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171.
P. Altieri M. Gurioli S. Sanguinetti E. Grilli M. Guzzi P. Frigeri S. Franchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):157-161
The presence of an extrinsic photoluminescence (PL) band peaked at 1.356 eV at low temperature is observed, on a large number
of self-assembled InAs and In0.5Ga0.5As quantum dot (QD) structures, when exciting just below the GaAs absorption edge. A detailed optical characterization allows
us to attribute the 1.356 eV PL band to the radiative transition between the conduction band and the doubly ionized Cu
Ga acceptor in GaAs. A striking common feature is observed in all investigated samples, namely a resonant quenching of the QD-PL
when exciting on the excited level of this deep defect. Moreover, the photoluminescence excitation (PLE) spectrum of the 1.356
eV emission turns out to be almost specular to the QD PLE. This correlation between the PL efficiency of the QDs and the Cu
centers evidences a competition in the carrier capture arising from a resonant coupling between the excited level of the defect
and the electronic states of the wetting layer on which the QDs nucleate. The estimated Cu concentration is compatible with
a contamination during the epitaxial growth.
Received 13 November 2001 / Received in final form 28 May 2002 Published online 19 July 2002 相似文献
172.
Magneto-spectroscopy to 17.5 T of the Zn acceptor impurity in InP in the Faraday configuration using unpolarised radiation is reported. Four components of the G line have been followed to higher fields than previously, allowing the g factors of the ground and the first excited states to be determined more reliably. The Zeeman splitting of the D line is reported—three principal components are evident. A hitherto unreported third series of Zeeman transitions is observed at energies just above the reststrahlen band. 相似文献
173.
G. Ewald K. -M. Knaak S. Götte K. D. A. Wendt H. -J. Kluge 《Applied physics. B, Lasers and optics》2005,80(4-5):483-487
We present two diode laser setups that employ volume holographic transmission gratings to provide optical feedback. The advantage of this kind of grating is high diffraction efficiency and the possibility to place optical elements on both sides of the grating. This allows for advanced external cavities and adjustable feedback efficiency. The first setup is a diode laser in the Littman configuration with the transmission grating replacing the conventional reflection grating. The second setup improves the frequency selectivity by substituting the feedback mirror with a passive resonator. This grating-enhanced external cavity diode laser (GECDL) achieves excellent frequency stability. A prototype of the GECDL setup demonstrates an intrinsic linewidth of 7 kHz and an operation range that covers the full amplification profile of the laser diode. 相似文献
174.
R. Zwierz S. Golka K. Kachel D. Siche R. Fornari P. Sennikov A. Vodopyanov A. V. Pipa 《Crystal Research and Technology》2013,48(4):186-192
We present an alternative approach to grow thick GaN single crystalline layers from Ga vapour, transported by an N2 carrier gas flow, and from nitrogen, excited very near the substrate by 2.45 GHz microwaves at pressure in the 200–800 mbar range. Crystal growth requires high stability of process parameters, especially of plasma operation. A major challenge arose from temperature dependent changes in cavity resonance. Optical emission spectroscopy (OES) was used for plasma characterization while the grown layers were characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). 相似文献
175.
A new equation of state for associating fluids has recently been presented by Medeiros and Tellez-Arredondo, the Cubic-Two-State Equation of State (CTS EoS) [Ind. Eng. Chem. Res. 47 (2008) 5723]. This equation arises from the coupling of the Soave–Redlich–Kwong EoS (SRK) with an association term from a two-state association model. The CTS EoS is polynomial in volume and it is able to describe vapor pressures and molar volume of associating fluids such as water, alcohol and phenol, among others. The equation is also able to describe the liquid–vapor equilibria of their mixtures with alkanes. In this paper, the physical and thermodynamic foundations of the CTS EoS are further investigated. In order to verify its applicability for cross-associating systems, the equation was employed in the prediction of phase equilibria behavior of binary alcohol–alcohol and water–alcohol mixtures. Very good agreement between predictions and experimental phase equilibria data was obtained with very simple combining rules and only one adjustable binary parameter. No additional parameters were necessary to describe ternary systems. With the purpose of checking the model's hypothesis and limitations, the two-state association term was coupled with the hard sphere Carnahan–Starling EoS, forming the CS-TS equation and the association characteristic parameters were determined theoretically for prototype association fluids. Monte Carlo NPT simulations of such fluids were performed and the results were compared with the equation's predictions. The CS-TS was able to describe qualitatively the pvT behavior of the prototype; nevertheless, it is not as accurate as those predictions obtained from the combination CS with Wertheim's association term. It seems that, when adjusting parameters of the CTS EoS to real substances, the discrepancies between the predicted and the real association contribution are dissipated among other adjustable parameters, specially on the dispersive term of the SRK equation. Finally, it is shown that CTS EoS isotherms can only have one or three real bigger roots than the co-volume for positive pressures, similar to cubic equations of state, and then it has the desirable form to describe vapor–liquid phase equilibria of associating compounds mixtures. 相似文献
176.
Muresan AS Ostrovskii BI Sánchez-Ferrer A Finkelmann H de Jeu WH 《The European physical journal. E, Soft matter》2006,19(4):385-388
We report a high-resolution X-ray lineshape study of main-chain smectic polymers. The results indicate that the layer ordering
differs fundamentally from the algebraic decay typical for other smectic liquid-crystalline systems. The lineshapes are best
described by broad squared Lorentzians indicating some form of short-range correlations. However, several higher harmonics
are observed, which excludes simple liquid-like short-range order. This behaviour is tentatively attributed to a random field
of defects associated with entangled hairpins in the main-chain polymer structure. 相似文献
177.
Teruaki Obata Jun-ichi Iwata Kenji Shiraishi Atsushi Oshiyama 《Journal of Crystal Growth》2009,311(10):2772-2775
In-related nitride semiconductors exhibit characteristic behavior which can be ascribed to the large difference in the covalent radius between In and N atoms. We consider atomic and electronic structures of N mono-vacancies (VN) in InGaN in detail by the first principles calculations. We find that the second nearest neighbor In–In interactions, which are not important in conventional semiconductors such as Si and InAs, are as crucial as the nearest neighbor In–N interaction in In-related nitride semiconductors. Moreover, we clearly show that the strong second nearest neighbor In–In interactions in InN are the physical origin of the unusually narrow band gap of InN. 相似文献
178.
A.Y. Polyakov N.B. Smirnov A.V. Govorkov A.V. Markov E.B. Yakimov P.S. Vergeles H. Amano T. Kawashima 《Journal of Crystal Growth》2009,311(10):2923-2925
Electrical properties, deep traps spectra and structural performance were studied for m-GaN films grown on m-SiC substrates by standard metalorganic chemical vapor deposition (MOCVD) and by MOCVD with lateral overgrowth (ELO) or sidewall lateral overgrowth (SELO). Standard MOCVD m-GaN films with a very high dislocation density over 109 cm−2 are semi-insulating n-type with the Fermi level pinned near Ec−0.7 eV when grown at high V/III ratio. For lower V/III they become more highly conducting, with the electrical properties still dominated by a high density (∼1016 cm−3) of Ec−0.6 eV electron traps. Lateral overgrowth that reduces the dislocation density by several orders of magnitude results in a marked increase in the uncompensated shallow donor density (∼1015 cm−3) and a substantial decrease of the density of major electron traps at Ec−0.25 and Ec−0.6 eV (down to about 1014 cm−3). Possible explanations are briefly discussed. 相似文献
179.
K. Mazaev V. Kalaev E. Galenin S. Tkachenko O. Sidletskiy 《Journal of Crystal Growth》2009,311(15):3933-3937
In the present work, numerical modeling has been performed to analyze heat transfer and melt convection during bismuth germanate Bi4Ge3O12 (BGO) crystal growth by the Czochralski growth method. In addition to global heat-transfer modeling, the suggested model accounts for the radiative heat exchange in the crystal and melt convection together with the crystallization front formation. The model helped to analyze the modification of the growth setup made by including additional heater. The numerical predictions obtained with CGSim software agree well with available experimental data. 相似文献
180.
Optical Potential Parameters for Halo Nucleus System ^6He+^12C from Transfer Reaction ^11B(^7Li, ^6He)^12C
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The optical potential parameters for the halo nucleus system ^6He+^12C are extracted from fits to the measured angular distributions of ^11B(^7Li, ^6He)12C reaction at energies of 18.3 and 28.3MeV with distorted-wave Born approximation analysis. The characters of the obtained optical potentiM parameters are basically consistent with the results extracted from the fits to the elastic-scattering angular distributions in the literature. 相似文献