Methods: Analytical calculations and computer simulations. The first appropriate theoretical treatment of excitons influenced by disorder has been suggested in the paper S.D. Baranovskii and A.L. Efros "Band Edge Smearing in Solid Solutions", Sov. Phys. Semicond. 12, 1328 (1978), that has received more than 100 citations in the scientific literature. Further studies in this field were carried out including those on the quantitative characterization of nanostructures.

Numerous invited talks were given at conferences and seminars, for example, "Temperature-Dependent Exciton Luminescnece in Quantum Wells" at "10^th International Workshop of Condensed Matter Physics", September 1998, Varna, Bulgaria.

Selected papers:

• A.G.Abdukadirov, S.D. Baranovskii et al. "Photoluminescence and Tunneling Relaxation of Localized Excitons in A_IIB_VI Anion Mixed Crystals", Sov. Phys. JETP 71, 1155 (1990).


• H. Kalt, ..., S.D. Baranovskii et al. "Optical- and Acoustic-Phonon Assisted Hopping of Localized Excitons in CdTe/ZnTe Quantum Wells", Phys. Rev. B 45, 4253 (1992).


• U.Siegner, ..., S.D. Baranovskii et al. "Optical Dephasing in Semiconductor Mixed Crystals", Phys. Rev. B 46, 4564 (1992).


• C. Klingshirn, ..., S.D. Baranovskii et al. "Dynamics of Localized Excitons and High-Excitation Effects in II-VI Quantum Wells and Heterostructures", Physica B 191, 90 (1993).


• S.D. Baranovskii et al. "Exciton Line Broadening by Compositional Disorder in Alloy Quantum Wells" Phys. Rev. B 48, 17149 (1993).


• A.N. Reznitsky, S.D. Baranovskii et al. "Recombination of Aloy-Trapped Excitons in Ternary Solid Solutions with Common Cation Components", Physica Status Solidi (b) 184, 159 (1994).


• S.D. Baranovskii et al. "Exciton Line Broadening by Compositional Disorder in ZnSe_xTe_1-x Quantum Wells", Solid State Communications 89, 5 (1994).


• S.Yu. Verbin, S.D. Baranovskii et al. "New Luminescence Band in II-VI Semiconductor Crystals with treated Surfaces", Mater. Sc. Forum 182-184, 279 (1995).


• J.E. Colub, S.D. Baranovskii, P.Thomas "Evidence for Dipole-Dipole Hopping of GaAs Quantum Well Excitons", Phys. Rev. Lett. 78, 4261 (1997).


• S.D. Baranovskii et al. "Temperature-Dependent Exciton Luminescence in Quantum Wells: Computer Simulation", Phys. Rev. B 58, 13081 (1998).


• S.D. Baranovskii and T. Faber "Transport Energy for Foerster Processes", Physica Status Solidi (b) 218, 59 (2000).


• S.A. Tarasenko, ..., S.D. Baranovskii et al. "Energy Relaxation of Localized Excitons at Finite Temperature", Semicond. Sci. Technol. 16, 486 (2001).

Methods: analytical calculations and computer simulations. Among other results, one can emphasize the first simulation proof of the Coulomb gap and the quantitative theory of the line shape in the photothermal magnetospectroscopy of semiconductors. The latter theory provides a basis for quantitative characterization of pure materials.

Numerous invited talks were given at conferences and seminars, for example, "Electron Glass Transition in Lightly Doped Semiconductors" at "4^th International Conference on Hopping and Related Phenomena", August 1991, Marburg, Germany ; "Quantitative Characterization of Impurities in III-V Semiconductors" at "International Conference on Cond. Mat. Physics and Applications", April. 1992, Bahrain; "Electron Glass Transition" at the International Workshop "Frontiers in the Physics of Complex Systems", March 2001, Tel Aviv, Israel.

Selected papers:

• S.D. Baranovskii, A.L. Efros, B.L. Gelmont, B.I. Shklovskii "Coulomb Gap in Disordered Systems", Solid State Communication. 27, 1 (1978).


• S.D. Baranovskii, A.L. Efros, B.L. Gelmont, B.I. Shklovskii "Coulomb Gap in Disordered Systems: Computer Simulation", J. Phys. C: Solid State Phys. 12, 1023 (1979).


• S.D. Baranovskii and A.A. Uzakov "On the High-Frequency Impurity Hopping Conductivity", Solid State Commun. 36, 829 (1980).


• S.D. Baranovskii, A.L. Efros, B.I. Shklovskii "Elementary Excitations in Disordered Systems with Localized Electrons", Sov. Phys. JETP 51, 199 (1980).


• S.D. Baranovskii and A.A. Uzakov "Interimpurity Absorption of Infrared Radiation in Lightly Doped Semiconductors", Sov. Phys. Semicond. 16, 1026 (1982).


• S.D. Baranovskii, A.A. Uzakov, A.L. Efros "Thermodynamic Properties of Impurity Band Electrons", Sov. Phys. JETP 56, 422 (1982).


• S.D. Baranovskii, A.L. Efros, B.I. Shklovskii "Screening in a System with Localized Electrons", Sov. Phys. JETP 60, 1031 (1984).


• S.D. Baranovskii et al. "Temperature Dependence of the Lineshape of 1s®2p Photothermal Ionization of Donors in GaAs", Sov. Phys. JETP Lett. 46, 510 (1987).


• S.D. Baranovskii et al. "Quadrupole Line-Broadening for Hydrogen-Like Impurities in Lightly Doped Compensated Semiconductors", Sov. Phys. Semicond. 22, 1002 (1988).


• S.D. Baranovskii and B.I. Shklovskii "Temperature Dependence of the Line Profile of Photoionization of Impurities in Lightly Doped Weakly Compensated Semiconductors", Sov. Phys. Semicond. 23, 122 (1989).


• S.D. Baranovskii "Theoretical Basis for Quantitative Characterization of Impurities in n-type III-V Semiconductors by Photoelectromagnetic Spectroscopy", Appl. Surface Science 50, 218 (1991).


• S.D. Baranovskii et al. "Electron Glass Transition in Lightly Doped Semiconductors", Philos. Mag. B 65, 685 (1992); J. Appl. Phys. 71, 2452 (1992).


• S.D. Baranovskii and P. Thomas, Comment on "Phase Transition of an Exciton System in GaAs Coupled Quantum Wells" and "Fermi-Dirac Distribution of Excitons in Coupled Quantum Wells", Phys. Rev. Lett. 69, 993 (1992).


• S.D. Baranovskii et al. "Spectroscopic Determination of the Compensation Degree and Impurity Concentration in High-Purity GaAs", in "Best of Soviet Semiconductor Physics and Technology", ed. M. Levinstein and M. Shur (World Scientific, Singapore, 1995) p.71.


• I.S. Shlimak, ..., S.D. Baranovskii et al. "Temperature-Induced Smearing of the Coulomb Gap by Hopping Electrons", Phys. Rev. Lett. 75, 4764 (1995).


• S.D. Baranovskii et al. "On the Potential Fluctuations in Amorphous Silicon", J. Non-Cryst. Solids 190, 117 (1995).


• J.E. Colub, S.D. Baranovskii, P.Thomas, "Role of Interactions in the Energy-Loss Hopping and Recombination of Two-Dimensional Electrons and Holes", Phys. Rev. B 55, 4575 (1997).

Theory of the transport and optical properties of such materials has been developed with taking into account the multiphonon nature of electronic transitions. A comprehensive review article on this topic was published.

Selected papers:

• Review article: S.D. Baranovskii and V.G. Karpov "Localized Electron States in Semiconductor Glasses", Sov. Phys. Semicond. 21, 1 (1987).


• S.D.Baranovskii and V.G. Karpov "Thermal Quenching of Photoluminescence in Chalcogenide Glasses", Sov. Phys. Semicond. 18, 828 (1984).


• M. Babacheva, S.D. Baranovskii et al. "Influence of Photostructural Transformations in As₂S₃ Films on Urbach Absorption Edge", Sov. Phys. Solid State 26, 1331 (1984).


• S.D.Baranovskii et al. "Ambipolar Photoconductivity in Glasses Ge-Pb-S", Sov. Phys. Semicond. 18, 633 (1984).


• S.D. Baranovskii and V.G. Karpov "Probability of Capture and Dispersive Transport in Non-Crystalline Semiconductors", Sov. Phys. Semicond. 19, 336 (1985).


• S. D. Baranovskii and E.A. Lebedev "Localized States Limiting Drift Mobility in Amorphous Se-Containing S, Te and As", Sov. Phys. Semicond. 19, 635 (1985).


• S.D. Baranovskii, B.L. Gelmont, K.D. Tsendin "Compensation Level in Modified Semiconductor Glasses", Sov. Phys. Semicond. 20, 1137 (1986); J. Non-Cryst. Solids 97-98, 487 (1987).


• S.D. Baranovskii and V.G. Karpov "Kinetics of Photoluminescence Decay in Semiconductor Glasses", Sov. Phys. Semicond. 20, 192 (1986).


• S.D. Baranovskii and V.G. Karpov "Multiphonon Hopping Conductivity", Sov. Phys. Semicond. 20, 1137 (1986).


• S.D. Baranovskii and V.G. Karpov "Frequency Dependence of the Capacitance of Metal-Insulator Semiconductor Structures on the Basis of Non-Crystalline Materials", Sov. Phys. Semicond. 21, 1280 (1987).


• S.D. Baranovskii and M. Silver "The Effect of Long-Range Coulomb Potential on the Electronic Structure of Localized States in Homogeneous Intrinsic Amorphous Semiconductors", Philos. Mag. Lett. 61, 77 (1990).


• S.D. Baranovskii, V.K. Tikhomirov, G.J. Adriaenssens "Evidence for a Temperature Dependence of the Intrinsic Dipoles in Chalcogenide Glasses", Phil. Mag. Lett. 77, 295 (1998).

Various regimes were considered with respect to the temperature conditions (low, intermediate and high temperatures), recombination mechanisms (radiative and non-radiative), electric fields (linear transport at low fields and non-linear transport at high fields) etc.. Special attention has been given to the development of the theoretical basis for various experimental techniques, such as the time-resolved and frequency-resolved spectroscopy, the thermally stimulated currents, the time-of-flight technique. Basic ideas are applicable to the description of electronic transport in various disordered semiconductors, for example, in microcrystalline silicon and in porous silicon.

Numerous invited talks were given at conferences and seminars, for example, "Low-Temperature Transport in Disordered Materials" at "Chelsea Meeting on Disordered Semiconductors", December 1990, London, U.K.; "Photoluminescence in Amorphous Silicon" at "International Workshop on Light-Emitting Silicon", July 1992, Munich, Germany; "Nonlinear Hopping Transport in Band Tails" at "16^th International Conference on Amorphous Semiconductors", September 1995, Kobe, Japan; "Thermally Stimulated Currents at Low Temperatures" at "7^th International Conference on Hopping and Related Phenomena", August 1997, Rackeve, Hungary.

Selected papers:

• S.D. Baranovskii, E.L. Ivchenko, B.I. Shklovskii "A Novel Tunneling Recombination Regime for Photoexcited Carriers in Amorphous Semiconductors", Sov. Phys. JETP 65,1260 (1987).


• S.D. Baranovskii, V.G. Karpov, B.I. Shklovskii "Theory of Non-Radiative Recombination in Amorphous Semiconductors", J. Non-Cryst. Solids. 97-98, 487 (1987); Sov. Phys. JETP 67, 538 (1988).


• S.D. Baranovskii et al. "Photoluminescence and Photoconductivity in Amorphous Semiconductors at Low Temperatures", Sov. Phys. JETP 69, 775 (1989).


• B.I. Shklovskii, H. Fritzsche, S.D. Baranovskii "Electronic Transport and Recombination in Amorphous Semiconductors at Low Temperatures", Phys. Rev. Lett. 62, 2989 (1989).


• M.E. Raikh, S.D. Baranovskii, B.I. Shklovskii "Dimensional Quantization in a-Si:H Quantum Well Structures: the Alloy Model", Phys. Rev. B 41, 7701 (1990).


• S.D. Baranovskii et al. "Low-Temperature Photoconductivity of Doped Amorphous Semiconductors", Solid State Communications 86, 549 (1993).


• S.D. Baranovskii et al. "Effective Temperature for Electros in Band Tails", J. Non-Cryst. Solids. 164-166 (1993).


• G.J. Adriaenssens, S.D. Baranovskii et al. "Photoconductivity Response Time in Amorphous Semiconductors", Phys. Rev. B 51, 9661 (1995).


• B. Cleve, B. Hartenstein, S.D. Baranovskii et al. "High-Field Hopping Transport in Band Tails of Disordered Semiconductors", Phys. Rev. B 51, 16705 (1995).


• S.D. Baranovskii et al. "On the Description of Hopping Energy Relaxation and Transport in Disordered Systems", J. Non-Cryst. Solids 198-200, 222 (1996).


• S.D. Baranovskii and P. Thomas "Nonlinear Hopping Transport in Band Tails", J. Non-Cryst. Solids 198-200, 140 (1996).


• S.D. Baranovskii et al. "Thermally Stimulated Conductivity in Disordered Semiconductors at Low Temperatures", Phys. Rev. B 55, 16226 (1997).


• J.-H. Zhou, S.D. Baranoskii, S. Yamasaki et al. "On the Transport Properties of Microcrystalline Silicon at Low Temperatures", Phys. Stat. Solidi (b) 205, 147 (1998).


• S.D. Baranovskii, Comment on "Absence of Carrier Hopping in Porous Silicon", Phys. Rev. Lett. 81, 3804 (1998).

In particular, a relation between the mobility and diffusivity for hopping charge carriers in the non-equilibrium regime has been derived. The latter replaces the well-known Einstein relation valid for equilibrium transport.

Numerous invited talks were given at conferences and seminars, for example, "Einstein Relation for Hoping Electrons" at "9^h International Workshop of Condensed Matter Physics", September 1996, Varna, Bulgaria.

Selected papers:

• S.D. Baranovskii et al. "Einstein Relation for Hopping Electrons", J. Non-Cryst. Solids 198-200, 214 (1996).


• S.D. Baranovskii et al. "Long-Time Asymptotics in the Diffusion-Controlled A+B®0 Reaction with Hopping Energy Relaxation", J. Chem. Phys. 106, 3157 (1997).


• S.D. Baranovskii et al. "On the Einstein Relation for Hopping Electrons", Physica Status Solidi (b) 205, 91 (1998).


• S.D. Baranovskii et al. " On the Einstein Relation for Hopping Electrons", J. Non-Cryst. Solids 227-230, 158 (1998).

In particular, a simple and general mechanism has been suggested for puzzling so far effect of photo-induced condensation. The latter was observed experimentally in a variety of species, though it has never been explained before on a general basis.

Selected papers:

• S.D. Baranovskii et al. "On the Time Decay of the Photoinduced Condensation in Supersaturated Vapors", J. Chem. Phys. 103, 7796 (1995).


• H. Uchtmann, R. Dettmer, S.D. Baranovskii, F. Hensel "Potoinduced Nucleation in Supersaturated Mercury Vapor", J. Chem. Phys. 108, 9775 (1998).


• H. Uchtmann, S. Yu. Kazitsyna, S.D. Baranovskii, F. Hensel "Light-Induced Nucleation and Optical Absorption in Cesium Vapor", J. Chem. Phys. 113, 4171 (2000).

A comprehensive theory has been developed that provides natural explanation for many effects, which are still often called "a challenge to science of 21^st century". One of these effects is an enormous nonlinearity of the conductivity with respect to the concentration of ions. For example, changing the latter by a factor of two leads to the changing of the conductivity by many orders of magnitude. Another puzzling and not yet explained effect known since 1925 is the so-called mixed-cation effect: gradual replacing of well-conducting cations in a glass matrix by not worse conducting cations leads to an enormous decrease of the conductivity. It appears possible to show that these effects as well as many other puzzling effects can be well accounted for by a routine percolation approach using a well- known structural model for ionic glasses.

Numerous invited talks were given at conferences and seminars, for example, "Transport Mechanism in Ionic Glasses" at "9^h International Conference on Hopping and Related Phenomena", September 1999, Murcia, Spain.

Selected papers:

• S.D. Baranovskii and H. Cordes "On the Transport Mechanism in Ionic Glasses", J. Chem. Phys. 111, 7546 (1999).


• H. Cordes and S.D. Baranovskii "On the Conduction Mechanism in Ionic Glasses", Physica Status Solidi (b) 218, 133 (2000).

A comprehensive theory has been developed that provides a natural explanation for experimentally observed dependencies of carrier mobility on temperature, electric field, concentration of localized states, localization length etc. in the conjugated polymers, molecularly doped polymers and organic glasses. Combined with experimental data, the theory gives rather precise estimates for material parameters, such as the energy spread of localized states, their concentration and the localization length.

Numerous invited talks were given at conferences and seminars, for example, "Transport Mechanism in Disordered Organic Solids" at "3^rd International Conference on Science and Technology of Synthetic Metals", July 2000, Bad Gastein, Austria.

Selected papers:

• S.D. Baranovskii et al. "On the Description of Charge Carrier Transport in Disordered Organic Solids", Phys. Rev. B 62, 7934 (2000).


• H. Cordes, S.D. Baranovskii et al. "One-Dimensional Hopping Transport in Disordered Organic Solids. I. Analytic Theory", Phys. Rev. B 63, No.9 (2001).


• K. Kohary, H. Cordes, S.D. Baranovskii et al. "One-Dimensional Hopping Transport in Disordered Organic Solids. II. Monte Carlo Simulations", Phys. Rev. B 63, No.9 (2001).