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17 May 2010

Volume 96, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 96, 203102 (2010); http://dx.doi.org/10.1063/1.3429125 (3 pages)

Qimin Quan, Parag B. Deotare, and Marko Loncar
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Improved interfacial state density in Al2O3/GaAs interfaces using metal-organic chemical vapor deposition

Cheng-Wei Cheng and Eugene A. Fitzgerald

Appl. Phys. Lett. 96, 202101 (2010); http://dx.doi.org/10.1063/1.3428790 (3 pages) | Cited 3 times

Online Publication Date: 17 May 2010

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In situ deposition of Al2O3 on GaAs was performed by chemical-vapor-deposition (CVD) with trimethyaluminum and isopropanol as precursors. A gallium-rich region in the Al2O3 thin film above the interface was spontaneously formed via the in situ CVD process. Ga-enrichment of the interface was observed using secondary ion mass spectrometry (SIMS) depth profile measurement. X-ray photoelectron spectroscopy (XPS) results show that the gallium-rich region consists of Al2O3 and Ga2O3, but no As2O3 was observed. The Ga2O3–Al2O3 layer above the oxide/GaAs interface reduces the frequency dispersion as measured with capacitance-voltage (C-V) characteristics and lowers the interfacial state density as compared to atomic-layer-deposition *(ALD) deposited films which do not display this gallium enrichment above the interface.
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73.20.At Surface states, band structure, electron density of states
68.55.aj Insulators
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Lattice thermal transport in BaxREyCo4Sb12 (RE = Ce, Yb, and Eu) double-filled skutterudites

S. Q. Bai, X. Shi, and L. D. Chen

Appl. Phys. Lett. 96, 202102 (2010); http://dx.doi.org/10.1063/1.3429606 (3 pages) | Cited 6 times

Online Publication Date: 18 May 2010

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We use the Debye model to investigate the phonon scattering mechanisms in BaxREyCo4Sb12 double-filled skutterudites. Filling two types of guest atoms (barium and rare-earth elements) into the voids of skutterudite introduces additional phonon point defect scattering from the extra mass fluctuation at the void site, and additional phonon resonant scattering by the fillers with different vibrational frequencies, leading to significant reduction in the lattice thermal conductivity.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
63.20.kp Phonon-defect interactions
61.72.Qq Microscopic defects (voids, inclusions, etc.)

High-order cumulants in the counting statistics of asymmetric quantum dots

Christian Fricke, Frank Hohls, Nandhavel Sethubalasubramanian, Lukas Fricke, and Rolf J. Haug

Appl. Phys. Lett. 96, 202103 (2010); http://dx.doi.org/10.1063/1.3430000 (3 pages) | Cited 1 time

Online Publication Date: 18 May 2010

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Measurements of single electron tunneling through a quantum dot (QD) using a quantum point contact as charge detector have been performed for very long time traces with very large event counts. This large statistical basis is used for a detailed examination of the counting statistics for varying symmetry of the QD system. From the measured statistics we extract high order cumulants describing the distribution. Oscillations of the high order cumulants are observed when varying the symmetry. We compare this behavior to the observed oscillation in time dependence and show that the variation in both system variables lead to the same kind of oscillating response.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Gk Tunneling
73.63.Kv Quantum dots
73.63.Rt Nanoscale contacts
02.50.-r Probability theory, stochastic processes, and statistics

Positive temperature coefficient resistor behavior in praseodymium-doped ZnO (000math)∣(000math) boundaries

Jong-Sook Lee, Yong Kim, Eui-Chol Shin, and Joachim Maier

Appl. Phys. Lett. 96, 202104 (2010); http://dx.doi.org/10.1063/1.3432444 (3 pages) | Cited 1 time

Online Publication Date: 18 May 2010

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Clear positive temperature coefficient resistor (PTCR) dc behavior has been shown in Pr-doped ZnO (000math)∣(000math) bicrystals by electrical characterization over an unprecedentedly wide temperature range between 40 and 1070 K. With subtraction of the PTCR dc, the admittance can be described by a deep trap level at 0.26 eV but no clue to the origin of the PTCR behavior is provided. Capacitance-voltage characteristics revealed a maximum in the Schottky barrier heights consistent with the PTCR behavior. The PTCR behavior in Pr-doped ZnO c-axis oriented bicrystals is thus phenomenologically analogous to that of the ferroelectric BaTiO3.
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73.40.Ns Metal-nonmetal contacts
71.55.Gs II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions

The importance of hole concentration in establishing carrier-mediated ferromagnetism in Mn doped Ge

Shengqiang Zhou, Danilo Bürger, Wolfgang Skorupa, Peter Oesterlin, Manfred Helm, and Heidemarie Schmidt

Appl. Phys. Lett. 96, 202105 (2010); http://dx.doi.org/10.1063/1.3428770 (3 pages) | Cited 8 times

Online Publication Date: 18 May 2010

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In the present work, we have prepared Mn-doped Ge using different annealing approaches after Mn ion implantation, and obtained samples with hole concentrations ranging from 1018 to 2.1×1020 cm−3, the latter being the highest reported so far. Based on the magnetotransport properties of Mn doped Ge, we argue that the hole concentration is a decisive parameter in establishing carrier-mediated ferromagnetism in magnetic Ge.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Pp Magnetic semiconductors
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Cc Kinetics of defect formation and annealing

Band gap tuning in GaN through equibiaxial in-plane strains

L. Dong, S. K. Yadav, R. Ramprasad, and S. P. Alpay

Appl. Phys. Lett. 96, 202106 (2010); http://dx.doi.org/10.1063/1.3431290 (3 pages) | Cited 14 times

Online Publication Date: 19 May 2010

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Structural transformations and the relative variation in the band gap energy (ΔEg) of (0001) gallium nitride (GaN) films as a function of equibiaxial in-plane strains are studied by density functional theory. For relatively small compressive misfits (−6%–0%), the band gap is estimated to be around its strain-free value, while for small tensile strains (0%–6%), it decreases by approximately 45%. In addition, at large tensile strains (>14.5%), our calculations indicate that GaN may undergo a structural phase transition from wurtzite to a graphitelike semimetallic phase.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
68.55.ag Semiconductors

High-temperature thermoelectric properties of thallium-filled skutterudites

Adul Harnwunggmoung, Ken Kurosaki, Hiroaki Muta, and Shinsuke Yamanaka

Appl. Phys. Lett. 96, 202107 (2010); http://dx.doi.org/10.1063/1.3430739 (3 pages) | Cited 11 times

Online Publication Date: 20 May 2010

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The high temperature thermoelectric (TE) properties of polycrystalline Tl-filled skutterudites TlxCo4Sb12 (x = 0, 0.05, 0.10, 0.15, 0.20, and 0.25) were examined from room temperature to 750 K. All samples exhibited negative Seebeck coefficients. The electrical resistivity, absolute values of the Seebeck coefficient, and the lattice thermal conductivity were found to decrease with increasing Tl content. Tl0.25Co4Sb12 exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.90 at 600 K.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
66.70.Df Metals, alloys, and semiconductors
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