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Electron-spin qubits have long coherence times suitable for quantum technologies. Spin–orbit coupling promises to greatly improve spin qubit scalability and functionality, allowing qubit coupling via photons, phonons or mutual capacitances, and enabling the realization of engineered hybrid and topological quantum systems. However, despite much recent interest, results to date have yielded short coherence times (from 0.1 to 1 μs). Here we demonstrate ultra-long coherence times of 10 ms for holes where spin–orbit coupling yields quantized total angular momentum. We focus on holes bound to boron acceptors in bulk silicon 28, whose wavefunction symmetry can be controlled through crystal strain, allowing direct control over the longitudinal electric dipole that causes decoherence. The results rival the best electron-spin qubits and are 104 to 105 longer than previous spin–orbit qubits. These results open a pathway to develop new artificial quantum systems and to improve the functionality and scalability of spin-based quantum technologies. Spin qubits in systems with strong spin–orbit coupling can be electrically controlled, but are usually affected by short coherence times. Here, coherence times up to 10 ms are obtained for strain-engineered hole states bound to boron acceptors in silicon 28.

Silicon, germanium and their alloys are classical semiconductors that play an important role in fundamental sciences and are the basis for modern microelectronics, optoelectronics, energy conversion, and other applications. The thermoelectric power (Seebeck coefficient) of p- and n-type materials in combination with the electrical and thermal conductivities characterizes the efficiency of thermal-to-electric energy conversion. In this work we experimentally show how one can effectively control the thermoelectric power of silicon-germanium alloys using an applied high pressure. We measured the Seebeck coefficient and the electrical resistance for several Si1−xGex crystals with different compositions under applied high pressure in (i) their original semiconductor cubic-diamond structure, (ii) across a phase transition to a metal phase at about 9–13 GPa, and (iii) across phase transformations to different metastable phases on pressure release. These studies were carried out for several pressurization and decompression cycles. The Si–Ge samples were examined by X-ray diffraction and Raman spectroscopy. After the high-pressure cycling the Si–Ge samples transformed into two metastable phases, namely, a cubic bc8 phase (Si-III) with a p-type electrical conductivity in the Si-dominant samples, and a tetragonal st12 phase (Ge-III) in the Ge-dominant alloys, whose conductivity type depended on the Si content. The dramatic pressure-driven changes in the thermoelectric power of Si–Ge crystals we found suggest that these semiconductors are promising for use in various stress-controlled electronic junctions, such as switches, p–n diode elements, n–p–n (p–n–p) transistors, and multi-layer heterostructures with alternating types of electrical conductivity.

Third-order non-linearities are important because they allow control over light pulses in ubiquitous high-quality centro-symmetric materials like silicon and silica. Degenerate four-wave mixing provides a direct measure of the third-order non-linear sheet susceptibility χ(3)L (where L represents the material thickness) as well as technological possibilities such as optically gated detection and emission of photons. Using picosecond pulses from a free electron laser, we show that silicon doped with P or Bi has a value of χ(3)L in the THz domain that is higher than that reported for any other material in any wavelength band. The immediate implication of our results is the efficient generation of intense coherent THz light via upconversion (also a χ(3) process), and they open the door to exploitation of non-degenerate mixing and optical nonlinearities beyond the perturbative regime., Light: Science & Applications, 10 (1), ISSN:2047-7538

A decrease of two-gamma annihilation rate of a positron in a strong spin–orbit field of the annihilation site of bismuth impurity center 209Bi (J = 9/2) in silicon with natural isotope composition was revealed (J is the nuclear spin). This decrease was observed along with increasing occupancy of Bi donor states (binding energy E{Bi} ≈ 69 meV). Atoms of 29Si (J = 1/2) isotope are involved in spin interactions of positron with Bi impurity centers. The growth of occupancy of Bi donor states inhibits two-gamma annihilation rate. The estimated cross-section of positron trapping by the Bi impurity center is σ + ≈ (1.23–1.5) × 10−13 cm2. Together with this surprisingly large value, the integral rate of two-gamma annihilation in a hypothetical polyelectron system of the Bi impurity center is by a factor of just Δ ∼ 2.18 higher compared to the magnitude ≈2.09 × 109 s−1 known for elemental isolated polyelectron, (e−e+e−). Possible formation of the positron-containing exciton-like states, (e+)D 0 X (D = Bi, P) is also discussed. Irradiation of material with 15 MeV protons results in decreasing the factor Δ by ∼11% due to forming the radiation complex in which Bi atom is in an open volume ambient it. Such complex is suggested to have D 3d symmetry and be the deep donor. Low-temperature measurements of both the positron annihilation rate and Hall effect have been applied for studying the isochronal annealing of these point radiation defects which were found to be thermally stable up to ∼370 °C; they can be annealed at ∼430 °C – 470 °C. According to available data of ab initio cluster calculations, the complex of Bi atom with a simulated vacancy has D 3d symmetry with the energy gain ∼0.92 eV, thus indicating qualitative agreement between experimental and theoretical data.

Minority carrier traps in Czochralski-grown (Cz) silicon crystals doped with either boron, aluminum, gallium, or indium impurity atoms have been investigated by means of deep-level transient spectroscopy and other junction-related techniques. The experimental data have suggested that minority carrier trapping effects in Cz-Si samples doped with different acceptor impurities are associated with complexes incorporating a substitutional group-III impurity atom and two oxygen atoms, which are found to be negative-U defects with close locations of E(-/+) occupancy level at about Eu + 0.32 eV. We have determined the energy barriers and frequency factors for the reversible transformations of the complexes between deep donor and shallow acceptor states. These parameters are discussed in relation to light-induced degradation behavior of solar cells on p-type Cz-Si crystals.

White beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection., White-beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation-free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.

International journal of tourism sciences 6(1), 40 (2020). doi:10.1038/s41534-020-0276-2, Published by Taylor & Francis, London

Experimental investigations of the relaxation times in germanium doped by shallow arsenic donors at low temperatures have been performed with use of pump-probe technique. The dedicated setup utilizes terahertz radiation from the NovoFEL free electron laser. Relaxation times of several excited states have been measured. The values of measured lifetimes fall into nanosecond range. Experimental results are compared with theoretical calculations which take into account acoustic phonon assisted relaxation.

Silicon doped with Se${}^{+}$ is particularly compelling as a spin-photon interface, because it could be the basis of all-silicon, hybrid spin-photon quantum information technology. This study pins down the most critical spin-photon properties of Si:Se${}^{+}$: the transition dipole moment of the spin-dependent optical transition, the radiative efficiency of the first excited state, and the zero-phonon emission fraction. The authors also measure a long ${T}_{1}$ spin lifetime in Earth's magnetic field of over 4.6 hours. Taken together, these favorable results indicate that an integrated quantum optoelectronic platform based on Si:Se+ is well within reach of current integrated photonic capabilities.

The vacancy-rich disordered regions (DR) playing a key role in improving the thermoelectric figure-of-merit of silicon thermoelectric generators by reducing (by ∼90%) the thermal conductivity, have been probed with positrons. The DR were created by irradiating n-Cz-Si(P) material with the fast reactor neutrons. The parameter of the electron density rs′ ≈ 2.18 a.u. contacting positrons in DR has been reconstructed using the data of the angular correlation of the annihilation radiation (ACAR); the amendments to the rs′ value associated with the ion core electrons were taken into account. It is argued that the ion cores of atoms of silicon as well as the ones of the as-grown impurities (O, C) are involved in the open vacancy volume to be probed with positrons: a relaxation of the ion cores directed inward toward the vacancy volume seems to take place. These positron traps are formed beyond the vacancy-rich area of the disordered region. In the course of isochronal annealing, the traps are stable up to Tanneal. ≈ 520 °C when a recovery of ACAR parameters begins and then it continues up to ∼1050 °C. A vacancy center containing positrons in the open vacancy volume beyond the vacancy-rich area of the disordered region is shown schematically. The emission of electron–positron annihilation gamma-quanta dominates from within these positron traps. The values of both the electron–positron ion core radius (rm) and electron density (parameter rs′) suggest a relaxation directed toward inwards the open vacancy volume: the impurity atoms of oxygen and carbon are, perhaps, involved in the center.

Experimental investigations of THz emission from silicon (Si) doped by shallow donors under uniaxial stress along the [001] crystal axis upon selective intracenter excitation by an infrared free electron laser are presented. spectral dependences of Si output integral emission on the pump wavelength and Si laser output terahertz emission spectra have been analyzed. Two mechanisms of stimulated emission have been recognized as inversion-population-based lasing and stimulated Raman scattering. It is shown that uniaxial stress allows to control the Stokes shift and by this the output Raman emission frequency in the active medium. The obtained results demonstrate the feasibility of broad range THz tuning in doped silicon by means of uniaxial stress.

A numerical scheme was developed to compute the thermal and stress fields of the Czochralski process in a quasi-time dependent mode. The growth velocity was computed from the geometrical changes in melt and crystal due to pulling for every stage, for which the thermal and stress fields were computed by using the open source software Elmer. The method was applied to the Czochralski growth of Ge crystals by inductive heating. From a series of growth experiments, we chose one as a reference to check the validity of the scheme with respect to this Czochralski process. A good agreement both for the shapes of the melt/crystal interface at various time steps and the change in power consumption with process time was observed. �� 2019 by the authors. Licensee MDPI, Basel, Switzerland.

In the growth of germanium (Ge) single crystals by Czochralski (Cz) method, a novel gas-phase doping procedure has been suggested to obtain heavily doped, both n-type (phosphorous) and p-type (boron) semiconducting crystals. The crystals were grown using the so-called “mini-Cz” technique and the pulled crystals are characterized for their structural and electrical properties. A narrow full width at half maximum (FWHM) of the X-ray diffraction rocking curves obtained for both symmetric (4 0 0) reflection (14 arcsec) and asymmetric (3 1 1) reflection (11 arcsec) indicate good crystalline quality. In addition, the grown crystals have a low dislocation density (etch pit density of ≈104 cm−2) without hot-zone optimization. Doping concentrations of up to 3 × 1018 cm−3 have been obtained so far, which implies that gas-phase doping is a viable route and may solve some of the conventional doping issues when using solids as dopants in the Cz melt. We also report here high doping of antimony (Sb) using a solid dopant source. Non-flat solid-liquid interface of the Sb-doped crystals during the growth process, as characterized by the typical ring structure of the growth striations, has been seen in lateral photovoltage scanning (LPS) measurements.

Donor spins in silicon are some of the most promising qubits for upcoming solid-state quantum technologies. The nuclear spins of phosphorus donors in enriched silicon have among the longest coherence times of any solid-state system as well as simultaneous qubit initialization, manipulation and readout fidelities near ~99.9%. Here we characterize the phosphorus in silicon system in the regime of "zero" magnetic field, where a singlet-triplet spin clock transition can be accessed, using laser spectroscopy and magnetic resonance methods. We show the system can be optically hyperpolarized and has ~10 s Hahn echo coherence times, even at Earth's magnetic field and below., Comment: 6 pages, 4 figures

We achieve the strong coupling regime between an ensemble of phosphorus donor spins in a highly enriched $^{28}$Si crystal and a 3D dielectric resonator. Spins were polarized beyond Boltzmann equilibrium using spin selective optical excitation of the no-phonon bound exciton transition resulting in $N$ = $3.6\cdot10^{13}$ unpaired spins in the ensemble. We observed a normal mode splitting of the spin ensemble-cavity polariton resonances of 2$g\sqrt{N}$ = 580 kHz (where each spin is coupled with strength $g$) in a cavity with a quality factor of 75,000 ($\gamma \ll \kappa \approx$ 60 kHz where $\gamma$ and $\kappa$ are the spin dephasing and cavity loss rates, respectively). The spin ensemble has a long dephasing time (T$_2^*$ = 9 $\mu$s) providing a wide window for viewing the dynamics of the coupled spin ensemble-cavity system. The free induction decay shows up to a dozen collapses and revivals revealing a coherent exchange of excitations between the superradiant state of the spin ensemble and the cavity at the rate $g\sqrt{N}$. The ensemble is found to evolve as a single large pseudospin according to the Tavis-Cummings model due to minimal inhomogeneous broadening and uniform spin-cavity coupling. We demonstrate independent control of the total spin and the initial Z-projection of the psuedospin using optical excitation and microwave manipulation respectively. We vary the microwave excitation power to rotate the pseudospin on the Bloch sphere and observe a long delay in the onset of the superradiant emission as the pseudospin approaches full inversion. This delay is accompanied by an abrupt $\pi$ phase shift in the peusdospin microwave emission. The scaling of this delay with the initial angle and the sudden phase shift are explained by the Tavis-Cummings model., Comment: 9 pages, 7 figures

Chalcogen donors in silicon enable a scalable photonic cavity quantum electrodynamics solution for universal quantum computing., Donor spins in silicon are highly competitive qubits for upcoming quantum technologies, offering complementary metal-oxide semiconductor compatibility, coherence (T2) times of minutes to hours, and simultaneous initialization, manipulation, and readout fidelities near ~99.9%. This allows for many quantum error correction protocols, which will be essential for scale-up. However, a proven method of reliably coupling spatially separated donor qubits has yet to be identified. We present a scalable silicon-based platform using the unique optical properties of “deep” chalcogen donors. For the prototypical 77Se+ donor, we measure lower bounds on the transition dipole moment and excited-state lifetime, enabling access to the strong coupling limit of cavity quantum electrodynamics using known silicon photonic resonator technology and integrated silicon photonics. We also report relatively strong photon emission from this same transition. These results unlock clear pathways for silicon-based quantum computing, spin-to-photon conversion, photonic memories, integrated single-photon sources, and all-optical switches.

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−1 K–1 at 24 K, the highest measured value among bulk dielectrics, which is ten times greater than the one fo...

For the first time the samples, cut from the same wafer of crystals of float-zone silicon, n−FZ−Si(P) and n−FZ−Si(Bi), were subjected to irradiation with 0.9-MeV electrons and 15-MeV protons at RT for studying them by low-temperature positron annihilation lifetime spectroscopy. Measurements of Hall effect have been used for the materials characterization. The discussion is focused on the open vacancy volume (Vop) of the thermally stable group-V-impurity-vacancy complexes comprising the phosphorus atoms; the bismuth-related vacancy complexes are briefly considered. The data of positron probing of PV pairs (E-centers), divacancies, and the thermally stable defects in the irradiated n−FZ−Si(P) materials are compared. Beyond a reliable detecting of the defect-related positron annihilation lifetime in the course of isochronal annealing at ∼ 500 °C, the recovery of concentration of phosphorus-related shallow donor states continues up to ∼650–700 °C. The open vacancy volumes Vop to be characterized by long positron lifetimes Δτ2 ∼271–289 ps in (gr.-V-atom)–Vop complexes are compared with theoretical data available for the vacancies, τ(V1), and divacancies, τ(V2). The extended semi-vacancies, 2Vs-ext, and relaxed vacancies, 2Vinw, are proposed as the open volume Vop in (gr.-V-atom)–Vop complexes. It is argued that at high annealing temperature the defect Ps–Vop–Ps is decomposed.

In the present study, the electrical and structural properties of two carbon-hydrogen related DLTS levels (E42 and E262) that appear after hydrogen plasma treatment are investigated in diluted Si1−xGex alloys. E42 and E262 were previously observed in pure Si after hydrogenation by a dc hydrogen plasma. They were correlated with different charge states of a carbon–hydrogen complex, where H is located on the anti-bonding position at the carbon atom (CH1AB). By utilizing the Laplace DLTS technique we show that the DLTS peaks E42 and E262 consist of several components in Si1−xGex. These components can be quantitatively explained by the presence of Ge atoms in the first and second nearest-neighborhood of the CH1AB complex. The observed Laplace DLTS spectra indicate a preference of hydrogen to bond to carbon with a Ge atom in its first nearest-neighborhood.

International audience; A Laue lens gamma-ray telescope represents an exciting concept for a future high-energy mission. The feasibility of such a lens has been demonstrated by the CLAIRE lens prototype; since then various mission concepts featuring a Laue lens are being developed. The latest, which is also the most ambitious, is the European Gamma-Ray Imager (GRI). However, advancing from the CLAIRE prototype to a scientifically exploitable Laue lens requires still substantial research and development. First and foremost, diffracting elements (crystals) that constitute the Laue lens have to be optimized to offer the best efficiency and imaging capabilities for the resulting telescope. The characteristics of selected candidate crystals were measured at the European Synchrotron Radiation Facility on the high-energy beamline ID 15A using a beam tuned at 292 keV. The studied low mosaicity copper crystals have shown absolute reflectivity reaching 30%. These crystals are promising for the realization of a Laue lens, despite the fact that they produce a diffracted beam featuring a Gaussian intensity profile, which contributes to the spread of the focal spot. A composition gradient Si1-x-Gex crystal has been investigated as well, which showed a diffraction efficiency reaching 50% (disregarding absorption) - half of the theoretical maximum - that represents an absolute reflectivity around 39 %, the best that we measured at this energy to date. This gradient crystal also showed a square-shaped rocking curve that is almost the best case to minimize the spread of the focal spot. We also show that bending a gradient crystal could still enhance the focusing. Thanks to the better focusing, a factor of 2 in sensitivity improvement may be achieved.

The next generation of instrumentation for nuclear astrophysics will have to achieve a factor of 10–100 improvement in sensitivity over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge: combining unprecedented sensitivity with high spectral and angular resolution, and the capability of measuring the polarization of the incident photons. The feasibility of such a crystal diffraction gamma-ray lens has recently been demonstrated with the prototype lens CLAIRE. MAX is a proposed mission which will make use of satellite formation flight to achieve 86 m focal length, with the Laue lens being carried by one satellite and the detector by the other. In the current design, the Laue diffraction lens of MAX will consist of 13740 copper and germanium (Ge1−x Si x , x ∼ 0.02) crystal tiles arranged on 36 concentric rings. It simultaneously focuses in two energy bands, each centred on one of the main scientific objectives of the mission: the 800–900 keV band is dedicated to the study of nuclear gamma-ray lines from type Ia supernovae (e.g. 56 Co decay line at 847 keV) while the 450–530 keV band focuses on electron-positron annihilation (511 keV emission) from the Galactic centre region with the aim of resolving potential point sources. MAX promises a breakthrough in the study of point sources at gamma-ray energies by combining high narrow-line sensitivity (better than 10−6 cm−2 s−1) and high energy resolution (E/dE ∼ 500). The mission has successfully undergone a pre-phase A study with the French Space Agency CNES, and continues to evolve: new diffracting materials such as bent or composite crystals seem very promising.