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.

This work explores the Zn vacancy in ZnO using hybrid density functional theory calculations. The Zn vacancy is predicted to be an exceedingly deep polaronic acceptor that can bind a localized hole on each of the four nearest-neighbor O ions. The hole localization is accompanied by a distinct outward relaxation of the O ions, which leads to lower symmetry and reduced formation energy. Notably, we find that initial symmetry-breaking is required to capture this effect, which might explain the absence of polaronic hole localization in some previous hybrid density functional studies. We present a simple model to rationalize our findings with regard to the approximately equidistant thermodynamic charge-state transition levels. Furthermore, by employing a one-dimensional configuration coordinate model with parameters obtained from the hybrid density functional theory calculations, luminescence lineshapes were calculated. The results show that the isolated Zn vacancy is unlikely to be the origin of the commonly observed luminescence in the visible part of the emission spectrum from n-type material, but rather the luminescence in the infrared region.

Self-trapped hole and impurity-related broad luminescence in β-Ga 2 O 3

Results from hybrid density functional theory calculations on the thermodynamic stability and optical properties of the Zn vacancy (VZn) complexed with common donor impurities in ZnO are reported. Complexing VZn with donors successively removes its charge-state transition levels in the band gap, starting from the most negative one. Interestingly, the presence of a donor leads only to modest shifts in the positions of the VZn charge-state transition levels, the sign and magnitude of which can be interpreted from a polaron energetics model by taking hole-donor repulsion into account. By employing a one-dimensional configuration coordinate model, luminescence lineshapes and positions were calculated. Due to the aforementioned effects, the isolated VZn gradually changes from a mainly non-radiative defect with transitions in the infrared region in n-type material, to a radiative one with broad emission in the visible range when complexed with shallow 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.