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7 Mar 2005

Volume 86, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 86, 103102 (2005); http://dx.doi.org/10.1063/1.1875734 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, and Motoichi Ohtsu
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Monte Carlo simulation of the effects of vacuum-ultraviolet radiation on dielectric materials

G. S. Upadhyaya, J. L. Shohet, and J. L. Lauer

Appl. Phys. Lett. 86, 102101 (2005); http://dx.doi.org/10.1063/1.1879100 (3 pages) | Cited 10 times

Online Publication Date: 1 March 2005

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Radiation-induced damage during plasma processing of semiconductor materials can adversely affect device reliability. However, it has been shown that vacuum ultraviolet (VUV) radiation (8–20 eV) can beneficially deplete previously deposited charge on the surface of dielectrics by temporarily increasing their conductivity. Incident VUV photons can cause photoemission and form electron-hole pairs in the dielectric thus producing the desired increased conductivity. To verify this, statistical information obtained from a Monte Carlo simulation is used to model VUV exposure of dielectrics. The simulation calculates the surface potential on the dielectric produced by electron photoemission, which compares favorably with experimental surface-potential measurements made using a Kelvin probe.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
72.40.+w Photoconduction and photovoltaic effects

High transparency of Ag/Zn–Ni solid–solution ohmic contacts for GaN-based ultraviolet light-emitting diodes

Dong-Seok Leem, June-O Song, Woong-Ki Hong, Jeong-Tae Maeng, J. S. Kwak, Y. Park, and Tae-Yeon Seong

Appl. Phys. Lett. 86, 102102 (2005); http://dx.doi.org/10.1063/1.1879084 (3 pages) | Cited 1 time

Online Publication Date: 1 March 2005

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Ag/Zn–Ni solid–solution scheme has been investigated to produce transparent ohmic contacts for ultraviolet (UV) light-emitting diodes (LEDs). The Ag/Zn–Ni solid–solution contacts annealed at 430 °C for 1 min in air show high transmittance of 67%–69% at 340 nm, which is much better than that (53%) of the conventional Ni/Au contact. The annealed contacts give specific contact resistance of 8.2×10−5 and 4.8×10−5 Ω cm2. Further, near UV LEDs (300×300 μm2) made with the annealed contact layers produce a forward-bias voltage of 3.32–3.46 V at 20 mA. Possible explanations are given to describe the annealing-induced improvement of the ohmic behaviors of the Ag/Zn–Ni solid–solution contacts.
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85.60.Jb Light-emitting devices
78.66.Bz Metals and metallic alloys
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
78.40.Kc Metals, semimetals, and alloys

Time-resolved photocurrent spectroscopy of the evolution of the electric field in optically excited superlattices and the prospects for Bloch gain

Alvydas Lisauskas, Claudia Blöser, Robert Sachs, Hartmut G. Roskos, Aušrius Juozapavičius, Gintaras Valušis, and Klaus Köhler

Appl. Phys. Lett. 86, 102103 (2005); http://dx.doi.org/10.1063/1.1867552 (3 pages) | Cited 5 times

Online Publication Date: 2 March 2005

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We report on photocurrent spectroscopy on undoped GaAs/AlGaAs semiconductor superlattices subjected to femtosecond optical excitation. The evolution of the carrier-drift-induced inhomogeneity of the electric field is studied by tracing the shifting and broadening of Wannier–Stark transitions as a function of delay time and bias field. Based on experimental data and results of numerical simulations, we find that the superlattice rapidly splits into two moving field regions, one with strong field gradient and low electron density, the other with partially screened field at low gradient and high electron density. Concerning future Bloch-gain measurements, we find that gain is expected in spite of the inhomogeneous field if the electron-rich region is not heavily screened. The time window during which Bloch gain exists is determined by the sweep out of the electrons (10–30 ps).
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68.65.Cd Superlattices
73.63.-b Electronic transport in nanoscale materials and structures
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance
78.47.-p Spectroscopy of solid state dynamics

Effect of inductively coupled plasma damage on performance of GaN–InGaN multiquantum-well light-emitting diodes

Hyuck Soo Yang, Sang Youn Han, K. H. Baik, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 86, 102104 (2005); http://dx.doi.org/10.1063/1.1882749 (3 pages) | Cited 9 times

Online Publication Date: 3 March 2005

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InGaN multiquantum-well light-emitting diodes (LEDs) in the form of unpackaged die with emission wavelengths from 420 to 505 nm were exposed to either Ar or H2 inductively coupled plasmas as a function of both rf chuck power (controlling incident ion energy) and source power (controlling ion flux). The forward turn-on voltage is increased by both types of plasma exposure and is a function of both the incident ion energy and flux. The reverse bias current in the LEDs is much larger in the case of H2 plasma exposure, indicating that preferential loss of nitrogen leads to increased surface leakage. The current transport in the LEDs is dominated by generation-recombination (ideality factor ∼ 2) both before and after the plasma exposures.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Hs Quantum wells
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Pressure-dependent thermopower of individual Bi nanowires

D. Gitsu, L. Konopko, A. Nikolaeva, and T. E. Huber

Appl. Phys. Lett. 86, 102105 (2005); http://dx.doi.org/10.1063/1.1873045 (3 pages) | Cited 10 times

Online Publication Date: 3 March 2005

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The 240–620 nm diameter nanowires were freely suspended and thermopower measurements were carried out over the temperature range 4–300 K and for stresses as high as 1 GPa. The peaks of up to 80 μV/K that are observed around 40 K are interpreted in terms of a model of diffusion thermopower under strong electron and hole-boundary scattering. The partial Seebeck coefficients are calculated from the stress-dependent carrier Fermi energies obtained from magnetoresistance measurements. The prospect of Bi nanowire arrays achieving high thermoelectric figure of merit is discussed.
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73.63.Bd Nanocrystalline materials
73.50.Lw Thermoelectric effects
75.47.Np Metals and alloys
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
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.40.Rs Electrical and magnetic properties related to treatment conditions

High mobility two-dimensional electron gas in AlGaN/GaN heterostructures grown on bulk GaN by plasma assisted molecular beam epitaxy

C. Skierbiszewski, K. Dybko, W. Knap, M. Siekacz, W. Krupczyński, G. Nowak, M. Boćkowski, J. Łusakowski, Z. R. Wasilewski, D. Maude, T. Suski, and S. Porowski

Appl. Phys. Lett. 86, 102106 (2005); http://dx.doi.org/10.1063/1.1873056 (3 pages) | Cited 19 times

Online Publication Date: 3 March 2005

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The results on growth and magnetotransport characterization of AlGaN/GaN heterostructures obtained by plasma assisted molecular beam epitaxy on dislocation-free (below 100 cm−2) GaN high pressure synthesized bulk substrates are presented. The record mobilities of the two dimensional electron gas (2DEG) exceeding 100 000 cm2/V s at liquid helium temperature and 2 500 cm2/V s at room temperature are reported. An analysis of the high field conductivity tensor components allowed us to discuss the main electron scattering mechanisms and to confirm unambiguously the 2DEG room temperature mobility values.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Fq High-field and nonlinear effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.63.-b Electronic transport in nanoscale materials and structures

Spin injection from the Heusler alloy Co2MnGe into Al0.1Ga0.9As/GaAs heterostructures

X. Y. Dong, C. Adelmann, J. Q. Xie, C. J. Palmstrøm, X. Lou, J. Strand, P. A. Crowell, J.-P. Barnes, and A. K. Petford-Long

Appl. Phys. Lett. 86, 102107 (2005); http://dx.doi.org/10.1063/1.1881789 (3 pages) | Cited 66 times

Online Publication Date: 4 March 2005

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Electrical spin injection from the Heusler alloy Co2MnGe into a p-i-n Al0.1Ga0.9As/GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co2MnGe decays more rapidly with increasing temperature.
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85.60.Jb Light-emitting devices
75.70.Ak Magnetic properties of monolayers and thin films
72.25.Mk Spin transport through interfaces
72.25.Dc Spin polarized transport in semiconductors
72.25.Ba Spin polarized transport in metals
73.40.Ns Metal-nonmetal contacts
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
78.60.Fi Electroluminescence

Activation of shallow boron acceptor in C/B coimplanted silicon carbide: A theoretical study

A. Gali, T. Hornos, P. Deák, N. T. Son, E. Janzén, and W. J. Choyke

Appl. Phys. Lett. 86, 102108 (2005); http://dx.doi.org/10.1063/1.1883745 (3 pages) | Cited 5 times

Online Publication Date: 4 March 2005

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Ab initio supercell calculations have been carried out to investigate the complexes of boron acceptors with carbon self-interstitials in cubic silicon carbide. Based on the calculated binding energies, the complex formation of carbon interstitials with shallow boron acceptor and boron interstitial is energetically favored in silicon carbide. These bistable boron defects possess deep, negative-U occupation levels in the band gap. The theoretical results can explain the observed activation rates in carbon-boron coimplantation experiments.
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61.72.up Other materials
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
61.72.J- Point defects and defect clusters
71.20.Nr Semiconductor compounds
71.15.Nc Total energy and cohesive energy calculations
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