Reliable single-photon emission is crucial for realizing efficient spin-photon entanglement and scalable quantum information systems. The silicon vacancy (V Si) in 4H-SiC is a promising single-photon emitter exhibiting millisecond spin coherence times, but suffers from low photon counts, and only one charge state retains the desired spin and optical properties. Here, we demonstrate that emission from V Si defect ensembles can be enhanced by an order of magnitude via fabrication of Schottky barrier diodes, and sequentially modulated by almost 50% via application of external bias. Furthermore, we identify charge state transitions of V Si by correlating optical and electrical measurements, and realize selective population of the bright state. Finally, we reveal a pronounced Stark shift of 55 GHz for the V1′ emission line state of V Si at larger electric fields, providing a means to modify the single-photon emission. The approach presented herein paves the way towards obtaining complete control of, and drastically enhanced emission from, V Si defect ensembles in 4H-SiC highly suitable for quantum applications.

It has recently been proposed and experimentally demonstrated that it is possible to generate large thermoelectric effects in ferromagnet/superconductor structures due to a spin-dependent particle-hole asymmetry. Here, we theoretically show that quasiparticle tunneling between two spin-split superconductors enhances the thermoelectric response manyfold compared to when only one such superconductor is used, generating Seebeck coefficients (S > 1 mV/K) and figures of merit (ZT 40) far exceeding the best bulk thermoelectric materials, and also becomes more resilient toward inelastic scattering processes. We present a generalized Onsager response-matrix which takes into account spin-dependent voltage and temperature gradients. Moreover, we show that thermally induced spin-currents created in such junctions, even in the absence of a polarized tunneling barrier, also become largest in the case where a spin-dependent particle-hole asymmetry exists on both sides of the barrier. We determine how these thermal spin-currents can be tuned both in magnitude and sign by several parameters, including the external field, temperature, and the superconducting phase-difference.

The development of defect populations after proton irradiation of n-type 4H-SiC and subsequent annealing experiments is studied by means of deep level transient (DLTS) and photoluminescence spectroscopy. A comprehensive model is suggested describing the evolution and interconversion of irradiation-induced point defects during annealing below 1000 • C. The model proposes the EH 4 and EH 5 traps frequently found by DLTS to originate from the (+/0) charge transition level belonging to different configurations of the carbon antisitecarbon vacancy (CAV) complex. Furthermore, we show that the transformation channel between the silicon vacancy (V Si ) and CAV is effectively blocked under n-type conditions, but becomes available in samples where the Fermi level has moved towards the center of the band gap due to irradiation-induced donor compensation. The annealing of V Si and the carbon vacancy (V C ) is shown to be dominated by recombination with residual self-interstitials at temperatures of up to 400 • C. Going to higher temperatures, a decay of the CAV pair density is reported which is closely correlated to a renewed increase of V C concentration. A conceivable explanation for this process is the dissociation of the CAV pair into separate carbon anitisites and V C defects. Lastly, the presented data supports the claim that the removal of free carriers in irradiated SiC is due to introduced compensating defects and not passivation of shallow nitrogen donors.

We investigate the migration mechanism of the carbon vacancy (V C) in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The V C , commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for V C removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that V C migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, V C (h), and pseudocubic, V C (k)] and their consequences for V C migration have not been considered so far. The first part of the paper presents a theoretical study of V C migration in 3C-and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for V C migration. In 3C-SiC, V C is found to migrate with an activation energy of E A = 4.0 eV. In 4H-SiC, on the other hand, we anticipate that V C migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of E A = 4.2 eV, and a striking preference for basal migration within the h plane with a barrier of E A = 3.7 eV, to the detriment of the k-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of V C in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the Z 1/2 electron trap in annealed samples that were subject to ion implantation. Activation energies of E A = (4.4 ± 0.3) eV and E A = (3.6 ± 0.3) eV were found for V C migration along the c and a directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of D 0 = 0.54 cm 2 /s and 0.017 cm 2 /s are in line with a simple jump process, as expected for a primary vacancy point defect.

Single-photon emitting point defects in semiconductors have emerged as strong candidates for future quantum technology devices. In the present work, we exploit crystalline particles to investigate relevant defect localizations, emission shifting and waveguiding. Specifically, emission from 6H-SiC micro-and nanoparticles ranging from 100 nm to 5 μm in size is collected using cathodoluminescence (CL), and we monitor signals attributed to the Si vacancy (VSi) as a function of its location. Clear shifts in the emission wavelength are found for emitters localized in the particle center and at the edges. By comparing spatial CL maps with strain analysis carried out in transmission electron microscopy, we attribute the emission shifts to compressive strain of 2-3% along the particle a-direction. Thus, embedding VSi qubit defects within SiC nanoparticles offers an interesting and versatile opportunity to tune single-photon emission energies, while simultaneously ensuring ease of addressability via a self-assembled SiC nanoparticle matrix.