Table of contents

In this paper we show that complex three-dimensional micro- and nanostructure shells can be formed by directional rolling up of thin strained Si/SiGe heterostructures. By lifting strain-designed Si/SiGe films using a sacrificial layer from the substrate and by a proper patterning prior to the etching almost arbitrary-shaped three-dimensional structures can be fabricated. A technique for controlling the shape and location of the structures is proposed and realized. In addition we show that it is possible to obtain cylindrical objects with the axes perpendicular to the substrate surface, and the objects themselves can be located at prescribed places on the substrate.

Initial stages of epitaxial growth and formation of CaF₂ nanostructures on Si(001) were studied. A variety of nanostructures were grown including ultrathin two-dimensional layers at 750 °C, quasi-one-dimensional stripes at 650 °C and well-ordered dots at lower growth temperatures. Atomic force microscopy and reflection high-energy electron diffraction were used to measure the nanostructure shape and lattice orientation. The evolution of the surface electronic structure under different growth conditions was studied by ultraviolet photoelectron spectroscopy and metastable de-excitation spectroscopy. The leading role of the wetting layer in high-temperature formation of the fluorite-silicon interface was established.

Semiconducting iron disilicide (β-FeSi₂) precipitate layers were synthesized by means of Fe⁺ implantation into Si(100) at an energy of 40 keV and a dose of 1×10¹⁶ cm^-2 followed by nanosecond pulsed ion-beam treatment of the implanted Si layers. Glancing incidence x-ray diffraction (GIXRD) and atomic force microscopy (AFM) were employed for the structural characterization, and optical absorption and photoluminescence (PL) spectroscopies were used for the optical characterization of the precipitate layers formed. The GIXRD results indicate the formation of oriented β-FeSi₂ precipitates surrounded by a polycrystalline Si matrix. AFM data show the precipitate sizes to be in the range of 25-90 nm. The results of measuring the optical absorption indicate that the formed precipitates have a direct-band structure with an energy gap of 0.83 eV. It is shown that the 1.5 µm PL signal of β-FeSi₂ precipitates is observed up to a temperature of 210 K and does not saturate up to the pump power of 250 mW.

Self-assembled 3D island formation during epitaxial growth was investigated using kinetic Monte Carlo models. Schwoebel barriers for the explanation of 3D kinetic growth were suggested. The diffusion hop probability ratio χ for atom hops up to atom hops down, leading to 2D, 3D and Stranski-Krastanov growth modes, was obtained. The necessity of atomic flux from the island edge to the upper layers for 3D island formation was demonstrated. Island size equalization during the growth process was observed for certain χ values. The reason for the equalization of separate 3D island lateral sizes is the increase in atomic flux to the upper layer. The new layer nucleus on the top of the island becomes the trap for atoms detached from the edges of the lower layer.

The optical and structural properties of the Ge submonolayer nano-inclusions in a Si matrix grown by molecular beam epitaxy are investigated. It is shown that at relatively high growth temperatures >600° C new features appear in the photoluminescence spectra. It is found that these features correspond to formation of the germanium nano-inclusions in a silicon matrix.

Phonon spectra of GaAs/AlAs superlattices (SLs) grown on (311)A, B and (001) surfaces were studied using Raman spectroscopy. The thickness of GaAs layers were varied from 1 to 10 monolayers (MLs); the thickness of AlAs barriers were 8 ML in the (311) direction. Different polarization geometries of Raman scattering were applied to study LO and TO modes. The splitting of TO_x (atoms displace in the direction [01] perpendicular to the facets on the (311)A surface) and TO_y (atoms displace in the [33] direction parallel to the facets) modes was observed for (311)A SLs. In the case of (311)B SLs no splitting was observed. The phonon anisotropy of (311)A SLs may be indirect evidence of anisotropic structure of quantum objects formed on the (311)A GaAs surface. In the Raman spectra of the SL containing GaAs submonolayers (SML) grown on a (2×4) reconstructed (100) surface, Raman peaks corresponding to additional lateral confinement of LO phonons were observed. The calculations of Raman spectra were carried out using the Born-von-Karman model (taking into account Coulomb interaction in the rigid-ion model) and the Wolkenstein bond polarizability model. According to the calculations, the interface structure strongly influences the Raman spectra of GaAs/AlAs heterostructures containing GaAs SML.

A comparative study of the surface morphology, photoluminescence, and photoelectric spectra of heterostructures with InAs/GaAs quantum dots (QDs) grown on the surface, uncovered by etching away the cladding layer, and built in the GaAs matrix is reported. The red-shift of the ground transition energy in the surface QDs compared to the built-in ones has been shown to be related not only to relaxation of the elastic strain, but also to the differences in size, shape, and chemical composition of the nanoclusters. The method of photoelectric spectroscopy in a semiconductor/electrolyte system has been applied to monitor the process of etching of the cladding layer in situ. Using this method, controlled uncovering of the buried QDs was shown to be possible. In turn, this makes it possible to study the actual morphology of the buried quantum-size layers by atomic force microscopy.

We have studied the correlation between nitrogen composition of bulk GaAsN layers grown by molecular beam epitaxy using rf plasma cell and photoluminescence (PL) intensity. We have carried out careful optimization of the plasma cell aperture layout and plasma operation regimes as well as the growth condition of the GaAsN. We have demonstrated the same efficiency of PL from GaAsN layers with up to 1.5% of nitrogen as for GaAs analogues grown at the same temperature. The integrated PL intensity of the sample containing 2.5% drops only three times. Using post-growth annealing we eliminated defects related to low-temperature growth and thereby achieved the same radiative efficiency for GaAsN samples grown at 520 °C as for the reference layer of GaAs grown at 600 °C.

The indium atom distribution in InGaAs/(Al)GaAs quantum wells (QWs) grown by metal-organic chemical vapour deposition was systematically studied. High-resolution grazing-sputter-angle Auger electron spectroscopy was used as a method of indium depth profile investigation. A broadening and shift to the surface of the indium concentration profile in a single QW and an increase of indium content in the upper QW for closely spaced QWs were found. These results were confirmed by photoluminescence measurements. It was observed that the use of AlGaAs barriers between QWs and growth interruptions at QW interfaces during the growth process reduce indium surface segregation.

For the very first time ensembles of Ge quantum dots have been formed in an unstrained heterosystem of GaAs/ZnSe/Ge. The geometric properties (dimensional characteristics) and electronic structure of the islands were studied using scanning tunnelling microscopy, Raman spectroscopy and photoluminescence.

This paper was presented at the 3rd Russian Workshop on Nanophotonics, Nizhnii Novgorod, Russia, 26-29 March 2001.

We study the effect of the interactions of electrons and holes on the optical properties of Ge/Si type-II quantum dots (QDs). In contrast to type-I systems, the excitonic absorption is found to be blueshifted when exciton-hole and exciton-exciton complexes are formed. For a positively charged dot, we argue that this is the consequence of dominance of the hole-hole interaction compared with the electron-hole interaction due to the spatial separation of the electron and hole. When two excitons are excited in the dot, the electrons are found to be spatially separated and have different quantization energies. This is the reason why the biexciton absorption is blueshifted as compared with a single exciton. The spatial separation of electrons makes it possible for a dot to trap more electrons than there are holes. As a result, the conductivity of stacked arrays of Ge/n-Si QDs is found to decrease under interband optical excitation. The negative photoeffect is explained by the trapping of mobile electrons in the quantum well created by the Hartree potential of holes photoexcited in the dots.

Results of a photoluminescence and electroluminescence study of vertically coupled In_0.5Ga_0.5As/GaAs quantum dot (QD) structures with an extended waveguide (1.24 µm thick) are presented. Spectra of spontaneous and stimulated near-infrared (λ≃1 µm) emission as well as spectra of spontaneous mid-infrared (MIR) (λ≃12 µm) emission are obtained under optical and electrical pumping. It is shown that the observed MIR emission is connected with intraband electron optical transitions in the QD structures.

A new scheme for the generation of coherent radiation on the intersubband transition without population inversion between subbands is presented. The scheme is based on the resonant nonlinear mixing of the optical laser fields on the two interband transitions that are intracavity generated in the same active region. The two-wavelength lasing on the interband transitions can be achieved at a substantially lower threshold current than gain on the intersubband transition. This may ensure cw room-temperature operation. Due to the parametric, inversionless nature of generation, the lasers proposed are especially promising for long-wavelength operation above 20 µm.

The characteristic time of the far-infrared response of a quantum Hall effect detector in GaA/AlGaAs has been investigated versus the magnetic field. The response time is shown to increase exponentially with the field due to the spatial separation of photoexcited electrons and holes captured by localized states formed by the disordered potential. The results obtained allow us to estimate the length scale of long-range potential fluctuations.

A new approach for calculation of resonant state parameters is developed. The method proposed allows us to solve different scattering problems, such as scattering and capture probability as well as calculations of shifts and widths of energy levels. It has been applied to the problem of resonant states induced by impurities in the barrier of quantum wells and by strain in uniaxially stressed germanium.

Optical phenomena in the mid-infrared range connected with interlevel and intersubband charge-carrier transitions in quantum dot and quantum well (QW) heterostructures under optical and electrical pumping were investigated. Spectra of interband photoluminescence are also presented. The existence of a metastable level in funnel-shaped QWs is experimentally confirmed. The intersubband transition dynamics in asymmetrical pairs of tunnel-coupled QWs was studied by means of pump-and-probe time-resolved spectroscopy.

This paper was presented at the 3rd Russian Workshop on Nanophotonics, Nizhnii Novgorod, Russia, 26-29 March 2001.

We provide a bird's-eye view of the optical properties of GaN-AlGaN and InGaN-GaN quantum wells and quantum dots.

The first successful results of the application of multifractal analysis to a quantitative description of mosaic-structure peculiarities, that are typical of a GaN epitaxial layer with hexagonal modification grown on (0001) sapphire substrates, have been obtained. The characteristic size of the mosaic structure has been measured to be 200-800 nm. The direct dependence of mobility on the multifractal parameters (the Renyi dimension or the self-organization degree and the order-degree index) of the surface topology of the mosaic structure has been observed for all GaN layers investigated.

Angle resolved emission spectra of microcavities with quantum wells embedded in the active layer have been investigated under the resonant and quasi-resonant excitation into the lower polariton (LP) branch. The conditions have been found at which macroscopic filling of polariton modes is reached in the strong coupling regime. The strong nonlinear effects in the intensity and the degree of polarization of polariton emission have been observed and investigated. Both experimentally observed renormalization of the dispersion and strong narrowing of polariton mode have been explained using an interacting polariton model predicting that the coupling between the LP mode E_LP(k) and the mode of composite polaritons E_CP(k) = 2ℏω(k₀)-E_LP(2k_excitation-k) is qualitatively different from that of the exciton and photon.

Results of a theoretical investigation of the plasmon-polaritons formed by the interaction of two-dimensional plasmons in a planar Bragg microresonator with guided modes of a dielectric substrate slab are presented. The dispersion and attenuation of guided plasmons are calculated. It is concluded that guided plasmon-polaritons may be used in the development of controllable guided-wave THz frequency filters and modulators based on GaAs heterostructures.

The current state of the art of electrostatic force microscopy (EFM) is presented. The principles of EFM operation and the interpretation of the obtained local voltage and capacitance data are discussed. In order to show the capabilities of the EFM method, typical results for semiconducting nanostructures and lasers are presented and discussed. Improvements to EFM and complementary electrical methods using scanning microscopy demonstrate the continuing interest in electrical probing at the nanoscale range.

We investigate resonant tunnelling in GaAs/(AlGa)As double-barrier resonant-tunnelling diodes in which a single layer of InAs self-assembled quantum dots is embedded in the centre of the GaAs quantum well. The dots provide a well-defined and controllable source of disorder in the well and we use resonant tunnelling to study the effect of this disorder on the electronic properties of the well.

A detailed analysis of electrostatic interactions between a dc-biased tip and a metallic or insulating sample is presented. For inhomogeneous thin dielectric films, the scanning probe signal is shown to be proportional to the convolution between an effective surface profile and a response function of the microscope. Based on the properties of the response function, tip-shape effects on the lateral resolution in electrostatic force microscopy are discussed. For tip-sample distances D smaller than the tip radius R, the resolution is found to be proportional to (DR)^1/2.

We analyse strain-induced effects on the capacitance-voltage (C-V) profile for an MBE-grown GaAs/In_0.1Ga_0.9As/GaAs HFET structure. The calculations of C-V profile were made using a new small-signal approach developed for the quantum well (QW) structures. The self-consistent numerical simulations and results of measurements show that strain causes significant changes in the electron distribution of the QW structure and its C-V profile.

We investigate the Γ₂-X_z1 intersubband dynamics in GaAs/AlAs quantum-well structures by time-resolved infrared pump and probe experiments. In the studied structure, the second Γ level in GaAs is nearly resonant to the first X_z level in AlAs. We observe bi-exponentially decaying signals with a short time constant of the order of 1 ps and a longer time constant of about 7 ps at 10 K and 4 ps at 300 K respectively. The long-term decay represents the X_z-Γ₂ transfer by elastic Γ-X scattering at low temperatures. At 300 K electron-LO phonon scattering accelerates the Γ-X transfer.

We have applied the Raman spectroscopy technique to the study of phonon-plasmon coupled modes in Si-doped GaAs_n/AlAs_m superlattices (SLs), grown on (001), (311)A and (311)B substrates. We have observed the shift and broadening of the Raman peaks in doped SLs, compared with undoped SLs. When the GaAs layers were thinned from 10 to 1 monolayer, the coupled phonon-plasmon modes became three-dimensional-like, and the interaction of plasmons with LO-phonons of AlAs-type took place. The phonon-plasmon interaction of the SLs was numerically simulated. There was a qualitative agreement between the experiment and the calculations. We observed a difference in dispersion between the coupled phonon-plasmon modes for SLs grown on facet surface (311)A and surface (311)B. This is probably due to differences in the electron spectra of such SLs caused by the difference in shape of GaAs quantum objects formed on AlAs reconstructed surfaces.

Time-resolved photoluminescence (PL) was studied to determine the radiative recombination lifetimes in InAs/GaAs quantum dots (QDs) fabricated on misoriented substrates by the Stransky-Krastanov method. The intensity of PL from the ground state, excited state and wetting layer of QD was also studied as a function of the excitation density. Measured lifetimes were as high as 3.1 ns. The measurements have clearly demonstrated the band state filling effect: it also provides the possibility of estimating the excitation power density corresponding to the manifestation of this effect at the excitation power of 30 A cm^-2.

We study p-i-n diodes incorporating InAs/AlAs self-assembled quantum dots (QDs) to probe the electron and hole levels of the dots. A comparative analysis of capacitance-voltage, current-voltage and electroluminescence measurements shows that p-i-n structures could be successfully used as QD spectrometers.

Two different mechanisms of homogeneous broadening of the zero-optical-phonon spectral line in CdSe nanocrystal quantum dots are analysed. The first mechanism is due to modulation of the optical-phonon mode frequencies. The second one is caused by multiple-acoustic-phonon-assisted transitions. We show that homogeneous broadening due to acoustic phonons dominates at low temperatures and for small nanocrystal radii. For large nanocrystal radii and at room temperature, the two mechanisms become comparable.

Non-equilibrium properties of quantum dots forming type-II heterostructures with the matrix material are analysed theoretically. Their main distinction from standard type-I dots results from the separation of non-equilibrium carriers in a staggered band diagram and, hence, a decisive role of Coulomb potentials creating potential barriers for recombination. Depending on the material parameters and temperature, these barriers are overcome either by activation or by tunnelling. For both recombination mechanisms, the amplitude of potential, the quantum dot charge, the recombination time, the luminescence spectrum and some other non-equilibrium characteristics are calculated for different intensities of optical excitation.

Spontaneous magnetization of single and coupled quantum dots formed by lateral confinement of a high-mobility two-dimensional electron gas is studied for a realistic GaAs/AlGaAs heterostructure. The modelling of the device takes into account contributions from a patterned gate, doping, surface states, and mirror charges. To explore the magnetic properties we use the Kohn-Sham local spin-density formalism including the contributions from electron correlation and exchange. We show by explicit calculations that the exchange is the dominant mechanism driving a spontaneous magnetization of a dot. The correlation potential reduces the amount of level splitting and usually affects the electron content in the dot at a given gate voltage. These effects are, however, small and may be neglected under present circumstances. Single dots with up to 50 electrons have been studied.

Tunnelling is a powerful tool for the determination of one-electron structures of two-dimensional systems. Recently a strong interaction between cyclotron and intersubband tunnelling resonances was observed in the case when one-particle Landau levels of different two-dimensional subbands do not interact. In this connection the long-wave structure of quasi-two-dimensional magnetoplasmons is calculated for the actual system of two quasi-two-dimensional layers divided by a barrier in a perpendicular magnetic field. It is shown that the Coulomb interaction between the intersubband, intrasubband and combined resonance magnetoplasmons is able to lead to strong anticrossing of their terms. Magnetoplasmon-assisted tunnelling processes will reveal themselves as the anticrossing of Landau levels of different two-dimensional subbands.

This paper was presented at the 3rd Russian Workshop on Nanophotonics, Nizhnii Novgorod, Russia, 26-29 March 2001.

A new NMR quantum computer scheme based on semiconductor nanostructures is discussed theoretically. We also propose using an infrared laser as a new independent instrument for manipulating qubits. Methods of single- and many-qubit gate realization are discussed. Resonant transfer of the electron to several quantum dots helps in implementing complex many-qubit gates. The energy spectrum of the spin-qubit system is obtained. This variant of a quantum computer is simpler to control and more coherent. The distance between qubits and hence the structural requirements are more achievable using modern nanotechnology.

Self-organized microcrystals and nanocrystals (quantum dots) of AgCl and AgBr embedded in KCl and KBr crystalline matrices and retaining the orientation of the host lattice were studied by optically detected magnetic resonance. It was unambiguously shown that self-organized microcrystalline silver halides can be grown inside alkali halide crystals with the properties of bulk crystals since the optically detected magnetic resonance spectra of the embedded microcrystals were practically the same or close to those in bulk AgCl and AgBr and could be used as a `fingerprint' for AgCl and AgBr. For AgCl nanocrystals in a KCl matrix the anisotropy of the g-factor both for isolated self-trapped holes and for self-trapped holes forming self-trapped excitons was found to be substantially reduced compared with those of bulk AgCl crystals. This implies a considerable suppression of the Jahn-Teller (JT) effect in nanoparticles. A rather general mechanism of the suppression of the JT effect in nanocrystals is proposed, taking into account the additional deformation field appearing because of the strong vibronic interaction at the interface. It was concluded that the distribution of exchange interactions for electron-hole pairs and triplet excitons in the KBr:AgBr system is due to a distribution of AgBr crystal sizes. The holes seem to be self-trapped in the AgBr because of the dynamical JT effect. The exchange splitting increases for distant electron-hole pairs with a decrease of AgBr size. The spectra with exchange splitting larger than that in bulk AgBr (1.9 cm^-1) seem to belong to AgBr nanocrystals. In contrast to AgCl the wavelength of the luminescence in AgBr micro- and nanocrystals embedded in a KBr matrix decreases with the decrease of AgBr crystal size.

Zn₂SiO₄:Mn²⁺ nanocrystals were grown in an oxidized porous silicon layer using a chemical impregnation method. Apparently two classes of samples have been obtained. One is characterized by the formation of α-phase zinc silicate crystalline particles, which show green luminescence, and the other one is characterized by β-phase particles, showing yellow luminescence. It was found that in general prolonged annealing, as well as a high degree of impregnation leads to the formation of green-luminescent samples. The decay time of both yellow and green luminescence decreases with the concentration of Mn activator, while generally the decay time of yellow luminescence is considerably larger than that of green luminescence.

Modulation-doped N-AlGaAs/GaAs/InAs/GaAs/InAs/GaAs heterostructures with InAs quantum dots (QDs) in the device channel have been grown and investigated. Their photoluminescence spectra and electron transport properties in both low and high electric fields were studied. Using these structures, modulation-doped field effect transistors have been fabricated and analysed. It was demonstrated that the QD field effect transistors present a new type of hot-electron device, promising for high-speed applications.

Dynamic properties of the resonant tunnelling structures (RTS) as an example of the dynamic nature of nanoelements are studied. Hysteresis and `plateaulike' behaviours of the time-averaged current-voltage (I-V) curve of resonant tunnelling structures may be obtained through analysing the high-frequency current oscillations in such structures. Our study shows that `soft' generation of oscillations leads to the characteristic `plateaulike' I-V form and `rigid' generation of oscillations leads to `hysteresis' I-V behaviour. The analysis is obtained by investigation of the limit cycles of the dynamical system corresponding to the modified equivalent circuit of the RTS developed by Buot and Jensen. In this paper it is clarified that RTS may be used not only as a device for generation of THz oscillations but it may also be used as the dynamic trigger which has two stable states: the stable limit cycle and stable static state.

We trace signatures of quantum chaos in the distribution of nodal points and streamlines for coherent electron transport through different types of quantum dots (chaotic and regular). We have calculated normalized distribution functions for the nearest distances between nodal points and found that this distribution may be used as a signature of quantum chaos for electron transport in open systems. Different chaotic billiards show the same characteristic distribution function for nodal points. This signature of quantum chaos is well reproduced using well known approaches for chaotic wavefunctions. We have also investigated the quantum flows which display some remarkable features.

It is shown that the strong enhancement of electron scattering by polar optical phonon absorption with increasing sheet electron concentration n_s is responsible for the negative change of conductivity in the Al_0.25Ga_0.75As/GaAs/Al_0.25Ga_0.75As quantum well (QW). The insertion of a thin AlAs barrier into the QW increases electron mobility by 1.6 times at n_s = 1×10¹⁶ m^-2 and extends the range of n_s at which the negative conductivity changes. A modulation-doped field-effect transistor based on the high-doped Al_0.25Ga_0.75As/GaAs/Al_0.25Ga_0.75As QW as a channel acquires new specific properties. The transistor transconductance, dependent on applied gate and drain voltages, can change sign, and its value at high doping level can be comparable to that at low doping level, in spite of the great decrease of channel electron mobility.

We investigate the transport properties of magnetic edge states in the presence of a perpendicular non-homogeneous magnetic field in a quantum wire. Systems are studied where the magnetic field exhibits a discontinuous jump in the transverse direction. The energy spectra and wavefunctions of these systems are calculated. The resistance of the quantum wire in the presence of such a magnetic interface is obtained as a function of the Fermi energy and of the homogeneous background magnetic field.

Illumination of a double p-Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As heterostructure by a red light-emitting diode results in a negative photoconductivity that, after the diode is switched off, slowly relaxes to a positive persistent photoconductivity (PPPC), characterized by about a 1.5 times increase of two-dimensional hole concentration and a 1.7 times increase of mobility in comparison with the initial state in the dark. This metastable state may be explained in the framework of the model in which deep electron traps are supposed to be located above the Fermi level on the inverted heterointerface. The calculated concentration of interface charges reveals a 2.4 times decrease between the dark and PPPC states that is in qualitative agreement with the assumed model.

We study the generation of femtosecond superradiance pulses due to collective recombination of electron-hole (eh) pairs in quantum wells placed in a strong magnetic field oriented perpendicular to the growth plane. Such a superradiant laser can work under the conditions of continuous pumping and at room temperature due to the complete quantization of particle motion, maximum possible spectral density of states, high volume density of cyclotron quantum dots and partial suppression of the intraband scattering. It is shown that two-colour superradiant generation is possible at frequencies resonant to frequencies of the neighbouring interband transitions defined by the electron and hole Landau levels.

Optically detected magnetic resonance (ODMR) and level anticrossing spectroscopy were applied to study g-factors and exchange splittings of localized excitons and separately localized electrons and holes at the X_z-Γ crossover of the conduction band states in a GaAs/AlAs superlattice with a composition gradient. g-factors, exchange splittings and the order of the exciton radiative levels were determined. In the transition region we clearly observed the disappearance of type II excitons created by the X_z electron in AlAs and a heavy hole in GaAs layers. Appearance of type I excitons with an order of magnitude larger exchange was verified by LAC spectroscopy. Intermediate `type II-like' and `type I-like' excitons were found in the transition region by ODMR and LAC with different exchange splittings and luminescence decay times. Besides ODMR of excitons with a definite value of exchange splitting, ODMR ascribed to separately localized electrons and holes with a distribution of exchange splittings was detected.

Low-temperature (T≈2 K) photoluminescence (PL) and photoluminescence excitation (PLE) spectra of GaAs/AlGaAs (x = 0.05) structures with shallow quantum wells (QWs) were investigated. It was found that the PLE spectra exhibit a number of broad bands in the above-barrier energy region; these bands alternate `in opposite phases' in the spectra of free excitons and excitonic complexes (trions) (i.e. an increase in the exciton luminescence intensity is accompanied by a decrease in the luminescence intensity of the complexes). Effects originating from simultaneous irradiation of the sample by two laser beams of different wavelengths were studied. In the case where the photon energy of the Ti-sapphire laser is tuned to excite only the QW states, additional pumping by a He-Ne or Ar-ion laser results in the shift of the equilibrium in the exciton-trion system towards an increase in the concentration of the latter species. On the other hand, upon excitation into certain barrier states with energies both below and above the barrier bandgap, additional pump shifts the equilibrium in the opposite direction.

A new simple variational wavefunction with a few variational parameters for two-dimensional X⁺ and X^- trions is suggested. The function gives accurate results for the singlet and triplet state energies of X⁺ and X^- trions in the whole range of electron-to-hole mass ratio. The mass ratio range where the triplet state exists has been found, and the behaviour of the triplet state energy has been examined near the critical mass ratio. The other excited states of the trion are analysed in the vicinity of their critical mass ratios.

The fine structure and intensity of resonant exciton-phonon (REP) spectra in a Zn_0.87Cd_0.13Se/ZnSe single quantum well (QW) have been investigated in detail at tunable laser excitation in the energy region of ground ZnCdSe exciton state at 8 K. Observed REP lines have been shown to go through two different mechanisms. The most intensive component corresponds to Raman scattering through extended exciton states. Other less intensive REP components correspond to hot luminescence of localized excitons. An analysis of optical phonon modes, which can be involved in the formation of the REP spectra in biaxially strained Zn_0.87Cd_0.13Se QWs, has been carried out.

It is found that the phonon flux generated by an external source induces a change of the luminescence bandshape of an ultrathin quantum well CdTe/ZnTe excited quasi-resonantly by a He-Ne laser. The effect of nonequilibrium phonons manifests even at small lasing power and large distance between the phonon generation zone and the quasi-resonant luminescence excitation zone. It is assumed that the phonon flux induces the tunnel transitions between localized exciton states; these transitions are accompanied by stimulated phonon emission.

This paper was presented at the 3rd Russian Workshop on Nanophotonics, Nizhnii Novgorod, Russia, 26-29 March 2001.

Absorption of surface acoustic waves by a two-dimensional electron gas in a perpendicular magnetic field is considered. The structure of such a system at the filling factor ν close to 1/2 can be understood as a gas of composite fermions. It is shown that the absorption at ν = 1/2 can be strongly nonlinear, while small deviation from 1/2 will restore the linear absorption. Study of nonlinear absorption allows one to determine the force acting upon the composite fermions from the acoustic wave at turning points of their trajectories.

The weak localization effect has been studied in macroscopically inhomogeneous diffusive 2D systems and diffusive constrictions. It is shown that such systems can reveal a saturated behaviour of the low-temperature dependence of that parameter, which is obtained from the standard analysis of the negative magnetoresistance and is usually identified by experimentalists with the phase breaking time.

Magneto-optical phenomena associated with cyclotron and magnetoplasma oscillations in a homogeneous two-dimensional electron system are theoretically studied. First, the electromagnetic wave (EW) polarization conversion under uniform cyclotron resonance (CR) conditions is discussed. A shift of the polarization conversion resonance with respect to conventional CR is calculated. This shift is more pronounced for a two-dimensional system with high electron density. Particular attention is given to the EW polarization conversion under non-uniform cyclotron and magnetoplasma resonances in two-dimensional electron plasma in the attenuated total reflection (ATR) arrangement. A crossover from magnetoplasma to a non-uniform cyclotron type of resonance, which takes place when the coupling between the ATR prism fields and the two-dimensional electron system grows, is studied. At any coupling strength, the polarization conversion at the resonance reaches 100% if the electron scattering in the two-dimensional system is neglected. The conclusion is drawn that the regime of non-uniform CR is more profitable from a practical point of view since the actual electron scattering in a two-dimensional system does not greatly deteriorate a high polarization conversion at resonance. The studied phenomena can be observed on gallium arsenide heterostructures at terahertz.

This paper was presented at the 3rd Russian Workshop on Nanophotonics, Nizhnii Novgorod, Russia, 26-29 March 2001.

Electronic devices have decreased in size to the extent that they are now in the nanometric range, and this requires quantum mechanics which understands their operation and optimization. Many features associated with quantum effects are not desirable from an engineering point of view: the charging of a nanocapacitor runs into a Coulomb blockade; the dielectric constants of nanoparticles is much reduced; the binding energy of the shallow dopants for nanoscale quantum dots is a multiple of k_BT resulting in intrinsic behaviour regardless of the doping density; etc. There are other serious problems preventing the implementation of redundancy and robustness which are so essential to electronic devices, for example, inadvertent defects cannot be avoided, contacts and input/output have to be sufficiently small resulting in pushing beyond current lithographic technology. This paper discusses some of the fundamental points which still require more understanding, and what lies ahead in nanoelectronics involving augmented cavity interactions.

The PDF file provided contains web links to all articles in this volume.

For the second time a special issue of Nanotechnology is formed as a collection of selected papers that were presented at the annual International Symposium on Nanostructures: Physics and Technology (www.ioffe.rssi.ru/NANO2001). The Symposia were chaired by two Nobel Prize winners, Professor Zh Alferov and Professor L Esaki, and are traditionally organized by the Ioffe Institute in Repino---a suburb of St Petersburg.

The symposia are essential events for the international community of physicists working in this very important area which covers the newest achievements in physics, technology and applications of solid state nanostructures. The constantly increasing number of papers submitted to the symposium could be considered as evidence of the intense growth and development in this area. It should be stressed that the volume of submissions takes place against the background of a growth in the number of conferences, symposia and workshops devoted to different aspects of the problem. The 10th International Symposium on Nanostructures: Physics and Technology will be held in St Petersburg, Russia, 17--21 June 2002.

A number of papers presented at the 3rd Russian Workshop on Nanophotonics are also included in this special issue. The annual workshop was organized in 2000 by the Institute for Physics of Microstructures of the Russian Academy of Sciences, Nizhnii Novgorod, Russia (www.ipm.sci-nnov.ru/eng) as a satellite conference of the Nanostructure Symposium. It is focused on Si-based optoelectronics, on the physics of stimulated emission of the mid- and far-IR range radiation and on nonlinear optics in the semiconductor nanostructures. The next workshop on Nanophotonics will be held next year on 11--14 March 2002.

R SurisGuest EditorInternational Symposium on Nanostructures: Physics and Technology

Z Krasil'nikGuest Editor3rd Russian Workshop on Nanophotonics