I. P. Ipatova

Formation of strained superlattices with a macroscopic period via spinodal decomposition of III–V semiconductor alloys

Abstract The theory of (in) stability of III–V A 1− x B x C 1− y D y -type quaternary alloys with respect to the coherent phase separation is developed on the basis of the regular solution approximation. It is shown that, in spite of the stabilizing factor of coherency elastic strains, the III–V quaternary alloys which have positive formation enthalpy become at some temperature unstable with respect to coherent phase separation. The equilibrium structure resulting after the phase separation is a one-dimensional modulated two-phase structure with alternating alloy composition ( a system of compositional domains, or, in the other words, a superlattice with a macroscopic periodicity ). Alloy compositions of both phases are determined by the conditions of the minimal homogeneous bulk free energy; the superlattice periodicity is governed by the interplay of the interface free energy and the inhomogeneous part of the elastic free energy. The coherent phase separation diagram and the periodicity of spontaneously formed superlattices are calculated for Ga 1− x In x As 1− y P y .

Spontaneously assembling periodic composition-modulated InGaAsP structures

InGaAsP epitaxial layers, which are obtained in the instability region on InP (001) and GaAs (001) substrates, are investigated by photoluminescence and transmission-electronmicroscopy methods. The results are discussed on the basis of the theory of spinodal decomposition of solid solutions. It is established experimentally that in certain temperature and composition ranges the solid solutions InGaAsP are a system of charged, alternating (in mutually perpendicular directions [100] and [010]) domains of a solid solution with two different compositions and different lattice constants. The domain structure is very clearly defined at the surface of the epitaxial film and becomes blurred in the film near the substrate. The data obtained very likely show spinodal decomposition of the solid solutions InGaAsP in the test samples.

Polaron in quantum nanostructures

Abstract The interest to blue–green lasers results in fabrication of nanostructures based on wide band gap ionic materials. The strong electron–phonon interaction with longitudinal optical phonons results in extra confinement of electrons within the nanostructure. This paper deals with theory of large radius polaron in quantum dots, wires and wells. It is shown that the binding polaron energy increase with decreasing of nanostructure dimensionality. The localized electrons are shown to interact with long wavelength optical phonons with wave vector q ⩽1/ L , L being the characteristic size of nanostructure.

The enhancement factor of hyper-Raman scattering from an inhomogeneous semiconductor surface

Hyper-Raman scattering (HRS) of light from the inhomogeneous surface region of a semiconductor is considered theoretically. The HRS enhancement factor induced by band-bending inhomogeneities in a heavily doped, degenerate semiconductor is evaluated. It is argued that such enhancement effects can be exploited for special applications, e.g., for a micro-HRS induced by a metal tip on a semiconductor surface.

Polar state of a particle with a degenerate band spectrum in a quantum dot

The energies of electron and hole polarons in spherical quantum dots based on materials with a high degree of ionicity are found. It is established that consideration of the valence-band degeneracy causes the hole polaron binding energy to be greater than the electron polaron binding energy. The polaron effects increase with decreasing quantum dot radius. Interband optical transitions are accompanied by partial compensation of the polaron effects, because the emergent electron and hole tend to create polarization potential wells with opposite signs. It is shown that complete compensation of the polaron effects does not occur when the valence-band degeneracy is taken into account. Therefore, interband transitions are accompanied by polarization of the medium. Such polarization is manifested by the appearance of a series of intense phonon replicas of the lines for the electronic transitions.

Inelastic light scattering in GaAsAlAs superlattices

Abstract The first- and second-order Raman scattering by confined LO phonons in (GaAs) m (AlAs) n superlattices are studied theoretically and experimentally. It is pointed out that the frequencies of these modes of (GaAs) 21 (AlAs) 6 superlattice only roughly correspond to bulk GaAs phonons. From linewidth measurements we find the life time of confined LO 1 phonons τ LO1 = (3.60 ± 0.40) ps; τ LO ( Γ ) = (6.30 ± 0.40) ps for bulk (MBE) GaAs. To analyze the symmetries of confined phonons and to obtain the selection rules, band representations of space groups D 2d 9 and D 2d 5 have been developed. We find that there are eight non-equivalent cases for the arrangement of atoms in the primitive cell over Wyckoff positions corresponding to different sets of m and n. We also establish that the contribution of specific atoms to the phonons with definite symmetry as well as vibrational representation, i.e. the number of phonon branches with given symmetry, depend on m and n. It is shown that the analysis of phonons from the Brillouin zone considerably increases the number of independent atomic groups and thus potentially increases the analytical applications of Raman scattering and thereby opens up new possibilities to obtain broad information about superlattice microstructure.

Russian Women in Physics

lya Pavlovna Ipatova is a principal researcher at the A.F. loffe Physico-Technical Institute of the Russian Academy of Sciences and professor of physics at Technical University in St. Petersburg. She received her Ph.D. in physics from St. Petersburg State University. Her areas of research include lattice dynamics of pure and defect crystals, disordered systems, physics of the surface, light scattering from semiconductors, and theory of physical processes in technology of semiconductors. Dr. Ipatova has authored or coauthored more than 300 publications, including four textbooks. She is a member of five national councils of the Russian Academy of Sciences.

Surface polaritons at nanoporous carbon-silicon interface

This paper deals with the effect of the electromagnetic field enhancement in three-layered system due to the propagation of a polariton wave at the interface of nanoporous carbon film -- silicon substrate.

Effect of local vibrations on the H and D atom densities at a Si surface

The equilibrium surface densities of passivating adatoms for a silicon crystal in equilibrium with H2 or D2 gas are calculated. The difference in the surface densities of H and D adatoms is determined by the difference in their local surface vibrations. The equilibrium deuterium surface densities are an order of magnitude higher than the hydrogen surface densities.

Isotope Effect in the Equilibrium between the Silicon Surface and the Gas Phase of Hydrogen or Deuterium

The equilibrium concentrations of passivating adatoms in the system of silicon crystal plus the gas of H 2 or D 2 molecules is calculated. The effect of adatom localized vibrations on the equilibrium concentrations is taken into consideration. It is shown that the major contribution to the ratio of deuterium and hydrogen surface concentrations is determined by the difference between the localized vibration frequencies of deuterium and hydrogen adatoms. The substitution of deuterium for hydrogen for passivating leads to a significant increase of the adatom concentration.