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15 Jan 2007

Volume 90, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 90, 032108 (2007); http://dx.doi.org/10.1063/1.2431702 (3 pages)

D. Buca, B. Holländer, S. Feste, St. Lenk, H. Trinkaus, S. Mantl, R. Loo, and M. Caymax
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Mapping the electrostatic potential across AlGaN/AlN/GaN heterostructures using electron holography

Z. H. Wu, M. Stevens, F. A. Ponce, W. Lee, J. H. Ryou, D. Yoo, and R. D. Dupuis

Appl. Phys. Lett. 90, 032101 (2007); http://dx.doi.org/10.1063/1.2431716 (3 pages) | Cited 11 times

Online Publication Date: 16 January 2007

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Electron holography has been used to study the properties of a nominally undoped AlGaN/AlN/GaN heterostructures. Important characteristics such as the electrostatic potential and the two-dimensional electron gas (2DEG) distribution have been determined with high spatial resolution across the thin film structure. The origin of 2DEG electrons is directly probed by analyzing the charge distribution in the AlGaN layer. It is shown that the contribution of residual donors is trivial and the ionized donorlike surface states are the major source of the 2DEG electrons.
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73.21.Ac Multilayers

Dynamic nuclear polarization induced by hot electrons

Yosuke Komori and Tohru Okamoto

Appl. Phys. Lett. 90, 032102 (2007); http://dx.doi.org/10.1063/1.2431779 (3 pages) | Cited 2 times

Online Publication Date: 16 January 2007

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A method for local dynamic nuclear polarization is demonstrated in a GaAs/AlGaAs heterostructure at the Landau level filling factor ν = 3. Using a narrow channel sample, where the width varies stepwise along the electron flow, the authors find that electron cooling (heating) causes the polarization of nuclear spins against (toward) the external magnetic field at liquid helium temperatures. The longitudinal nuclear spin relaxation rate varies exponentially with inverse temperature.
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76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
76.60.Es Relaxation effects
71.70.Di Landau levels

Work function of Ni3Si2 on HfSixOy and SiO2 and its implication for Ni fully silicided gate applications

J. A. Kittl, B. J. O’Sullivan, V. S. Kaushik, A. Lauwers, M. A. Pawlak, T. Hoffmann, C. Demeurisse, C. Vrancken, A. Veloso, P. Absil, and S. Biesemans

Appl. Phys. Lett. 90, 032103 (2007); http://dx.doi.org/10.1063/1.2430687 (3 pages) | Cited 4 times

Online Publication Date: 16 January 2007

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The effective work function (WF) of Ni3Si2 was evaluated on HfSixOy and SiO2 dielectrics. Ni3Si2 forms, in thin film Ni–Si diffusion couples with Ni to Si composition ratios between 1 and 2, after formation of a Ni2Si/NiSi stack and by its reaction at moderate thermal budgets (comparable to those used in back end processing of complementary metal-oxide-semiconductor circuits). Ni3Si2 formation limits, on the Ni-rich side, the process window for NiSi fully silicided (FUSI) gates (NiSi at interface with dielectric) to reacted Ni–Si ratios <1.5. The WF of Ni3Si2 was found to have similar values and behavior to that of NiSi, both on SiO2 (showing similar modulation with dopants) and on HfSixOy, in contrast to Ni-richer silicides such as Ni2Si and Ni31Si12 which do not exhibit significant WF modulation with dopants on SiO2 and have considerably higher WF on HfSixOy. This suggests that the chemistry and structure of the original NiSi/dielectric interface are not modified significantly by the subsequent growth of Ni3Si2 and implies that its formation may be tolerable when targeting NiSi FUSI gates, thereby expanding the process window for this application.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Fx Diffusion; interface formation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Ct Interface structure and roughness

Electron transport in degenerate Mn-doped ZnO nanowires

J. Salfi, U. Philipose, S. Aouba, S. V. Nair, and H. E. Ruda

Appl. Phys. Lett. 90, 032104 (2007); http://dx.doi.org/10.1063/1.2431788 (3 pages) | Cited 10 times

Online Publication Date: 16 January 2007

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The authors have performed variable-temperature electrical measurements on individual single-crystalline, Mn-doped ZnO nanowires. Using a back-gated field-effect transistor structure fabricated with electron-beam lithography, they have established that nanowires exhibit n-type conduction. At a temperature of 225 K, the field-effect mobility and free electron concentration are ≈ 35 cm2 V−1 s−1 and ≈ 3.6×1017 cm−3, respectively. Carrier concentration varies weakly with temperature down to 12 K, signifying that the material is degenerate. Mobility decreases with decreasing temperature down to 12 K, in a manner consistent with ionized impurity scattering in a degenerate semiconductor.
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73.63.Nm Quantum wires
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
72.20.Fr Low-field transport and mobility; piezoresistance
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Mesoscopic conductance effects in InMnAs structures

S. Lee, A. Trionfi, T. Schallenberg, H. Munekata, and D. Natelson

Appl. Phys. Lett. 90, 032105 (2007); http://dx.doi.org/10.1063/1.2432165 (3 pages) | Cited 2 times

Online Publication Date: 16 January 2007

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Quantum corrections to the electrical conduction of magnetic semiconductors are comparatively unexplored. The authors report measurements of time-dependent universal conductance fluctuations (TDUCFs) and magnetic field dependent universal conductance fluctuations (MFUCFs) in micron-scale structures fabricated from two different In1−xMnxAs thin films. TDUCF and MFUCF increasing in magnitude with decreasing temperature are observed. At 4 K and below, TDUCFs are suppressed at finite magnetic fields independent of field orientation.
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73.23.-b Electronic transport in mesoscopic systems
73.61.Ey III-V semiconductors
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials

Cyclotron localization in a sub-10-nm silicon quantum dot single electron transistor

M. C. Lin, K. Aravind, C. S. Wu, Y. P. Wu, C. H. Kuan, Watson Kuo, and C. D. Chen

Appl. Phys. Lett. 90, 032106 (2007); http://dx.doi.org/10.1063/1.2431565 (3 pages) | Cited 2 times

Online Publication Date: 16 January 2007

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The authors have fabricated and measured a lateral Si single electron transistor consisting of a succession of a big island and small quantum dots. The big island gives rise to a small period Coulomb oscillation riding on the large irregular oscillation arising from the small quantum dots. The peaks of the latter shift in the presence of a magnetic field, which is analyzed in the context of field-induced Landau level shift with a soft-wall confinement potential. Furthermore, the current peak was suppressed for fields beyond a threshold value. An explanation based on cyclotron localization at noninteracting Landau levels is presented.
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85.35.Gv Single electron devices

Fano resonance in the luminescence spectra of donor bound excitons in polar semiconductors

Kui-juan Jin and S. J. Xu

Appl. Phys. Lett. 90, 032107 (2007); http://dx.doi.org/10.1063/1.2432286 (3 pages) | Cited 1 time

Online Publication Date: 17 January 2007

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An unusual response in the luminescence measurements of GaN thin film and ZnO bulk crystal is observed at low temperatures. The authors demonstrate theoretically that such an unusual response is due to the longitudinal optical phonon mediated Fano resonance involved in the recombination process of the donor bound exciton. The line shapes obtained by the calculation in the present mechanism are in excellent agreement with the experimental results.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.55.Et II-VI semiconductors
71.35.Gg Exciton-mediated interactions
63.20.kk Phonon interactions with other quasiparticles

Asymmetric strain relaxation in patterned SiGe layers: A means to enhance carrier mobilities in Si cap layers

D. Buca, B. Holländer, S. Feste, St. Lenk, H. Trinkaus, S. Mantl, R. Loo, and M. Caymax

Appl. Phys. Lett. 90, 032108 (2007); http://dx.doi.org/10.1063/1.2431702 (3 pages) | Cited 10 times

Online Publication Date: 18 January 2007

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Strain relaxation in patterned Si0.77Ge0.23 stripes grown on Si(001) by chemical vapour deposition was investigated after He+ ion implantation and annealing. Ion channeling measurements indicate asymmetric strain relaxation with a significantly higher residual strain parallel to the stripes than perpendicular to the stripes. These results are confirmed by plan view transmission electron microscopy showing a much higher density of misfit dislocations running along the stripes than across the stripes. Estimates based on a piezoresistivity model indicate significant enhancements of electron and hole mobilities for asymmetrically strained Si cap layers on such SiGe stripes.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Le Other inorganic semiconductors
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Wavelength control across the near IR spectrum with GaInNAs

R. S. Williams, W. M. McGee, M. J. Ashwin, T. S. Jones, E. Clarke, P. Stavrinou, J. Zhang, S. Tomić, and C. P. A. Mulcahy

Appl. Phys. Lett. 90, 032109 (2007); http://dx.doi.org/10.1063/1.2431756 (3 pages) | Cited 2 times

Online Publication Date: 18 January 2007

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Accurate control of the photoluminescence (PL) emission wavelength over the range of 1.00–1.55 μm has been achieved using GaIn(N)As multiple quantum well (MQW) structures, grown by plasma-assisted molecular beam epitaxy. By limiting the In content to 30%, hence limiting the overall strain, wavelength-specific MQWs can be grown through simple control over the N content (0%–5%). High crystalline quality and compositional control are demonstrated using high-resolution x-ray diffraction, secondary-ion mass spectroscopy, PL, and subsequent comparison to theoretical calculations using a ten-band k∙p band-anticrossing model. The results reveal adherence to Vegard’s law over a larger compositional range for GaInNAs than GaNAs.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.65.Fg Quantum wells
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Sputtered gold as an effective Schottky gate for strained Si/SiGe nanostructures

G. D. Scott, M. Xiao, H. W. Jiang, E. T. Croke, and E. Yablonovitch

Appl. Phys. Lett. 90, 032110 (2007); http://dx.doi.org/10.1063/1.2430935 (3 pages) | Cited 4 times

Online Publication Date: 18 January 2007

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Metallization of Schottky surface gates by sputtering Au on strained Si/SiGe heterojunctions enables the depletion of the two dimensional electron gas at a relatively small voltage while maintaining an extremely low level of leakage current. A fabrication process has been developed to enable the formation of submicron Au electrodes sputtered onto Si/SiGe without the need of a wetting layer.
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73.40.Ns Metal-nonmetal contacts
81.15.Cd Deposition by sputtering
85.40.Ls Metallization, contacts, interconnects; device isolation
81.05.Bx Metals, semimetals, and alloys
73.30.+y Surface double layers, Schottky barriers, and work functions

SiGeO layer formation mechanism at the SiGe/oxide interfaces during Ge condensation

S. Balakumar, Suo Peng, K. M. Hoe, A. Agarwal, G. Q. Lo, R. Kumar, N. Balasubramanian, D. L. Kwong, and S. Tripathy

Appl. Phys. Lett. 90, 032111 (2007); http://dx.doi.org/10.1063/1.2432252 (3 pages) | Cited 10 times

Online Publication Date: 19 January 2007

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The letter presents the fabrication processes to realize high Ge content SiGe on insulator using Ge condensation technique with and without intermittent oxide etching. During condensation process with intermittent silicon oxide etching, the formation of an undesirable amorphous SiGeO is observed. This is due to uncontrolled oxidation of silicon when the oxide layer is etched away. In the case of Ge condensation process without oxide etching, the authors could achieve a SiGe layer with 91% Ge concentration. A crystalline SiGeO layer at the interfaces of the top silicon oxide and buried oxide with SiGe was also observed. Possible formation mechanisms of amorphous and crystalline SiGeO are presented. Ge condensation process without SiO2 etching utilizes four steps of oxidation and intermittent annealing cycles at each temperature resulted in Si0.09Ge0.91OI substrate.
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81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
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