Many body effects in the excitation spectrum of a defect in SiC

We show that electron correlations control the photophysics of defects in SiC through both renormalization of the quasiparticle bandstructure and exciton effects. We consider the carbon vacancy, which is a well-identified defect with two possible excitation channels that involve conduction and valence band states. Corrections to the Kohn-Sham ionization levels are found to strongly depend on the occupation of the defect state. Excitonic effects introduce a red shift of 0.23 eV. The analysis unambigiously re-assigns excitation mechanism at the thresholds in photo-induced paramagnetic resonance measurements [J. Dashdorj \emph{et al.}, J. Appl. Phys. \textbf{104}, 113707 (2008)]

Carbon antisite clusters in SiC: a possible pathway to the D_{II} center

The photoluminescence center D_{II} is a persistent intrinsic defect which is common in all SiC polytypes. Its fingerprints are the characteristic phonon replicas in luminescence spectra. We perform ab-initio calculations of vibrational spectra for various defect complexes and find that carbon antisite clusters exhibit vibrational modes in the frequency range of the D_{II} spectrum. The clusters possess very high binding energies which guarantee their thermal stability--a known feature of the D_{II} center. The di-carbon antisite (C_{2})_{Si} (two carbon atoms sharing a silicon site) is an important building block of these clusters.Comment: RevTeX 4, 6 pages, 3 figures Changes in version 2: Section headings, footnote included in text, vibrational data now given for neutral split-interstitial, extended discussion of the [(C_2)_Si]_2 defect incl. figure Changes version 3: Correction of binding energy for 3rd and 4th carbon atom at antisite; correction of typo

Structure and vibrational spectra of carbon clusters in SiC

The electronic, structural and vibrational properties of small carbon interstitial and antisite clusters are investigated by ab initio methods in 3C and 4H-SiC. The defects possess sizable dissociation energies and may be formed via condensation of carbon interstitials, e.g. generated in the course of ion implantation. All considered defect complexes possess localized vibrational modes (LVM's) well above the SiC bulk phonon spectrum. In particular, the compact antisite clusters exhibit high-frequency LVM's up to 250meV. The isotope shifts resulting from a_{13}C enrichment are analyzed. In the light of these results, the photoluminescence centers D_{II} and P-U are discussed. The dicarbon antisite is identified as a plausible key ingredient of the D_{II}-center, whereas the carbon split-interstitial is a likely origin of the P-T centers. The comparison of the calculated and observed high-frequency modes suggests that the U-center is also a carbon-antisite based defect.Comment: 15 pages, 6 figures, accepted by Phys. Rev.

Removing the orientational degeneracy of the TS defect in 4H–SiC by electric fields and strain

AbstractWe present a photoluminescence (PL) study of the recently discovered TS defect in 4H silicon carbide. It investigates the influence of static electric fields and local strain on the spectral properties by means of low temperature (≈4 K) ensemble measurements. Upon application of static electric fields exerted by graphene electrodes, line splitting patterns are observed, which are investigated for four different angles of the electric field with respect to the principal crystallographic axes. More detailed information can be gained when additionally the excitation polarization angle is systematically varied. Altogether, the data allow for extracting the direction of the associated electric dipole moments, revealing three distinct orientations of the underlying TS defect inside the crystal’s basal plane. We also present three so far unreported PL lines (836.7 nm, 889.7 nm, 950.0 nm) as candidates for out-of-plane oriented counterparts of the TS lines. Similar to symmetry breaking by the electric field applied, strain can reduce the local symmetry. We investigate strain-induced line splitting patterns that also yield a threefold directedness of the TS lines in accordance with the Stark effect measurements. The response to both electrical and strain fields is remarkably strong, leading to line shifts of ±12 meV of the TS1 line. Combining our findings, we can narrow down possible geometries of the TS defect

Electrical Charge State Manipulation of Single Silicon Vacancies in a Silicon Carbide Quantum Optoelectronic Device

Colour centres with long-lived spins are established platforms for quantum sensing and quantum information applications. Colour centres exist in different charge states, each of them with distinct optical and spin properties. Application to quantum technology requires the capability to access and stabilize charge states for each specific task. Here, we investigate charge state manipulation of individual silicon vacancies in silicon carbide, a system which has recently shown a unique combination of long spin coherence time and ultrastable spin-selective optical transitions. In particular, we demonstrate charge state switching through the bias applied to the colour centre in an integrated silicon carbide opto-electronic device. We show that the electronic environment defined by the doping profile and the distribution of other defects in the device plays a key role for charge state control. Our experimental results and numerical modeling evidence that control of these complex interactions can, under certain conditions, enhance the photon emission rate. These findings open the way for deterministic control over the charge state of spin-active colour centres for quantum technology and provide novel techniques for monitoring doping profiles and voltage sensing in microscopic devices