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

Abstract

The identification of a microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, silicon-vacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin-3/2 ground and excited states. Although, these centers were observed decades ago, two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett. 115, 247602 (2015)], are still argued as an origin. By means of high-precision first-principles calculations and high-resolution electron spin resonance measurements, we here unambiguously identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively charged silicon vacancies. Moreover, we identify the Si-vacancy qubit configurations that provide room-temperature optical readout. DOI: 10.1103/PhysRevB.96.161114 Point defects in solids acting as quantum bits (qubits) are a highly promising platform for quantum information processing (QIP) and nanoscale sensor applications where typically their electron spin provides the functional quantum states. There are qubits that have long electron spin coherence times [1][2][3][4][5], and some of them have been demonstrated to persist up to room temperature [1,4]. These electron spins can be optically initialized and read out [2,6-9], making them very attractive candidates for QIP and related applications [10][11][12]. Among these qubits, silicon-vacancy related defects in hexagonal polytypes of SiC, such as 4H -and 6H -SiC, have shown favorable spin properties [13,14], demonstrated even at a single defect level at room temperature [4]. Two and three different silicon-vacancy related centers were observed in 4H -and 6H -SiC, where the corresponding photoluminescence (PL) lines are denoted as V1 and V2, and V1, V2, and V3, [15,16], respectively. The V2 line in 4H -SiC [4] and the V2 and V3 lines in 6H -SiC [13] are sufficiently strong to observe their corresponding electron spin via optically detected magnetic resonance (ODMR) measurements at room temperature. In particular, it has been demonstrated that the V2 color center in 4H -SiC can be used for magnetometer [17][18][19][20] and nanoscale thermometer [21] applications and as a room-temperature maser [14].Today, it is widely accepted that V1-V3 PL lines and T V1 -T V3 electron paramagnetic resonance (EPR) signals in 4H -and 6H -SiC are related to spin-3/2 negatively charged silicon vacancies [22][23][24][25]. 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 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 t...

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

“…Note that we follow the recent assignment of the cubic and hexagonal defect of V Si in Ref. 47 . Generic values are provided in panels In the p ++ -and p + -type layers and in most of the intrinsic layer, which is slightly p-type, the Fermi level is below the (0|-) transition level.…”

“…See the Supplementary Note 3 for the density of the created silicon vacancies as a function of the electron irradiation dose. The density of V C defects is in the range from 5×10 12 to 1×10 13 cm -3 , which is measured by deep-level transient spectroscopyIdentification of single silicon vacancies.In 4H-SiC, the silicon vacancy can be created at the two inequivalent lattice sites, namely the hexagonal and cubic sites, called V1 and V2 centre, respectively47 . Both defects possess very similar optical spectra with slightly different PL peaks.…”

Silicon carbide color centers for quantum applications

“…The most studied defects are the neutral divacancy or V Si V C (0) and negatively Color centers in SiC plotted versus their observed ZPL by PL measurements and their spin ZFS from electron paramagnetic resonance (EPR) or optically detected magnetic resonance (ODMR) measurements (left) for spin defects with proved optical spin polarization. Among these the V Si [40] V C V Si , [41,42] the N C V Si [43,44] in various polytypes. In addition, some transition metal color centers such as Ti [45], V [45][46][47], and Mo [48].…”

“…Only recently the V Si (−) role as qubit and charge state have been fully identified by means of high-precision first-principles calculations and high-resolution EPR resonance measurements, as an isolated negatively charged silicon-vacancy and it is associated to so-called V1 line being a V (−) Si at h (hexagonal)-site and V2 a V (−) Si at k (cubic) site for 4H-SiC [40], as for 6H V (−) Si the V1 is an h-site, V2 is a k2 site and V3 a k1 site [42]. In figures 3(A)-(C) the comparison between the cubic 3C and hexagonal 4H and 6H polytype SiC stacking layers seen from the top along the main crystallographic axis c, where the atoms of Si and C are shown along axis c or off-axis in different cubic h sites or hexagonal sites-k. For a single vacancy, it is expected that it occupies one of the 2 sites in 4H and 3 sites in 6H, as such the ZPLs are 2 or 3, plus excited state doublet.…”

Relaxation dynamics of spin- 32 silicon vacancies in 4H -SiC

“…Here we study the V2 defect with a zero phonon line at 916 nm at low temperature, since it can be detected in ODMR at room temperature [4,5]. The V2 is associated with the cubic k-site [15], and a zero-field fine structure splitting of 70 MHz.The sample used was purchased from CREE. The substrate is n-type LPBD.…”