Reliable single-photon emission is crucial for realizing efficient spin-photon entanglement and scalable quantum information systems. The silicon vacancy ( $${V}_{{\rm{Si}}}$$VSi ) 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 $${V}_{{\rm{Si}}}$$VSi defect ensembles can be enhanced by an order of magnitude via fabrication of Schottky barrier diodes, and sequentially modulated by almost $$50 \%$$50% via application of external bias. Furthermore, we identify charge state transitions of $${V}_{{\rm{Si}}}$$VSi 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 $${V}_{{\rm{Si}}}$$VSi 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, $${V}_{{\rm{Si}}}$$VSi defect ensembles in 4H-SiC highly suitable for quantum applications.

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 $1000{}^{\circ }\mathrm{C}$. The model proposes the ${\mathrm{EH}}_4$ and ${\mathrm{EH}}_5$ traps frequently found by DLTS to originate from the ($+$/0) charge transition level belonging to different configurations of the carbon antisite-carbon vacancy (CAV) complex. Furthermore, we show that the transformation channel between the silicon vacancy (${\mathrm{V}}_{\mathrm{Si}}$) 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 ${\mathrm{V}}_{\mathrm{Si}}$ and the carbon vacancy (${\mathrm{V}}_{\mathrm{C}}$) is shown to be dominated by recombination with residual self-interstitials at temperatures of up to $400{}^{\circ }\mathrm{C}$. Going to higher temperatures, a decay of the CAV pair density is reported which is closely correlated to a renewed increase of ${\mathrm{V}}_{\mathrm{C}}$ concentration. A conceivable explanation for this process is the dissociation of the CAV pair into separate carbon anitisites and ${\mathrm{V}}_{\mathrm{C}}$ 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.

Point defects in semiconductors are emerging as an important contender platform for quantum technology (QT) applications, showing potential for quantum computing, communication, and sensing. Indeed, point defects have been employed as nuclear spins for nanoscale sensing and memory in quantum registers, localized electron spins for quantum bits, and emitters of single photons in quantum communication and cryptography. However, to utilize point defects in semiconductors as single‐photon sources for QT, control over the influence of the surrounding environment on the emission process must be first established. Recent works have revealed strong manipulation of emission energies and intensities via coupling of point defect wavefunctions to external factors such as electric fields, strain and photonic devices. This review presents the state‐of‐the‐art on manipulation, tuning, and control of single‐photon emission from point defects focusing on two leading semiconductor materials—diamond and silicon carbide.

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 show theoretically 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 ($\mathcal{S}>1$ mV/K) and figures of merit ($ZT\simeq 40$) far exceeding the best bulk thermoelectric materials, and it also becomes more resilient toward inelastic-scattering processes. We present a generalized Onsager response-matrix that 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 in which 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, the temperature, and the superconducting phase difference.

Significant progress has been achieved with silicon carbide (SiC) high power electronics and quantum technologies, both drawing upon the unique properties of this material. In this Perspective, we briefly review some of the main defect characterization techniques that have enabled breakthroughs in these fields. We consider how key data have been collected, interpreted, and used to enhance the application of SiC. Although these fields largely rely on separate techniques, they have similar aims for the material quality and we identify ways in which the electronics and quantum technology fields can further interact for mutual benefit.

We investigate the migration mechanism of the carbon vacancy $\left(V_{\text{C}}\right)$ in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The $V_{\text{C}}$, 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 $V_{\text{C}}$ removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that $V_{\text{C}}$ 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, $V_{\text{C}}\left(h\right)$, and pseudocubic, $V_{\text{C}}\left(k\right)]$ and their consequences for $V_{\text{C}}$ migration have not been considered so far. The first part of the paper presents a theoretical study of $V_{\text{C}}$ 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 $V_{\text{C}}$ migration. In 3C-SiC, $V_{\text{C}}$ is found to migrate with an activation energy of $E_{\text{A}}=4.0$ eV. In 4H-SiC, on the other hand, we anticipate that $V_{\text{C}}$ 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 $E_{\text{A}}=4.2$ eV, and a striking preference for basal migration within the $h$ plane with a barrier of $E_{\text{A}}=3.7$ 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 $V_{\text{C}}$ in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the ${\mathrm{Z}}_{1/2}$ electron trap in annealed samples that were subject to ion implantation. Activation energies of $E_{\text{A}}=(4.4\pm 0.3)$ eV and $E_{\text{A}}=(3.6\pm 0.3)$ eV were found for $V_{\text{C}}$ migration along the $c$ and $a$ directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of $D_0=0.54{\mathrm{cm}}^2/\mathrm{s}$ and 0.$017{\mathrm{cm}}^2/\mathrm{s}$ are in line with a simple jump process, as expected for a primary vacancy point defect.