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1

Stochastic Carrier Dynamics in Semiconductor Superlattices

100%

Fromhold T., Bujkiewicz S., Patanè A., Stapleton S., Sherwood D., Fowler D., Cooper J., Eaves L., Belyaev A., Krokhin A., Neumann A., Wilkinson P., Sankeshwar N., Henini M., Sheard F.

Acta Physica Polonica A

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2006

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vol. 109

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issue 1

43-52

EN

We explore a new regime of hot carrier dynamics, in which electrons in a superlattice miniband exhibit a unique type of stochastic motion when a magnetic field is tilted at an angleθ to the superlattice axis. Remarkably, the dynamics of a miniband electron in a tilted magnetic field reduce to a one-dimensional simple harmonic oscillator, of angular frequencyω_C cosθ, whereω_C is the cyclotron frequency, driven by a time-dependent plane wave whose angular frequency equals the Bloch frequencyω_B. At bias voltages for whichω_B=nω_C cosθ, where n is an integer, the electron orbits change from localised Bloch-like trajectories to unbounded stochastic orbits, which diffuse rapidly through intricate web patterns in phase space. To quantify how these webs affect electron transport, we make drift-diffusion calculations of the current-voltage curves including the effects of space-charge build up. When the magnetic field is tilted, our simulations reveal a large resonant peak, which originates from stochastic delocalisation of the electron orbits. We show that the corresponding quantised eigenstates change discontinuously from a highly localised character when the system is off resonance to a fully delocalised form when the resonance condition is satisfied.

2

From High Electron Mobility GaN/AlGaN Heterostructures to Blue-Violet InGaN Laser Diodes. Perspectives of MBE for Nitride Optoelectronics

80%

Skierbiszewski C.

Acta Physica Polonica A

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2005

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vol. 108

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issue 4

635-651

EN

The recent progress in growth of nitride based semiconductor structures made by plasma assisted MBE is presented. This technology is ammonia free and nitrogen for growth is activated in RF plasma source from nitrogen molecules. The new growth mechanism - adlayer enhanced lateral diffusion of adatoms on semiconductor surface is studied in plasma assisted MBE. This mechanism enables us to achieve high quality step-flow epitaxy at temperatures 600-750ºC, much lower than expected from classical estimates based on the melting point of GaN. We show that growth at low temperatures in metal rich (gallium or indium) regime, together with use of low dislocation bulk GaN substrates, results in high quality of (In, Al, Ga)N layers and sharp interfaces. We demonstrate record high mobility of two-dimensional electron gas at GaN/AlGaN interface (with mobility exceeding 100 000 cm^2/(V s) at 4.2 K and 2500 cm^2/(V s) at 300 K) and report on first blue-violet InGaN multiquantum well laser diodes, operating in 407-422 nm wavelengths range. In this paper, we discuss also properties of strain compensated InAlN/InGaN multiquantum wells grown by plasma assisted MBE which are very attractive for telecommunication applications at 1.5μm wavelengths like electro-optical modulators or all-optical switches.

3

Potential and Carrier Distribution in AlGaN Superlattice

80%

Korona K., Pakuła K., Bożek R., Drabińska A., Surowiecka K., Stępniewski R., Zielińska-Rohozińska E., Baranowski J.

Acta Physica Polonica A

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2005

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vol. 108

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issue 4

723-729

EN

Photocurrent spectroscopy and Kelvin force microscopy have been used in order to determine charge, field, and potential distributions in spontaneously grown superlattice. The spectra show that light can generate currents and potentials in both directions depending on photon energy. A numerical model made for superlattice of periodλ_{SL} = 33 nm shows that electric field in superlattice oscillates coherently with Al content. The oscillations of electric field explain the different directions of photocurrent. The electric field can also separate electrons and holes, making carrier lifetimes longer and lowering excitation intensity threshold for occupation inversion.

4

Electronic States in Type-II Superlattices

80%

Machowska-Podsiadlo E., Bugajski M.

Acta Physica Polonica A

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2009

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vol. 116

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issue S

S-65-S-68

EN

In this paper the electronic states in type-II superlattices are demonstrated. Band dispersions of InAs/GaSb periodic structure were calculated with the respect of the light and the heavy holes states mixing at InAs/GaSb interfaces. The effect of narrow energy band gap of InAs was taken into account and the wavelengths corresponding to optical transitions in the superlattice were presented.

5

High Power Continuous Wave Blue InAlGaN Laser Diodes Made by Plasma Assisted MBE

80%

Skierbiszewski C., Siekacz M., Wiśniewski P., Perlin P., Feduniewicz-Żmuda A., Cywiński G., Smalc J., Grzanka S., Grzegory I., Leszczyński M., Porowski S.

Acta Physica Polonica A

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2006

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vol. 110

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issue 3

345-351

EN

Room temperature, continuous wave operation of InGaN multi-quantum wells laser diodes made by rf plasma assisted molecular beam epitaxy at 411 nm wavelength is demonstrated. The threshold current density and voltage were 4.2 kA/cm^2 and 5.3 V, respectively. High optical power output of 60 mW was achieved. The lifetime of these laser diodes exceeds 5 h with 2 mW of optical output power. The laser diodes are fabricated on low dislocation density bulk GaN substrates, at growth conditions which resembles liquid phase epitaxy. We demonstrate that relatively low growth temperatures (600-700°C) pose no intrinsic limitations for fabrication of nitride optoelectronic components by plasma assisted molecular beam epitaxy.

6

Effects of Dissipation and Noise on Chaotic Transport in Superlattices

80%

Balanov A., Greenaway M., Fromhold T.

Acta Physica Polonica A

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2009

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vol. 116

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issue 5

733-740

EN

We study the effects of dissipation and noise on chaotic electron dynamics, which accompany charge transport in semiconductor superlattices with an applied bias voltage and a tilted magnetic field. We consider the evolution of different chaotic trajectories as decoherence increases, and show that below a critical level of the dissipation rate, dissipative chaos plays an important role in the electron transport. However, by increasing the dissipation rate above the critical level, chaotic dynamics disappear and electrons only demonstrate regular motion. We also investigate how the presence of random fluctuations affects magnetotransport in superlattices and reveal a counter-intuitive non-monotonic dependence of electron drift velocity upon the noise intensity.

7

Influence of Simultaneous Doping of Li^+ and Fe^{3+} Ions in the LiMn_2O_4 Spinel Structure

80%

Nowicki W.

Acta Physica Polonica A

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2008

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vol. 114

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issue 2

375-382

EN

A series of compounds Li_xMn_{3-x-y}Fe_yO_4 (x=1.0125;0≤y≤0.05) were synthesized by solid state reaction of Li_2CO_3 with the manganese oxide or iron-manganese oxide precursors. Investigations of the structure transformation effect of double substitution with Li^+ and Fe^{3+} ions in LiMn_2O_4, in the temperature range of 10-300 K, were undertaken using high-resolution X-ray powder diffraction at the HASYLAB (DESY) synchrotron. The Li_{1.0125}Mn_{1.9625}Fe_{0.025}O_4 transforms from cubic (Fd3̅ m) to orthorhombic (Fddd) below 250 K, and is stable to 10 K. Whereas in the Li_{1.0125}Mn_{1.9375}Fe_{0.05}O_4 oxide no phase transition was observed, this spinel remains in cubic structure down to the temperature of 10 K.

8

Interplays between Mesoscopic Josephson Junctions and the Harper Equation

80%

Papp E., Micu C., Bica I.

Acta Physica Polonica A

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2009

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vol. 116

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issue 4

486-488

EN

Proofs are given that by resorting to the discretization of the superconducting phase variable leads to the conversion of the eigenvalue equation of a mesoscopic Josephson junction under a dc voltage into a generalized version of the Harper equation with anisotropy parameter. A full conversion proceeds, however, in terms of selected parameters. Classical limits and further generalizations are also shortly discussed.

9

Infrared Detectors for the Future

70%

Rogalski A.

Acta Physica Polonica A

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2009

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vol. 116

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issue 3

389-406

EN

In the paper, fundamental and technological issues associated with the development and exploitation of the most advanced infrared detector technologies are discussed. In this class of detectors both photon and thermal detectors are considered. Special attention is directed to HgCdTe ternary alloys on silicon, type-II superlattices, uncooled thermal bolometers, and novel uncooled micromechanical cantilever detectors. Despite serious competition from alternative technologies and slower progress than expected, HgCdTe is unlikely to be seriously challenged for high-performance applications, applications requiring multispectral capability and fast response. However, the nonuniformity is a serious problem in the case of LWIR and VLWIR HgCdTe detectors. In this context, it is predicted that type-II superlattice system seems to be an alternative to HgCdTe in long wavelength spectral region. In well established uncooled imaging, VO_x microbolometer arrays are clearly the most used technology. In spite of successful commercialization of uncooled microbolometers, the infrared community is still searching for a platform for thermal imagers that combine affordability, convenience of operation, and excellent performance. Recent advances in microelectromechanical systems have led to the development of uncooled IR detectors operating as micromechanical thermal detectors. Between them the most important are biomaterial microcantilevers.

10

Influence of TDMAAs Acceptor Precursor on Performance Improvement of HgCdTe Photodiodes

70%

Madejczyk P., Gawron W., Piotrowski A., Kłos K., Rutkowski J., Rogalski A.

Acta Physica Polonica A

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2010

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vol. 118

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issue 6

1199-1204

EN

One of the key factor which determine HgCdTe photodiode quality is acceptor doping efficiency. This paper presents significant progress made over the past three years in development of acceptor doping technology in metalorganic chemical vapour deposition HgCdTe photovoltaic detectors. High acceptor doping is required for P^{+}-contact layers, whereas low doping is necessary for p-type absorbing base layer. Previously, AsH_3 precursor was used as an acceptor dopant. This precursor is partially incorporated as electrically neutral As-H pairs, which are likely to be recombination centres in HgCdTe and in consequence influence on the carriers lifetime lowering. Substituting of AsH_3 by TDMAAs resulted in higher carrier lifetimes and thereby about one order of magnitude higher R_0A product of HgCdTe photodiodes in temperatures close to 230 K.

11

Universality of the Empty-Lattice Approximation to Predict the Topology of Energy Spectra of High-Symmetry Crystals and Superlattices Based upon Them

70%

Sznajder M., Bercha D., Glukhov K., Slipukhina I.

Acta Physica Polonica A

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2006

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vol. 110

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issue 3

369-378

EN

O_h^7, T_d^2 and O_h^5 symmetry crystals were discussed to demonstrate universality of the empty-lattice approximation to obtain the topology and symmetry of the elementary energy bands creating the valence band of those crystals and to predict a localization of the maximum of valence electron density distribution in the unit cell. The elaborated concept of the elementary energy bands was applied to the (GaAs)_5/(AlAs)_5 superlattice and ordered solid solution Pb_{0.5}Sn_{0.5}S.

12

Electro-Optical Properties of II-VI Superlattices

70%

Schillak P., Czajkowski G.

Acta Physica Polonica A

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2007

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vol. 112

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issue 2

301-304

EN

We show how to compute electro-optical spectra of semiconductor superlattices in the region of interband electronic transitions. The method uses the microscopic calculation of eigenvalues and eigenfunctions and the macroscopic real density matrix approach to compute the electromagnetic fields and susceptibilities. The electron-hole screened Coulomb potential is adapted and the valence band structure is taken into account in the cylindrical approximation, thus separating light- and heavy-hole motions. We calculate the electro-optical functions, including the optical Stokes parameters and ellipsometric functions for the case of oblique incidence. Results are given for Zn_{1-x}Cd_xSe/ZnSe superlattices and a good agreement with experiments is obtained.

13

Electronic and Optical Properties of Heterostructures based on Indium Chalcogenides

61%

Kharkhalis L., Glukhov K., Babuka T.

Acta Physica Polonica A

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2017

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vol. 132

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issue 2

319-321

EN

The models of the heterostructures based on the β-InSe, In₄Se₃ and In₄Te₃ crystals were proposed and the first-principles study of their electronic and optical properties were presented. The band spectra, the spatial distributions of the electron density and the absorption coefficients for different polarizations along crystal axes for the heterostructures of the (In₄Se₃)_m/(In₄Te₃)_m and β-InSe/In₄Se₃ type were calculated. The evolution of the changes in both energy spectrum and optical functions of the heterostructures in comparison with the bulk crystals has been analyzed. Our calculations point out the heterostructures stability and good agreement with the experimental investigations of the photosensitivity in the near and middle infrared region.

Refine search results

Stochastic Carrier Dynamics in Semiconductor Superlattices

From High Electron Mobility GaN/AlGaN Heterostructures to Blue-Violet InGaN Laser Diodes. Perspectives of MBE for Nitride Optoelectronics

Potential and Carrier Distribution in AlGaN Superlattice

Electronic States in Type-II Superlattices

High Power Continuous Wave Blue InAlGaN Laser Diodes Made by Plasma Assisted MBE

Effects of Dissipation and Noise on Chaotic Transport in Superlattices

Influence of Simultaneous Doping of Li^+ and Fe^{3+} Ions in the LiMn_2O_4 Spinel Structure

Interplays between Mesoscopic Josephson Junctions and the Harper Equation

Infrared Detectors for the Future

Influence of TDMAAs Acceptor Precursor on Performance Improvement of HgCdTe Photodiodes

Universality of the Empty-Lattice Approximation to Predict the Topology of Energy Spectra of High-Symmetry Crystals and Superlattices Based upon Them

Electro-Optical Properties of II-VI Superlattices

Electronic and Optical Properties of Heterostructures based on Indium Chalcogenides