40 research outputs found
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