Search

Once called a "classically non-describable two-valuedness" by Pauli , the electron spin is a natural resource for long-lived quantum information since it is mostly impervious to electric fluctuations and can be replicated in large arrays using silicon quantum dots, which offer high-fidelity control. Paradoxically, one of the most convenient control strategies is the integration of nanoscale magnets to artificially enhance the coupling between spins and electric field, which in turn hampers the spin's noise immunity and adds architectural complexity. Here we demonstrate a technique that enables a \emph{switchable} interaction between spins and orbital motion of electrons in silicon quantum dots, without the presence of a micromagnet. The naturally weak effects of the relativistic spin-orbit interaction in silicon are enhanced by more than three orders of magnitude by controlling the energy quantisation of electrons in the nanostructure, enhancing the orbital motion. Fast electrical control is demonstrated in multiple devices and electronic configurations, highlighting the utility of the technique. Using the electrical drive we achieve coherence time $T_{2,{\rm Hahn}}\approx50 \mu$s, fast single-qubit gates with ${T_{\pi/2}=3}$ ns and gate fidelities of 99.93 % probed by randomised benchmarking. The higher gate speeds and better compatibility with CMOS manufacturing enabled by on-demand electric control improve the prospects for realising scalable silicon quantum processors.

The recent successes in the isolation and characterization of several bismuth radicals inspire the development of new spectroscopic approaches for the in-depth analysis of their electronic structure. Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for the characterization of main group radicals. However, the large electron-nuclear hyperfine interactions of Bi (

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.

The recent successes in the isolation and characterization of several bismuth radicals inspire the development of new spectroscopic approaches for the in-depth analysis of their electronic structure. Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for the characterization of main group radicals. However, the large electron-nuclear hyperfine interactions of Bi (209Bi, I = 9/2) have presented difficult challenges to fully interpret the spectral properties for some of these radicals. Parallel-mode EPR (B1 || B0) is almost exclusively employed for the study of S > 1/2 systems but becomes feasible for S = 1/2 systems with large hyperfine couplings, offering a distinct EPR spectroscopic method. Herein, we demonstrate the application of conventional X-band parallel-mode EPR for S = 1/2, I = 9/2 spin systems: Bi doped crystalline silicon (Bi:Si) and the molecular Bi radicals: [L(X)Ga]2Bi• (X = Cl, I) and [L(Cl)GaBi(MecAAC)]• (L = HC[MeCN(2,6-iPr2C6H3)]2). In combination with multifrequency perpendicular-mode EPR (X-, Q-, and W-band frequency), we were able to fully refine both of the anisotropic g- and A-tensors of these molecular radicals. The parallel-mode EPR experiments demonstrated and discussed here have the potential to enable the characterization of other S = 1/2 systems with large hyperfine couplings, which is often challenging by conventional perpendicular-mode EPR techniques. Considerations pertaining to the choice of microwave frequency are discussed for relevant spin-systems.

Funding Information: The authors would like to thank EPSRC (UK) for funding this work via grant EP/TO25131/1. J.A.T.D.G. would like to thank the Government of the Philippines through the Department of Science and Technology (DOST) for her Ph.D. funding. J.C. is thankful for the support of the i3N projects, Refs. UIDB/50025/2020 and UIDP/50025/2020, financed by the Fundação para a Ciência e a Tecnologia in Portugal. Publisher Copyright: © 2021 The Authors. physica status solidi (a) applications and materials science published by Wiley-VCH GmbH Indium-doped silicon is considered a possible p-type material for solar cells to avoid light-induced degradation (LID), which occurs in cells made from boron-doped Czochralski (Cz) silicon. Herein, the defect reactions associated with indium-related LID are examined and a deep donor is detected, which is attributed to a negative-U defect believed to be InsO2. In the presence of minority carriers or above bandgap light, the deep donor transforms to a shallow acceptor. An analogous transformation in boron-doped material is related to the BsO2 defect that is a precursor of the center responsible for BO LID. The electronic properties of InsO2 are determined and compared to those of the BsO2 defect. Structures of the BsO2 and InsO2 defects in different charges states are found using first-principles modeling. The results of the modeling can explain both the similarities and the differences between the BsO2 and InsO2 properties.

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.

We report high-harmonic generation up to the ninth order from boron-doped Si at room temperature, pumped by intense THz pulses. For comparison with the experiment, we also performed FDTD simulations coupled to a full-band Monte Carlo device model. The simulations predict a significantly stronger flattening of the conversion efficiency with pump power than that observed in the experiments, which points to less pronounced scattering at high fields than expected.

High-harmonic generation (HHG) is a phenomenon resulting from the strongly nonlinear, non-perturbative interaction between intense electromagnetic pulses and matter. It has been intensively investigated ever since its first observation with optically excited noble-gas atoms in the late 1980s [1] . The HHG effect is not only widely applied in table-top, coherent X-ray sources but is also the key for the generation of intense attosecond pulses [2] . Gases and atom clusters are the most intensively employed materials for HHG. Recently, HHG has also been observed in bulk crystals [3] , which has triggered a surge of research interest in HHG from solids [4] .

Silicon, a ubiquitous material in modern computing, is an emerging platform for realizing a source of indistinguishable single photons on demand. The integration of recently discovered single-photon emitters in silicon into photonic structures is advantageous to exploit their full potential for integrated photonic quantum technologies. Here, we show the integration of an ensemble of telecom photon emitters in a two-dimensional array of silicon nanopillars. We developed a top-down nanofabrication method, enabling the production of thousands of nanopillars per square millimeter with state-of-the-art photonic-circuit pitch, all the while being free of fabrication-related radiation damage defects. We found a waveguiding effect of the 1278 nm-G center emission along individual pillars accompanied by improved brightness compared to that of bulk silicon. These results unlock clear pathways to monolithically integrating single-photon emitters into a photonic platform at a scale that matches the required pitch of quantum photonic circuits.

The subject of hydrogen–boron interactions in crystalline silicon is revisited with reference to light and elevated temperature-induced degradation (LeTID) in boron-doped solar silicon. Ab initio modeling of structure, binding energy, and electronic properties of complexes incorporating a substitutional boron and one or two hydrogen atoms is performed. From the calculations, it is confirmed that a BH pair is electrically inert. It is found that boron can bind two H atoms. The resulting BH2 complex is a donor with a transition level estimated at E c–0.24 eV. Experimentally, the electrically active defects in n-type Czochralski-grown Si crystals co-doped with phosphorus and boron, into which hydrogen is introduced by different methods, are investigated using junction capacitance techniques. In the deep-level transient spectroscopy (DLTS) spectra of hydrogenated Si:P + B crystals subjected to heat-treatments at 100 °C under reverse bias, an electron emission signal with an activation energy of ≈0.175 eV is detected. The trap is a donor with electronic properties close to those predicted for boron–dihydrogen. The donor character of BH2 suggests that it can be a very efficient recombination center of minority carriers in B-doped p-type Si crystals. A sequence of boron–hydrogen reactions, which can be related to the LeTID effect in Si:B is proposed.

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.

Valley splitting is a key feature of silicon-based spin qubits. Quantum dots in $\mathrm{Si}$/${\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ heterostructures reportedly suffer from a relatively low valley splitting, limiting the operation temperature and the scalability of such qubit devices. Here, we demonstrate a robust and large valley splitting exceeding 200 $\ensuremath{\mu}\mathrm{eV}$ in a gate-defined single quantum dot, hosted in molecular-beam-epitaxy-grown $^{28}\mathrm{Si}/{\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$. The valley splitting is monotonically and reproducibly tunable up to 15% by gate voltages, originating from a 6-nm lateral displacement of the quantum dot. We observe static spin relaxation times ${T}_{1}g1$ s at low magnetic fields in our device containing an integrated nanomagnet. At higher magnetic fields, ${T}_{1}$ is limited by the valley hotspot and by phonon noise coupling to intrinsic and artificial spin-orbit coupling, including phonon bottlenecking.

It is well established that boron reacts with two oxygen atoms in Czochralski-grown silicon (Cz-Si) to form a defect, which is responsible for the dominant light-induced degradation (LID) in solar cells made from Cz-Si:B material. The detrimental effect of LID has stimulated a move by solar cell manufacturers to the use of silicon with other group-III dopants, particularly with gallium. Cz-Si:Ga is immune to the BO-type LID. The information available in the literature on the interactions of oxygen with either Al, Ga, or In impurities in Si is limited. We use ab initio modeling and junction spectroscopy techniques to study a family of defects with unusual electronic properties, which have been detected in Cz-Si samples doped with different shallow acceptor species. We have carried out detailed measurements of the temperature dependencies of hole emission rate, equilibrium occupancy, and hole capture kinetics for the traps observed in differently doped p-type Cz-Si samples. It is found from the analysis of the changes in magnitude of the deep-level-transient signals with temperature that the equilibrium occupancy function of the traps is characteristic for a defect with negative-U properties in all the samples. The positions of the E(-/+) occupancy level of the defects are very close in differently doped samples, E(-/+) = Ev + (0.31 ± 0.01) eV. It is argued that the oxygen dimer interacts with group-III atoms in silicon and these interactions result in the formation of AsO2 complexes (A is either B, Al, Ga, or In atom) with very similar electronic properties.

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.

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 10

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.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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

Electrical properties of radiation-produced defects in p-Ge irradiated with MeV electrons and protons are investigated. The dominant defects in electron-irradiated p-Ge were found to be neutral for the most part, whereas they are electrically active in proton-irradiated materials. Evidently, the reactions between impurity atoms and intrinsic point defects leading to formation of secondary Ga-related defects in electron-and proton-irradiated p-Ge appear to be distinct. Production rates of radiation defects in n-Ge and p-Ge are compared. A marked difference in the removal rates of shallow donor/acceptor impurity states, at least by an order-of-magnitude, is thought to be due to greatly enhanced annihilation of Frenkel pairs in p-type Ge.

We report a detailed study of electron longitudinal and transverse spin relaxation times for Li donors in monoisotopic 28Si over the temperature range 4–20 K using continuous wave and pulsed electron paramagnetic resonance. Comparison of the obtained spin-lattice relaxation times for the states of the isolated donor center and lithium complex LiO showed that due to the presence of orbital degeneracy, relaxation is faster for single lithium than for the LiO complexes with the nondegenerate ground state. For the isolated lithium center in silicon the relaxation is well described by Blume-Orbach process, with the parameters of the spin-orbit coupling ~ 1·10-6 meV compare to Orbach process for LiO complex with spin-orbit coupling parameter ~ 1.5·10-2 meV.

The paper considers two main approaches discussed in literature for conversion of gaseous fluorides SiF4, GeF4 and hydrogen-containing compound of germanium, i.e., GeH4, isotopic enriched by centrifugal method, into target products—stable isotopes of silicon and germanium in the form of bulk polycrystals and thin layers. In the first two-step (chemical) approach the fluorides are converted into intermediate compounds which are further subjected either to pyrolysis or to reduction by hydrogen. In the second single-step (plasma-chemical) approach the gaseous fluorides are reduced by hydrogen in plasma sustained by the discharges of different types.

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.

Laue lenses constitute a promising option for concentrating soft gamma rays with a large collection area and reasonable focal lengths. In astronomy they could lead to increased telescope sensitivity by one to two orders of magnitude, in particular for faint nuclear gamma-ray lines, but also for continua like hard X-ray tails from a variety of compact objects. Other fields like Homeland security and nuclear medicine share the same need for more sensitive gamma-ray detection systems and could find applications for gamma-ray focusing optics. There are two primary challenges for developing Laue lenses: the search for high-reflectivity and reproducible crystals, and the development of a method to accurately orient and fix the thousands of crystals constituting a lens. In this paper we focus on the second topic. We used our dedicated X-ray beamline and Laue lens assembly station to build a breadboard lens made of 15 crystals. This allowed us to test our tools and methods, as well as our simulation code and calibration procedure. Although some critical points were identified, the results are very encouraging, with a crystal orientation distribution lower than $10''$, as required to build a Laue lens telescope dedicated to the study of Type Ia supernovae (30-m focal length). This breadboard lens represents an important step towards raising the technology readiness level of Laue lenses., Comment: Accepted for publication in Nuclear Instrument and Methods in Physics Research Section A

We present an overview on generation of direct gap photo- and electroluminescence in Ge bulk wafers, Ge thin films deposited on Si, and Ge p-i-n diodes prepared on Si substrates. We analyzed the emission in a spectral range from 0.45 eV to 0.95 eV, covering the radiation caused by direct gap transitions, the indirect one, and also the luminescence related to transition on dislocations. The temperature and excitation level strongly influence the intensities of direct and indirect photoluminescence in bulk samples. As it could be expected, high temperature and excitation favour the generation of direct gap luminescence. Intrinsic bulk Ge shows a quadratic dependence of the direct gap luminescence on the excitation and a sub-quadratic one for the indirect. The photoluminescence spectra taken from intrinsic Ge on Si layers show features related to dislocations. There are two spectral regions associated with dislocation recombination. At room temperature one is at around 0.45 eV and the other at 0.72 eV. We found strong direct gap radiation from the Ge p-i-n diodes with intrinsic, highly dislocated active area (dislocation density of about 108-1010 cm-2). There is a threshold current density of 8 kA/cm2, at which the direct band luminescence becomes a super-quadratic. The dependence of the radiation intensity on the excitation is governed by a power law with exponent of 1.7 before reaching that threshold and 4.5 after exceeding it. Above the threshold the dislocation radiation shows similar dependence on the excitation as the direct band luminescence.

The inverted structure of the 1s ground state of lithium in silicon provides a unique opportunity to study inter-valley spin-orbit interactions of donor electrons. A study of lithium doped silicon enriched in the 28Si isotope with a low oxygen content (N 21014 cm3) has demonstrated at low temperatures (T = 3.8 K) a family of electron spin resonance (ESR) spectra with anisotropic g factors associated with Li donor centres. The spectra were investigated without and with application of external stress to the sample and their g factors were found to be less then 2.000. The analysis of experimental data and numerical simulation of the spectra and their angular dependencies in the second order perturbation theory assuming the splitting of states due to internal strains in the crystal is larger than the Zeeman and spin-orbit splitting have shown that the spectrum, having g tensor components corresponding to the tetragonal symmetry, consists of two lines belonging to the triplet state T2, and the other two lines in the spectrum have an angular dependence behaviour of the doublet states E. The ratio of the inter-valley spin-orbit coupling λ and λ' to the Δ parameters, characterizing the splitting of the states under internal strains have been defined. From the dependencies of the triplet ESR lines intensity on the compressive stress of the crystal along the [11 it was obtained the value of the internal strains, which allowed to determine the parameters of the spin-orbit coupling λ and λ'. Their values were found to be three orders of magnitude smaller than were obtained earlier for Li spectra with g > 2. Since experimentally observed Δ value was of the order of the Zeeman splitting parameter the spectra were analyzed using the full matrix of the spin Hamiltonian for the fivefold degenerate ground state. We found that angular dependencies of the spectra observed for the triplet and doublet states with g < 2 are well described by the solutions of the spin Hamiltonian with parameters λ and λ' obtained from our experimental data. At the same time, we are not able to find solutions that satisfy the data obtained for the spectra with g > 2.000 in previous studies.

The effect of tin on the formation and temperature transformation of VO centers in Ge upon annealing has been investigated. It was found that the doping of Ge with tin leads to a change of reactions involving oxygen and vacancies and the new defect SnVO appears upon VO annealing. Doping Ge with tin gives rise to a considerable decrease in the formation efficiency of divacancies and VO centers and the latter exist in a very narrow temperatures range. VO2 complexes appear only upon annealing of SnVO centers. The assumption is made that the absorption bands situated at 718.9 and 733.6 cm-1 belong to the less stable configuration VO2* and the bands at 731.5 and 771.7 cm-1 correspond to stable configuration of VO2 centers.

Si1-xGex alloys with small atomic fraction of Ge, x≤ 0.05 are investigated. The Hall mobility of electrons in n-type materials was measured at cryogenic temperatures, T≤ 100 K. Taking into account the partial mobility due to charge carrier scattering by ionized centers and phonons it is possible to estimate the partial mobility associated with alloy scattering. It appears that this contribution to the electron mobility in n-Si1-xGex at low temperatures is important even at x≈0.01. The obtained results can be useful for understanding the nature of SiGe alloys and their transport properties.

Photoluminescence from excitons bound to shallow donors or acceptors was studied in Al-, As-, B-, Ga- and P-doped Ge. Excitons bound to Al and B acceptors were identified for the first time. The dissociation energy of the excitons satisfies Haynes rule and changes with a factor of 0.1 linearly with the ionization energy of the dopants.