.4756693 (3 pages)

Brandon G. Cook, William R. French, and Kálmán Varga
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Excellent p-n control in a high temperature thermoelectric boride

Satofumi Maruyama, Yuzuru Miyazaki, Kei Hayashi, Tsuyoshi Kajitani, and Takao Mori

Appl. Phys. Lett. 101, 152101 (2012); http://dx.doi.org/10.1063/1.4758297 (4 pages)

Online Publication Date: 8 October 2012

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Polycrystalline samples of YxAlyB14 (x ∼ 0.57) with different fractional occupancies y (0.41 ≤ y ≤ 0.63) were synthesized and their thermoelectric properties investigated. Electrical conductivities generally followed three-dimensional variable range hopping with a rapid delocalization indicated as electrons were increased. Positive Seebeck coefficients were obtained for the Al-poor sample, y = 0.41, which was shifted in the negative direction with increase of y. Maximum Seebeck coefficient values were approximately 400 μV K−1 at 850 K and −200 μV K−1 at 1000 K, for p-type and n-type, respectively. Excellent control of p-n characteristics was achieved in a system with the same crystal structure and consisting of the same elements.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.50.Dn Low-field transport and mobility; piezoresistance
61.66.Dk Alloys

Large linear magnetoresistance and magnetothermopower in layered SrZnSb2

Kefeng Wang and C. Petrovic

Appl. Phys. Lett. 101, 152102 (2012); http://dx.doi.org/10.1063/1.4758298 (3 pages)

Online Publication Date: 9 October 2012

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We report the large linear magnetoresistance ( ∼ 300% in 9 T field at 2 K) and magnetothermopower in layered SrZnSb2 crystal with quasi-two-dimensional Sb layers. A crossover from the semiclassical parabolic field dependent magnetoresistance to linear field dependent magnetoresistance with increasing magnetic field is observed. The magnetoresistance behavior can be described very well by combining the semiclassical cyclotron contribution and the quantum limit magnetoresistance. Magnetic field also enhances the thermopower. Our results can be well understood by the magnetotransport of Dirac states in the bulk band structure.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
72.15.Jf Thermoelectric and thermomagnetic effects
75.47.De Giant magnetoresistance

Simple tuning of carrier type in topological insulator Bi2Se3 by Mn doping

Y. H. Choi, N. H. Jo, K. J. Lee, H. W. Lee, Y. H. Jo, J. Kajino, T. Takabatake, K.-T. Ko, J.-H. Park, and M. H. Jung

Appl. Phys. Lett. 101, 152103 (2012); http://dx.doi.org/10.1063/1.4755767 (4 pages)

Online Publication Date: 9 October 2012

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Bi2Te3 is a well-known thermoelectric material for room-temperature operations because it has a high Seebeck coefficient, and the charge carrier type is easily tunable. However, the carrier type of Bi2Se3 is not tunable, which is one of the weaknesses for the thermoelectric applications, in spite of its high Seebeck coefficient. Here, we report the tuning of charge carriers in Bi2Te3 from n type to p type by doping Mn into the Bi sites. The carrier type is n type up to the Mn doping level of 5% and changes to p type above 5% Mn doping. The temperature-dependent resistivity of Bi2−xMnxSe3 shows a metallic behavior for x < 0.05, while for x ≥ 0.05, it shows an upturn at low temperatures. This provides evidence that by Mn doping, the Fermi level is continuously tuned from the bulk conduction band to the bulk valence band. The Seebeck coefficient increases monotonically with increasing temperature, and the absolute values are same for both n- and p-type samples. This implies that Bi2Se3 is another candidate of high-temperature thermoelectric materials, like Bi2Te3, simply by Mn doping.
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72.80.Sk Insulators
73.20.Hb Impurity and defect levels; energy states of adsorbed species
61.72.up Other materials
71.20.Ps Other inorganic compounds
72.20.Pa Thermoelectric and thermomagnetic effects

Influence of V/III growth flux ratio on trap states in m-plane GaN grown by ammonia-based molecular beam epitaxy

Z. Zhang, C. A. Hurni, A. R. Arehart, J. S. Speck, and S. A. Ringel

Appl. Phys. Lett. 101, 152104 (2012); http://dx.doi.org/10.1063/1.4759037 (4 pages)

Online Publication Date: 10 October 2012

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Deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) were utilized to investigate the behavior of deep states in m-plane, n-type GaN grown by ammonia-based molecular beam epitaxy (NH3-MBE) as a function of systematically varied V/III growth flux ratios. Levels were detected at EC − 0.14 eV, EC − 0.21 eV, EC − 0.26 eV, EC − 0.62 eV, EC − 0.67 eV, EC − 2.65 eV, and EC − 3.31 eV, with the concentrations of several traps exhibiting systematic dependencies on V/III ratio. The DLTS spectra are dominated by traps at EC − 0.14 eV and EC − 0.67 eV, whose concentrations decreased monotonically with increasing V/III ratio and decreasing oxygen impurity concentration, and by a trap at EC − 0.21 eV that revealed no dependence of its concentration on growth conditions, suggestive of different physical origins. Higher concentrations of deeper trap states detected by DLOS with activation energies of EC − 2.65 eV and EC − 3.31 eV in each sample did not display measureable sensitivity to the intentionally varied V/III ratio, necessitating further study on reducing these deep traps through growth optimization for maximizing material quality of NH3-MBE grown m-plane GaN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Strain effects and band parameters in MgO, ZnO, and CdO

Qimin Yan, Patrick Rinke, Momme Winkelnkemper, Abdallah Qteish, Dieter Bimberg, Matthias Scheffler, and Chris G. Van de Walle

Appl. Phys. Lett. 101, 152105 (2012); http://dx.doi.org/10.1063/1.4759107 (4 pages)

Online Publication Date: 10 October 2012

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We have derived consistent sets of band parameters (bandgaps, crystal-field splittings, effective masses, Luttinger, and EP parameters) and strain deformation potentials for MgO, ZnO, and CdO in the wurtzite phase. To overcome the limitations of density-functional theory in the local-density and generalized gradient approximations, we employ a hybrid functional as well as exact-exchange-based quasiparticle energy calculations in the G0W0 approach. We demonstrate that the band and strain parameters derived in this fashion are in very good agreement with the available experimental data and provide predictions for all parameters that have not been determined experimentally so far.
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81.40.Lm Deformation, plasticity, and creep
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.22.-f Electronic structure of nanoscale materials and related systems
62.25.-g Mechanical properties of nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
62.20.F- Deformation and plasticity

Hall effect measurements on InAs nanowires

Ch. Blömers, T. Grap, M. I. Lepsa, J. Moers, St. Trellenkamp, D. Grützmacher, H. Lüth, and Th. Schäpers

Appl. Phys. Lett. 101, 152106 (2012); http://dx.doi.org/10.1063/1.4759124 (4 pages) | Cited 4 times

Online Publication Date: 11 October 2012

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We have processed Hall contacts on InAs nanowires grown by molecular beam epitaxy using an electron beam lithography process with an extremely high alignment accuracy. The carrier concentrations determined from the Hall effect measurements on these nanowires are lower by a factor of about 4 in comparison with those measured by the common field-effect technique. The results are used to evaluate quantitatively the charging effect of the interface and surface states.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.16.Nd Micro- and nanolithography
73.63.Nm Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.Hb Quantum wires

Angular-dependences of giant in-plane and interlayer magnetoresistances in Bi2Te3 bulk single crystals

Z. J. Yue, X. L. Wang, and S. X. Dou

Appl. Phys. Lett. 101, 152107 (2012); http://dx.doi.org/10.1063/1.4756941 (4 pages)

Online Publication Date: 11 October 2012

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Angular-dependences of in-plane and interlayer magnetotransport properties in n-type Bi2Te3 bulk single crystals have been investigated over a broad range of temperatures and magnetic fields. Giant in-plane magnetoresistances (MR) of up to 500% and interlayer MR of up to 200% were observed, respectively. The observed MR exhibits quadratic field dependences in low fields and linear field dependences in high fields. The angular dependences of the MR represent strong anisotropy and twofold oscillations. The observed angle-dependent, giant MR might result from the strong coulomb scattering of electrons as well as impurity scattering in the bulk conduction bands of n-type Bi2Te3. The strong anisotropy of the MR may be attributable to the anisotropy of electron mobility, effective mass, and relaxation time in the Fermi surface. The observed giant anisotropic MR in n-type Bi2Te3 bulk single crystals paves the way for Bi2Te3 single crystals to be useful for practical applications in magnetoelectronic devices such as disk reading heads, anisotropic magnetic sensors, and other multifunctional electromagnetic applications.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Degenerate crystalline silicon films by aluminum-induced crystallization of boron-doped amorphous silicon

J. D. Hwang, L. C. Luo, T. J. Hsueh, and S. B. Hwang

Appl. Phys. Lett. 101, 152108 (2012); http://dx.doi.org/10.1063/1.4759151 (4 pages)

Online Publication Date: 11 October 2012

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Degenerate p-type crystalline silicon film with a hole concentration of 4 × 1021 cm−3 was investigated using aluminum-induced crystallization (AIC) of boron-doped amorphous silicon (a-Si). The AIC mechanism is different from that in the undoped AIC-Si. Boron atoms accumulate at Al layer forming a boron bump and segregate the Al atoms into Si layer, resulting to the formation of AlSi alloy. The degeneracy is not attributed to boron doping but instead to the AlSi alloy. Observations show that Al and Si layer transfer occurs not at original interface of Al and Si, but at the boron bump.
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68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.43.Dq Amorphous semiconductors, metals, and alloys
81.05.Gc Amorphous semiconductors
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
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