Electron paramagnetic resonance and theoretical studies of Nb in 4H- and 6H-SiC

Abstract

High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H-and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H-and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C 1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S ¼ 1/2 and the nuclear spin of 93 Nb. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of $37.4% was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (V C ). Calculations of the , support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H-and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others. V C 2012 American Institute of Physics. [http://dx

Optical properties and Zeeman spectroscopy of niobium in silicon carbide

“…We assume that without any photoexcitation the Nb center is in the neutral charge state, in agreement with the ESR results [17,23]. On the other hand, if an electron or hole is captured to form one of the charged states, this charged center becomes a Coulomb center capable of capturing a particle of the opposite charge, a hole for Nb − or an electron for Nb + , respectively.…”

“…Thus, this configuration (denoted hereafter as ASV h-h) is expected to form in significantly larger concentrations than any other. Electron spin resonance (ESR) measurements are consistent with the ASV h-h configuration for the case of Nb-doped 4H-SiC [16] (more details on the ESR spectra are presented in [17]). The observed ESR spectrum clearly shows the hyperfine interaction of an S = 1/2 spin with two Si atoms, demonstrating also the Jahn-Teller distortion to C 1h symmetry, in accord with the calculation.…”