Pulsed laser annealing is a relevant alternative to conventional thermal processes for future technology nodes as it enables the application of a fast and local thermal budget. Such high-energy process can lead to the formation of a liquid phase that recrystallizes upon heat dissipation, through a high velocity liquid/solid interface moving towards the surface. Here, we report on the evolution of the liquid/solid interface roughness and its influence on the crystallinity of Si1-xGex layers depending on multiple parameters (strain state, doping level, Ge content, and pulse duration). This has been conducted with a roughness quantification method based on cross-section STEM-HAADF micrographs. It has been established that the liquid/solid roughness can be decreased by: (i) a compressive strain decrease, (ii) the use of short duration laser pulses or (iii) a reduction of the initial Ge content. The Ge content and strain must correspond to suitable values for optimized MOSFET performances. Consequently, strain and pulse duration were found to be pertinent levers for liquid/solid interface roughness reduction. Increasing the amount of boron atoms in s-Si1-xGex:B/Si systems is another relevant strategy, as compressive strain decrease would then be associated with a beneficial contact resistance lowering in the source-drain regions of p-type MOSFET devices.

Superconductivity in ultradoped Si 1− x Ge x :B epilayers is demonstrated by nanosecond laser doping, which allows introducing substitutional B concentrations well above the solubility limit and up to 7 at%. A Ge fraction x ranging from 0 to 0.21 is incorporated in Si:B: 1) through a precursor gas, by gas immersion laser doping; 2) by ion implantation, followed by nanosecond laser annealing; and 3) by ultrahigh‐vacuum‐chemical vapor deposition growth of a thin Ge layer, followed by nanosecond laser annealing. The 30 and 75 nm‐thick Si 1− x Ge x :B epilayers display superconducting critical temperatures T c tuned by B and Ge between 0 and 0.6 K. Within Bardeen Cooper Schrieffer (BCS) weak‐coupling theory, T c evolves exponentially with both the density of states and the electron–phonon potential. While B doping affects both, through the increase of the carrier density and the tensile strain, Ge incorporation allows addressing independently the lattice deformation influence on superconductivity. To estimate the lattice parameter modulation with B and Ge, Vegard's law is validated for the ternary SiGeB bulk alloy by density functional theory calculations. Its validity is furthermore confirmed experimentally by X‐ray diffraction. A global linear dependence of T c versus lattice parameter, common for both Si:B and Si 1− x Ge x :B, with δ T c / T c ≈ 50% for δ a / a ≈1%, is highlighted.

Superconductivity in ultra-doped Si_1-xGe_x:B epilayers is demonstrated by nanosecond laser doping, which allows introducing substitutional B concentrations well above the solubility limit and up to 7 at.%. A Ge fraction x ranging from 0 to 0.21 is incorporated in Si:B : 1) through a precursor gas by Gas Immersion Laser Doping; 2) by ion implantation, followed by nanosecond laser annealing; 3) by UHV-CVD growth of a thin Ge layer, followed by nanosecond laser annealing. The 30 nm and 80 nm thick Si_1-xGe_x:B epilayers display superconducting critical temperatures T_c tuned by B and Ge between 0 and 0.6 K. Within BCS weak-coupling theory, T_c evolves exponentially with both the density of states and the electron-phonon potential. While B doping affects both, through the increase of the carrier density and the tensile strain, Ge incorporation allows addressing independently the lattice deformation influence on superconductivity. To estimate the lattice parameter modulation with B and Ge, Vegard's law is validated for the ternary SiGeB bulk alloy by Density Functional Theory calculations. Its validity is furthermore confirmed experimentally by X-Ray Diffraction. We highlight a global linear dependence of T_c vs. lattice parameter, common for both Si:B and Si_1-xGe_x:B, with δ T_c/T_c ∼ 50 % for δ a/a ∼ 1 %.

We present superconducting monocrystalline silicon-on-insulator thin 33 nm epilayers. They are obtained by nanosecond laser annealing under ultra-high vacuum on 300 mm wafers heavily pre-implanted with boron (2.5 × 1016 at./cm2, 3 keV). Superconductivity is discussed in relation to the structural, electrical, and material properties, a step toward the integration of ultra-doped superconducting Si at large scale. In particular, we highlight the effect of the nanosecond laser annealing energy and the impact of multiple laser anneals. Increasing the energy leads to a linear increase in the layer thickness and to the increase in the superconducting critical temperature Tc from zero (< 35 mK) to 0.5 K. This value is comparable with superconducting Si layers realized by gas immersion laser doping, where dopants are incorporated without introducing the deep defects associated with implantation. Superconductivity only appears when the annealed depth exceeds the initial amorphous layer induced by the boron implantation. Multiple subsequent anneals result in a more homogeneous doping with reduced amount of structural defects and increased conductivity. The quantitative analysis of Tc concludes on a superconducting–non-superconducting bilayer with an extremely low resistance interface. This highlights the possibility to efficiently couple superconducting Si to Si channels.

Superconductivity in ultra-doped $Si_{1-x}Ge_{x}:B$ epilayers is demonstrated by nanosecond laser doping, which allows introducing substitutional B concentrations well above the solubility limit and up to $7\,at.\%$. A Ge fraction $x$ ranging from 0 to 0.21 is incorporated in $Si:B$ : 1) through a precursor gas by Gas Immersion Laser Doping; 2) by ion implantation, followed by nanosecond laser annealing; 3) by UHV-CVD growth of a thin Ge layer, followed by nanosecond laser annealing. The 30 nm and 80 nm thick $Si_{1-x}Ge_{x}:B$ epilayers display superconducting critical temperatures $T_c$ tuned by B and Ge between 0 and 0.6 K. Within BCS weak-coupling theory, $T_c$ evolves exponentially with both the density of states and the electron-phonon potential. While B doping affects both, through the increase of the carrier density and the tensile strain, Ge incorporation allows addressing independently the lattice deformation influence on superconductivity. To estimate the lattice parameter modulation with B and Ge, Vegard's law is validated for the ternary $SiGeB$ bulk alloy by Density Functional Theory calculations. Its validity is furthermore confirmed experimentally by X-Ray Diffraction. We highlight a global linear dependence of $T_c$ vs. lattice parameter, common for both $Si:B$ and $Si_{1-x}Ge_{x}:B$, with $\delta T_c/T_c \sim 50\,\%$ for $\delta a/a \sim 1\,\%$.

A new method is presented to measure strain over a large area of a single crystal. The 4D-ED data are collected by recording a 2D diffraction pattern at each position in the 2D area of the TEM lamella scanned by the electron beam of STEM. Data processing is completed with a new computer program (available free of charge) that runs under the Windows operating system. Previously published similar methods are either commercial or need special hardware (electron holography) or are based on HRTEM, which involves limitations with respect to the size of the field of view. All these limitations are overcome by our approach. The presence of defects results in small local changes in orientation that change the subset of experimentally available diffraction spots in the individual patterns. Our method is based on a new principle, namely fitting a lattice to (a subset of) measured diffraction spots to improve the precision of the measurement. Although a spot to be measured may be missing in some of the patterns even the missing spot can be precisely measured by the lattice determined from the available spots. Application is exemplified by heavily boron-doped silicon with intended usage as a low-temperature superconductor in qubits.

We report on the structural properties of highly B-doped silicon (up to 10 at.% of active doping) realised by nanosecond laser doping. The crystalline quality, lattice deformation and B distribution profile of the doped layer are investigated by scanning transmission electron microscopy followed by high-angle annular dark field contrast studies and geometrical phase analysis, and compared to the results of secondary ions mass spectrometry and Hall measurements. When increasing the active B concentration above 4 at.%, the fully strained, perfectly crystalline, Si:B layer starts showing dislocations and stacking faults. These only disappear around 8 at.% when the Si:B layer is well accommodated to the substrate. With increasing B incorporation, an increasing number of small precipitates is observed, together with filaments with a higher active B concentration and stacking faults. At the highest concentrations studied, large precipitates form, related to the decrease of active B concentration. The structural information, defect type and concentration, and active B distribution are connected to the initial increase and subsequent gradual loss of superconductivity.

Secondary Ions Mass Spectroscopy and Hall effect measurements were performed on boron doped silicon with concentration between 0.02 at.% and 12 at.%. Ultra-high boron doping was made by saturating the chemisorption sites of a Si wafer with BCl3, followed by nanosecond laser anneal (Gas Immersion Laser Doping). The boron concentration varies thus nearly linearly with the number of process repetitions. However, it is not the case for the hole concentration which tends to saturate at high boron concentration. The difference between boron and hole concentration increases as the square of boron concentration, pointing towards the formation of boron pairs as the dominant contribution to the increase of inactive boron.

Superconducting boron doped silicon is a promising material for integrated silicon quantum devices. In particular, its low electronic density and moderate disorder make it a suitable candidate for the fabrication of large inductances with low losses at microwave frequencies. Here, we study experimentally the electrodynamics of superconducting silicon thin layers patterned in coplanar waveguide resonators, targeting three key properties: kinetic inductance, internal losses, and the variation of these quantities with the read-out power. We report the first observation in a doped semiconductor of microwave resonances with internal quality factors of a few thousand. As expected in the BCS framework, superconducting silicon presents a large sheet kinetic inductance, in the 50-500 pH range comparable to strongly disordered superconductors, whose temperature dependence is well described by Mattis-Bardeen theory. We find, though, an unexpectedly strong non-linearity of the complex surface impedance which cannot be explained either as a non-linearity induced by depairing or as quasiparticle heating.

This chapter is devoted to the application of nanosecond laser annealing to the realization of superconducting silicon layers and quantum devices. Though predicted since more than 50 years, superconducting behavior in highly boron-doped Si was only discovered in 2006, leveraging the gas immersion laser doping (GILD) technique. Indeed, only a nonequilibrium technique allowed to access the boron active concentrations, well above the solubility limit, necessary to cross the superconductivity threshold. This chapter first presents the GILD fabrication method and the characteristics of the obtained superconducting Si layers. Then, this chapter focuses on the efforts made to develop the first quantum devices implementing this new material, such as superconducting quantum interference devices (SQUIDs), all-silicon Josephson junctions, or superconducting microwave resonators. Finally, the recent developments targeting the large-scale integration of superconducting silicon are presented. In this view, GILD, the historical fabrication method, is tentatively replaced by the pulsed laser-induced epitaxy (PLIE) technique, combining high-dose boron implantation and subsequent nanosecond laser annealing.

In weakly spin-orbit coupled materials, the spin-selective nature of recombination can give rise to large magnetic-field effects, e.g. on the electro-luminescence of molecular semiconductors. Although silicon has weak spin-orbit coupling, observing spin-dependent recombination through magneto-electroluminescence is challenging: silicon's indirect band-gap causes an inefficient emission and it is difficult to separate spin-dependent phenomena from classical magneto-resistance effects. Here we overcome these challenges and measure magneto-electroluminescence in silicon light-emitting diodes fabricated via gas immersion laser doping. These devices allow us to achieve efficient emission while retaining a well-defined geometry, thus suppressing classical magnetoresistance effects to a few percent. We find that electroluminescence can be enhanced by up to 300% near room temperature in a seven Tesla magnetic field, showing that the control of the spin degree of freedom can have a strong impact on the efficiency of silicon LEDs.

We have realized laser-doped all-silicon superconducting (S)/normal metal (N) bilayers of tunable thickness and dopant concentration. We observed a strong reduction of the bilayers' critical temperature when increasing the normal metal thickness, a signature of the highly transparent S/N interface associated to the epitaxial sharp laser doping profile. We extracted the interface resistance by fitting with the linearized Usadel equations, demonstrating a reduction of 1 order of magnitude from previous superconductor/doped Si interfaces. In this well-controlled crystalline system we exploited the low-resistance S/N interfaces to elaborate all-silicon lateral SNS junctions with long-range proximity effect. Their dc transport properties, such as the critical and retrapping currents, could be well understood in the diffusive regime. Furthermore, this work led to the estimation of important parameters in ultradoped superconducting Si, such as the Fermi velocity, the coherence length, or the electron-phonon coupling constant, fundamental to conceive all-silicon superconducting electronics.

We have realised laser-doped all-silicon superconducting (S)/ normal metal (N) bilayers of tunable thickness and dopant concentration. We observed a strong reduction of the bilayers critical temperature when increasing the normal metal thickness, a signature of the highly transparent S/N interface associated to the epitaxial sharp laser doping profile. We extracted the interface resistance by fitting with the linearised Usadel equations, demonstrating a reduction of one order of magnitude from previous superconductor/doped Si interfaces. In this well controlled crystalline system we exploited the low resistance S/N interfaces to elaborate all-silicon lateral SNS Josephson junctions with long range proximity effect. Their dc transport properties, such as the critical and retrapping currents, could be well understood in the diffusive regime. Furthermore, this work lead to the estimation of important parameters in ultra-doped superconducting Si, such as the Fermi velocity, the coherence length, or the electron-phonon coupling constant, fundamental to conceive an all-silicon superconducting electronics.

We have studied a Superconducting Quantum Interference Device (SQUID) made from a single layer thin film of superconducting silicon. The superconducting layer is obtained by heavily doping a silicon wafer with boron atoms using the gas immersion laser doping technique. The SQUID is composed of two nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at low temperature and low magnetic field. The overall behavior shows very good agreement with numerical simulations based on the Ginzburg-Landau equations.

We achieved ohmic contacts down to 5 K on standard n-doped Ge samples by creating a strongly doped thin Ge layer between the metallic contacts and the Ge substrate. Thanks to the laser doping technique used, Gas Immersion Laser Doping, we could attain extremely large doping levels above the solubility limit, and thus reduce the metal/doped Ge contact resistance. We tested independently the influence of the doping concentration and doped layer thickness, and showed that the ohmic contact improves when increasing the doping level and is not affected when changing the doped thickness. Furthermore, we characterised the doped Ge/Ge contact, showing that at high doping its contact resistance is the dominant contribution to the total contact resistance.

We investigate the critical temperature Tc of a thin s-wave superconductor (Nb) proximity coupled to a helical rare earth ferromagnet (Ho). As a function of the Ho layer thickness, we observe multiple oscillations of Tc superimposed on a slow decay, that we attribute to the influence of the Ho on the Nb proximity effect. Because of Ho inhomogeneous magnetization, singlet and triplet pair correlations are present in the bilayers. We take both into consideration when solving the self consistent Bogoliubov-de Gennes equations, and we observe a reasonable agreement. We also observe non-trivial transitions into the superconducting state, the zero resistance state being attained after two successive transitions which appear to be associated with the magnetic structure of Ho.

We report on the superconducting properties of a series of heavily doped Si:B epilayers grown by gas immersion laser doping with boron content (nB) ranging from ∼3 × 1020 cm−3 to ∼6 × 1021cm−3 and thickness (d) varying between ∼20 nm and ∼210 nm. We show that superconductivity is only observed for nB values exceeding a threshold value (nc,S ) which scales as nc,S ∝ 1/d. The critical temperature (Tc) then rapidly increases with nB, largely exceeding the theoretical values which can be estimated by introducing the electron-phonon coupling constant (λe-ph) deduced from ab initio calculations into the McMillan equation. Surprisingly Tc(nB,d) is fully determined by the boron dose (nB × d) and can be well approximated by a simple Tc(nB,d) ≈ Tc,0[1 − A/(nB.d)] law, with Tc,0 ∼ 750 mK and A ∼ 8(±1) × 1015 cm−2.

We have conceived and fabricated Superconductor/Normal metal/Superconductor Josephson junctions made entirely of boron doped Silicon. We have used Gas Immersion Laser Doping to fabricate SN bilayers with good ohmic interfaces and well controlled concentration and doping depth. Standard fabrication processes, optimised for silicon, were employed to nanostructure the bilayers without affecting their transport properties. The junctions thus fabricated are proximity superconducting and show well understood I-V characteristics. This research opens the road to all-silicon, non-dissipative, Josephson Field Effect Transistors. (C) 2013 Elsevier B.V. All rights reserved.

Conventional spin-singlet Cooper pairs convert into spin-triplet pairs in ferromagnetic Josephson junctions in which the superconductor/ferromagnet interfaces (S/F) are magnetically inhomogeneous. Although much of the theoretical work describing this triplet proximity effect has considered ideal junctions with magnetic domain walls (DW) at the interfaces, in practice it is not easily possible to isolate a DW and propagate a supercurrent through it. The rare-earth magnet Gd can form a field-tuneable in-plane Bloch DW if grown between non-co-linearly aligned ferromagnets. Here we report supercurrents through magnetic Ni-Gd-Ni nanopillars: by field annealing at room temperature, we are able to modify the low temperature DW-state in Gd and this result has a striking effect on the junction supercurrent at 4.2 K. We argue that this result can only be explained in terms of the interconversion of triplet and singlet pairs, the efficiency of which depends on the magnetic helicity of the structure.

We have measured the critical current dependence on the magnetic flux of two long SNS junctions differing by the normal wire geometry. The samples are made by a Au wire connected to W contacts, via Focused Ion Beam assisted deposition. We could tune the magnetic pattern from the monotonic gaussian-like decay of a quasi 1D normal wire to the Fraunhofer-like pattern of a square normal wire. We explain the monotonic limit with a semiclassical 1D model, and we fit both field dependences with numerical simulations of the 2D Usadel equation. Furthermore, we observe both integer and fractional Shapiro steps. The magnetic flux dependence of the integer steps reproduces as expected that of the critical current Ic, while fractional steps decay slower with the flux than Ic.