Quantum information storage for over 180 s using donor spins in a 28Si "semiconductor vacuum".

A quantum computer requires systems that are isolated from their environment, but can be integrated into devices, and whose states can be measured with high accuracy. Nuclear spins in solids promise long coherence lifetimes, but they are difficult to initialize into known states and to detect with high sensitivity. We show how the distinctive optical properties of enriched (28)Si enable the use of hyperfine-resolved optical transitions, as previously applied to great effect for isolated atoms and ions in vacuum. Together with efficient Auger photoionization, these resolved hyperfine transitions permit rapid nuclear hyperpolarization and electrical spin-readout. We combine these techniques to detect nuclear magnetic resonance from dilute (31)P in the purest available sample of (28)Si, at concentrations inaccessible to conventional measurements, measuring a solid-state coherence time of over 180 seconds

Ultrahigh thermal conductivity of isotopically enriched silicon

Most of the stable elements have two and more stable isotopes. The physical properties of materials composed of such elements depend on the isotopic abundance to some extent. A remarkably strong isotope effect is observed in the phonon thermal conductivity, the principal mechanism of heat conduction in nonmetallic crystals. An isotopic disorder due to random distribution of the isotopes in the crystal lattice sites results in a rather strong phonon scattering and, consequently, in a reduction of thermal conductivity. In this paper, we present new results of accurate and precise measurements of thermal conductivity κ(T) for silicon single crystals having three different isotopic compositions at temperatures T from 2.4 to 420 K. The highly enriched crystal containing 99.995% of 28Si, which is one of the most perfect crystals ever synthesized, demonstrates a thermal conductivity of about 450 ± 10 W cm-1K-1 at 24 K, the highest measured value among bulk dielectrics, which is ten times greater than the one for its counterpart natSi with the natural isotopic constitution. For highly enriched crystal 28Si and crystal natSi, the measurements were performed for two orientations [001] and [011], a magnitude of the phonon focusing effect on thermal conductivity was determined accurately at low temperatures. The anisotropy of thermal conductivity disappears above 31 K. The influence of the boundary scattering on thermal conductivity persists sizable up to much higher temperatures (∼80 K). The κ(T) measured in this work gives the most accurate approximation of the intrinsic thermal conductivity of single crystal silicon which is determined solely by the anharmonic phonon processes and diffusive boundary scattering over a wide temperature range

Composition ffnhomogeneity and structural defects in czochralsi grown GexSi1-x solid solution crystals

The relationship between the plastic strain and the inhomogeneity of germanium distribution in single crystals of GexSi1 (-x) (x = 4-9 at %) solid solutions grown using the Czochralski method has been studied. It is established that plastic straining develops via the nucleation of dislocations at their sources occurring in the Ge segregation bands, while the inhomogeneous profile of Ge distribution across the growth direction is caused by thermoelastic stresses.X114sciescopu

X-ray studies of Si1-xGex single crystals

Structural imperfections were studied in Si1 - xGex (1 - 9 at. % Ge) solid-solution single crystals grown using the Czochralski method. The studies were performed using x-ray diffraction topography with laboratory and synchrotron radiation sources, x-ray diffractometry, and synchrotron radiation phase radiography. In all crystals studied, irrespective of the Ge concentration, impurity bands (growth bands) were observed. An increase in the Ge concentration in the range 7 - 9 at. % was shown to bring about the nucleation and motion of dislocations on a few slip systems and the formation of slip bands. Local block structures were observed in the places where slip bands intersected. The most likely reason for the formation of slip bands is the inhomogeneous distribution of Ge atoms over the ingot diameter and along the growth axis. Therefore, the structure of Si1 - xGex solid-solution single crystals can be improved by making them more uniform in composition. (c) 2005 Pleiades Publishing, Inc.X115sciescopu

Competition between homogeneous and inhomogeneous broadening of orbital transitions in Si:Bi

Contains fulltext : 180733.pdf (publisher's version ) (Open Access

Investigation of dislocations in Czochralski grown Si1-xGex single crystals

Dislocations in p-type Si1-xGex single crystals (2-8 at% Ge) grown with the Czochralski technique are investigated by synchrotron white beam topography in transmission geometry. As the Ge concentration increases, the dislocation structure evolves from individual dislocations to slip bands and sub-grain boundaries, and the dislocation density increases from < 10(2) cm(-2) to 10(5)-10(6) cm(-2) at 8 at%. We discuss the effect of dislocations on the electrical characteristics such as resistivity rho(v), Hall hole mobility mu p, carrier lifetime tau(e) and I-V characteristics. Here tau(e) and I-V characteristics are measured from the diodes fabricated by bonding the p-Si1-xGex to n-Si wafers. I-V characteristics are not deteriorated in spite of a five times decrease in tau(e) with the Ge concentration.X1133sciescopu

White X-ray beam topography and radiography of Si1-xGex crystals bonded to silicon

The defect structure of Si1-xGex. wafers with 4% of germanium and their interfaces with Si wafers were studied using white radiation topography and phase-sensitive radiography. The heterostructures were manufactured by direct bonding of Si1-xGex. and Si crystalline wafers made of bulk crystals that were grown by the Czochralski technique. In Si1-xGex. crystals, the segregations of Ge act as dislocation nucleation sites. In Si1-xGex/Si bonded structures, the segregation of Ge as well as the accumulation of dislocations induce elastic strain and plastic deformation during high-temperature bonding annealing. With the topography-radiography combination, we are able not only to detect microcracks, indicating nonbonded areas, by radiography, but also to reveal dislocations and long-range strain fields by topography at the same time. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.X114sciescopu