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

Abstract

We discovered uniaxial oriented centers in silicon carbide having unusual performance. Here we demonstrate that the family of silicon-vacancy related centers with S= 3/2 in rhombic 15R-SiC crystalline matrix possess unique characteristics such as optical spin alignment existing at temperatures up to 250• C. Thus the concept of optically addressable silicon vacancy related centers with half integer ground spin state is extended to the wide class of SiC rhombic polytypes. The structure of these centers, which is a fundamental problem for quantum applications, has been established using high frequency ENDOR. It has been shown that a family of silicon-vacancy related centers is a negatively charged silicon vacancy in the paramagnetic state with the spin S= 3/2, VSi − , perturbed by neutral carbon vacancy in non-paramagnetic state, VC 0 , having no covalent bond with the silicon vacancy and located adjacently to the silicon vacancy on the c crystal axis.Spin centers in Silicon Carbide (SiC) have recently been put forward as favorable candidates for a new generation quantum spintronics and sensorics, as well as quantum information processing because of the unique properties of their electron spins which can be optically polarized and read out [1][2][3][4][5][6][7][8][9][10][11]. Particularly the optical control of the single defect spin in SiC has been realized at room temperature for the first time on the well studied silicon vacancy-related center with ground spin state S= 3/2 in 4H-SiC [10]. The centers of the same origin persist also in 6H-SiC polytype and were proposed for use in quantum magnetometry [6] and room temperature operated MASERs [8]. Thus the family of the V Si related centers can be considered to form the basis of the SiC-based quantum sensors and quantum spintronics. The first solid state system on which optical detection and manipulation of the single spin has been shown is the negatively charged nitrogen-vacancy (NV − ) center in diamond. There are two main reasons why successful realization of single spin control in this system was possible. First, the NV − centers possess high optically detected magnetic resonance (ODMR) contrast and their spin alignment persists at elevated temperatures [12], thusthe polarized spin state can be readout with high fidelity even on the single spin [13]. Second, the precise atomic structure of the center has been elucidated [14][15]. This gave rise to the precise technology of NV's production in predetermined topology and concentrations [16], [17], allowing one to organize precise control of the NV's electron spin interactions with the environment. This permits to develop NV − based quantum registers [18], [19] and quantum sensors [20], [21].Therefore for the successful development of the SiC two major issues have to be addressed. On the one hand spin centers with high breakdown characteristics and high ODMR contrast must be explored, on the other hand the proper model for these spin centers must be established. We focused our efforts on these two tasks and present...

Identification of Si-vacancy related room-temperature qubits in 4H silicon carbide

“…Using electron nuclear double-resonance (ENDOR) measurements, negative 29 Si hyperfine coupling constants, i.e., negative electron spin density, were observed for the V2 center in 15R-SiC. As a proof of model II, this observation was attributed to the hyperfine coupling of the weakly negatively polarized silicon nuclei around the carbon vacancy [27]. The identification of the microscopic structure of the V1-V2 centers in 4H SiC, i.e., validating one of these models, is essential for an appropriate theoretical description and for controlled single defect fabrication purposes.…”

“…We further note that the negative anisotropic 29 Si hyperfine splitting in the range of 1.3-2.2 MHz observed by ENDOR [27] can be explained by isolated V Si (−) and it is not evidence of the presence of a carbon vacancy. As the spin density is the fingerprint of a complex many-body wave function, sign changes in the spin density may occur even for a simple point defect, for instance, the NV center diamond [35].…”

“…1(c)] that lowers the symmetry of the silicon vacancy, thus causing a finite ZFS. In a recent experiment on rhombic 15R-SiC [27], silicon-vacancy related centers were reported with similar characteristics to those in hexagonal SiC. Using electron nuclear double-resonance (ENDOR) measurements, negative 29 Si hyperfine coupling constants, i.e., negative electron spin density, were observed for the V2 center in 15R-SiC.…”

“…On the other hand, the actual microscopic configuration of these vacancy related centers is still debated. The unanswered question is whether these centers are isolated silicon vacancies [V Si (−) as model I] [23,25,26] or axial symmetric defect pairs, including a negatively charged silicon vacancy and a proximate neutral carbon vacancy [14,27] difference between the two models is how the observed finite zero-field splitting (ZFS) of the ground-state spin sublevels is explained. In model I, it is assumed that the C 3v symmetric crystal field, allowing nonzero ZFS [26], is strong enough to cause a finite ZFS that accounts for the observations.…”

“…We consider the nearest V Si (−) + V C (0) pair not sharing the same Si-C bilayer [see Fig. 1(c)], which is the suggested configuration for the V2 center in 4H -, 6H -, and 15R-SiC [14,27]. In the simulations, we observe a notable interaction between the vacancies that results in a weakly bonded defect pair with an electronic structure that significantly differs from the electronic structure of the isolated silicon vacancy (see Fig.…”