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30 Jan 2006

Volume 88, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 88, 051101 (2006); http://dx.doi.org/10.1063/1.2168491 (3 pages)

H. Lohmeyer, K. Sebald, C. Kruse, R. Kröger, J. Gutowski, D. Hommel, J. Wiersig, N. Baer, and F. Jahnke
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Manipulation of g-factor in diluted magnetic semiconductors quantum dots: Optical switching control

V. López-Richard, S. J. Prado, G. E. Marques, C. Trallero-Giner, and A. M. Alcalde

Appl. Phys. Lett. 88, 052101 (2006); http://dx.doi.org/10.1063/1.2168499 (3 pages) | Cited 5 times

Online Publication Date: 30 January 2006

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We propose an optical switch based on a spin tuning mechanism in diluted-magnetic semiconductor quantum dots. At certain critical magnetic field, Bc, the Zeeman spin-splitting energies can cross leading to a zero value of the effective electron g-factor and the Fermi level undergoes a spin-flip transition. Magneto-optical switching is obtained for magnetic fields below and above Bc. Correlations between Bc, confinement shapes, dot sizes, and host material compositions have been established within well-defined temperature and magnetic impurity composition ranges. The generality of the presented theoretical framework allows for its application to magnetic field controlled quantum dot arrays, and spin-injection among others.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects
72.25.Dc Spin polarized transport in semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
75.50.Pp Magnetic semiconductors

A (4×2) reconstruction of CuInSe2 (001) studied by low-energy electron diffraction and soft x-ray photoemission spectroscopy

Th. Deniozou, N. Esser, Th. Schulmeyer, and R. Hunger

Appl. Phys. Lett. 88, 052102 (2006); http://dx.doi.org/10.1063/1.2162677 (3 pages) | Cited 1 time

Online Publication Date: 30 January 2006

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Clean and flat (001) surfaces of CuInSe2/GaAs grown by molecular-beam epitaxy could be prepared by the combination of a Se capping and decapping process and subsequent Ar+ ion sputtering and annealing. The formation of a (4×2) reconstruction was observed with low-energy electron diffraction. Soft x-ray photoemission spectroscopy was performed on the prepared surfaces and revealed surface core-level binding energy shifts in the Cu 2p3/2, Se 3d, and In 4d levels which are associated with surface atoms. The structure model of a combined metal adatom-Se dimer structure is proposed to refer to the (4×2) reconstruction.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Wide-band gap oxide alloy: BeZnO

Y. R. Ryu, T. S. Lee, J. A. Lubguban, A. B. Corman, H. W. White, J. H. Leem, M. S. Han, Y. S. Park, C. J. Youn, and W. J. Kim

Appl. Phys. Lett. 88, 052103 (2006); http://dx.doi.org/10.1063/1.2168040 (2 pages) | Cited 58 times

Online Publication Date: 31 January 2006

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A wide-band gap oxide alloy, BeZnO, is proposed and studied in this letter. The BeZnO films were deposited on sapphire substrates by our hybrid beam deposition growth method. The value of the energy band gap of BeZnO can be efficiently engineered to vary from the ZnO band gap (3.4 eV) to that of BeO (10.6 eV). BeZnO can be used for fabricating films and heterostructures of ZnO-based electronic and photonic devices and for other applications. Changes in the measured energy band gap and lattice constant values with Be content are described for BeZnO alloys.
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81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology

Bimolecular recombination in polymer/fullerene bulk heterojunction solar cells

L. J. A. Koster, V. D. Mihailetchi, and P. W. M. Blom

Appl. Phys. Lett. 88, 052104 (2006); http://dx.doi.org/10.1063/1.2170424 (3 pages) | Cited 131 times

Online Publication Date: 31 January 2006

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Bimolecular recombination in organic semiconductors is known to follow the Langevin expression, i.e., the rate of recombination depends on the sum of the mobilities of both carriers. We show that this does not hold for polymer/fullerene bulk heterojunction solar cells. The voltage dependence of the photocurrent reveals that the recombination rate in these blends is determined by the slowest charge carrier only, as a consequence of the confinement of both types of carriers to two different phases.
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84.60.Jt Photoelectric conversion
85.60.-q Optoelectronic devices
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects

Extraordinary optoconductance in metal-semiconductor hybrid structures

K. A. Wieland, Yun Wang, L. R. Ram-Mohan, S. A. Solin, and A. M. Girgis

Appl. Phys. Lett. 88, 052105 (2006); http://dx.doi.org/10.1063/1.2170429 (3 pages) | Cited 7 times

Online Publication Date: 31 January 2006

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We provide the first demonstration of extraordinary optoconductance (EOC) in macroscopic metal-semiconductor hybrid structures fabricated from GaAs and In and the first example of an extraordinary transport (EXX) effect that is based on a perturbation of the relative bulk conductances of the constituents. Four-lead van der Pauw plate structures show a gain of order 500% in the optocondutance when shunted by In relative to unshunted devices. The dependence of the optocondutance on the position of a focussed Ar laser beam has been measured and is in agreement with a Gaussian broadened point charge model that accounts for the Dember effect. We also account quantitatively for the temperature dependence of the EOC.
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72.40.+w Photoconduction and photovoltaic effects

p-type ZnO films with solid-source phosphorus doping by molecular-beam epitaxy

F. X. Xiu, Z. Yang, L. J. Mandalapu, J. L. Liu, and W. P. Beyermann

Appl. Phys. Lett. 88, 052106 (2006); http://dx.doi.org/10.1063/1.2170406 (3 pages) | Cited 64 times

Online Publication Date: 31 January 2006

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Phosphorus-doped p-type ZnO films were grown on r-plane sapphire substrates using molecular-beam epitaxy with a solid-source GaP effusion cell. X-ray diffraction spectra and reflection high-energy electron diffraction patterns indicate that high-quality single crystalline (11math0) ZnO films were obtained. Hall and resistivity measurements show that the phosphorus-doped ZnO films have high hole concentrations and low resistivities at room temperature. Photoluminescence (PL) measurements at 8 K reveal a dominant acceptor-bound exciton emission with an energy of 3.317 eV. The acceptor energy level of the phosphorus dopant is estimated to be 0.18 eV above the valence band from PL spectra, which is also consistent with the temperature dependence of PL measurements.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
61.72.uj III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors

Two-dimensional electron gas in InGaAs/InAlAs quantum wells

E. Diez, Y. P. Chen, S. Avesque, M. Hilke, E. Peled, D. Shahar, J. M. Cerveró, D. L. Sivco, and A. Y. Cho

Appl. Phys. Lett. 88, 052107 (2006); http://dx.doi.org/10.1063/1.2168666 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2006

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We designed and performed low-temperature dc transport characterization studies on two-dimensional electron gases confined in lattice-matched In0.53Ga0.47As/In0.52Al0.48As quantum wells grown by molecular beam epitaxy on InP substrates. The nearly constant mobility for samples with the setback distance larger than 50 nm and the similarity between the quantum and transport lifetime suggest that the main scattering mechanism is due to short range scattering, such as alloy scattering, with a scattering rate of 2.2 ps−1. We also obtain the Fermi level at the In0.53Ga0.47As/In0.52Al0.48As surface to be 0.36 eV above the conduction band, when fitting our experimental densities with a Poisson-Schrödinger model.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells

Strain-induced changes in the gate tunneling currents in p-channel metal–oxide–semiconductor field-effect transistors

X. Yang, J. Lim, G. Sun, K. Wu, T. Nishida, and S. E. Thompson

Appl. Phys. Lett. 88, 052108 (2006); http://dx.doi.org/10.1063/1.2168671 (3 pages) | Cited 18 times

Online Publication Date: 31 January 2006

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Changes in the direct gate tunneling current are measured for strained p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) on (100) wafers for uniaxial and biaxial stress. Decreases/increases in the gate tunneling current for various stresses primarily result from repopulation into a subband with a larger/smaller out-of-plane effective mass. Strain-induced changes in the valence band offset between Si and SiO2 are also important but play a secondary role. Hole tunneling current is found to decrease for biaxial and uniaxial compressive stress and increase for biaxial tensile stress. The hole tunneling data is modeled using k∙p self-consistent solution to Poisson and Schrödinger’s equation, and a transfer matrix method.
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85.30.Tv Field effect devices
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Phase formation and work function tuning in fully silicided Co–Ni metal gates with variable Co:Ni ratios

J. Liu and D. L. Kwong

Appl. Phys. Lett. 88, 052109 (2006); http://dx.doi.org/10.1063/1.2167799 (3 pages) | Cited 3 times

Online Publication Date: 31 January 2006

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Dual work function metal gates fabricated by full silicidation of a Co–Ni bilayer with different Co:Ni ratios were investigated by both physical and electrical measurements. Full silicidation, sheet resistance and phase confirmation of CoxNi1−xSi2 were studied by physical characterizations. Complementary metal-oxide-semiconductor work functions were extrapolated by electrical characterization and correlated with dopant accumulation at the gate/oxide interface. The quality of underlying oxide was measured by gate leakage current density and found to be impacted by the Co:Ni ratio in CoxNi1−xSi2.
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85.30.Tv Field effect devices
73.30.+y Surface double layers, Schottky barriers, and work functions

Lifetime-limiting defects in n− 4H-SiC epilayers

P. B. Klein, B. V. Shanabrook, S. W. Huh, A. Y. Polyakov, M. Skowronski, J. J. Sumakeris, and M. J. O’Loughlin

Appl. Phys. Lett. 88, 052110 (2006); http://dx.doi.org/10.1063/1.2170144 (3 pages) | Cited 35 times

Online Publication Date: 1 February 2006

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Low-injection minority carrier lifetimes (MCLs) and deep trap spectra have been investigated in n− 4H-SiC epilayers of varying layer thicknesses, in order to enable the separation of bulk lifetimes from surface recombination effects. From the linear dependence of the inverse bulk MCL on the concentration of Z1/Z2 defects and from the behavior of the deep trap spectra in 4H-SiC p-i-n diodes under forward bias, we conclude that it is Z1/Z2 alone that controls the MCL in this material.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Ht Other nonmetals
78.40.Fy Semiconductors
78.66.Li Other semiconductors

Current flow and energy dissipation in low-dimensional semiconductor superlattices

D. Fowler, A. Patané, A. Ignatov, L. Eaves, M. Henini, N. Mori, D. K. Maude, and R. Airey

Appl. Phys. Lett. 88, 052111 (2006); http://dx.doi.org/10.1063/1.2171800 (3 pages) | Cited 5 times

Online Publication Date: 3 February 2006

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By applying high magnetic and electric fields to a semiconductor superlattice (SL) we create quasi-one-dimensional or quasi-zero-dimensional electronic states. This reduced dimensionality restricts the range of inelastic scattering processes available to the conduction electrons, leading to an increase of the inelastic scattering time and a corresponding decrease of the electrical conductance. Our study reveals the fundamental link between current flow and energy dissipation in low-dimensional conductors, which is relevant to the exploitation of artificial nanowires and quantum dot SLs for novel applications, including recently proposed thermoelectric devices.
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73.63.-b Electronic transport in nanoscale materials and structures
73.21.Cd Superlattices

Capacitance-voltage investigation of high-purity InAs/GaSb superlattice photodiodes

Andrew Hood, Darin Hoffman, Yajun Wei, Frank Fuchs, and Manijeh Razeghi

Appl. Phys. Lett. 88, 052112 (2006); http://dx.doi.org/10.1063/1.2172399 (3 pages) | Cited 28 times

Online Publication Date: 3 February 2006

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The residual carrier backgrounds of binary type-II InAs/GaSb superlattice photodiodes with cutoff wavelengths around 5 μm have been studied in the temperature range between 20 and 200 K. By applying a capacitance-voltage measurement technique, a residual background concentration below 1015 cm−3 has been found. At temperatures below 100 K carrier freeze-out is observed with a thermal activation energy of 4.5 meV, leading to net carrier concentrations at 77 K in the mid 1014 cm−3.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Observation of the subgap optical absorption in polymer-fullerene blend solar cells

L. Goris, A. Poruba, L. Hod’ákova, M. Vaněček, K. Haenen, M. Nesládek, P. Wagner, D. Vanderzande, L. De Schepper, and J. V. Manca

Appl. Phys. Lett. 88, 052113 (2006); http://dx.doi.org/10.1063/1.2171492 (3 pages) | Cited 52 times

Online Publication Date: 3 February 2006

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This letter reports on highly sensitive optical absorption measurements on organic donor-acceptor solar cells, using Fourier-transform photocurrent spectroscopy (FTPS). The spectra cover an unprecedented dynamic range of eight to nine orders of magnitude making it possible to detect defect and disorder related sub-band gap transitions. Direct measurements on fully encapsulated solar cells with an active layer of poly[2-methoxy-5-(3′,7′-dimethyl-octyloxy)]-p-phenylene-vinylene:(6,6)-phenyl-C61-butyric-acid (1:4 weight ratio) enabled a study of the intrinsic defect generation due to UV illumination. Solar cell temperature annealing effects in poly(3-hexylthiophene):PCBM (1:2 weight ratio) cells and the induced morphological changes are related to the changes in the absorption spectrum, as determined with FTPS.
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84.60.Jt Photoelectric conversion
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments

Negative refraction of spintronics and spin beam splitter

Xiangdong Zhang

Appl. Phys. Lett. 88, 052114 (2006); http://dx.doi.org/10.1063/1.2167792 (3 pages) | Cited 12 times

Online Publication Date: 3 February 2006

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The spin-polarized injections through the lateral interface between two regions with different strengths of spin-orbit interactions have been investigated. In the presence of the spin-orbit coupling of both Rashba and Dresselhaus types, the phenomena of negative refraction of spintronics have been found. An electron beam with some angles of incidence after passing through such an interface splits into two beams with different spin polarizations propagating in negative and positive directions, respectively. Thus, a spin beam splitter has been proposed based on such an interface.
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72.25.Mk Spin transport through interfaces
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
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