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6 Dec 2004

Volume 85, Issue 23, pp. 5499-5791

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Appl. Phys. Lett. 85, 5694 (2004); http://dx.doi.org/10.1063/1.1828575 (3 pages)

M. Y. Shen, C. H. Crouch, J. E. Carey, and E. Mazur
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Dimensional structural transition in CdTe∕CdxZn1−xTe nanostructures

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

Appl. Phys. Lett. 85, 5598 (2004); http://dx.doi.org/10.1063/1.1832749 (3 pages) | Cited 11 times

Online Publication Date: 8 December 2004

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CdTe nanostructures were grown on CdxZn1−xTe buffer layers by using molecular-beam epitaxy and atomic-layer epitaxy. The atomic force microscopy image showed that uniform CdTe quantum dots were formed on ZnTe buffer layer. Photoluminescence measurements showed that the excitonic peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band in the CdTe∕CdxZn1−xTe nanostructure shifted to a higher energy with increasing Cd mole fraction. The activation energy of the electrons confined in the CdTe∕ZnTe quantum dots was higher than those of electrons in CdTe∕CdxZn1−xTe nanostructures. These results can help improve understanding of the dimensional structural transition in CdTe∕CdxZn1−xTe nanostructures.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)
78.55.Et II-VI semiconductors

“Hidden hydrogen” in as-grown ZnO

G. Alvin Shi, Marjan Saboktakin, Michael Stavola, and S. J. Pearton

Appl. Phys. Lett. 85, 5601 (2004); http://dx.doi.org/10.1063/1.1832736 (3 pages) | Cited 43 times

Online Publication Date: 8 December 2004

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An O–H stretching line at 3326.3 cm−1 was previously assigned to a shallow donor that is introduced into ZnO by H. This infrared line has been found to appear in as-grown ZnO samples when they are annealed near 400 °C without an external source of H, showing that there is an H-containing defect in commercially available ZnO that is not seen by infrared spectroscopy that can be converted into a shallow donor. The interstitial H2 molecule in ZnO is suggested as a candidate for the “hidden” H species.
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81.05.Dz II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
78.40.Fy Semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.30.Fs III-V and II-VI semiconductors
81.40.Gh Other heat and thermomechanical treatments

Thermally stimulated current in self-organized InAs quantum dots

J. C. Fan, Y. C. Wang, I. S. Chen, K. J. Hsiao, and Y. F. Chen

Appl. Phys. Lett. 85, 5604 (2004); http://dx.doi.org/10.1063/1.1832760 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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We have measured the thermally stimulated current from self-organized InAs quantum dots grown by molecular-beam epitaxy. The glow curve exhibits peaks at 43, 82, and 127 K with accompanying attenuated current oscillations at 107 K. Based on the excitation energy above and below the GaAs band gap, the oscillations are ascribed to AsGa-related point defects in the conduction GaAs matrix. By comparing with the photoluminescence and photoconductivity measurements, we conclude that the peaks at 82 and 43 K arise from the electron trapping in the InAs quantum dots. We point out that the technique of thermally stimulated current provides a simple alternative method to obtain the energy levels in self-organized quantum-dot systems.
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72.20.Pa Thermoelectric and thermomagnetic effects
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Cr III-V semiconductors
73.63.Kv Quantum dots
78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters
73.50.Pz Photoconduction and photovoltaic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Effect of band offset on the open circuit voltage of heterojunction CuIn1−xGaxSe2 solar cells

Akimasa Yamada, Koji Matsubara, Keiichiro Sakurai, Shogo Ishizuka, Hitoshi Tampo, Paul J. Fons, Kakuya Iwata, and Shigeru Niki

Appl. Phys. Lett. 85, 5607 (2004); http://dx.doi.org/10.1063/1.1831566 (3 pages) | Cited 12 times

Online Publication Date: 8 December 2004

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The reasons behind why the theoretically estimated open circuit voltage (Voc) of CuIn1−xGaxSe2 solar cells with large x values has not been realized are discussed. Typically, the reduction in Voc is estimated only on the basis of the conduction-band offset between the absorber and the window material. The importance of the electron affinity difference between the window and the transparent electrode must also be taken into account. Based upon both of these factors, a material selection guideline is reported for the window and the transparent electrode layers suitable for high-x CuIn1−xGaxSe2 absorber-based solar cells.
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84.60.Jt Photoelectric conversion
71.20.Nr Semiconductor compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Electronic charge effects on dislocation cores in silicon

M. M. de Araújo, J. F. Justo, and R. W. Nunes

Appl. Phys. Lett. 85, 5610 (2004); http://dx.doi.org/10.1063/1.1830073 (3 pages) | Cited 3 times

Online Publication Date: 8 December 2004

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Using first-principles calculations, we investigate electronic charge effects on the structural stability of partial dislocations in silicon. For the 30° partial dislocation, we find that the unreconstructed core sustains all possible charge states associated with the dislocation-related electronic bands, as the Fermi level (μe) sweeps the electronic band gap, while the reconstructed core remains neutral for p-type doping and intrinsic regimes. Both core configurations become negatively charged for n-type doping. In the case of the 90° partial dislocation, the three known core configurations (namely, the single-period and double-period reconstructed cores and the unreconstructed one) remain neutral in the p-type and intrinsic regimes, but the negatively charged states become stable in the n-type region, for all three geometries. More important, we find that the relative stability between the three structures is strongly charge-state dependent, with the unreconstructed core becoming energetically favorable in the n-type regime. Our results provide elements for understanding the role of doping on dislocation mobility in semiconductors.
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61.72.Bb Theories and models of crystal defects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.55.Cn Elemental semiconductors
71.20.Mq Elemental semiconductors
61.72.S- Impurities in crystals
73.20.At Surface states, band structure, electron density of states

Al–Si multilayers: A synthetic material with large thermoelectric anisotropy

A. Kyarad and H. Lengfellner

Appl. Phys. Lett. 85, 5613 (2004); http://dx.doi.org/10.1063/1.1830680 (3 pages) | Cited 6 times

Online Publication Date: 8 December 2004

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A synthetic material with large thermoelectric anisotropy has been prepared from a metal–semiconductor multilayer structure. By an alloying process, a multilayer stack A–B–A…, where A and B are pure aluminum and n-silicon, is produced with a thermoelectric anisotropy ΔS=S∥−S⊥≅1.5 mV∕K, where S∥ and S⊥ are the absolute Seebeck coefficients along and perpendicular to the layers, respectively. The use of this synthetic material for light sensing applications is demonstrated.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Conductivity and Hall effect of free-standing highly resistive epitaxial GaN:Fe substrates

P. Kordoš, M. Morvic, J. Betko, J. Novák, J. Flynn, and G. R. Brandes

Appl. Phys. Lett. 85, 5616 (2004); http://dx.doi.org/10.1063/1.1831568 (3 pages) | Cited 3 times

Online Publication Date: 8 December 2004

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Free-standing highly resistive Fe-doped GaN layers grown by hydride vapor phase epitaxy were characterized by temperature-dependent conductivity and Hall effect measurements. Samples with a room-temperature resistivity of 1.6×107–6×108 Ω cm and a Hall mobility of ∼330 cm2 V−1 s−1 showed simple band conduction with the mobility power x=−1.5 and an activation energy 0.58–0.60 eV, which can be attributed to a Fe acceptor. Samples with a lower mobility, ⩽10 cm2 V−1 s−1, exhibited an increase of the mobility with temperature. Here, the conduction seems to be strongly influenced by potential barriers at inhomogeneities, with an activation energy of 0.21 eV and a barrier height of 0.14–0.18 eV. The activation energy 0.36 and 0.40 eV, evaluated from the resistivity measurements, does not correspond to that of the Fe acceptor.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.Ey III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
61.72.S- Impurities in crystals

Strain modulation of transport criticality in RuO2-based thick-film resistors

Sonia Vionnet-Menot, Claudio Grimaldi, Peter Ryser, Thomas Maeder, and Sigfrid Strässler

Appl. Phys. Lett. 85, 5619 (2004); http://dx.doi.org/10.1063/1.1835996 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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We show that in RuO2–glass composites the nonuniversal resistivity exponent can be modulated by an applied mechanical strain, signaled by a logarithmic divergence of the piezoresistive response at the percolation threshold. We interpret this phenomenon as being due to a tunneling-distance dependence of the transport exponent, supporting therefore a theory of transport nonuniversality proposed some years ago.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
73.40.Gk Tunneling
72.80.Tm Composite materials

Pinning a domain wall in (Ga,Mn)As with focused ion beam lithography

A. W. Holleitner, H. Knotz, R. C. Myers, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 85, 5622 (2004); http://dx.doi.org/10.1063/1.1829797 (3 pages) | Cited 4 times

Online Publication Date: 8 December 2004

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We utilize a focused beam of Ga+ ions to define magnetization pinning sites in a ferromagnetic epilayer of (Ga,Mn)As. The nonmagnetic defects locally increase the magnetocrystalline anisotropy energies, by which a domain wall is pinned at a given position. We demonstrate techniques for manipulating domain walls at these pinning sites as probed with the giant planar Hall effect. By varying the magnetic field angle relative to the crystal axes, an upper limit is placed on the local effective anisotropy energy.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
81.16.Nd Micro- and nanolithography
68.55.-a Thin film structure and morphology

Linear collapse of the depolarization shift in very dilute two-dimensional hole gases

A. S. Plaut, A. Pinczuk, B. S. Dennis, C. F. Hirjibehedin, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 85, 5625 (2004); http://dx.doi.org/10.1063/1.1833562 (3 pages)

Online Publication Date: 8 December 2004

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Very dilute two-dimensional hole systems were probed by resonant inelastic light scattering. This extremely high mobility system occurs in AlxGa1−xAs∕GaAs quantum wells designed specifically for their light insensitivity. We find that the depolarization shift in intersubband transitions decreases linearly for hole densities below p=6.6×1010 cm−2, dropping to zero below p=1×1010 cm−2.
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78.67.De Quantum wells
73.21.Fg Quantum wells
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering

Liang-Yih Chen, Wen-Hwa Chen, Jia-Jun Wang, Franklin Chau-Nan Hong, and Yan-Kuin Su

Appl. Phys. Lett. 85, 5628 (2004); http://dx.doi.org/10.1063/1.1835991 (3 pages) | Cited 47 times

Online Publication Date: 8 December 2004

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Hydrogen-doped zinc oxide (ZnO:H) films were deposited by rf magnetron sputtering as transparent conductive films. The resistivity of ZnO:H film was significantly reduced by the addition of H2 in Ar during rf sputtering. The electrical resistivity of ZnO:H films reached 2×10−4 Ω cm. The carrier concentration increased with increasing H2 concentration during deposition. X-ray diffraction results showed that the d0002 interplanar spacing increased with increasing H2 concentrations. The carrier concentration was significantly reduced in two orders of magnitude by increasing the substrate temperature from 150 to 250 °C during deposition. Both results suggested that the increase of carrier concentration by adding H2 during sputtering was due to the hydrogen donor rather than the oxygen vacancies in ZnO films, consistent with the theoretical predictions by Van de Walle. UV–visible spectroscopy further showed that the transmittance is high up to 100% in the visible range. The band gap determined by optical absorption increased with increasing H2 composition. The phenomenon is interpreted as the filling of conduction band by electrons in n-type semiconductor.
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68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.J- Point defects and defect clusters
81.15.Cd Deposition by sputtering

Enhanced photoluminescence from GaAsSb quantum wells

Alan R. Kost, Xiaolan Sun, Nasser Peyghambarian, Nayer Eradat, Espen Selvig, Bjorn-Ove Fimland, and David H. Chow

Appl. Phys. Lett. 85, 5631 (2004); http://dx.doi.org/10.1063/1.1759381 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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We describe promising semiconductor materials for optoelectronics. GaAsSb/AlSb quantum wells on GaSb substrates show photoluminescence near 1.54 μm (0.8 eV) that increases with increasing arsenic fraction. The materials can be monolithically integrated with AlGaSb/AlSb or AlGaAsSb/AlAsSb Bragg mirrors. © 2004 American Institute of Physics.
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81.07.St Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
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