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101.
Mechanical strains in a multilayer Ge/Si(001) heterostructure with vertically aligned Ge nanoclusters (quantum dots) are calculated using an interatomic potential based on the Keating valence-force-field model. It is found that the nonuniform spatial elastic strain distribution in this medium gives rise to a three-dimensional potential well for electrons in the strained Si layers near Ge nanoclusters. The depth of the potential well reaches 100 meV, and its spatial dimensions are determined by the diameter of the Ge nanoclusters. For a structure consisting of four Ge islands 23 nm in diameter arranged one above another, the electron binding energies in this well and the spatial electron density distribution are determined. The ground state has an s-like symmetry and is characterized by an electron binding energy of ~95 and ~60 meV for the elemental composition of Ge in the nanoclusters c = 1 and c = 0.7, respectively. The existence of bound electron states in the conduction band of strained Si must lead to a relaxation of the selection rules that determine the low efficiency of the radiative recombination in indirect-gap semiconductors. This explains the high value of the oscillator strength observed for the interband transitions in multilayer Ge/Si(001) structures with vertical correlation of the arrangement of Ge nanoclusters. 相似文献
102.
N. P. Stepina A. I. Yakimov A. V. Nenashev A. V. Dvurechenskiĭ N. A. Sobolev J. P. Leitao V. V. Kirienko A. I. Nikiforov E. S. Koptev L. Pereira M. C. Carmo 《Journal of Experimental and Theoretical Physics》2006,103(2):269-277
The photoconduction in a tunnel-coupled Ge/Si quantum dot (QD) array has been studied. The photoconductance (PC) sign can be either positive or negative, depending on the initial filling of QDs with holes. The PC kinetics has a long-term character (102?104 s at T = 4.2 K) and is accompanied by persistent photoconduction (PPC), whereby the PC value is not restored on the initial level even after relaxation for several hours. These phenomena are observed upon illumination by light with photon energies both greater and smaller than the silicon bandgap. A threshold light wavelength corresponding to a long-term PC kinetics depends on the QD filling with holes. A model describing the observed PC kinetics is proposed, according to which the main contribution to the PC is related to the degree of QD filling with holes. By applying the proposed model to the analysis of PC kinetics at various excitation levels, it is possible to determine the dependence of the hopping conductance on the number of holes per QD. The rate of the charge carrier density relaxation exponentially depends on the carrier density. 相似文献
103.
I.L. Drichko A.M. Diakonov V.I. Kozub I.Yu. Smirnov Yu.M. Galperin A.I. Yakimov A.I. Nikiforov 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):450
Dense (n=4×1011 cm-2) arrays of Ge quantum dots in a Si host were studied using attenuation of surface acoustic waves (SAWs) propagating along the surface of a piezoelectric crystal located near the sample. The SAW magneto-attenuation coefficient, ΔΓ=Γ(ω,H)-Γ(ω,0), and change of velocity of SAW, ΔV/V=(V(H)-V(0))/V(0), were measured in the temperature interval T=1.5–4.2 K as a function of magnetic field H up to 6 T for the waves in the frequency range f=30–300 MHz. Based on the dependences of ΔΓ on H, T and ω, as well as on its sign, we believe that the AC conduction mechanism is a combination of diffusion at the mobility edge with hopping between localized states at the Fermi level. The measured magnetic field dependence of the SAW attenuation is discussed based on existing theoretical concepts. 相似文献
104.
V. I. Zinchenko A. S. Yakimov 《Journal of Applied Mechanics and Technical Physics》1999,40(4):697-703
New methods of controlling thermal regimes in a high-enthalpy spatial flow around a body are considered. They are related
to gas injection from the blunted surface and heat overflow in the material of the shell. The effect of injection is analyzed
for different thermal conductivities. It is shown that highly heat-conducting materials can be successfully used to decrease
the maximum temperatures at the windward side due to intense heat removal to the region of a porous spherical bluntness.
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 4, pp. 162–169, July–August, 1999. 相似文献
105.
106.
Photoluminescence enhancement by localized surface plasmons in AlGaN/GaN/AlGaN double heterostructures
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Alexander Y. Polyakov Jin‐Hyeon Yun Haeng‐Keun Ahn Alexander S. Usikov Eugene B. Yakimov Sergey A. Tarelkin Nikolai B. Smirnov Kirill D. Shcherbachev Heikki Helava Yuri N. Makarov Sergey Yu Kurin Sergey I. Didenko Boris P. Papchenko In‐Hwan Lee 《固体物理学:研究快报》2015,9(10):575-579
Double heterostructures AlGaN/GaN/AlGaN grown by hydride vapor phase epitaxy and designed for use as light emitting diodes for 360 nm wavelength were patterned by shallow nanoholes and injected with Ag/SiO2 or Al nanoparticles. A 1.8 times increase in the photoluminescence and microcathodoluminescence signal from the GaN active region was observed for 100 nm diameter Al nanoparticles, the efficiency decreased compared to the reference planar samples for small Al nanoparticles of 30–40 nm diameter, and a moderate increase of 1.2 times was detected for Ag/SiO2 nanoparticles. The observed phenomena are explained by the GaN emitter coupling with localized surface plasmons produced by metallic nanoparticles. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
107.
Milen Yakimov 《Advances in Mathematics》2007,208(1):40-74
We define an affine Jacquet functor and use it to describe the structure of induced affine Harish-Chandra modules at noncritical levels, extending the theorem of Kac and Kazhdan on the structure of Verma modules in the Bernstein-Gelfand-Gelfand categories O for Kac-Moody algebras. This is combined with a vanishing result for certain extension groups to construct a block decomposition of the categories of affine Harish-Chandra modules of Lian and Zuckerman. The latter provides an extension of the works of Rocha-Caridi and Wallach [A. Rocha-Caridi, N.R. Wallach, Projective modules over infinite dimensional graded Lie algebras, Math. Z. 180 (1982) 151-177] and Deodhar, Gabber and Kac [V. Deodhar, O. Gabber, V. Kac, Structure of some categories of representations of infinite-dimensional Lie algebras, Adv. Math. 45 (1982) 92-116] on block decompositions of BGG categories for Kac-Moody algebras. We also derive a compatibility relation between the affine Jacquet functor and the Kazhdan-Lusztig tensor product and apply it to prove that the affine Harish-Chandra category is stable under fusion tensoring with the Kazhdan-Lusztig category. This compatibility will be further applied in studying translation functors for the affine Harish-Chandra category, based on the fusion tensor product. 相似文献
108.
We analyze the accuracy of digital estimation of the signal spectrum. Quantization noise introduced by the analog-to-digital converter (ADC) and fast Fourier transform (FFT) is allowed for. The basic analysis is carried out using the example of a test harmonic signal. The characteristic of the signal-to-noise ratio, called the effective binary word size of a harmonic signal is introduced. Optimal combinations between the ADC word size and the FFT type used are discussed. 相似文献
109.
The problem of the interaction of a high-density moving snow mass with various obstacles is examined.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 13–17, May–June, 1993.The authors are grateful to Ts. I. Stavskii, A. I. Denisov and the other participants in the experiments. 相似文献
110.