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We investigate the quenching of the photoluminescence (PL) from the divacancy defect in 4H-SiC consisting of a nearest-neighbour silicon and carbon vacancies. The quenching occurs only when the PL is excited below certain photon energies (thresholds), which differ for the four different inequivalent divacancy configurations in 4H-SiC. Accurate theoretical ab initio calculation for the charge-transfer levels of the divacancy show very good agreement between the position of the (0/−) level with respect to the conduction band for each divacancy configurations and the corresponding experimentally observed threshold, allowing us to associate the PL decay with conversion of the divacancy from neutral to negative charge state due to capture of electrons photoionized from other defects (traps) by the excitation. Electron paramagnetic resonance measurements are conducted in dark and under excitation similar to that used in the PL experiments and shed light on the possible origin of traps in the different samples. A simple model built on this concept agrees well with the experimentallyobserved decay curves.

Color centers in wide-bandgap semiconductors are attractive systems for quantum technologies since they can combine long-coherent electronic spin and bright optical properties. Several suitable centers have been identified, most famously the nitrogen-vacancy defect in diamond. However, integration in communication technology is hindered by the fact that their optical transitions lie outside telecom wavelength bands. Several transition-metal impurities in silicon carbide do emit at and near telecom wavelengths, but knowledge about their spin and optical properties is incomplete.We present all-optical identification and coherent control of molybdenum-impurity spins in silicon carbide with transitions at near-infrared wavelengths. Our results identify spin S = 1/2 for both the electronic ground and excited state, with highly anisotropic spin properties that we apply for implementing optical control of ground-state spin coherence. Our results show optical lifetimes of ∼60 ns and inhomogeneous spin dephasing times of ∼0.3 µs, establishing relevance for quantum spin-photon interfacing.2 Electronic spins of lattice defects in wide-bandgap semiconductors have come forward as an important platform for quantum technologies 1 , in particular for applications that require both manipulation of long-coherent spin and spin-photon interfacing via bright optical transitions. In recent years this field showed strong development, with demonstrations of distribution and storage of non-local entanglement in networks for quantum communication 2-6 , and quantum-enhanced field-sensing 7-11 . The nitrogen-vacancy defect in diamond is the material system that is most widely used 12,13 and best characterized 14-16 for these applications.However, its zero-phonon-line (ZPL) transition wavelength (637 nm) is not optimal for integration in standard telecom technology, which uses near-infrared wavelength bands where losses in optical fibers are minimal. A workaround could be to convert photon energies between the emitter-resonance and telecom values 17-19 , but optimizing these processes is very challenging.This situation has been driving a search for similar lattice defects that do combine favorable spin properties with bright emission directly at telecom wavelength. It was shown that both diamond and silicon carbide (SiC) can host many other spin-active color centers that could have suitable properties 20-23 (where SiC is also an attractive material for its established position in the semiconductor device industry 24,25 ). However, for many of these color centers detailed knowledge about the spin and optical properties is lacking. In SiC the divacancy 26-28 and silicon vacancy 10,29-31 were recently explored, and these indeed show millisecond homogeneous spin coherence times with bright ZPL transitions closer to the telecom band.We present here a study of transition-metal impurity defects in SiC, which exist in great variety [32][33][34][35][36][37] . There is at least one case (the vanadium impurity) that has ZPL transitions at telecom wavel...

Transition metal defects were studied in different polytypes of silicon carbide (SiC) by ab initio supercell calculations. We found asymmetric split-vacancy (ASV) complexes for these defects that preferentially form at only one site in hexagonal polytypes, and they may not be detectable at all in cubic polytype. Electron spin resonance study demonstrates the existence of ASV complex in niobium doped 4H polytype of SiC.Funding Agencies|Swedish Foundation for Strategic Research||Swedish Research Council||Swedish Energy Agency||Swedish National Infrastructure for Computing|SNIC 011/04-8SNIC001-10-223|Knut and Alice Wallenberg Foundation|

We investigate the neutral divacancy in SiC by means of first principles calculations and group theory analysis. We identify the nature of the PL transitions associated with this defect. We show that how the spin state may be manipulated optically in this defect.

SiC is a promising material for high power and high frequency devices due to its wide band gap, high break down field and high thermal conductivity. For very high voltage SiC devices thick (>100 µm) low-doped epilayers are needed. In order to grow such thick epilayers in a reasonable time, a chloride-based CVD technique has been developed [1][2][3][4][5][6], where chlorine is added to the gas mixture either as HCl or by use of some chlorinated siliconor carbon precursor, allowing growth rates higher than 100 µm/h, as compared to about 5 µm/h for the standard growth process (with silane and hydrocarbon precursors). Also a bulk CVD process, called halide CVD (HCVD), using the chlorinated silicon precursor SiCl 4 at temperatures in the 2000-2200 °C range, has been developed [7-9] and growth rates as high as 300 µm/h and 300 µm thick boules have been demonstrated. In this study, we have used methyltrichlorosilane (MTS), CH 3 SiCl 3 , as SiC precursor, providing carbon, silicon and chlorine to the gas mixture. We have recently showed that MTS can be used to grow 4H-SiC epilayers with growth rates up to 170 µm/h [10], and in this letter we now show that it is possible to grow epilayers as thick as 200 µm, a thickness sufficient for 25 kV blocking SiC devices, in a very short time.The epilayers were homoepitaxially grown in a horizontal hot wall CVD reactor [11] using n-type 4H-SiC (0001) wafers as substrates, which were Si-face and off-cut 8° towards the [1120] direction. The epilayers were grown for two hours with a MTS-molar fraction corresponding to a growth rate of 100 µm/h [5]. No intentional dopant was added to the gas mixture during the growth. The growth process has previously been described in detail [5].The epilayer thickness was measured by Fourier transform infrared (FTIR) reflectance and by studying the cross section of the epilayer by optical microscopy. The net doping was studied with capacitance-voltage measurements (CV) using a mercury probe. The crystalline quality of the grown material was investigated by (i) high-resolution X-ray diffraction (HRXRD), using a triple axis diffractometer equipped with a four-crystal monochromator in Ge(220) configuration and a channel cut analyzer with 12 arcsec acceptance in triple axis setup, and by (ii) low temperature photoluminescence (LTPL) in a bath cryostat with the temperature kept at 2 K; the 351 nm Ar + laser line was used as excitation (the luminescence was dispersed by a single monochromator on which a UV sensitive CCD camera was mounted to rapidly detect the LTPL spectrum).200 µm thick 4H-SiC epilayers have been grown by chloridebased chemical-vapor deposition using methyltrichlorosilane (MTS) as single precursor. The very high crystalline quality of the grown epilayer is demonstrated by high resolution X-Ray Diffraction rocking curve with a full-width-halfmaximum value of only 9 arcsec. The high quality of the epi-layer is further shown by low temperature photoluminescence showing strong free exciton and nitrogen bound exciton lines. The very high crysta...

High-phase-purity zinc-blende ͑zb͒ InN thin film has been grown by plasma-assisted molecular-beam epitaxy on r-plane sapphire substrate pretreated with nitridation. X-ray diffraction analysis shows that the phase of the InN films changes from wurtzite ͑w͒ InN to a mixture of w-InN and zb-InN, to zb-InN with increasing nitridation time. High-resolution transmission electron microscopy reveals an ultrathin crystallized interlayer produced by substrate nitridation, which plays an important role in controlling the InN phase. Photoluminescence emission of zb-InN measured at 20 K shows a peak at a very low energy, 0.636 eV, and an absorption edge at ϳ0.62 eV is observed at 2 K, which is the lowest bandgap reported to date among the III-nitride semiconductors.

A model is presented for the silicon vacancy in SiC. The previously reported photoluminescence spectra in 4H and 6H SiC attributed to the silicon vacancy are in this model due to internal transitions in the negative charge state of the silicon vacancy. The magnetic resonance signals observed are due to the initial and final states of these transitions.