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Wyszukujesz frazę "Łepkowski, S. P." wg kryterium: Autor

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    Wyświetlanie 1-8 z 8
    Tytuł:
    The Role of Internal Electric Fields in III-N Quantum Structure
    Autorzy:
    Perlin, P.
    Łepkowski, S. P.
    Teisseyre, H.
    Suski, T.
    Grandjean, N.
    Massies, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2027477.pdf
    Data publikacji:
    2001-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.20.Hp
    78.55.Cr
    78.67.Hc
    Opis:
    Binary nitrides: of wurtzite GaN, AlN, InN, and their solid solutions represent a family of semiconductors of crucial importance for modern optoelectronics. Strained quantum wells, like GaN/AlGaN and specially InGaN/GaN, form active layers of the light emitters working in green-UV part of the spectrum. The operation of these devices strongly depends on the emission spectra of considered quantum structures which are greatly influenced by the presence of built-in electric fields. The electric field acting via quantum confined Stark effect in the mentioned structures changes the energies and intensity of the emitted light. The effect can lead to the spectral shift of a photo- and electroluminescence by many hundreds of meV. In this review we will briefly cover the influence of internal electric fields on both optical and electrical properties of nitride based heterostructures and quantum wells. We would like to draw reader's attention to the usefulness of high-pressure investigation in the study of electric fields in nitrides and to show how the interpretation of these experiments influences the way we calculate the electric fields in the quantum structures.
    Źródło:
    Acta Physica Polonica A; 2001, 100, 2; 261-270
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Structural and Elastic Properties of Wurtzite Al-Rich In$\text{}_{x}$Al$\text{}_{1 - x}$N Alloys
    Autorzy:
    Łepkowski, S. P.
    Gorczyca, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/2048088.pdf
    Data publikacji:
    2011-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    62.20.de
    Opis:
    We present theoretical study of lattice parameters and elastic constants of wurtzite Al-rich In$\text{}_{x}$Al$\text{}_{1 - x}$N (x = 0.125, 0.1875 and 0.25) alloys using self-consistent ab initio calculations with a supercell model. Two different atomic arrangements have been considered for a given x, by either distributing the In atoms as uniformly as possible over the supercell or by clustering the In atoms together in a small part of the supercell. Our calculations reveal that the a and c lattice parameters show almost linear dependence on composition for the alloys with uniform distribution of In atoms, while for the case of alloys with clustered In atoms the c lattice parameter deviates from linearity quite significantly. For the alloys with clustered In atoms, we observe that the values of C$\text{}_{11}$, C$\text{}_{12}$, and C$\text{}_{44}$ elastic constants are significantly smaller than the linear interpolated values between the elastic constants of AlN and InN, and the values of C$\text{}_{33}$ elastic constant are significantly larger than the corresponding interpolated values. For the alloys with uniform distribution of In atoms, only C$\text{}_{11}$ elastic constant deviates significantly from linear dependence on composition.
    Źródło:
    Acta Physica Polonica A; 2011, 119, 5; 666-668
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pressure Dependence of Exciton Binding Energy in GaN/Al$\text{}_{x}$Ga$\text{}_{1 - x}$N Quantum Wells
    Autorzy:
    Bardyszewski, W.
    Łepkowski, S. P.
    Teisseyre, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/2048086.pdf
    Data publikacji:
    2011-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.40.Fy
    78.20.Bh
    78.30.Fs
    Opis:
    We present a theoretical study of excitons in GaN/Al$\text{}_{x}$Ga$\text{}_{1 - x}$N wurtzite (0001) quantum wells subjected to hydrostatic pressure. Our results show that the combined effect of pressure induced changes in band structure and piezoelectric field leads to reduction of the exciton binding energy. This subtle effect is described quite accurately by our multiband model of excitons in quantum wells.
    Źródło:
    Acta Physica Polonica A; 2011, 119, 5; 663-665
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pressure Dependence of Elastic Constants in Zinc-Blende III-N and Their Influence on the Light Emission in Nitride Heterostructures
    Autorzy:
    Łepkowski, S. P.
    Majewski, J. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2038098.pdf
    Data publikacji:
    2004-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    62.20.Dc
    62.50.+p
    Opis:
    We studied the nonlinear elasticity effects for the case of III-N compounds. Particularly, we determined the pressure dependences of elastic constants, in zinc-blende InN, GaN, and AlN by performing ab initio calculations in the framework of plane-wave pseudopotential implementation of the density-functional theory. We found significant and almost linear increase in C$\text{}_{11}$, C$\text{}_{12}$ with pressure for considered nitrides compounds. Much weaker dependence on pressure was observed for C$\text{}_{44}$. We also discussed pressure dependences of two-dimensional Poisson's ratio and elastic anisotropy coefficient. Finally, we showed that the pressure dependence of elastic constants results in significant reduction of the pressure coefficient of the energy emission in cubic InGaN/GaN quantum wells and essentially improves the agreement between experimental and theoretical values.
    Źródło:
    Acta Physica Polonica A; 2004, 105, 6; 559-566
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Nonlinear Elasticity in Wurtzite GaN/AlN Planar Superlattices and Quantum Dots
    Autorzy:
    Łepkowski, S. P.
    Majewski, J. A.
    Jurczak, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/2044495.pdf
    Data publikacji:
    2005-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.-n
    62.20.Dc
    62.50.+p
    Opis:
    The elastic stiffness tensors for wurtzite GaN and AlN show a significant hydrostatic pressure dependence, which is the evidence of nonlinear elasticity of these compounds. We have examined how pressure dependence of elastic constants for wurtzite nitrides influences elastic and piezoelectric properties of GaN/AlN planar superlattices and quantum dots. Particularly, we show that built-in hydrostatic pressure, present in both quantum wells of the GaN/AlN superlattices and GaN/AlN quantum dots, increases significantly by 0.3-0.7 GPa when nonlinear elasticity is used. Consequently, the compressive volumetric strain in quantum wells and quantum dots decreases in comparison to the case of the linear elastic theory. However, the z-component of the built-in electric field in the quantum wells and quantum dots increases considerably when nonlinear elasticity is taken into account. Both effects, i.e., a decrease in the compressive volumetric strain as well as an increase in the built-in electric field, decrease the band-to-band transition energies in the quantum wells and quantum dots.
    Źródło:
    Acta Physica Polonica A; 2005, 108, 5; 749-754
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effects of Nonlinear Elasticity and Electromechanical Coupling on Optical Properties of InGaN/GaN and AlGaN/AlN Quantum Wells
    Autorzy:
    Łepkowski, S. P.
    Majewski, J. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2046928.pdf
    Data publikacji:
    2006-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.De
    62.20.Dc
    77.65.-j
    Opis:
    We present theoretical studies of effects of the nonlinear elasticity and the electromechanical coupling on the optical properties of InGaN/GaN and AlGaN/AlN quantum wells. In these structures, due to the lattice misfit between constituents, the quantum wells are compressively strained and the intrinsic hydrostatic pressure is present. Therefore, the nonlinear elasticity is investigated by taking into account the pressure dependence of elastic stiffness tensor for the strained quantum wells. We show that this effect leads to (i) decrease in the volumetric strain and (ii) increase in the polarization-induced built-in electric field in the quantum wells. Consequently, the interband transition energies in the quantum wells decrease when the nonlinear elasticity of nitrides is considered. On the other hand, we show that the effect of electromechanical coupling, i.e., co-existence of ordinary and converse piezoelectric effects results in increase in the interband transition energies in the considered quantum wells. It turns out that the influence of the nonlinear elasticity on the optical properties is stronger than the influence of electromechanical coupling for InGaN/GaN quantum wells, while for AlGaN/GaN the opposite situation is observed.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 2; 237-242
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effect of Nonlinear Elasticity on Interband and Intersubband Transition Energies in GaN/AlN Superlattices
    Autorzy:
    Łepkowski, S. P.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047688.pdf
    Data publikacji:
    2007-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.Pt
    62.20.Dc
    77.65.Ly
    77.65.-j
    Opis:
    We present a theoretical study of the effect of nonlinear elasticity on interband and intersubband transition energies in wurtzite GaN/AlN superlattices. The effect of nonlinear elasticity is considered by taking into account the changes of elastic constants caused by the intrinsic hydrostatic pressure, originating from lattice misfit between constituents of the superlattice. We show that the influence of the effect of the nonlinear elasticity on the interband and intersubband transition energies in the GaN/AlN superlattices depends crucially on the strain state of structures, in particular on the in-plane lattice constant of the buffer or the substrate. For the superlattices strained to AlGaN buffers with small aluminum concentrations, the effect of nonlinear elasticity increases significantly the interband transition energy and decreases the intersubband transition energy. For the superlattices strained to AlGaN buffers with large aluminum concentrations, the effect of nonlinear elasticity leads to a decrease in the interband transition energy and an increase in the intersubband transition energy.
    Źródło:
    Acta Physica Polonica A; 2007, 112, 2; 315-319
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Blue Laser on High N$\text{}_{2}$ Pressure-Grown Bulk GaN
    Autorzy:
    Grzegory, I.
    Boćkowski, M.
    Krukowski, S.
    Łucznik, B.
    Wróblewski, M.
    Weyher, J.
    Leszczyński, M.
    Prystawko, P.
    Czernecki, R.
    Lehnert, J.
    Nowak, G.
    Perlin, P.
    Teisseyre, H.
    Purgał, W.
    Krupczyński, W.
    Suski, T.
    Dmowski, L.
    Litwin-Staszewska, E.
    Skierbiszewski, C.
    Łepkowski, S.
    Porowski, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2030423.pdf
    Data publikacji:
    2001-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Opis:
    In this note we report briefly on the details of pulsed-current operated "blue" laser diode, constructed in our laboratories, which utilizes bulk GaN substrate. As described in Ref. [1] the substrate GaN crystal was grown by HNPSG method, and the laser structure was deposited on the conducting substrate by MOCVD techniques (for the details see Sec. 2 and Sec. 4 of Ref.~[1], respectively).
    Źródło:
    Acta Physica Polonica A; 2001, 100, Supplement; 229-232
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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