Mode Coupling at around M-Point in PZT

The question of the microscopic origin of the M-superstructure and additional satellite peaks in the Zr-rich lead zirconate-titanate is discussed for nearly 50 years. Clear contradiction between the selection rules of the critical scattering and the superstructure was found preventing unambiguous attributing of the observed superstructure either to the rotation of the oxygen octahedra or to the antiparallel displacements of the lead cations. Detailed analysis of the satellite pattern explained it as the result of the incommensurate phase transition rather than antiphase domains. Critical dynamics is the key point for the formulated problems. Recently, the oxygen tilt soft mode in the PbZr0.976Ti0.024O3 (PZT2.4) was found. But this does not resolve the extinction rules contradiction. The results of the inelastic X-ray scattering study of the phonon spectra of PZT2.4 around M-point are reported. Strong coupling between the lead and oxygen modes resulting in mode anticrossing and creation of the wide flat part in the lowest phonon dispersion curves is identified. This flat part corresponds to the mixture of the displacements of the lead and oxygen ions and can be an explanation of the extinction rules contradiction. Moreover, a flat dispersion surface is a typical prerequisite for the incommensurate phase transition.

Влияние состава зародышевого слоя AlGaAs на формирование антифазных доменов в структурах (Al)GaAs, выращенных газофазной эпитаксией на подложках Ge/Si(100)

GaAs-based heterostructures grown by metalorganic vapor-phase epitaxy on virtual Ge/Si substrates using an AlxGa1-xAs seed layer with different aluminum content x in the solid solution are investigated. The effect of solid solution composition on the density and size of antiphase domains emerging on the sample surface and on the optical properties of the GaAs layer is shown. Si(100) substrates with a small unintentional miscut of 0.7° to [110] were used for growth.

GaAs Compounds Heteroepitaxy on Silicon for Opto and Nano Electronic Applications

III-V semiconductors present interesting properties and are already used in electronics, lightening and photonic devices. Integration of III-V devices onto a Si CMOS platform is already in production using III-V devices transfer. A promising way consists in using hetero-epitaxy processes to grow the III-V materials directly on Si and at the right place. To reach this objective, some challenges still needed to be overcome. In this contribution, we will show how to overcome the different challenges associated to the heteroepitaxy and integration of III-As onto a silicon platform. We present solutions to get rid of antiphase domains for GaAs grown on exact Si(100). To reduce the threading dislocations density, efficient ways based on either insertion of InGaAs/GaAs multilayers defect filter layers or selective epitaxy in cavities are implemented. All these solutions allows fabricating electrically pumped laser structures based on InAs quantum dots active region, required for photonic and sensing applications.

Влияние кристаллографической ориентации пленок GaSb на их структурные свойства при гетероэпитаксии на вицинальных подложках Si(001) методом молекулярно-лучевой эпитаксии

GaSb films were grown by molecular beam epitaxy using AlSb/As/Si transition layers on vicinal Si (001) substrates deflected 6 to the (111) plane. The influence of the GaSb films crystallographic orientation on their structural properties and surface morphology is investigated. It was found that GaSb(001 ̅)/Si films are characterized by better structural perfection, lower concentration of point defects and more planar and isotropic surface topography, compared with GaSb(001) films. Possible reason for the observed differences between GaSb films with different orientations is increased density of antiphase domains in GaSb(001) films. The morphological features of the grown films are caused by the terraces edges basically and by the anisotropy of the incorporation of Ga adatoms into the terraces edges, to a lesser extent.

Особенности структуры промежуточной фазы в цирконате-титанате свинца с высоким содержанием циркония

Results of X-ray diffraction in the intermediate ferroelectric phase of single crystal PbZr$_{0.993}$Ti$_{0.007}$O$_{3}$ are presented. Existence of M-type superstructures $q_{M}$ = \{$\frac{1}{2}$, $\frac{1}{2}$, 0\} and satellites around them, $q_{M}+\{\delta,\delta,\delta\}$, is confirmed. For the first time second order satellites $\{2\delta,2\delta,2\delta\}$ have been observed in the vicinity of $q_{M}$ and fundamental Bragg peaks. Structural model of regular system of antiphase domains is used for diffraction calculation. Calculated pattern includes M-type superstructures as well as first and second order satellites around $q_{M}$. It is shown that second order satellites around fundamental Bragg peaks could not be reproduced in the context of this model. The possible origin of the system of the superstructure reflection observed in the intermediate phase is discussed.