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26 Dec 2005

Volume 87, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 87, 263102 (2005); http://dx.doi.org/10.1063/1.2150278 (3 pages)

Z. Zhong, G. Katsaros, M. Stoffel, G. Costantini, K. Kern, O. G. Schmidt, N. Y. Jin-Phillipp, and G. Bauer
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Electrochemical preparation of a stable accumulation layer on Si: A synchrotron radiation photoelectron spectroscopy study

K. Skorupska, M. Lublow, M. Kanis, H. Jungblut, and H. J. Lewerenz

Appl. Phys. Lett. 87, 262101 (2005); http://dx.doi.org/10.1063/1.2150267 (3 pages) | Cited 19 times

Online Publication Date: 19 December 2005

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Chronoamperometric conditioning of float zone n-Si(111) in 2 M NaOH solution in the potential range negative from open-circuit potential is performed in a combined electrochemistry/ultrahigh-vacuum surface analysis experiment. Synchrotron Radiation Photoelectron Spectroscopy measurements at the U49/2 beamline at Bessy II using the SoLiAs facility show formation of a ultrahigh-vacuum-stable permanent accumulation layer without junction formation. Comparison of the Thomas–Fermi screening potential and the mean inelastic scattering length λesc of photoelectrons at hν = 150 eV (λesc = 4 Å) and hν = 585 eV (λesc = 15 Å) indicates a surface electron concentration of 3×1018 cm−3 for a bulk doping level of 1015 cm−3. The observed shift of the Si 2p3/2 and 2p1/2 core level with photon energy is in excellent agreement with the shifted onset of the x-ray photoelectron spectroscopy valence-band spectrum measured at hν = 150 eV.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
82.45.-h Electrochemistry and electrophoresis

Dielectric properties of ultrathin SiO2 slabs

N. Shi and R. Ramprasad

Appl. Phys. Lett. 87, 262102 (2005); http://dx.doi.org/10.1063/1.2150584 (3 pages) | Cited 6 times

Online Publication Date: 19 December 2005

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First-principles total energy calculations have been performed to determine the extent to which surfaces impact the dielectric properties of ultrathin dielectric materials. SiO2 (0001) slabs in α-quartz phase with various thicknesses were considered in this study, using a new method that allows for the partitioning of the surface and bulk contributions to the total field-induced polarization. It was found that the bulk polarization and the dielectric constant can be determined even from ultrathin films terminated with Si atoms, and that surface effects do not significantly impact the dielectric properties of (0001) α-quartz slabs.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Carrier dynamics in laterally strain-modulated InGaAs quantum wells

Vadim Talalaev, Jens W. Tomm, Thomas Elsaesser, Ute Zeimer, Jörg Fricke, Arne Knauer, Heiko Kissel, Markus Weyers, Georgiy G. Tarasov, J. Grenzer, and U. Pietsch

Appl. Phys. Lett. 87, 262103 (2005); http://dx.doi.org/10.1063/1.2151248 (3 pages) | Cited 2 times

Online Publication Date: 19 December 2005

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We investigate the transient recombination and transfer properties of nonequilibrium carriers in an In0.16Ga0.84As/GaAs quantum well (QW) with an additional lateral confinement implemented by a patterned stressor layer. The structure thus contains QW- and quantum-wire-like areas. At low excitation densities, photoluminescence (PL) transients from both areas are well described by a rate equation model for a three-level system with a saturable interlevel carrier transfer representing the lateral drift of carriers from the QW regions into the wires. Small-signal carrier lifetimes for QW, wires, and transfer time from QW to wire are 180, 190, and 28 ps, respectively. For high excitation densities the time constants of the observed transients increase, in agreement with the model. In addition, QW and wire PL lines merge indicating a smoothening of the potential difference, i.e., the effective carrier confinement caused by the stressor structure becomes weaker with increasing excitation.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors

Investigation of silicon-germanium fins fabricated using germanium condensation on vertical compliant structures

Tsung-Yang Liow, Kian-Ming Tan, Yee-Chia Yeo, Ajay Agarwal, Anyan Du, Chih-Hang Tung, and Narayanan Balasubramanian

Appl. Phys. Lett. 87, 262104 (2005); http://dx.doi.org/10.1063/1.2151257 (3 pages) | Cited 6 times

Online Publication Date: 19 December 2005

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We report the formation of defect-free SiGe vertical heterostructures using Ge condensation on vertical SiGe structures. To evaluate the effectiveness of substrate compliance in vertical structures, SiGe fins of various widths were subjected to Ge condensation. This formed vertical fin heterostructures comprising a SiGe core region sandwiched by Ge-rich regions. Using cross-sectional transmission electron microscopy (TEM), wide fins were found to contain more dislocations than narrower fins, in which we observed few or no dislocations. Lattice strain analysis using high-resolution TEM image analysis was used to confirm that strain relaxation has occurred. In the wide fins (noncompliant substrate), strain relaxation was dislocation mediated. In the narrow fins, substrate compliance enabled strain relaxation in the Ge-rich layer with reduced dislocation formation. Hence, we also demonstrated the formation of a strain-relaxed homogeneous SiGe fin ( ∼ 90% Ge concentration) with no observable dislocations.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.60.Bs Mechanical and acoustical properties
64.70.F- Liquid-vapor transitions

Local p-type conductivity in zinc oxide dual-doped with nitrogen and arsenic

A. Krtschil, A. Dadgar, N. Oleynik, J. Bläsing, A. Diez, and A. Krost

Appl. Phys. Lett. 87, 262105 (2005); http://dx.doi.org/10.1063/1.2149171 (3 pages) | Cited 30 times

Online Publication Date: 20 December 2005

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A doping approach for p-type ZnO is reported which is reproducible and long-time stable. For p-type doping the zinc oxide layers were doped simultaneously with nitrogen and arsenic in metal organic vapor phase epitaxy. The conductivity type of the layers was investigated by scanning capacitance microscopy, a technique based on local capacitance-voltage analysis (C-V) with submicron spatial resolution. Depending on the growth parameters, largely extended p-type domains were observed, surrounded by n-type regions. The differences in local conductivity type are directly correlated to the topography as measured with atomic force microscopy revealing p-type for smooth, two-dimensional surfaces and n-type signals in the case of three-dimensional island growth or structural defects, i.e., microcracks or surface pits.
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73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.47.Fg Semiconductor surfaces
68.37.Ps Atomic force microscopy (AFM)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
72.60.+g Mixed conductivity and conductivity transitions

Demonstration of Rashba spin splitting in GaN-based heterostructures

W. Weber, S. D. Ganichev, S. N. Danilov, D. Weiss, W. Prettl, Z. D. Kvon, V. V. Bel’kov, L. E. Golub, Hyun-Ick Cho, and Jung-Hee Lee

Appl. Phys. Lett. 87, 262106 (2005); http://dx.doi.org/10.1063/1.2158024 (3 pages) | Cited 40 times

Online Publication Date: 20 December 2005

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The circular photogalvanic effect, induced by infrared radiation, has been observed in (0001)-oriented n‐GaN low dimensional structures. The photocurrent changes sign upon reversing the radiation helicity demonstrating the existence of spin splitting of the conduction band in k space in this type of materials. The observation suggests the presence of a sizeable Rashba type of spin splitting, caused by the built-in asymmetry at the AlGaN/GaN interface.
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73.21.Fg Quantum wells
73.50.Pz Photoconduction and photovoltaic effects
73.63.Hs Quantum wells
73.20.At Surface states, band structure, electron density of states

Surface conductive layers on oxidized (111) diamonds

Sung-Gi Ri, Daisuke Takeuchi, Hiromitsu Kato, Masahiko Ogura, Toshiharu Makino, Satoshi Yamasaki, Hideyo Okushi, Bohuslav Rezek, and Christoph E. Nebel

Appl. Phys. Lett. 87, 262107 (2005); http://dx.doi.org/10.1063/1.2158020 (3 pages) | Cited 6 times

Online Publication Date: 20 December 2005

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Surface conductive layers (SCL) on oxidized (111) diamonds with smooth surfaces after exposure to air were detected and characterized by Hall effect measurements. Hall effect measurements show that the conductivity is p type with sheet hole concentrations around of 1012 cm−2 and Hall mobilities between 5 and 130 cm2/V s. The SCL vanishes by thermal annealing at a temperature higher than 460 K in He atmosphere, and recovers in air. These characteristics are similar to those generated by hydrogen termination. The experiments revealed that these SCLs are present on boron doped (111) and undoped (111) diamond films with smooth surfaces and natural IIa (111) diamonds, but not on (111) diamond films with rough surfaces and not on (100) diamonds.
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73.25.+i Surface conductivity and carrier phenomena
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.Cc Kinetics of defect formation and annealing

Fast-forming boron-oxygen-related recombination center in crystalline silicon

Karsten Bothe and Jan Schmidt

Appl. Phys. Lett. 87, 262108 (2005); http://dx.doi.org/10.1063/1.2147727 (3 pages) | Cited 5 times

Online Publication Date: 21 December 2005

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The mechanism of a fast carrier lifetime degradation effect proceeding within seconds in boron-doped Czochralski silicon is investigated. The decrease in the carrier lifetime is attributed to the formation of a deep boron-oxygen-related recombination center with a strongly asymmetric electron-to-hole capture cross section ratio of 100. The center is activated in a two-step process. In a first step, the electron quasi-Fermi level has to be shifted above an energy level at EV+0.635 eV before, in the second step, the actual activation occurs via a thermally activated process with an energy barrier of 0.23 eV. A defect model is proposed to explain the observed activation behavior.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Effect of strain on p-channel metal-oxide-semiconductor field-effect-transistor current enhancement using stress-modulated silicon nitride films

Cha-Hsin Lin, Zingway Pei, Siddheswar Maikap, Ching-Chiun Wang, Ching-Sen Lu, Lurng-Shehng Lee, Ming-Jinn Tsai, and Yi-Jen Chan

Appl. Phys. Lett. 87, 262109 (2005); http://dx.doi.org/10.1063/1.2149987 (3 pages) | Cited 1 time

Online Publication Date: 21 December 2005

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The stress in chemical-vapor-deposited silicon nitride films ( ∼ 100 nm thick) is modulated by an ion implantation technique. The tensile-strained silicon nitride film is deposited on the back and front sides of a Si wafer. After implantation of P+, As+, Sb+, or BF2+ ion species, the stress of the silicon nitride film becomes compressive on the front side. It can be explained by strain relaxation of Si–N bond on the front side and highly tensile-strained Si–N bond on the back side of wafer. The compressive stress is increased with a double-implantation process because of more atomic collisions in the silicon nitride film, as well as more strain relaxation of Si–N bond on the front side of wafer. After a thermal annealing process, the compressive stress in the silicon nitride film with P+, As+, or Sb+ implantation is reduced, while compressive stress is increased for BF2+ ion implantation due to formation of the B–N bond in silicon nitride film. To justify the stress-modulated silicon nitride film by the ion implantation technique, the p-channel metal-oxide-semiconductor field-effect transistor (p-MOSFET) is fabricated. The drive current of a p-MOSFET is improved by 7–13% for implanted silicon nitride films, due to the compressive strain-induced effective mass lowering in the channel.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing

Elliptically polarized absorption spectroscopy and observation of spin coherence in intrinsic GaAs

Tianshu Lai, Xiaodong Liu, Haihong Xu, Zhongxing Jiao, Liang Lei, Jinhui Wen, and Weizhu Lin

Appl. Phys. Lett. 87, 262110 (2005); http://dx.doi.org/10.1063/1.2150276 (3 pages) | Cited 6 times

Online Publication Date: 23 December 2005

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The elliptically polarized absorption spectroscopy is further developed to observe electron spin coherence dynamics in an intrinsic bulk GaAs in Voigt geometry. Absorption saturation quantum beats are observed and explained as spin-precession-dependent state filling. An analytical model is developed quantitatively to describe the quantum beats and used to fit experimental data to retrieve spin coherence lifetime. Comparing to the reported data reveals that the spin coherence dynamics of the real and imaginary of a complex refractive index is much different.
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78.47.-p Spectroscopy of solid state dynamics
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.20.Ls Magneto-optical effects
78.30.Fs III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Noninterfacial-nitride formation ohmic contact mechanism in Si-containing Ti/Al/Mo/Au metallizations on AlGaN/GaN heterostructures

Fitih M. Mohammed, Liang Wang, and Ilesanmi Adesida

Appl. Phys. Lett. 87, 262111 (2005); http://dx.doi.org/10.1063/1.2149968 (3 pages) | Cited 8 times

Online Publication Date: 23 December 2005

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Excellent ohmic contact formation to undoped-AlGaN/GaN heterostructures is achieved by the incorporation of silicon into Ti/Al/Mo/Au metallization. Contact resistance and specific contact resistivity as low as 0.16 Ω mm and 6.77×10−7 Ω cm2, respectively, have been obtained for the Ti/Si/Al/Si/Mo/Au scheme. Transmission electron microscopy has revealed that the ohmic contact formation mechanism depends on the competing interfacial nitride and silicide formation reactions, the latter giving rise to improved contact performance. The formation and penetration of non-nitride reaction products of Si-containing Al–Au intermetallics to depths beyond the AlGaN/GaN interface were observed. The superior ohmic performance of these schemes suggests that silicide-based low Schottky barrier contact formation may be preferable to an interfacial nitride contact mechanism in achieving improved ohmic behavior.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation
73.30.+y Surface double layers, Schottky barriers, and work functions

Impact of N-induced potential fluctuations on the electron transport in Ga(As,N)

F. Ishikawa, G. Mussler, K.-J. Friedland, H. Kostial, K. Hagenstein, L. Däweritz, and K. H. Ploog

Appl. Phys. Lett. 87, 262112 (2005); http://dx.doi.org/10.1063/1.2158511 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2005

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We investigate the electron transport in Ga(As,N) layers focusing on the influence of potential fluctuations. With increasing electron concentration, a metal-insulator transition is observed in the temperature dependence of the resistivity for a series of samples containing 0.8% of N. The observed behavior is discussed in the frame of Anderson transition. By increasing the N concentration up to 2.2%, we observe an increase of the potential fluctuations’ amplitude. Mean-square values for the intrinsic N-induced fluctuation γN are obtained from percolation theory to be larger than 30 meV. Rapid thermal annealing reduces γN significantly for samples with higher N concentration. These large potential fluctuations lead to electron localization and induce thermally activated conductivity which is observable up to 300 K.
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73.61.Ey III-V semiconductors
71.30.+h Metal-insulator transitions and other electronic transitions
61.72.Cc Kinetics of defect formation and annealing

Avalanche breakdown and breakdown luminescence of AlGaN multiquantum wells

S. K. Zhang, W. B. Wang, A. M. Dabiran, A. Osinsky, A. M. Wowchak, B. Hertog, C. Plaut, P. P. Chow, S. Gundry, E. O. Troudt, and R. R. Alfano

Appl. Phys. Lett. 87, 262113 (2005); http://dx.doi.org/10.1063/1.2158489 (3 pages) | Cited 1 time

Online Publication Date: 28 December 2005

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AlGaN p-i-n diodes were fabricated on 6H-SiC substrate using Al0.1Ga0.9N/Al0.15Ga0.85N multiquantum wells (MQWs) for the active region. Avalanche breakdown and breakdown luminescence of these AlGaN MQW diodes were experimentally investigated. Breakdown electroluminescence from the MQW active layers was observed for unusually low bias values of 9 V. A continuous red shift of the interband luminescence resulting from the Stark effect was observed with increasing reverse bias. The breakdown threshold was found to be as low as 9 V. Polarization-induced electric fields in the Al0.1Ga0.9N well layers were found to have the same direction as the applied field. These polarization fields greatly enhance the ionization coefficient of electrons and help lower the threshold for avalanche breakdown. Substantial enhancement of the ionization coefficient produced by the polarization fields is quantitatively demonstrated with GaN/AlGaN quantum wells by considering a polarization field with the same direction as the applied field within the GaN well layers.
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85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Inelastic mean-free path of electrons at nanocrystalline diamond surfaces

J. Zemek, J. Potmesil, M. Vanecek, B. Lesiak, and A. Jablonski

Appl. Phys. Lett. 87, 262114 (2005); http://dx.doi.org/10.1063/1.2159575 (2 pages) | Cited 14 times

Online Publication Date: 28 December 2005

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Surprisingly large difference between inelastic mean-free path (IMFP) values of signal electrons calculated from optical data and from the predictive TPP-2M formulae for diamond or graphite has motivated us to verify both sources of IMFP by measuring these values using different method. Thin, perfectly transparent nanocrystalline diamond films were characterized by x-ray induced photoelectron and Auger electron spectroscopy. Elastic peak electron spectroscopy measurements and the Monte Carlo calculations of electron transport were applied to determine the IMFPs for medium electron energy. The surface energy losses were also considered when evaluating these IMFPs.
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73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Fv Electron impact: Auger emission
68.35.Md Surface thermodynamics, surface energies

Approach for investigating lateral conduction in self-assembled monolayers

Srivardhan Gowda, Guru Mathur, Qiliang Li, Shyam Surthi, and Veena Misra

Appl. Phys. Lett. 87, 262115 (2005); http://dx.doi.org/10.1063/1.2152112 (3 pages) | Cited 1 time

Online Publication Date: 29 December 2005

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Lateral conductivity within a monolayer is a key factor in the implementation of emerging dense molecular memory devices since it determines the degree of cross talk between cells. Lateral interactions within a monolayer could also lead to loss of charge through defective sites. Existing characterization techniques are limited to probing the electrical communication between molecules and attached electrodes. In this paper we demonstrate a test structure consisting of n type and p type doped silicon islands to isolate vertical conduction from lateral conduction. This structure is a useful characterization tool for tailoring the intrinsic properties of the molecules for information storage.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
73.61.Cw Elemental semiconductors
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