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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Electrical transport in laser-crystallized polycrystalline silicon-germanium thin-films

L.-P. Scheller, M. Weizman, N. H. Nickel, and B. Yan

Appl. Phys. Lett. 95, 062101 (2009); http://dx.doi.org/10.1063/1.3194147 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2009

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We report on the electrical transport properties of intentionally undoped, laser-crystallized polycrystalline silicon-germanium thin-films. The electrical transport in this material strongly depends on the alloy composition and the crystallization procedure. At low temperatures the undoped germanium-rich samples show an unexpected high p-type conductivity with a weak temperature dependence. Posthydrogenation results in a pronounced decrease in the conductivity and a change in the dominating low temperature transport behavior. The results are discussed in terms of a grain-boundary dominated transport model.
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73.61.Le Other inorganic semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.ag Semiconductors
61.72.Mm Grain and twin boundaries

Characterization of boron charge traps at the interface of Si/SiO2 using second harmonic generation

H. Park, J. Qi, Y. Xu, K. Varga, S. M. Weiss, B. R. Rogers, G. Lüpke, and N. Tolk

Appl. Phys. Lett. 95, 062102 (2009); http://dx.doi.org/10.1063/1.3202420 (3 pages) | Cited 10 times

Online Publication Date: 10 August 2009

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We report results from optical second harmonic generation studies of boron charge traps near the interface of Si/SiO2. Our data suggest that a static electric field at the interface is formed during the oxide growth process due to the presence of negative boron ions (B−) in the silicon substrate and positive boron ions (B+) in the oxide. We demonstrated that the B+ state traps could be filled through the creation of neutral boron states created by internal photoelectron emission. By fitting our data, we found that the effective interface susceptibility |χ(2)| depends on doping concentration.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.uf Ge and Si
79.60.Jv Interfaces; heterostructures; nanostructures

Stress-induced anomalous shift of optical band gap in ZnO:Al thin films

Bhaskar Chandra Mohanty, Yeon Hwa Jo, Deuk Ho Yeon, Ik Jin Choi, and Yong Soo Cho

Appl. Phys. Lett. 95, 062103 (2009); http://dx.doi.org/10.1063/1.3202399 (3 pages) | Cited 24 times

Online Publication Date: 11 August 2009

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Thickness-dependent stress relaxation and its unreported effect on optical band gap of Al-doped ZnO thin films have been investigated. The thinnest film ( ∼ 84 nm) had a stress of −8.39×109 Nm−2, carrier concentration of 1.73×1019 cm−3 and optical band gap of 3.69 eV, a value significantly higher than the reported ones. With increase in thickness, magnitude of the stress decreased, and correspondingly a redshift of fundamental absorption band edge was observed. A linear dependence of optical band gap on stress in the films with a coefficient of 54.6 meV/GPa has been observed.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.jd Thickness
81.05.Dz II-VI semiconductors

Defect reduction in epitaxial GaSb grown on nanopatterned GaAs substrates using full wafer block copolymer lithography

Smita Jha, C.-C. Liu, T. S. Kuan, S. E. Babcock, P. F. Nealey, J. H. Park, L. J. Mawst, and T. F. Kuech

Appl. Phys. Lett. 95, 062104 (2009); http://dx.doi.org/10.1063/1.3204013 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2009

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Defect reduction in the large lattice mismatched system of GaSb on GaAs, ∼ 7%, was accomplished using full wafer block copolymer (BCP) lithography. A self-assembled BCP mask layer was used to generate a hexagonal pattern of ∼ 20 nm holes on ∼ 40 nm centers in a 20 nm SiO2 layer. GaSb growth initially takes place selectively within these holes leading to a dense array of small, strain-relaxed epitaxial GaSb islands. The GaSb grown on the patterned SiO2 layer exhibits a reduction in the x-ray linewidth attributed to a decrease in the threading dislocation density when compared to blanket pseudomorphic film growth.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.55.ag Semiconductors

Controllable resistance switching behavior of NiO/SiO2 double layers for nonvolatile memory applications

Ji-Hyuk Choi, Sachindra Nath Das, and Jae-Min Myoung

Appl. Phys. Lett. 95, 062105 (2009); http://dx.doi.org/10.1063/1.3204450 (3 pages) | Cited 7 times

Online Publication Date: 12 August 2009

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Resistive switching characteristics of the double layer (NiO/SiO2) were studied for possible nonvolatile memory applications. The effect of SiO2 thickness variation in the memory device was investigated. A repeatable resistance switching behavior was observed with on/off ratio 105. The operation voltage of the device depended on the thickness of SiO2 layer and it increases with increasing SiO2 thickness. High-resolution transmission electron microscopy analyses revealed that the formation/rapture of Ni filament like percolation path inside SiO2 layer is responsible for the current transport mechanism.
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73.61.-r Electrical properties of specific thin films
84.30.Sk Pulse and digital circuits
68.55.-a Thin film structure and morphology

Magnetic-field asymmetry of nonlinear transport in narrow channels with asymmetric hybrid confinement

Bettina Brandenstein-Köth, Lukas Worschech, and Alfred Forchel

Appl. Phys. Lett. 95, 062106 (2009); http://dx.doi.org/10.1063/1.3204462 (3 pages) | Cited 2 times

Online Publication Date: 12 August 2009

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The authors realized narrow constrictions in a two-dimensional electron gas (2DEG) with an in-plane asymmetry by means of a hybrid confinement. Unequal sidewalls of the constrictions were formed by combination of a single etched trench in a modulation doped GaAs/AlGaAs heterostructure which cuts through the 2DEG with an adjacent metallic top-gate, which depletes the underlying 2DEG. The two-terminal conductance was analyzed in magnetic fields applied perpendicular to the sample surface. In nonlinear transport, the conductance shows pronounced differences for an inversion of the magnetic field. The asymmetric conductance is related to scattering asymmetries caused by the different sidewalls in the asymmetric constriction.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.-b Electronic transport in nanoscale materials and structures

Generation of valley polarized current in bilayer graphene

D. S. L. Abergel and Tapash Chakraborty

Appl. Phys. Lett. 95, 062107 (2009); http://dx.doi.org/10.1063/1.3205117 (3 pages) | Cited 13 times

Online Publication Date: 14 August 2009

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We propose a device for the generation of valley polarized electronic current in bilayer graphene. By analyzing the response of this material to intense terahertz frequency light in the presence of a transverse electric field, we demonstrate that dynamical states are induced in the gapped energy region, and if the system parameters are properly tuned, these states exist only in one valley. The valley polarized states can then be used to filter an arbitrary electron current, so generating a valley polarized current.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states

Effects of Ni cladding layers on suppression of Ag agglomeration in Ag-based Ohmic contacts on p-GaN

Jun Ho Son, Yang Hee Song, Hak Ki Yu, and Jong-Lam Lee

Appl. Phys. Lett. 95, 062108 (2009); http://dx.doi.org/10.1063/1.3206742 (3 pages) | Cited 6 times

Online Publication Date: 14 August 2009

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We investigate effects of Ni cladding layers on suppression of Ag agglomeration in Ag contacts on p-GaN using high-resolution x-ray diffraction. In the annealed Ag contact, Ag (100) grains disappear and agglomerate to form a selectively epitaxial growth of Ag (111). An ultrathin Ni contact layer (10 Å) below Ag film plays a role to epitaxially grow (111) Ag films on GaN, leading to the suppression of Ag agglomeration. A 20-Å-thick Ni overlayer effectively acts as a passivation layer to prevent the surface diffusion of Ag atoms during annealing, leading to high light reflectance and low contact resistivity.
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81.65.-b Surface treatments
73.40.Ns Metal-nonmetal contacts
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
73.40.Cg Contact resistance, contact potential

Influence of N interstitials on the electronic properties of GaAsN alloys

Y. Jin, R. M. Jock, H. Cheng, Y. He, A. M. Mintarov, Y. Wang, C. Kurdak, J. L. Merz, and R. S. Goldman

Appl. Phys. Lett. 95, 062109 (2009); http://dx.doi.org/10.1063/1.3187915 (3 pages) | Cited 6 times

Online Publication Date: 14 August 2009

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We have used rapid thermal annealing to investigate the influence of N interstitials on the electronic properties of GaAsN alloys. Nuclear reaction analysis reveals an annealing-induced decrease in the interstitial N concentration, while the total N composition remains constant. Corresponding signatures for the reduced interstitial N concentration are apparent in Raman spectra. Following annealing, both the room-T carrier concentration, n, and the mobility increase. At higher measurement-Ts, a thermally activated increase in n suggests the presence of a trap near GaAsN conduction band edge with activation energy 85±15 meV. The annealing-induced increase in n suggests the association of the trap with interstitial N.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing
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