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24 Mar 2003

Volume 82, Issue 12, pp. 1809-1988

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 1935 (2003); http://dx.doi.org/10.1063/1.1563051 (3 pages)

S. V. Roth, M. Burghammer, C. Riekel, P. Müller-Buschbaum, A. Diethert, P. Panagiotou, and H. Walter
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Phase-unifying mirrors for high-power XeF excimer lasers

F. De Tomasi, P. Aghamkar, M. R. Perrone, M. L. Protopapa, A. Piegari, B. Andre’, and G. Ravel

Appl. Phys. Lett. 82, 1809 (2003); http://dx.doi.org/10.1063/1.1562345 (3 pages) | Cited 1 time

Online Publication Date: 18 March 2003

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A phase-unifying unstable cavity of magnification factor M = 5.8 has been applied to a high-power, commercial XeF laser, and the measurements for characterizing near- and far-field beam properties are reported. A laser beam of 280 mJ, 30 ns duration, a cross section of 2.4×1.3 cm2, and a beam quality factor of 4.3 along the discharge direction (x axis) and of 2.1 along the y direction has been obtained. The beam exhibits a smooth far-field profile with more than 90% of the total near-field energy within a far-field full angle θ ⩽ 0.04 mrad. The beam angular stability is of 0.009 and of 0.004 mrad along x and y, respectively. © 2003 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Polariton emission from polysilane-based organic microcavities

Noriyuki Takada, Toshihide Kamata, and Donal D. C. Bradley

Appl. Phys. Lett. 82, 1812 (2003); http://dx.doi.org/10.1063/1.1559950 (3 pages) | Cited 37 times

Online Publication Date: 18 March 2003

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We report the observation of strong coupling between exciton and photon modes in a conjugated polymer-based semiconductor microcavity. Thin films of the σ-conjugated poly[bis(p-butylphenyl)silane] (PBPS) were inserted between metal and dielectric mirrors to form the microcavity structures. Variation of the PBPS film thickness between 80 and 140 nm allowed the cavity photon resonance to be tuned in the vicinity of the free exciton energy. The expected anticrossing behavior, with intensity and linewidth averaging, was observed at room temperature in the cavity reflection spectra and the vacuum Rabi splitting was found to be ⩽ 430 meV. This large value is consistent with the expectations of transfer matrix reflectivity calculations performed with optical constants data derived from a Kramers–Kronig analysis of the PBPS absorption spectrum. Angle-dependent photoluminescence measurements were performed for the microcavity with a 120 nm thickness PBPS layer. Unlike the emission from a standard, weakly coupled, cavity, the polariton emission shows almost no blueshift with angle, a desirable feature for potential display applications. © 2003 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena
78.55.Kz Solid organic materials
78.55.Qr Amorphous materials; glasses and other disordered solids
78.66.Jg Amorphous semiconductors; glasses
78.66.Qn Polymers; organic compounds

Growing evanescent waves in negative-refractive-index transmission-line media

Anthony Grbic and George V. Eleftheriades

Appl. Phys. Lett. 82, 1815 (2003); http://dx.doi.org/10.1063/1.1561167 (3 pages) | Cited 40 times

Online Publication Date: 18 March 2003

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We show the enhancement of evanescent waves by a realizable negative-refractive-index (NRI) medium consisting of a periodic 2-D L,C loaded transmission-line (TL) network. This network is referred to as a dual TL structure. Growing evanescent waves within the dual TL structure are predicted analytically and demonstrated through simulation. These findings confirm that the dual TL structure is not simply a phase compensator that corrects the phase of propagating waves, but is in fact a NRI medium, since it also enhances the amplitudes of evanescent waves. This structure is a likely candidate for microwave subwavelength focusing and imaging applications. © 2003 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
84.30.Bv Circuit theory
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment

Simultaneous two-state lasing in quantum-dot lasers

A. Markus, J. X. Chen, C. Paranthoën, A. Fiore, C. Platz, and O. Gauthier-Lafaye

Appl. Phys. Lett. 82, 1818 (2003); http://dx.doi.org/10.1063/1.1563742 (3 pages) | Cited 96 times

Online Publication Date: 18 March 2003

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We demonstrate simultaneous lasing at two well-separated wavelengths in self-assembled InAs quantum-dot lasers, via ground-state (GS) and excited-state (ES) transitions. This effect is reproducible and strongly depends on the cavity length. By a master-equation model, we attribute it to incomplete clamping of the ES population at the GS threshold. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots

Tomographic imaging with a terahertz binary lens

S. Wang and X.-C. Zhang

Appl. Phys. Lett. 82, 1821 (2003); http://dx.doi.org/10.1063/1.1563043 (3 pages) | Cited 8 times

Online Publication Date: 18 March 2003

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The focal length of a binary lens is linearly proportional to the frequency of the imaging beam; this property allows objects at various positions along the beam propagation path to be uniquely imaged on the same imaging plane with different corresponding frequencies. We reconstructed tomographic images of objects by assembling the frequency-dependent images, and demonstrated three-dimensional tomographic imaging using a binary lens with broadband terahertz pulses. © 2003 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.30.Wb Image reconstruction; tomography
42.79.Bh Lenses, prisms and mirrors
07.05.Pj Image processing
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Fluorocarbon plasma etching and profile evolution of porous low-dielectric-constant silica

Arvind Sankaran and Mark J. Kushner

Appl. Phys. Lett. 82, 1824 (2003); http://dx.doi.org/10.1063/1.1562333 (3 pages) | Cited 22 times

Online Publication Date: 18 March 2003

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To achieve shorter RC-delay times in integrated circuits low-dielectric-constant (low-k) materials are being investigated for interconnect wiring. Porous silicon dioxide (PS) is one such material. To address scaling issues during fluorocarbon plasma etching of PS, a feature profile model has been integrated with a plasma equipment model. To focus on issues related to the morphology of porous materials, the PS was treated as stoichiometric SiO2. The model was validated by comparison to experiments for PS etching in CHF3 plasmas sustained in an inductively coupled reactor. We found that etch rates (ER) for PS are generally higher than for SiO2 due to the inherent smaller mass density, although ER do not necessarily scale linearly with pore size or porosity. Mass-corrected ER can be either larger or smaller than that of solid SiO2. For example, in polymerizing environments, at high porosities and large pore radii, there is a reduction in ER due to pore filling with polymer. Profile scaling parameters, such as for tapering, observed for solid SiO2, are generally applicable to PS. © 2003 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)

The importance of bias pulse rise time for determining shallow implanted dose in plasma immersion ion implantation

D. T. K. Kwok, M. M. M. Bilek, D. R. McKenzie, and P. K. Chu

Appl. Phys. Lett. 82, 1827 (2003); http://dx.doi.org/10.1063/1.1563063 (3 pages) | Cited 17 times

Online Publication Date: 18 March 2003

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The composition of the low-energy ions arising from the rise and fall time periods of the voltage pulse in plasma immersion ion implantation (PIII) are simulated by particle-in-cell (PIC) modeling. It is shown that more than 70% of the low-energy ions with an energy corresponding to less than half of the applied voltage come from the short rise time period. Although the fall time period is typically 30 times longer than the rise time, less than 25% of the low-energy ions originate from it. Based on the PIC results, the depth profile of the implanted ions is derived using the Monte-Carlo code SRIM2000 [J. F. Ziegler, The Stopping and Range of Ions in Solids (Pergamon, New York, 1985)]. The low-energy ions are found to be implanted to a much shallower depth than ions introduced during the fall time period the concentration profile which decays more sharply into the bulk. These results indicate that the most effective way to reduce or increase the surface concentration is by adjusting the rise time of the PIII voltage pulse. This will require a power supply capable of fast rise times and good matching between power supply and load. © 2003 American Institute of Physics.
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52.77.Dq Plasma-based ion implantation and deposition
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.uf Ge and Si
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Surface segregation of boron in BxGa1−xAs/GaAs epilayers studied by x-ray photoelectron spectroscopy and atomic force microscopy

H. Dumont, D. Rutzinger, C. Vincent, J. Dazord, Y. Monteil, F. Alexandre, and J. L. Gentner

Appl. Phys. Lett. 82, 1830 (2003); http://dx.doi.org/10.1063/1.1561164 (3 pages) | Cited 8 times

Online Publication Date: 18 March 2003

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The behavior of boron incorporation into GaAs has been studied by x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy. As the boron content of the film was increased, both the characteristic peak for the B 1s core level at 188 eV and As Auger transition (260 eV) could be detected by XPS. At 550–600 °C, single crystalline films could only be grown for x ⩽ 0.06. Upon increasing the diborane flux in the gas phase, the film stoichiometry and the boron surface composition evolved rapidly towards a boron-rich subarsenide compound. This trend is followed by a clear degradation of the surface morphology and an increase in the surface roughness. A surface segregation of boron is suggested due to the high diborane vapor supersaturation needed during growth. © 2003 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
68.55.Nq Composition and phase identification
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Ps Atomic force microscopy (AFM)
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Nitride-mediated epitaxy of CoSi2 on Si(001)

R. K. K. Chong, M. Yeadon, W. K. Choi, E. A. Stach, and C. B. Boothroyd

Appl. Phys. Lett. 82, 1833 (2003); http://dx.doi.org/10.1063/1.1555708 (3 pages) | Cited 18 times

Online Publication Date: 18 March 2003

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Epitaxial layers of CoSi2 have been grown on Si(100) by the technique of nitride-mediated epitaxy. An ultrathin layer of silicon nitride was formed on the Si(001) surface by exposure to ammonia gas at 900 °C, followed by the deposition of a layer of Co ∼ 20 Å in thickness at room temperature. The sample was then annealed at 600 °C and the microstructure monitored by in situ transmission electron microscopy and diffraction. The formation of epitaxial islands of CoSi2 was observed directly, with no evidence of the formation of intermediate phases. The CoSi2 islands were found to be elongated along the in-plane Si〈110〉 directions, consistent with reports of the deposition of Co by molecular beam epitaxy on clean Si(100) at low deposition rates and elevated temperature. This technique of silicidation may be of particular interest in the fabrication of advanced devices incorporating multilayer oxide/nitride gate stacks. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.40.Sz Deposition technology
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys

Superheating systematics of crystalline solids

Sheng-Nian Luo and Thomas J. Ahrens

Appl. Phys. Lett. 82, 1836 (2003); http://dx.doi.org/10.1063/1.1563046 (3 pages) | Cited 51 times

Online Publication Date: 18 March 2003

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Systematics of superheating (θ = T/Tm−1) of crystalline solids as a function of heating rate (Q) are established as β = A(Q)(θ+1)θ2, where the normalized energy barrier for homogeneous nucleation is β = 16πγsl3/(3kTmΔHm2), T is temperature, Tm melting temperature, A a Q-dependent parameter, γsl interfacial energy, ΔHm heat of fusion, and k Boltzmann’s constant. For all elements and compounds investigated, β varies between 0.2 and 8.2. At 1 and 1012 K/s, A = 60 and 31, θ = 0.05–0.35 and 0.06–0.45, respectively. Significant superheating is achievable via ultrafast heating. We demonstrate that the degree of superheating achieved in shock-wave loading and intense laser irradiation as well as in molecular dynamics simulations (Q ∼ 1012 K/s) agrees with the θ–β–Q systematics. © 2003 American Institute of Physics.
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64.70.D- Solid-liquid transitions
64.60.Q- Nucleation
62.50.-p High-pressure effects in solids and liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

First-principles study of phosphorus diffusion in silicon: Interstitial- and vacancy-mediated diffusion mechanisms

Xiang-Yang Liu, Wolfgang Windl, Keith M. Beardmore, and Michael P. Masquelier

Appl. Phys. Lett. 82, 1839 (2003); http://dx.doi.org/10.1063/1.1562342 (3 pages) | Cited 33 times

Online Publication Date: 18 March 2003

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A vacancy-mediated diffusion mechanism has been assumed in traditional models of P diffusion in Si. However, recent experiments have suggested that for intrinsic P diffusion in Si, the interstitial-assisted diffusion mechanism dominates. Here, we describe first-principles calculations of P diffusion in Si performed to study interstitial- and vacancy-mediated diffusion mechanisms. Special care is taken with regard to structural minimization, charge state effects and corrections. We calculated the defect formation energies and migration barriers for the various competing P–interstitial diffusion mechanisms, as well as P–vacancy diffusion energetics in different charge states. For P–interstitial diffusion, we find overall diffusion activation energies of 3.1–3.5 eV for neutral and +1 charge states, in close agreement with experiments at intrinsic conditions. For P–vacancy diffusion, our calculation is in agreement with previous calculations in the neutral case, but suggests that only P+V = plays a role in the heavily doped n region while the interstitial mechanisms may dominate in near-intrinsic regions. © 2003 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters

Epitaxial growth of CoSi2 on hydrogen-terminated Si(001)

K. Ishida, Y. Miura, K. Hirose, S. Harada, and T. Narusawa

Appl. Phys. Lett. 82, 1842 (2003); http://dx.doi.org/10.1063/1.1562335 (3 pages) | Cited 6 times

Online Publication Date: 18 March 2003

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We demonstrate that CoSi2 grows epitaxially on H-terminated Si(001) and present the growth mechanism. It was found that direct reaction of Co with Si is suppressed on H-terminated Si below 400 °C. Thus, the hydrogen at the Co/Si interface hinders the formation of Co2Si and CoSi. Upon thermal desorption of hydrogen at around 400–550 °C, CoSi2, which is closely lattice-matched to Si(001), grows on Si(001) and thus, thin epitaxial CoSi2 films are formed on Si(001). The {111}-faceting was completely suppressed in the epitaxial CoSi2/Si(001), leading to the atomically flat interface. © 2003 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.At Metal and metallic alloys

GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy emitting above 1.5 μm

E. Tournié, M.-A. Pinault, M. Laügt, J.-M. Chauveau, A. Trampert, and K. H. Ploog

Appl. Phys. Lett. 82, 1845 (2003); http://dx.doi.org/10.1063/1.1563062 (3 pages) | Cited 26 times

Online Publication Date: 18 March 2003

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We demonstrate that a careful optimization of the molecular-beam-epitaxy growth conditions allows us to obtain high-quality GaInNAs/GaAs quantum-well (QW) heterostructures exhibiting a perfect two-dimensional microstructure at high In and N contents. Room-temperature emission is achieved up to 1.61 and 1.51 μm for as-grown and annealed samples, respectively. High-resolution x-ray diffraction and transmission electron microscopy reveal that post-growth annealing does not affect the QW composition and width. This confirms that the GaInNAs semiconducting material is well suited for emission in the telecommunication wavelength range near 1.55 μm. © 2003 American Institute of Physics.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)

Confinement-enhanced biexciton binding energy in ZnO/ZnMgO multiple quantum wells

C. H. Chia, T. Makino, K. Tamura, Y. Segawa, M. Kawasaki, A. Ohtomo, and H. Koinuma

Appl. Phys. Lett. 82, 1848 (2003); http://dx.doi.org/10.1063/1.1561158 (3 pages) | Cited 40 times

Online Publication Date: 18 March 2003

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By employing a nanosecond pump-probe method, biexciton formation process was investigated in ZnO/Zn1−xMgxO (x = 0.26) multiple quantum wells (MQWs) grown on ScAlMgO4 substrate by laser molecular-beam epitaxy. Bleaching of absorption due to the saturation of excitonic states, and induced absorption related to the exciton–biexciton transition were observed in their spectra. It is demonstrated that the pump-probe method allows us to precisely determine binding energies of exciton complexes even applied to the semiconductor quantum structures where the localization effect are not negligible. This is because a transition from free-excitonic states to free-biexcitonic states is involved in the induced absorption process. The biexciton binding energy is a monotonically decreasing function of well width (Lw). For the MQWs with Lw smaller than 2.5 nm, the biexciton binding energy is larger than 25 meV, comparable to the thermal energy of room temperature. © 2003 American Institute of Physics.
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73.21.Fg Quantum wells
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
78.67.De Quantum wells
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.40.Fy Semiconductors
78.47.-p Spectroscopy of solid state dynamics
68.65.Fg Quantum wells

Electrical and thermal properties of single-crystalline (Ca2CoO3)0.7CoO2 with a Ca3Co4O9 structure

Masahiro Shikano and Ryoji Funahashi

Appl. Phys. Lett. 82, 1851 (2003); http://dx.doi.org/10.1063/1.1562337 (3 pages) | Cited 126 times

Online Publication Date: 18 March 2003

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Single crystals of (Ca2CoO3)0.7CoO2 were grown using a modified strontium chloride flux technique, and their electrical and thermal properties were determined. Growth conditions were established for obtaining plate-like single crystals of a relatively large size (5×10×0.05 mm3). At 973 K, thermoelectric power S and electrical resistivity ρ of the specimens are ≈240 μV K−1 and ≈ 2.3×10−5 Ω m, respectively, and their thermal conductivity κ is nearly 3 W m1 K−1, as determined by mathematical extrapolation. The figure of merit ZT = S2T/ρκ derived therefrom is ≈0.87 at 973 K. The relatively low κ is likely the result of a misfit structure between the CoO2 layer and the Ca2CoO3 slab. © 2003 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
72.80.Jc Other crystalline inorganic semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Excitonic luminescence from nonsymmetric heterovalent AlAs/GaAs/ZnSe quantum wells

A. Kudelski, U. Bindley, J. K. Furdyna, M. Dobrowolska, and T. Wojtowicz

Appl. Phys. Lett. 82, 1854 (2003); http://dx.doi.org/10.1063/1.1563055 (3 pages) | Cited 5 times

Online Publication Date: 18 March 2003

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We report the observation of excitons localized in an asymmetric GaAs quantum well (QW) embedded between AlAs and ZnSe barriers. Samples with different QW thicknesses (10, 15, and 18 monolayers) have been studied, showing clear confining effects in the photoluminescence emission. To achieve confinement in the GaAs QWs, it was necessary to design the band alignment across the AlAs/GaAs/ZnSe layer sequence, and to carefully tailor the growth conditions in order to achieve the required band alignment profile. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Et II-VI semiconductors
78.67.De Quantum wells

Ultrafast directional nickel-silicide-induced crystallization of amorphous silicon under high-density current stressing

C. H. Yu, H. H. Lin, S. L. Cheng, and L. J. Chen

Appl. Phys. Lett. 82, 1857 (2003); http://dx.doi.org/10.1063/1.1563060 (3 pages) | Cited 6 times

Online Publication Date: 18 March 2003

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Ultrafast directional crystallization that combined the electric current stressing with metal-induced crystallization has been achieved for BF2+-implanted amorphous Si (a-Si) at room temperature. Polycrystalline Si was observed to grow from anode towards cathode and the channels of a-Si strips with a length of 140 μm and a width of 10 μm can be fully crystallized with a stressing time less than 0.2 s. The directional growth of crystalline Si nanowires, 50 nm in width and as long as 3 μm in length, with an extraordinarily high aspect ratio of 60, indicates a strong electric-field-induced effect on the growth. The growth method provides a promising scheme to solve the problems caused by high-temperature and long-term annealing treatment for the applications of optoelectronic devices. © 2003 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
81.07.Lk Nanocontacts
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
68.47.Fg Semiconductor surfaces
68.35.Ct Interface structure and roughness

Annealing of isolated amorphous zones in silicon

S. E. Donnelly, R. C. Birtcher, V. M. Vishnyakov, and G. Carter

Appl. Phys. Lett. 82, 1860 (2003); http://dx.doi.org/10.1063/1.1562336 (3 pages) | Cited 22 times

Online Publication Date: 18 March 2003

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In situ transmission electron microscopy has been used to observe the production and annealing of individual amorphous zones in silicon resulting from impacts of 200-keV Xe ions at room temperature. As has been observed previously, the total amorphous volume fraction decreases over a temperature range from room temperature to approximately 500 °C. When individual amorphous zones were monitored, however, there appeared to be no correlation of the annealing temperature with initial size: zones with similar starting sizes disappeared (crystallized) at temperatures anywhere from 70 °C to more than 400 °C. Frame-by-frame analysis of video recordings revealed that the recovery of individual zones is a two-step process that occurred in a stepwise manner with changes taking place over seconds, separated by longer periods of stability. © 2003 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.82.Fk Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
61.80.Jh Ion radiation effects
61.72.uf Ge and Si

Room-temperature grain growth in sputter-deposited Cu films

C. Detavernier, D. Deduytsche, R. L. Van Meirhaeghe, J. De Baerdemaeker, and C. Dauwe

Appl. Phys. Lett. 82, 1863 (2003); http://dx.doi.org/10.1063/1.1563048 (3 pages) | Cited 18 times

Online Publication Date: 18 March 2003

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The microstructure of sputter-deposited Cu films is shown to be unstable at room temperature (RT). The average grain size increases significantly during RT storage for a couple of hours after deposition. This RT grain growth is shown to be very dependent on the deposition parameters (substrate temperature and sputter gas pressure) and hence on the microstructure of the as-deposited film. The microstructure of sputter-deposited films is usually summarized in a structure-growth-zone model. It is found that significant RT grain growth only occurs for Cu layers with a zone-T-type, as-deposited microstructure. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Nanoscale investigation of longitudinal surface acoustic waves

Jianshu Yang, P. U. Voigt, and R. Koch

Appl. Phys. Lett. 82, 1866 (2003); http://dx.doi.org/10.1063/1.1561578 (3 pages) | Cited 2 times

Online Publication Date: 18 March 2003

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Scanning tunneling microscopy of longitudinally polarized surface acoustic waves (SAWs) yields amplitude and phase images with nanometer resolution. The eccentricity of the surface oscillation calculated from the experimental data by the model of Chilla et al. is 88°±5° in good agreement with the macroscopic value for high velocity pseudo SAWs. Our study reveals that reliable amplitude and phase information can be deduced even from atomic scale features; however, the local surface geometry and tip shape need to be treated in more detail. © 2003 American Institute of Physics.
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43.35.Pt Surface waves in solids and liquids
68.35.Iv Acoustical properties
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
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Local impedance imaging and spectroscopy of polycrystalline ZnO using contact atomic force microscopy

Rui Shao, Sergei V. Kalinin, and Dawn A. Bonnell

Appl. Phys. Lett. 82, 1869 (2003); http://dx.doi.org/10.1063/1.1561168 (3 pages) | Cited 51 times

Online Publication Date: 18 March 2003

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A current detection scanning probe technique is developed that quantifies frequency-dependent local transport properties. The approach, referred to as nanoimpedance microscopy/spectroscopy (NIM), is based on impedance spectroscopy with a conductive atomic force microscopy (AFM) tip. NIM is applied to study the quality of a tip/surface contact and transport behavior of individual grains and grain boundaries in polycrystalline ZnO. Impedance spectra were measured in the frequency range 40 Hz to 110 MHz, and the grain boundary properties are studied by nonlinear fitting of experimental data to an equivalent circuit. Two-terminal measurements are performed in the vicinity of a single ZnO grain boundary and the Cole–Cole plot indicates two major relaxation processes attributed to grain boundary relaxation and tip/surface contact. © 2003 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
07.79.Lh Atomic force microscopes
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
61.72.Mm Grain and twin boundaries
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts

Transport properties of two-dimensional electron gas in different subbands in triangular quantum wells at AlxGa1−xN/GaN heterointerfaces

Z. W. Zheng, B. Shen, Y. S. Gui, C. P. Jiang, N. Tang, R. Zhang, Y. Shi, Y. D. Zheng, S. L. Guo, G. Z. Zheng, J. H. Chu, T. Someya, and Y. Arakawa

Appl. Phys. Lett. 82, 1872 (2003); http://dx.doi.org/10.1063/1.1557772 (3 pages) | Cited 10 times

Online Publication Date: 18 March 2003

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Magnetotransport properties of modulation-doped Al0.22Ga0.78N/GaN heterostructures were investigated by means of magnetoresistance measurements at low temperatures and high magnetic fields. Strong Shubnikov–de Haas oscillations with the double periodicity are observed. The mobility spectrum is obtained, which demonstrates that the mobilities of the two-dimensional electron gas (2DEG) in the two subbands in the triangular quantum well at heterointerface. It is found that the mobility of the 2DEG in the second subband is much higher than that in the first one. This is explained that interface roughness scattering and alloy disorder scattering have much stronger influence on transport properties of the 2DEG in the first subband than that in the second subband in AlxGa1−xN/GaN heterostructures. © 2003 American Institute of Physics.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
68.65.Fg Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Pq Other materials

p-type doping of II–VI heterostructures from surface states: Application to ferromagnetic Cd1−xMnxTe quantum wells

W. Maślana, P. Kossacki, M. Bertolini, H. Boukari, D. Ferrand, S. Tatarenko, J. Cibert, and J. A. Gaj

Appl. Phys. Lett. 82, 1875 (2003); http://dx.doi.org/10.1063/1.1560873 (3 pages) | Cited 17 times

Online Publication Date: 18 March 2003

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We present a study of p-type doping of CdTe and Cd1−xMnxTe quantum wells from surface states. We show that this method is as efficient as usual modulation doping with nitrogen acceptors, and leads to hole densities exceeding 2×1011 cm−2. Surface doping was applied to obtain samples with Cd1−xMnxTe quantum well with up to x = 9.3% containing hole gas. We could also increase the growth temperature up to 280 °C, which results in sharper photoluminescence lines, when compared to the similar nitrogen doped samples. Carrier-induced ferromagnetism was observed in surface doped samples. © 2003 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
73.20.At Surface states, band structure, electron density of states
75.50.Pp Magnetic semiconductors
68.65.Fg Quantum wells
78.55.Et II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
73.21.Fg Quantum wells
78.67.De Quantum wells

Silver thick-film contacts on highly doped n-type silicon emitters: Structural and electronic properties of the interface

C. Ballif, D. M. Huljić, G. Willeke, and A. Hessler-Wyser

Appl. Phys. Lett. 82, 1878 (2003); http://dx.doi.org/10.1063/1.1562338 (3 pages) | Cited 56 times

Online Publication Date: 18 March 2003

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The properties of Ag thick-film contacts screen-printed on P-diffused [100] Si wafers have been investigated. In cross-sectional transmission electron microscopy, the interface is found to be composed of 200–500-nm-diameter Ag crystallites penetrating the silicon on average by up to 130 nm. The smaller crystallites are in epitaxial relation with the Si substrate, indicating their growth from the glass frit melt. A quasicontinuous glassy layer is present between the interface Ag crystallites and the larger Ag grains, which form the bulk of the contact. Conductive atomic force microscopy of cross sections shows that the interface crystallites form a low contact resistivity with the Si emitter in the range of 10−7 Ω cm2. We discuss the mechanisms of contact formation and propose a model in which the current flow from the emitter into the contact is not uniform, but occurs via a few isolated Ag crystallites that are directly connected or in close distance to the Ag grains forming the contact bulk. © 2003 American Institute of Physics.
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68.35.Ct Interface structure and roughness
73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
84.60.Jt Photoelectric conversion
73.40.Cg Contact resistance, contact potential
68.37.Ps Atomic force microscopy (AFM)
68.37.Lp Transmission electron microscopy (TEM)
85.40.Xx Hybrid microelectronics; thick films

Nitrogen-enhanced negative bias temperature instability: An insight by experiment and first-principle calculations

Shyue Seng Tan, T. P. Chen, Jia Mei Soon, Kian Ping Loh, C. H. Ang, and L. Chan

Appl. Phys. Lett. 82, 1881 (2003); http://dx.doi.org/10.1063/1.1563045 (3 pages) | Cited 33 times

Online Publication Date: 18 March 2003

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The nitrogen-enhanced negative bias temperature instability (NBTI) effect has been studied experimentally and theoretically. It is observed that both the interface state and positive fixed charge generation increase linearly with interfacial nitrogen concentration. The experimental results can be understood in terms of the reaction energies of the hydrogen trapping reactions at the interface, which are obtained from first-principle calculations. These results improve our understanding of the mechanisms responsible for the nitrogen-enhanced NBTI effect. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.20.Hb Impurity and defect levels; energy states of adsorbed species
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