Capture of carriers to screened charged centres and low temperature shallow impurity electric field break down in semiconductors

Free carrier capture by a screened Coulomb potential in semiconductors are considered. It is established that with decreasing screening radius the capture cross section decreases drastically, and it goes to zero when $$. On the basis of this result a new mechanism of shallow impurity electric field break down in semiconductors is suggested.Comment: 8 pages, latex, 1 figure in gif format, to be submitted to "Journal of Condensed Matter

Polaron Energy Spectrum in Quantum Dots

Energy spectrum of a weak coupling polaron is considered in a cylindrical quantum dot. An analytical expression for the polaron energy shift is obtained using a modified pertubation theory.Comment: 7 pages, IOP style LaTeX fil

Time-Reversal Invariant Topological Superconductivity in Quasi-One-Dimensional Structures

It is shown that a time-reversal invariant topological superconductivity can be realized in a quasi-onedimensional structure, which is fabricated by filling the superconducting materials into the periodic channel of dielectric matrices like zeolite and asbestos under high pressure. The topological superconducting phase sets up in the presence of large spin-orbit interactions when s-wave intra-wire and d-wave inter-wire pairings take place. Kramers pairs of Majorana bound states emerge at the edges of each wire. The time-reversal topological superconductor belongs to DIII class of symmetry with a Z2 invariant

A New Low-Noise Avalanche Photodiode With Micro-Pixel Structure

A new design of the avalanche photodiodes with an array of micro-pixel p-n-junctions was developed on base of metal-oxide-silicon structure. The thermal oxide layer of 1000A thickness contains tunnel oxide regions with about 25A thickness. The device exhibits a noise factor ~ 4 at a high multiplication factor (M~10000). A high space uniformity of sensitivity was found for gain of M~ 1000

Unoccupied Topological States on Bismuth Chalcogenides

The unoccupied part of the band structure of topological insulators Bi$_2$Te$_{x}$Se$_{3-x}$ ($x=0,2,3$) is studied by angle-resolved two-photon photoemission and density functional theory. For all surfaces linearly-dispersing surface states are found at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Theoretical analysis shows that this feature appears in a spin-orbit-interaction induced and inverted local energy gap. This inversion is insensitive to variation of electronic and structural parameters in Bi$_2$Se$_3$ and Bi$_2$Te$_2$Se. In Bi$_2$Te$_3$ small structural variations can change the character of the local energy gap depending on which an unoccupied Dirac state does or does not exist. Circular dichroism measurements confirm the expected spin texture. From these findings we assign the observed state to an unoccupied topological surface state