P. G. Baranov

Silicon carbide light-emitting diode as a prospective room temperature source for single photons

Generation of single photons has been demonstrated in several systems. However, none of them satisfies all the conditions, e.g. room temperature functionality, telecom wavelength operation, high efficiency, as required for practical applications. Here, we report the fabrication of light-emitting diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate our devices we used a standard semiconductor manufacturing technology in combination with high-energy electron irradiation. The room temperature electroluminescence (EL) of our LEDs reveals two strong emission bands in the visible and near infrared (NIR) spectral ranges, associated with two different intrinsic defects. As these defects can potentially be generated at a low or even single defect level, our approach can be used to realize electrically driven single photon source for quantum telecommunication and information processing.Generation of single photons has been demonstrated in several systems. However, none of them satisfies all the conditions, e.g. room temperature functionality, telecom wavelength operation, high efficiency, as required for practical applications. Here, we report the fabrication of light emitting diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate our devices we used a standard semiconductor manufacturing technology in combination with high-energy electron irradiation. The room temperature electroluminescence (EL) of our LEDs reveals two strong emission bands in visible and near infrared (NIR), associated with two different intrinsic defects. As these defects can potentially be generated at a low or even single defect level, our approach can be used to realize electrically driven single photon source for quantum telecommunication and information processing.

Room temperature coherent spin alignment of silicon vacancies in 4H- and 6H-SiC.

We report the realization of the optically induced inverse population of the ground-state spin sublevels of the silicon vacancies (V(Si)) in silicon carbide (SiC) at room temperature. The data show that the probed silicon vacancy spin ensemble can be prepared in a coherent superposition of the spin states. Rabi nutations persist for more than 80 μs. Two opposite schemes of the optical alignment of the populations between the ground-state spin sublevels of the silicon vacancy upon illumination with unpolarized light are realized in 4H- and 6H-SiC at room temperature. These altogether make the silicon vacancy in SiC a very favorable defect for spintronics, quantum information processing, and magnetometry.

Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide

Quantum systems can provide outstanding performance in various sensing applications, ranging from bioscience to nanotechnology. Atomic-scale defects in silicon carbide are very attractive in this respect because of the technological advantages of this material and favorable optical and radio frequency spectral ranges to control these defects. We identified several, separately addressable spin-3/2 centers in the same silicon carbide crystal, which are immune to nonaxial strain fluctuations. Some of them are characterized by nearly temperature independent axial crystal fields, making these centers very attractive for vector magnetometry. Contrarily, the zero-field splitting of another center exhibits a giant thermal shift of −1.1 MHz/K at room temperature, which can be used for thermometry applications. We also discuss a synchronized composite clock exploiting spin centers with different thermal response.

EPR identification of the triplet ground state and photoinduced population inversion for a Si-C divacancy in silicon carbide

It is shown that intrinsic defects responsible for the semi-insulating properties of SiC represent Si-C divacancies in a neutral state (VSi-VC)0, which have the triplet ground state. The energy level scheme and the mechanism of creating the photoinduced population inversion of the triplet sublevels of the divacancy ground state are determined. It is concluded that there is a singlet excited state through which spin polarization is accomplished, and this fact opens the possibility of detecting magnetic resonance on single divacancies.

Excitation and recombination dynamics of vacancy-related spin centers in silicon carbide

We generate silicon vacancy related defects in high-quality epitaxial silicon carbide layers by means of electron irradiation. By controlling the irradiation fluence, the defect concentration is varied over several orders of magnitude. We establish the excitation profile for optical pumping of these defects and evaluate the optimum excitation wavelength of 770 nm. We also measure the photoluminescence dynamics at room temperature and find a monoexponential decay with a characteristic lifetime of 6.1 ns. The integrated photoluminescence intensity depends linear on the excitation power density up to 20 kW/cm2, indicating a relatively small absorption cross section of these defects.

Optically Addressable Silicon Vacancy-Related Spin Centers in Rhombic Silicon Carbide with High Breakdown Characteristics and ENDOR Evidence of Their Structure.

We discovered a family of uniaxially oriented silicon vacancy-related centers with S=3/2 in a rhombic 15R-SiC crystalline matrix. We demonstrate that these centers exhibit unique characteristics such as optical spin alignment up to the temperatures of 250°C. Thus, the range of robust optically addressable vacancy-related spin centers is extended to the wide class of rhombic SiC polytypes. To use these centers for quantum applications it is essential to know their structure. Using high frequency electron nuclear double resonance, we show that the centers are formed by negatively charged silicon vacancies V_{Si}^{-} in the paramagnetic state with S=3/2 that is noncovalently bonded to the neutral carbon vacancy V_{C}^{0} in the nonparamagnetic state, located on the adjacent site along the SiC symmetry c axis.

Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect, for the first time, room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers, but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical and biological processes.

Identification of iron transition group trace impurities in GaN bulk crystals by electron paramagnetic resonance

Abstract We report on the observation of electron paramagnetic resonance of iron, manganese and nickel trace impurities in bulk GaN crystals grown by the sublimation sandwich method. The resolved hyperfine structure due to interaction with 55Mn ( I = 5 2 ) nuclei has been observed in GaN, allowing unambiguous identification of the impurity. Manganese and nickel exist in Mn2+ (3d5) and Ni3+ (3d7) charge states with electron spin S = 5 2 and S = 3 2 , respectively, and occupy gallium sites in the GaN lattice. For Mn2+ we found g = 1.999, hyperfine structure constant A = 70.10−4 cm−1 and fine structure parameter /D/ = 240.10−4 cm−1. The EPR spectrum of Ni3+ in GaN had the characteristic anisotropy of an S = 3 2 system in a strong axial crystalline field. The effective g-factor values were found to be g′∥ = 2.10 and g′⊥ ≅ 4.20 for a system with an effective spin S′ = 1 2 . An analogy was revealed between the parameters of Mn2+ and Ni3+ in GaN and ZnO crystals. The zero-phonon line at 1.047 eV seems to belong to transition 4T2(F)-4A2(F) within 3d levels of Ni3+ ion with a 3d7 electronic configuration.

High-Precision Angle-Resolved Magnetometry with Uniaxial Quantum Centers in Silicon Carbide

We show that uniaxial color centers in silicon carbide with hexagonal lattice structure can be used to measure not only the strength but also the polar angle of the external magnetic field with respect to the defect axis with high precision. The method is based on the optical detection of multiple spin resonances in the silicon vacancy defect with quadruplet ground state. We achieve a perfect agreement between the experimental and calculated spin resonance spectra without any fitting parameters, providing angle resolution of a few degrees in the magnetic field range up to several millitesla. Our approach is suitable for ensembles as well as for single spin-3/2 color centers, allowing for vector magnetometry on the nanoscale at ambient conditions.

Spin polarization induced by optical and microwave resonance radiation in a Si vacancy in SiC: A promising subject for the spectroscopy of single defects

Depending on the temperature, crystal polytype, and crystal position, two opposite schemes have been observed for the optical alignment of the populations of spin sublevels in the ground state of a Si vacancy in SiC upon irradiation with unpolarized light at frequencies of zero-phonon lines. A giant change by a factor of 2–3 has been found in the luminescence intensity of zero-phonon lines in zero magnetic field upon absorption of microwave radiation with energy equal to the fine-structure splitting of spin sublevels of the vacancy ground state, which opens up possibilities for magnetic resonance detection at a single vacancy.