Nonstoichiometry and Properties of SnTe Semiconductor Phase of Variable Composition

According to the modern views, all semiconductor compounds have a homogeneity region (HR), i. e. represent phases of variable composition. The existence of thermodynamically equilibrium deviation from stoichiometry in a chemical compound is connected with a decrease in the crystal free energy under introduction of nonstoichiometric defects (NSD) whose appearance leads to a growth in configurational entropy. The location and size of HR depend on the ratio of the formation energies for different types of defects. The stoichiometric composition may lie inside or outside HR (which corresponds to two-sided and one-sided HR, respectively). Changing properties through deviation from stoichiometry is one of the most important methods of controlling properties of semiconductors

Phase Diagrams of Bi1-xSbx Thin Films with Different Growth Orientations

A closed-form model is developed to evaluate the band-edge shift caused by quantum confinement for a two-dimensional non-parabolic carrier-pocket. Based on this model, the symmetries and the band-shifts of different carrier-pockets are evaluated for BiSb thin films that are grown along different crystalline axes. The phase diagrams for the BiSb thin film systems with different growth orientations are calculated and analyzed

Size effects in lead telluride thin films and thermoelectric properties

The influence of thickness d on thermoelectric properties (the Seebeck coefficient S, electric conductivity σ, the Hall coefficient RH, charge carrier mobility μН) of films d = 8 – 170 nm in thickness, prepared by vacuum evaporation of PbTe crystals with lead excess onto (001) KCl substrates coated with Al2O3 layer has been studied. It has been established that films with d 75 nm carrier transport is determined by n-type charge carriers. The inversion of conductivity sign close to d ≈ 75 nm is attributed to a change in thermodynamic equilibrium conditions in the films as compared to crystal, as well as to material evaporation and condensation features. Oscillations on the d-dependences of the kinetic coefficients of films with p-type conductivity are attributable to quantization of the hole gas of carriers. Calculation of oscillation period Δd using a model of infinitely deep rectangular potential well is in good agreement with the experimentally determined Δd value. For n-type conductivity films the values of kinetic coefficients increase with increase in d, which points to manifestation of a classical size effect

Constructing a Large Variety of Dirac-Cone Materials in the Bi1−x{}_{1-x}Sbx{}_{x} Thin Film System

We theoretically predict that a large variety of Dirac-cone materials can be constructed in Bi${}_{1-x}$Sb${}_{x}$ thin films, and we here show how to construct single-, bi- and tri- Dirac-cone materials with various amounts of wave vector anisotropy. These different types of Dirac cones can be of special interest to electronic devices design, quantum electrodynamics and other fields

Quantum Size Effects and Transport Phenomena in PbSe Quantum Wells and PbSe/EuS Superlattices

It is established that the room-temperature dependences of transport properties on the total thickness of PbSe layers d in PbSe/EuS superlattices exhibit an oscillatory behavior. It is shown that the oscillation period Δd practically coincides with the period of the thickness oscillations observed earlier in single PbSe/EuS quantum well. The non-monotonic character of these dependences is attributed to quantum size effects. The theoretically estimated and experimentally determined Δd values are in good agreement

Gebrukothuria profundus, a new genus and species of laetmogonid holothurian (Elasipodida, Laetmogonidae) from around the Crozet Plateau in the Southern Indian Ocean

A new genus and species of laetmogonid holothurian (Elasipodida, Laetmogonidae), collected from around the Crozet Plateau in the Southern Indian Ocean, is described. It differs from other members of the family in that the body wall lacks the wheel-shaped calcareous deposits completely. Instead only rods are present. The genus is also distinguished by the combination of other morphological characters lacking in other known genera: absence of circum-oral and ventrolateral papillae together with development of midventral tube feet. All other members of the family Laetmogonidae are known to have wheel-shaped deposits, therefore diagnosis of the family is refined

Size Effects in Transport Properties of PbSe Thin Films

This paper presents an overview and analysis of our earlier obtained experimental results on the dependences of kinetic properties of single PbSe quantum wells and PbSe-based superlattices on the PbSe layer thickness d. The observed oscillatory character of these dependences is attributed to quantum size effects due to electron or hole confinement in quantum wells. Some general regularities and factors that determine the character of these quantum size effects are established. The influence of the oxidation processes and doping on the d-dependences of the transport properties is revealed. A periodic change in the conductivity type related to quantum size oscillations is detected. It is shown that the experimentally determined values of the oscillation period Dd are in good agreement with the results of theoretical calculations based on the model of a rectangular quantum well with infinitely high walls, taking into account the dependence of the Fermi energy eF on d and the availability of subbands below eF. It is established that the Dd value for the superlattices is practically equal to the Dd value observed for the single PbSe thin film