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10 Dec 2001

Volume 79, Issue 24, pp. 3909-4053

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Towards Si1−xGex quantum-well resonant-state terahertz laser

I. V. Altukhov, E. G. Chirkova, V. P. Sinis, M. S. Kagan, Yu. P. Gousev, S. G. Thomas, K. L. Wang, M. A. Odnoblyudov, and I. N. Yassievich

Appl. Phys. Lett. 79, 3909 (2001); http://dx.doi.org/10.1063/1.1423771 (3 pages) | Cited 28 times

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We report on the experimental evidence for terahertz (THz) lasing of boron-doped strained Si1−xGex quantum-well structures. The lasing arises under strong electric fields (300–1500 V/cm) applied parallel to interfaces. The spectrum of THz stimulated emission is presented showing the lasing wavelength near 100 μm and the modal structure caused by a resonator. The mechanism of population inversion is based on the formation of resonant acceptor states in strained SiGe layer. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
78.67.De Quantum wells
78.45.+h Stimulated emission
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Problems in recent analysis of injected carrier dynamics in semiconductor quantum dots

Roy Lang

Appl. Phys. Lett. 79, 3912 (2001); http://dx.doi.org/10.1063/1.1426265 (2 pages) | Cited 5 times

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This brief letter discusses conceptual problems that appeared in recent analysis of injected carrier dynamics in semiconductor quantum dots. It is pointed out that the frequently adopted approximation of neglecting the upward relaxation transitions severely restricts the validity of rate equations analysis. The proposed alternative approach with master equations for the transitions between microstates has, in principle, validity equivalent with conventional rate equations, but the presented form of equations neglects the upward transitions and has inaccurate expressions for the downward flow contributions. © 2001 American Institute of Physics.
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73.63.Kv Quantum dots
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.La Quantum dots

Turn-off transients in current-modulated multitransverse-mode vertical-cavity surface-emitting lasers

A. Valle and L. Pesquera

Appl. Phys. Lett. 79, 3914 (2001); http://dx.doi.org/10.1063/1.1426269 (3 pages) | Cited 15 times

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Turn-off transients in current-modulated weakly index-guided vertical-cavity surface-emitting lasers (VCSELs) are analyzed by using a model that takes into account all the transverse modes supported by the waveguide. The turn-off transients strength is maximum for the current at which the VCSEL enters the multitransverse-mode regime. Their strength significatively decreases for the multimode regime and then operation in several modes is beneficial to avoiding turn-off transients when modulating the VCSEL well above threshold in order to achieve a required modulation rate or a sufficient optical output power. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Measurement of complex optical constants of a highly doped Si wafer using terahertz ellipsometry

Takeshi Nagashima and Masanori Hangyo

Appl. Phys. Lett. 79, 3917 (2001); http://dx.doi.org/10.1063/1.1426258 (3 pages) | Cited 31 times

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We propose and demonstrate a terahertz (THz) time-domain spectroscopy combined with ellipsometry. The complex optical constants of a Si wafer with low resistivity are deduced from the measurements of the wave forms of reflected s- and p-polarized THz pulses without reference measurement. The obtained dispersion of refractive index above ∼ 0.2 THz shows good agreement with that predicted by the Drude theory. The complex optical constants deduced by the THz ellipsometry in the low-frequency region are strongly affected by the slight error of the ellipsometric angle originating mainly from the misalignment of the rotation angles of the polarizer and analyzer. © 2001 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Design and simulation of terahertz quantum cascade lasers

Rüdeger Köhler, Rita C. Iotti, Alessandro Tredicucci, and Fausto Rossi

Appl. Phys. Lett. 79, 3920 (2001); http://dx.doi.org/10.1063/1.1423777 (3 pages) | Cited 52 times

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Strategies and concepts for the design of THz emitters based on the quantum cascade scheme are analyzed and modeled in terms of a fully three-dimensional Monte Carlo approach; this allows for a proper inclusion of both carrier–carrier and carrier–phonon scattering mechanisms. Starting from the simulation of previously published far-infrared emitters, where no population inversion is achieved, two designs are proposed. The first one follows the well-established chirped-superlattice scheme whereas the second one employs a double-quantum well superlattice to allow energy relaxation through optical phonon emission. For both cases a significant population inversion is predicted at temperatures up to 80 K.© 2001 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Cd Superlattices
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Measurement of optical properties of highly doped silicon by terahertz time domain reflection spectroscopy

S. Nashima, O. Morikawa, K. Takata, and M. Hangyo

Appl. Phys. Lett. 79, 3923 (2001); http://dx.doi.org/10.1063/1.1413498 (3 pages) | Cited 22 times

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Optical properties of doped silicon wafers have been measured by means of terahertz time domain reflection spectroscopy. A method is proposed to obtain the relative phase by reflection accurately. By using this method, the relative phase is obtained within an error of less than 10 mrad at 1 THz. The experimentally obtained complex conductivity of relatively high-doped silicon (ρ = 0.136 Ω cm) in the terahertz region agrees with the simple Drude model. © 2001 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.70.Gq Microwave and radio-frequency interactions
78.47.-p Spectroscopy of solid state dynamics

Local structure and chemical valency of Mn impurities in wide-band-gap III–V magnetic alloy semiconductors Ga1−xMnxN

Y. L. Soo, G. Kioseoglou, S. Kim, S. Huang, Y. H. Kao, S. Kuwabara, S. Owa, T. Kondo, and H. Munekata

Appl. Phys. Lett. 79, 3926 (2001); http://dx.doi.org/10.1063/1.1423406 (3 pages) | Cited 64 times

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Local structure and effective chemical valency of Mn impurity atoms incorporated in wide-band-gap (Ga,Mn)N epilayers have been investigated by using x-ray absorption fine structure techniques. The x-ray results provide direct evidence for the substitution of majority Mn atoms for the Ga sites in GaN, with an effective valency close to Mn(II), up to a rather high Mn concentration about 2 at. %. A small fraction of the impurity atoms could also form Mn clusters. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra

Polarization effects of imperfections in conducting and dielectric samples imaged with polarization-sensitive scanning near-field optical microscopy

G. Eggers, A. Rosenberger, N. Held, G. Güntherodt, and P. Fumagalli

Appl. Phys. Lett. 79, 3929 (2001); http://dx.doi.org/10.1063/1.1419039 (3 pages) | Cited 1 time

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The influence of intrinsic birefringence and of surface imperfections on the polarization of near-field light is investigated in thin films by polarization-sensitive scanning near-field optical microscopy in transmission mode. The experimental results will be discussed and a simple simulation algorithm is proposed. © 2001 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
75.50.Gg Ferrimagnetics
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
78.66.Bz Metals and metallic alloys
77.55.-g Dielectric thin films
68.37.Uv Near-field scanning microscopy and spectroscopy
78.20.Fm Birefringence
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Self-assembled GaIn(N)As quantum dots: Enhanced luminescence at 1.3 μm

T. Hakkarainen, J. Toivonen, M. Sopanen, and H. Lipsanen

Appl. Phys. Lett. 79, 3932 (2001); http://dx.doi.org/10.1063/1.1425082 (3 pages) | Cited 10 times

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Self-assembled GaIn(N)As quantum dots are fabricated on GaAs by atmospheric pressure metalorganic vapor-phase epitaxy using dimethylhydrazine (DMHy) precursor as a nitrogen source. The incorporation of nitrogen into the islands is observed to be negligible. However, the areal density of the islands is increased by up to one order of magnitude compared to that of the respective GaInAs islands. The GaIn(N)As island size can also be controlled by varying the DMHy flow. An enhancement of the room-temperature luminescence at 1.3 μm is observed in the GaIn(N)As samples grown with DMHy. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
78.55.Cr III-V semiconductors
81.16.Dn Self-assembly
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Individually injected current pulses with conducting-tip, tapping-mode atomic force microscopy

Asa Fein, Yanming Zhao, Charles A. Peterson, Ghassan E. Jabbour, and Dror Sarid

Appl. Phys. Lett. 79, 3935 (2001); http://dx.doi.org/10.1063/1.1424473 (3 pages) | Cited 4 times

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Individually injected current pulses during the operation of a conducting-tip tapping-mode atomic force microscope have been measured under a range of experimental conditions. The bias pulses, applied during the tip-sample contact time, did not perturb the tapping operations, and eliminated artifacts associated with displacement currents. The reproducible injection of current density pulses on the order of 10 μA/nm2 per tap can be applied to spreading resistance measurements and to storage applications employing, for example, phase change by Joule heating and magnetic switching by spin-polarized current. © 2001 American Institute of Physics.
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68.37.Ps Atomic force microscopy (AFM)
07.79.Lh Atomic force microscopes
75.60.-d Domain effects, magnetization curves, and hysteresis

Chemical ordering in lanthanum-doped lead magnesium niobate relaxor ferroelectrics probed by A1g Raman mode

Fuming Jiang, Seiji Kojima, Changlei Zhao, and Chude Feng

Appl. Phys. Lett. 79, 3938 (2001); http://dx.doi.org/10.1063/1.1425957 (3 pages) | Cited 29 times

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Chemical ordering of the B-site cations in undoped, 5, 10, 20, and 30 mol % La3+-doped Pb(Mg1/3Nb2/3)O3 (PMN) ceramics with perovskite structure, has been examined by Raman scattering. Two B-site chemical ordering models, the space-charge model, and the random layer model assume a space group of Fmmathm for the ordered nanoregions. It is found that A1g Raman mode around 780 cm−1 from the B-site ordered nanoregions with a space group Fmmathm, is very sensitive to the delicate changes of the chemical order at B site. Frequency changes of this A1g characteristic mode with La3+ doping, are analyzed according to the lattice parameters and chemical order effects. The present results provide stronge evidence supporting the random layer model in La-doped PMN. © 2001 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
61.66.Fn Inorganic compounds
78.30.Hv Other nonmetallic inorganics
61.50.Lt Crystal binding; cohesive energy

Nanometric inversion domains in conventional molecular-beam-epitaxy GaN thin films observed by atomic-resolution high-voltage electron microscopy

C. Iwamoto, X. Q. Shen, H. Okumura, H. Matuhata, and Y. Ikuhara

Appl. Phys. Lett. 79, 3941 (2001); http://dx.doi.org/10.1063/1.1427147 (3 pages) | Cited 9 times

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GaN films grown on sapphire substrates by conventional molecular-beam epitaxy were investigated by means of atomic-resolution high-voltage electron microscopy (ARHVEM). The atomic positions of Ga and N could be directly discriminated by ARHVEM to determine the polarity in GaN. It was revealed that N polarity GaN films possessed a high density of nanometric inversion domains (IDs) with Ga polarity. The ID boundary was constructed by an inversion and a c/2 translation, and formed fourfold and eightfold coordination along the boundary. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
68.37.-d Microscopy of surfaces, interfaces, and thin films

Luminescence from stacking faults in 4H SiC

S. G. Sridhara, F. H. C. Carlsson, J. P. Bergman, and E. Janzén

Appl. Phys. Lett. 79, 3944 (2001); http://dx.doi.org/10.1063/1.1425084 (3 pages) | Cited 41 times

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A previously unreported photoluminescence spectrum observed in certain 4H SiC bipolar diodes after extended forward voltage operation is reported. We assign this emission to exciton recombination at local potential fluctuations caused by stacking faults, which are created during operation of the diodes. Possible recombination mechanisms responsible for the spectrum are discussed. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
61.72.Nn Stacking faults and other planar or extended defects
71.35.Gg Exciton-mediated interactions
85.30.Kk Junction diodes

Equation of state of bulk metallic glasses studied by an ultrasonic method

Wei Hua Wang, Ping Wen, Li Min Wang, Yong Zhang, Ming Xiang Pan, De Qian Zhao, and Ru Ju Wang

Appl. Phys. Lett. 79, 3947 (2001); http://dx.doi.org/10.1063/1.1426272 (3 pages) | Cited 26 times

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The acoustic velocities and their pressure dependence of various Zr- and Pd-based bulk metallic glasses (BMGs) have been measured by using a pulse echo overlap method. The elastic constants as well as their pressure dependence of the BMGs have been determined, and the equation of state of these BMGs was obtained and compared to that of other glasses and crystalline solids. The structural characteristic of the BMGs is discussed. © 2001 American Institute of Physics.
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64.30.-t Equations of state of specific substances
62.65.+k Acoustical properties of solids
62.20.D- Elasticity
61.43.Fs Glasses
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Annealing behavior of vacancies and Z1/2 levels in electron-irradiated 4H–SiC studied by positron annihilation and deep-level transient spectroscopy

A. Kawasuso, F. Redmann, R. Krause-Rehberg, M. Weidner, T. Frank, G. Pensl, P. Sperr, W. Triftshäuser, and H. Itoh

Appl. Phys. Lett. 79, 3950 (2001); http://dx.doi.org/10.1063/1.1426259 (3 pages) | Cited 20 times

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Annealing behavior of vacancies and the Z1/2 levels in n-type 4H–SiC epilayers after 2 MeV electron irradiation has been studied using positron annihilation and deep-level transient spectroscopy. Isochronal annealing studies indicate that silicon vacancy-related defects are primarily responsible for positron trapping. The Z1/2 levels are the predominant deep centers after irradiation and subsequent annealing at 1200 °C. Both the positron-trapping rate at vacancies and the Z1/2 concentration decrease in a similar manner while annealing from 1200 to 1500 °C. It is thus proposed that the Z1/2 levels originate from silicon vacancy-related defects. © 2001 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
78.70.Bj Positron annihilation
71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors

Structural and optical properties of ZnO films grown on R–Al2O3 substrates

B. P. Zhang, Y. Segawa, K. Wakatsuki, Y. Kashiwaba, and K. Haga

Appl. Phys. Lett. 79, 3953 (2001); http://dx.doi.org/10.1063/1.1426255 (3 pages) | Cited 12 times

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Structural and optical properties of ZnO films grown on R–Al2O3 substrates by atmospheric pressure chemical-vapor deposition were investigated using x-ray diffraction and photoluminescence. The (11math0) plane of the ZnO film tilted 0.3° with respect to the (1math02) plane of the substrate and rotated about 7° around the normal of the sample surface. Symmetric (11math0) and asymmetric (20math2) x-ray reflection on ZnO films with different thicknesses were carried out. Comparison with photoluminescence measurements allowed us to conclude that the optical properties of the ZnO films are predominately determined by the in-plane, rather than out-of-plane, structural features. © 2001 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

Orientation-controlled nucleation of crystal silicon grains in amorphous silicon on a rolled nickel tape substrate

Hwang Huh and Jung H. Shin

Appl. Phys. Lett. 79, 3956 (2001); http://dx.doi.org/10.1063/1.1421420 (3 pages) | Cited 3 times

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Crystal silicon grains with grain sizes in excess of 10 μm and orientation control over all three directions were produced by depositing an amorphous silicon thin film on a cold-rolled and annealed nickel tape and annealing at 600 °C for 2 h. The needle-like morphology of the grains indicated that the crystallization was mediated by NiSi2. All grains had their [110] axis about 21° off the surface normal. Furthermore, nearly all of them had the same rotation about the [110] axis except for presence of twins and/or type A–B formations. Despite the use of the nickel substrate, the Ni concentration within the Si film was below the detection limit of energy-dispersive x-ray spectroscopy (1019 cm−3). This low-Ni contamination level is attributed to the presence of an oxide layer between the Ni substrate and the Si film. © 2001 American Institute of Physics.
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81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

In situ sensor for interstitial trapping during Si thermal oxidation using He implantation-induced voids

Vito Raineri, Stella Giuffrida, and Emanuele Rimini

Appl. Phys. Lett. 79, 3959 (2001); http://dx.doi.org/10.1063/1.1426693 (3 pages) | Cited 4 times

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The shrinkage of voids created by He implants in silicon has been measured during thermal oxidation. The empty volume is filled by self-interstitials injected during oxidation. The increase in volume is proportional to the oxide thickness and follows the same time dependence. The captured interstitial surface density ranges between 1015 and 1016 cm−2. The amount of captured interstitials for a given oxide thickness is temperature independent above 1050 °C, but below that it decreases, indicating the presence of competing defect centers for the capture of interstitials. The method demonstrates the possibility to use void layers as in situ sensors for interstitials. © 2001 American Institute of Physics.
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61.72.J- Point defects and defect clusters
71.55.Cn Elemental semiconductors
81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
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A self-passivated Cu(Mg) gate electrode for an amorphous silicon thin-film transistor

W. H. Lee, B. S. Cho, B. J. Kang, H. J. Yang, J. G. Lee, I. K. Woo, S. W. Lee, J. Jang, G. S. Chae, and H. S. Soh

Appl. Phys. Lett. 79, 3962 (2001); http://dx.doi.org/10.1063/1.1424062 (3 pages) | Cited 21 times

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The feasibility of using Cu(Mg) alloy film as a gate electrode for thin-film transistor (TFT) liquid crystal displays has been investigated. When pure Cu was used as a gate electrode, severe interdiffusion occurred between Cu and the gases SiH4, NH3, and CF4 during plasma-enhanced chemical vapor deposition of a gate dielectric, SiNx, and dry etching of the SiNx. On the other hand, the deposition of a Cu(Mg) alloy film gives rise to the formation of a MgO/Cu bilayer structure with low Cu resistivity, good adhesion to SiO2, higher leakage current density, and excellent passivation capability. A hydrogenated amorphous silicon TFT with a MgO encapsulated Cu gate exhibited a gate voltage swing of 0.91 V/dec. and a threshold voltage of 6.8 V, resulting in a reduction of process steps and better performance. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
42.79.Kr Display devices, liquid-crystal devices
85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.Rv Passivation
85.40.Sz Deposition technology

Grain boundary transport and vapor sensing in α-sexithiophene

J. H. Schön, Ch. Kloc, A. Dodabalapur, and B. Crone

Appl. Phys. Lett. 79, 3965 (2001); http://dx.doi.org/10.1063/1.1423787 (3 pages) | Cited 3 times

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The charge transport through an α-sexithiophene bi-crystal exposed to various gaseous agents is investigated in the temperature range from 4 to 300 K. This method allows a comparison between intragrain and grain boundary effects. The importance of grain boundaries for gas sensing applications is demonstrated. Charged trap states are formed at the grain boundaries, which lead to the change of the potential barrier at the boundary. Consequently, the charge transport properties are affected by the gas exposure. © 2001 American Institute of Physics.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.Mm Grain and twin boundaries
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
71.55.Ht Other nonmetals

Capture and thermal re-emission of carriers in long-wavelength InGaAs/GaAs quantum dots

M. De Giorgi, C. Lingk, G. von Plessen, J. Feldmann, S. De Rinaldis, A. Passaseo, M. De Vittorio, R. Cingolani, and M. Lomascolo

Appl. Phys. Lett. 79, 3968 (2001); http://dx.doi.org/10.1063/1.1421235 (3 pages) | Cited 32 times

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We investigate the ultrafast carrier dynamics in metalorganic chemical vapor deposition-grown InGaAs/GaAs quantum dots emitting at 1.3 μm. Time-resolved photoluminescence upconversion measurements show that the carriers photoexcited in the barriers relax to the quantum-dot ground state within a few picoseconds. At low temperatures and high carrier densities, the relaxation dynamics is dominated by carrier–carrier scattering. In contrast, at room temperature, the dominant relaxation process for electrons is scattering between quantum-dot levels via multiple longitudinal optical (LO)-phonon emission. The reverse process, i.e., multiple LO-phonon absorption, governs the thermal re-emission of electrons from the quantum-dot ground state. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.63.Kv Quantum dots
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.Hc Quantum dots
71.38.-k Polarons and electron-phonon interactions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhanced dopant activation and elimination of end-of-range defects in BF2+-implanted silicon-on-insulator by high-density current

H. H. Lin, S. L. Cheng, L. J. Chen, Chih Chen, and K. N. Tu

Appl. Phys. Lett. 79, 3971 (2001); http://dx.doi.org/10.1063/1.1423773 (3 pages) | Cited 4 times

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Enhanced dopant activation and elimination of end-of-range (EOR) defects in BF2+-implanted silicon-on-insulator (SOI) have been achieved by high-density current stressing. With the high-density current stressing, the implantation amorphous silicon underwent recrystallization, enhanced dopant activation and elimination of the (EOR) defects. The current stressing method allows the complete removal of EOR defects that has not been possible with conventional thermal annealing in the processing of high-performance SOI devices. © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.uf Ge and Si
71.55.Cn Elemental semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Cc Kinetics of defect formation and annealing

Composition dependence of Raman intensity of the nitrogen localized vibrational mode in GaAs1−xNx

M. J. Seong, M. C. Hanna, and A. Mascarenhas

Appl. Phys. Lett. 79, 3974 (2001); http://dx.doi.org/10.1063/1.1424469 (3 pages) | Cited 22 times

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We have investigated the nitrogen-localized vibrational mode (LVM) Raman intensity and its frequency (ωLVM) as a function of nitrogen concentration in GaAs1−xNx (x ⩽ 0.04) at 300 K. The normalized Raman intensity of nitrogen LVM with respect to that of GaAs–LO phonon as well as ωLVM exhibits a remarkable linear dependence on the nitrogen concentration for x ⩽ 0.03. This provides excellent calibration to determine nitrogen composition not only in the ternary alloy GaAs1−xNx but also in the quaternaries such as Ga1−yInyAs1−xNx. © 2001 American Institute of Physics.
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63.20.Pw Localized modes
78.30.Fs III-V and II-VI semiconductors
82.80.Gk Analytical methods involving vibrational spectroscopy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
78.66.Fd III-V semiconductors

Enhancement of parametric pumping due to Andreev reflection

Jian Wang, Yadong Wei, Baigeng Wang, and Hong Guo

Appl. Phys. Lett. 79, 3977 (2001); http://dx.doi.org/10.1063/1.1421236 (3 pages) | Cited 28 times

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We report properties of parametric electron pumping in the presence of a superconducting lead. Due to a constructive interference between the direct reflection and the multiple Andreev reflection, the pumped current is greatly enhanced. For both quantum point contacts and double barrier structures at resonance, we obtain exact solutions in the weak pumping regime showing that IpNS = 4IpN, which should be compared with the result of conductance GNS = 2GN. Numerical results are also provided for the strong pumping regime showing interesting Andreev assisted pumping behavior. © 2001 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
74.50.+r Tunneling phenomena; Josephson effects

Growth and characterization of p-type HgTe/Hg1−xCdxTe single quantum wells using nitrogen and arsenic

K. Ortner, X. C. Zhang, S. Oehling, J. Gerschütz, A. Pfeuffer-Jeschke, V. Hock, C. R. Becker, G. Landwehr, and L. W. Molenkamp

Appl. Phys. Lett. 79, 3980 (2001); http://dx.doi.org/10.1063/1.1425465 (3 pages) | Cited 4 times

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p-type HgTe/Hg0.3Cd0.7Te(001) quantum wells (QWs) have been grown with molecular-beam epitaxy (MBE) on Cd0.96Zn0.04Te substrates using modulation doping techniques. Both plasma-excited nitrogen and evaporated cadmium arsenide have been utilized for in situ doping during MBE growth. A comparison of the electrical and structural properties of QWs fabricated by the two doping techniques has been made. Two-dimensional hole concentrations in nitrogen-doped QWs (up to 1.0×1012 cm−2) were significantly higher than in arsenic-doped QWs (below 0.5×1012 cm−2). However, by means of a gate-controlled Hall bar, hole densities up to 1.1×1012 cm−2 have been achieved in the latter system. Hall mobilities up to 1.0×105 cm2/(V s) have been measured. Whereas all samples exhibit pronounced although irregular Shubnikov–de Haas oscillations, quantum Hall plateaus in the arsenic-doped samples are broader and better defined. © 2001 American Institute of Physics.
Show PACS
73.63.Hs Quantum wells
73.61.Ga II-VI semiconductors
68.65.Fg Quantum wells
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
68.35.Ct Interface structure and roughness
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
73.43.Qt Magnetoresistance
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