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1
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Study of Two-Dimensional Hole Gas at Si/SiGe/Si Inverted Interface

100%
Sadeghzadeh M., Mironov O., Emeleus C., Parry C., Phillips P., Parker E., Whall T.
Acta Physica Polonica A
|
1998
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vol. 94
|
issue 3
503-508
EN
We have studied the transport properties of a two-dimensional hole gas (2DHG) at the inverted interface of a strained Si_{0.8}Ge_{0.2} quantum well. By application of a bias voltage to a Schottky gate on top of this inverted heterostructure the 2DHG density n_{s} can be controlled, in the range of (1.5-5.2)×10^{11} cm^{-2}. At a temperature T=0.33 K, the Hall mobility is 4650 cm^{2} V^{-1} s^{-1} at the maximum carrier density. For lower sheet densities (n_{s}<2×10^{11} cm^{-2}) the system undergoes a transition from a weak to strongly localised phase of significantly reduced mobility. From low temperature Shubnikov-de Haas oscillation measurements we have extracted the hole effective masses m*=(0.25 → 0.28)m_{0} and the ratio of transport to quantum lifetimes α=(0.92 → 0.85) for the corresponding carrier density change of n_{s}=(5.2 → 2.5)×10^{11} cm^{-2}. These results can be explained in terms of the abnormal movement of the hole wave function towards the interface with decreasing n_{s}, short range interface charge and interface roughness scattering.
2
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Weak Localization and Electron-Electron Interaction in Si/SiGe Quantum Wells

100%
Prinz A., Stőger G., Brunthaler G., Bauer G., Ismail K., Meyerson B. S.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
873-876
EN
A negative magnetoresistance is observed in Si/SiGe modulation doped heterostructures which is attributed to the single particle quantum interference (weak localization) effect. From analysis of the experimental data the electron phase coherence time τ_{ϕ} is extracted to follow a (aT + bT^{2} )^{-1} dependence. The evaluated prefactor α = 0.25 is below the theoretical limit of 0.5, but agrees with observations in Si and GaAs/AlGaAs heterostructures.
3
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Electron Transport in Submicron Wires of Semiconductors

51%
Wróbel J.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
691-701
EN
We review the methods of fabrication and transport properties of submicron II-VI, IV-VI and III-V semiconductor wires. Devices were prepared by electron-beam lithography and used for detailed magnetotransport studies, carried out at low (down to 30 mK) temperatures. We discuss a number of novel features obtained in ballistic, diffusive and localized transport regimes. In particular, we describe the universal conductance fluctuations for semimagnetic materials (CdMnTe) and discuss the edge channel transport for PbTe, PbSe and GaAs/GaAlAs systems.
4
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Influence of Magnetic Impurities upon Universal conductance Fluctuations

51%
Dietl T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 1
161-171
EN
Mesoscopic phenomena in quantum structures which incorporate magnetic impurities with localized spins may exhibit a number of novel features driven by spin-disorder scattering, exchange spin-splitting of electron bands, and the formation of bound magnetic polarons. After brief information on these effects, their influence on universal conductance fluctuations as well as on low frequency noise and quantum localization is presented. Millikelvin investigations of diffusive charge transport, which have been carried out for submicron wires of n^{+}-Cd_{1-x}Mn_{x}Te epilayers, are reviewed in some details. These studies have provided information on the significance of spin-disorder scattering in semiconductors and put into the evidence a new driving mechanism of the magnetoconductance fluctuations - the redistribution of the electrons between energy levels of the system, induced by the giant s-d exchange spin-splitting. Important implications of these findings for previous interpretations of spin effects in semiconductor and metal nanostructures are discussed.
5
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Alternative Equation of Motion Approach to the Single-Impurity Anderson Model

51%
Górski G., Mizia J., Kucab K.
|
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vol. 126
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issue 4a
A-97-A-100
EN
Solving the single-impurity Anderson model is a basic problem of solid state physics. The single-impurity Anderson model is very important, at present it is also used for systems with quantum impurities, e.g. semiconductor quantum dots and molecular transistors. Its main application is in the scheme of dynamical mean field theory describing strong correlation electron systems. To solve the single-impurity Anderson model problem we use the equation of motion Green function approach. In this report we present the novel equation of motion approximation in which we differentiate the Green function over both time variables. This differs from the commonly used equation of motion solution by Appelbaum, Penn and Lacroix where the authors take time derivative only over primary time variable. After extending calculations to higher order Green functions we find the new approximate dynamical solution of single-impurity Anderson model. The results are compared with the solutions to the single-impurity Anderson model problem at intermediate Coulomb repulsion U such as the modified iterative perturbation theory. Our approach is suitable for describing quantum dots.
6
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Magnetization Steps in Cd_{1-x}Mn_{x}Te Observed in Coherent Transport

51%
Jaroszyński J., Dietl T., Wróbel J., Karczewski G., Wojtowicz T., Kossut J., Maude D. K., van der Linden P., Portal J. C.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
797-800
EN
Magnetoconductance measurements on submicron wires of n^{+}-Cd_{1-x}Mn_{x}Te were carried out up to 27 T and down to 100 mK. The inverse correlation field of the universal conductance fluctuations is found to increase abruptly in the vicinity of the magnetization steps due to Mn pairs in CdMnTe. No such effect is observed in similar wires of CdTe. These findings support a recent model, according to which the correlation field of the universal conductance fluctuations in magnetic systems is inversely proportional to the magnetic susceptibility of the localized spins.
7
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Binding Energy of a Bound Polaron in a Quantum Well Wire

51%
Bouhassoune M., Charrour R., Fliyou M., Bria D., Nougaoui A.
Acta Physica Polonica A
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2000
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vol. 98
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issue 1-2
111-122
EN
Theoretical study of the binding energies of an off-center donor hydrogenic impurity in a cylindrical quantum well wires semiconductor is presented. Calculations are performed in the framework of the effective mass approximation using the variational approach. We describe the effect of the quantum confinement by an infinitely deep potential well and we take into consideration the interaction between the charge carrier (electron and ion) and the optical phonons (confined longitudinal optical and surface optical). Our results show that the impurity binding energy depends strongly on the spatial confinement, the impurity position and the polaronic corrections.
8
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Influence of Growth Conditions on Exciton Properties in Thin Quantum Wells of GaAs/AlGaAs

51%
Godlewski M., Bergman J. P., Holtz P. O., Monemar B., Bugajski M., Regiński K., Kaniewska M.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
719-722
EN
Exciton properties in growth interrupted quantum wells of GaAs/AlGaAs are compared with those observed for structures grown with­out growth interruption during the molecular beam epitaxy process. We report observation of quasi-localized excitons in quantum well structures grown without growth interruptions. Quasi-localized excitons drift towards the states of a lower potential energy in the quantum well. For growth in­terrupted MBE structures islands with a constant quantum well thickness become large compared to the exciton radius. Free or lightly localized exci­tons are observed in that case.
9
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Zero Field Spin Splitting in GaN/AlGaN Heterostructures Probed by the Weak Antilocalization

51%
Dybko K., Siekacz M., Skierbiszewski C.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1109-1113
EN
We present the magnetoconductivity measurements of a high mobility two-dimensional electron gas confined at GaN/AlGaN interface. The sensitive measurements of low field conductivity revealed both quantum corrections, the weak localization and antilocalization effects. It indicates the importance of the spin-orbit coupling in this wide band gap material. The analysis of the data provided the information about the temperature dependence of the dephasing time and total spin-orbit relaxation time. The conduction band spin splitting energy amounts to 0.23 meV and 0.35 meV at electron densities 2.2×10¹² cm¯² and 5.7×10¹² cm¯², respectively.
10
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Electron Localization in Sb-Doped Si/SiGe Superlattices

51%
Dietl T., Jaroszyński J., Sawicki M., Głód P., Wróbel J., Stöger G., Brunthaler G., Bauer G., Schäffler F.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
699-702
EN
Millikelvin studies of in-plane magnetoconductance in short period Si/Ge:Sb superlattices have been carried out in order to examine the effect of anisotropy on quantum localization. The field-induced metal-to-insulator transition has been observed, indicating the existence of extended states. This suggests that despite anisotropy as large as D_{∥}/D_{⊥} ≈ 10^{3} the system behaves as 3D in respect of localization by disorder.
11
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Content available

Magnetotransport through Nanoconstriction in Ferromagnetic Semiconductor (Ga,Mn)As

51%
Figielski T., Wosiński T., Pelya O., Sadowski J., Morawski A., Mąkosa A., Dobrowolski W., Jagielski J., Wróbel J.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
525-531
EN
We studied narrow (submicron) constrictions in the layers of ferromagnetic semiconductor (Ga,Mn)As. We have demonstrated a contribution of the quantum localization effects to the magnetoresistance of the constricted samples. We have also found a negative contribution of a domain wall trapped in the constriction to the resistance, due presumably to the erasing of the localization effects by the domain wall.
12
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Weak Antilocalization in Quantum Wells

51%
Knap W., Skierbiszewski C., Litwin-Staszewska E., Kobbi F., Zduniak A., Robert J., Pikus G., Iordanskii S., Mosser V., Zekentes K.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
427-432
EN
Spin relaxation in degenerated two-dimensional (2D) electron gas is studied by measurements of the magnetic field dependence of the weak an­tilocalization corrections to the conductivity in GaInAs quantum wells. Con­sistent quantitative (up to order of magnitude) description of weak antilocal­ization data on GaAs like heterojunctions and quantum wells was obtained. Our results show that spin precession around the effective magnetic field direction as described by the Dyakonov-Perel model is the main spin relax­ation mechanism in degenerated 2D electron gas in semiconductors with no inversion symmetry.
13
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Role of Correlations and Off-Diagonal Terms in Binary Disordered One-Dimensional Systems

51%
Kosior A., Major J., Płodzień M., Zakrzewski J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 6
1002-1007
EN
We investigate one-dimensional tight binding model in the presence of a correlated binary disorder. The disorder is due to the interaction of particles with heavy immobile other species. Off-diagonal disorder is created by means of a fast periodic modulation of interspecies interaction. The method based on transfer matrix techniques allows us to calculate the energies of extended modes in the correlated binary disorder. We focus on N-mer correlations and regain known results for the case of purely diagonal disorder. For off-diagonal disorder we find resonant energies. We discuss ambiguous properties of those states and compare analytical results with numerical calculations. Separately we describe a special case of the dual random dimer model.
14
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Magnetotransport in Si ⟨Sb⟩ Delta-Layer after Swift Heavy Ion-Induced Modification

51%
Fedotov A., Skuratov V., Yurasov D., Novikov A., Svito I., Apel P., Fedotov A., Zukowski P., Fedotova V.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
229-232
EN
In the present paper the investigations of the influence of swift heavy ion irradiation on the magnetotransport in the antimony (Sb) δ-layer in silicon are reported. Temperature and magnetic field dependences of the resistance R(T,B) and the Hall coefficient R_H(T,B) in the temperature range of 2K < T < 300K and B ≤ 8T before and after the 167 MeV Xe⁺²⁶ ion irradiation (ion fluence of 10⁸ cm¯²) were measured. At the temperatures below 50K there is observed the transition from the Arrhenius log R(1/T) to a logarithmic R ≈ -log(T) dependence both before and after the swift heavy ion exposure which confirms the assumption that the carrier transport goes through the δ-layer mainly. Moreover, the transition from the positive to negative magnetoresistance was observed with the temperature decrease that is characteristic of the two-dimensional quantum corrections to the conductivity in the case of weak localization regime. The appropriate Thouless lengths L_{Th}(T) ≈ A × T^{p} (where p and A are dependent on the scattering mechanism) indicated their ≈ 25-30% decrease after the swift heavy ion exposure. It was shown that the exponent p values were close to the theoretical one of p = 1, confirming the realization of 2D weak localization regime in the carrier transport.
15
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Spin-Orbit Coupling in n-Type PbTe/PbEuTe Quantum Wells

51%
Peres M., Chitta V., Maude D., Oliveira N., Rappl P., Ueta A., Abramof E.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
602-605
EN
Magnetoresistance measurements were performed on an n-type PbTe/PbEuTe quantum well and weak antilocalization effects were observed. This indicates the presence of spin-orbit coupling phenomena and we showed that the Rashba effect is the main mechanism responsible for this spin-orbit coupling. Using the model developed by Iordanskii et al., we fitted the experimental curves and obtained the inelastic and spin-orbit scattering times. Thus we could compare the zero field energy spin-splitting predicted by the Rashba theory with the energy spin-splitting obtained from the analysis of the experimental curves. The final result confirms the theoretical prediction of strong Rashba effect on IV-VI based quantum wells.
16
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Conductance Fluctuations in Quantum Wires of n-CdTe and n-Cd_{1-x}Mn_{x}Te

51%
Jaroszyński J., Wróbel J., Sawicki M., Skośkiewicz T., Karczewski G., Wojtowicz T., Kossut J., Dietl T., Kamińska E., Papis E., Barcz A., Piotrowska A.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
1000-1004
EN
We present millikelvin studies of magnetoconductance in submicron wires of In-doped n^{+}-CdTe and n^{+}-Cd_{0.99}Mn_{0.01}Te epilayers. Weak-field magnetoresistance which arises from quantum localization as well as universal conductance fluctuations have been observed. The exchange coupling to magnetic impurities is shown to decrease the correlation field of the fluctuations. This novel effect is interpreted by invoking a new driving mechanism of the magnetoconductance fluctuations - the redistribution of the electrons between energy levels of the system, induced by the giant s-d spin-splitting of the electronic states.
17
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Exciton Dynamics in CdTe/CdMnTe Multiquantum Well Structures Grown by Molecular Beam. Epitaxy on GaAs Substrate

51%
Godlewski M., Koziarska B., Suchocki A., Karczewski G., Wojtowicz T., Kossut J., Bergman J. P., Monemar B.
Acta Physica Polonica A
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1995
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vol. 88
|
issue 5
985-989
EN
The results of picosecond photoluminescence kinetics of four different CdTe/CdMnTe multiquantum well structures grown by MBE on GaAs substrates are presented. The experimental results show that excitons in CdTe quantum wells are strongly localized by potential fluctuations. Photoluminescence decay times of the localized excitons are considerably shorter (about 120 ps) than those reported for free or quasi-free excitons. An influence of Mn in the barriers on exciton properties is demonstrated. For narrow quantum wells as well as for the multiquantum well structure with the highest Mn mole fraction the excitons migrate during their decay to the states with a lower potential energy. Longer decay times are observed for quasi-localized excitons. We show also that for strongly localized excitons the energy transfer between localized and donor bound excitons is less efficient.
18
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Content available

Phase Space Description of Localization in Disordered One-Dimensional Systems

51%
Wołoszyn M., Spisak B., Maksymowicz A.
|
EN
The degree of electronic localization in disordered one-dimensional systems is discussed. The model is simplified to a set of Diracδ-like functions used for the potential in the Schrödinger equation and calculations are carried out for the ground state. The disorder of topological character is introduced by the random shifts of the potential peaks. For comparison, we also discuss two aperiodic systems of the potential peaks: Thue-Morse and Fibonacci sequences. The localization, both in the momentum and the real space, is analyzed for different disorder strengths and sizes of the system. We calculate the localization length, and additionally we express the localization effects in terms of the inverse participation function and also by means of the Husimi quasi-classical distribution function in the phase space of the electron (position, momentum) coordinate system. We present the influence of disorder generated by the random and aperiodic sequences of potential on the energy spectrum.
19
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Anomalous Magnetoresistance in Multi-Level Quantum Wells

51%
Averkiev N., Golub L., Pikus G.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
229-234
EN
Effect of intensive interlevel transitions in quantum well and strong spin-orbit interaction on weak localization is considered. Anomalous magnetoresistance in classically weak fields is calculated for p-type quantum wells based on A_{3}B_{5} semiconductors. It is shown that the sign of magnetoresistance changes with varying doping level and the role of the intersubband transitions in weak localization effects depends dramatically on a view of the scattering potential.
20
Content available remote

Atomistic Calculation of Coulomb Interactions in Semiconductor Nanocrystals: Role of Surface Passivation and Composition Details

45%
Chwastyk M., Różanski P., Zieliński M.
Acta Physica Polonica A
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2012
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vol. 122
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issue 2
324-328
EN
We report a theoretical investigation of electronic properties of semiconductor InAs and GaAs nanocrystals. Our calculation scheme starts with the single particle calculation using atomistic tight-binding model including spin-orbital interaction and d-orbitals. Then the exciton binding energies are calculated with screened Coulomb interaction. We study the role of surface passivation effects by varying value of surface passivation potential. We compare results obtained with dot center positioned on different lattice sites thus containing different number of anion and cations. We conclude that passivation of surface states affects significantly single particle energies and the value of electron-hole Coulomb attraction. Interestingly, due to limited screening, the short-range (on-site) contribution to the electron-hole Coulomb attraction plays significant role for small nanocrystals with radius smaller than 1 nm.
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