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1
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Effect of Nonlinear Elasticity on Interband and Intersubband Transition Energies in GaN/AlN Superlattices

100%
Łepkowski S.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
315-319
EN
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.
2
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Pressure Dependence of the Light Emission in Zinc-Blende InGaAs/GaAs and InGaN/GaN Quantum Wells

64%
Łepkowski S., Gorczyca I.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
857-858
EN
We present theoretical study of the pressure coefficient of the light emission (dE_{E}/dP) in compressively strained zinc-blende InGaAs/GaAs and InGaN/GaN quantum wells, grown in a (001) direction. We investigate the contributions to dE_{E}/dP arising from (i) third-order (nonlinear) elasticity, (ii) nonlinear elasticity, originating from pressure dependence of elastic constants, and (iii) nonlinear dependence of elastic constants on composition in InGaAs and InGaN alloys. The obtained results indicate that the use of nonlinear elasticity is essential for determination of dE_{E}/dP in the strained InGaAs/GaAs and InGaN/GaN quantum wells, while the inclusion of the nonlinear dependence of elastic constants on composition of InGaAs and InGaN alloys does not improve agreement between the theoretical end experimental values of dE_{E}/dP in the considered structures.
3
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Poisson Ratio and Biaxial Relaxation Coefficient in In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N Alloys

64%
Łepkowski S., Gorczyca I.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
902-904
EN
We present theoretical results showing dependence of Poisson ratio and biaxial relaxation coefficient on composition and atomic arrangement in wurtzite In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys. Our calculations reveal that the Poisson ratio determined for In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys subjected to a uniaxial stress parallel to the c axis of the wurtzite structure shows significant superlinear dependence on composition. The superlinear bowing in Poisson ratio is enlarged by the effect of In clustering. The biaxial relaxation coefficient determined for In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys subjected to a biaxial stress in the plane perpendicular to the c axis of the wurtzite structure changes superlinearly and linearly with x in In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N, respectively. The effect of In atom clustering results in sublinear dependence of the biaxial relaxation coefficient in both In_{x}Ga_{1-x}N and In_{x}Al_{1-x}N alloys.
4
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Pressure Dependence of Elastic Constants in Zinc-Blende III-N and Their Influence on the Light Emission in Nitride Heterostructures

64%
Łepkowski S., Majewski J.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
559-566
EN
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_{11}, C_{12} with pressure for considered nitrides compounds. Much weaker dependence on pressure was observed for C_{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.
5
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Symmetry of the Top Valence Band States in GaN/AlGaN Quantum Wells and its Influence on the Polarization of Emitted Light

64%
Bardyszewski W., Łepkowski S.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
894-896
EN
We show theoretically that for narrow GaN/AlGaN quantum wells, lattice matched to GaN substrate/buffer and grown along the (0001) crystallographic direction the topmost valence subband symmetry depends critically on such parameters as quantum well thickness and barrier composition. This effect determines polarization of the emitted light. It is noted that the symmetry of the topmost valence band level is sensitive to the values of the D_3 and D_4 deformation potentials and can be employed in verification of existing literature values of these parameters.
6
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Pressure-Driven Reordering of Valence Band States in AlGaN/AlN Quantum Wells

64%
Łepkowski S., Bardyszewski W.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1029-1030
EN
We study theoretically the influence of external hydrostatic pressure on the valence band structure in [0001]-oriented Al_{x}Ga_{1-x}N/AlN quantum wells used in deep-ultraviolet light emitting devices. The calculations performed using the multi-band k·p method with excitonic effects show that for Al_{x}Ga_{1-x}N/AlN quantum wells with x = 0.7 and quantum well width of 1.5 nm, reordering of the topmost valence subbands having different symmetries occurs with increasing pressure. In these structures, at low pressure values the topmost valence level is of Γp_9 symmetry whereas it changes to the Γp_7 state for pressures about 2.5 GPa. We also find that the excitonic effects increase the critical value of pressure at which the change in the polarization of the emitted light occurs to 7 GPa. This behavior is opposite to the pressure-dependent reordering of the topmost valence band states in thin GaN/AlGaN quantum wells which occurs from Γp_7 to Γp_9 states.
7
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Structural and Elastic Properties of Wurtzite Al-Rich In_{x}Al_{1 - x}N Alloys

64%
Łepkowski S., Gorczyca I.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
666-668
EN
We present theoretical study of lattice parameters and elastic constants of wurtzite Al-rich In_{x}Al_{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_{11}, C_{12}, and C_{44} elastic constants are significantly smaller than the linear interpolated values between the elastic constants of AlN and InN, and the values of C_{33} elastic constant are significantly larger than the corresponding interpolated values. For the alloys with uniform distribution of In atoms, only C_{11} elastic constant deviates significantly from linear dependence on composition.
8
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Effects of Nonlinear Elasticity and Electromechanical Coupling on Optical Properties of InGaN/GaN and AlGaN/AlN Quantum Wells

64%
Łepkowski S., Majewski J.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
237-242
EN
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.
9
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Nonlinear Elasticity in Wurtzite GaN/AlN Planar Superlattices and Quantum Dots

51%
Łepkowski S., Majewski J., Jurczak G.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
749-754
EN
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.
10
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Effect of the Built-In Strain on the In-Plane Optical Anisotropy of m-Plane GaN/AlGaN Quantum Wells

51%
Łepkowski S., Bardyszewski W., Teisseyre H.
Acta Physica Polonica A
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2011
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vol. 120
|
issue 5
897-898
EN
We study theoretically the influence of the anisotropic biaxial strain originating from the lattice mismatch between the m-plane GaN/AlGaN quantum wells structure and the substrate on the optical anisotropy of such systems. It is demonstrated that the oscillator strengths for optical transitions with polarization of light parallel and perpendicular to the crystal axis c strongly depend on strain to such an extent that, by increasing the concentration of Al in the substrate from x = 0 to x = 0.5 one can change the polarization of the emitted light with respect to the c-axis by 90 degrees.
11
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Pressure Dependence of Exciton Binding Energy in GaN/Al_{x}Ga_{1 - x}N Quantum Wells

51%
Bardyszewski W., Łepkowski S., Teisseyre H.
Acta Physica Polonica A
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2011
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vol. 119
|
issue 5
663-665
EN
We present a theoretical study of excitons in GaN/Al_{x}Ga_{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.
12
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Polarization-Induced Band Inversion in In-Rich InGaN/GaN Quantum Wells

51%
Łepkowski S., Bardyszewski W., Rodak D.
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vol. 126
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issue 5
1154-1155
EN
We theoretically study the polarization-induced band inversion phenomenon in c-plane In-rich InGaN/GaN quantum wells. Our calculations performed using the k·p method with the 8×8 Rashba-Sheka-Pikus Hamiltonian for the structures with the indium content between 90% and 100% show that the reordering of the conduction and valence bands occurs for the quantum well widths below the theoretical values of critical thickness for InGaN layers pseudomorphically grown on GaN substrates.
13
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The Role of Internal Electric Fields in III-N Quantum Structure

39%
Perlin P., Łepkowski S., Teisseyre H., Suski T., Grandjean N., Massies J.
Acta Physica Polonica A
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2001
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vol. 100
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issue 2
261-270
EN
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.
14
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Blue Laser on High N_2 Pressure-Grown Bulk GaN

21%
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.
Acta Physica Polonica A
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2001
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vol. 100
|
issue Supplement
229-232
EN
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).
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