Electron paramagnetic resonance and theoretical studies of shallow phosphorous centers in3C-,4H-, and6H−SiC

Abstract

Continuous-wave (cw) electron paramagnetic resonance (EPR) at both $X$-band and $W$-band frequencies, pulsed-EPR, and pulsed electron nuclear double resonance (ENDOR) were used to study phosphorus shallow donors in $3C$-, $4H$-, and $6H\text{\ensuremath{-}}\mathrm{SiC}$ doped with phosphorus (P) during chemical vapor deposition (CVD) growth. In $3C\text{\ensuremath{-}}\mathrm{SiC}$, a spectrum with ${D}_{2d}$ symmetry and the principal $g$ values, ${g}_{\ensuremath{\Vert}}=2.0051$, ${g}_{\ensuremath{\perp}}=2.0046$, was detected. The $^{31}\mathrm{P}$ hyperfine (hf) constants of the center, ${A}_{\ensuremath{\Vert}}=0.53\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ and ${A}_{\ensuremath{\perp}}=\ensuremath{-}0.13\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, were determined from pulsed-ENDOR measurements. A doublet with ${C}_{3\mathrm{v}}$ symmetry (${g}_{\ensuremath{\Vert}}=2.0065$, ${g}_{\ensuremath{\perp}}=2.0006$, and $^{31}\mathrm{P}$ hf constants ${A}_{\ensuremath{\Vert}}=8.24\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, ${A}_{\ensuremath{\perp}}=5.89\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$) was detected in P-doped $4H\text{\ensuremath{-}}\mathrm{SiC}$. In the $6H$ polytype, the same ${\mathrm{P}}_{1}$ and ${\mathrm{P}}_{2}$ doublets [Greulich-Weber, Phys. Status Solidi A 162, 95 (1997)] or $d{\mathrm{P}}_{\mathrm{h}}$, $d{\mathrm{P}}_{\mathrm{c}1}$, and $d{\mathrm{P}}_{\mathrm{c}2}$ doublets [Baranov et al., Phys. Rev. B 66, 165206 (2002)] previously reported in material doped with P by neutron transmutation were detected. Our cw-EPR, two-dimensional EPR, and electron spin-echo envelope modulation (ESEEM) results confirm that the $d{\mathrm{P}}_{\mathrm{c}1}$ and $d{\mathrm{P}}_{\mathrm{c}2}$ doublets are related to different allowed and forbidden transitions of the ${\mathrm{P}}_{2}$ center with $S=1∕2$ and $I=1∕2$. Based on the observed $^{31}\mathrm{P}$ hf interaction (for three polytypes) and the $^{13}C$ hf interaction with nearest neighbors (for $4H$- and $6H\text{\ensuremath{-}}\mathrm{SiC}$), the P-related spectra are assigned to the ground states of the isolated shallow P at Si site. The valley-orbit splitting of the shallow P donors was estimated from the temperature dependence of the spin-lattice relaxation time and of the cw-EPR signal intensities. Based on the ab initio supercell calculations of the spin localizations on the P atom and the nearest C neighbors in $4H\text{\ensuremath{-}}\mathrm{SiC}$ and the similarity between the spectra in the $4H$ and $6H$ polytypes, we reassign the spectrum in $4H\text{\ensuremath{-}}\mathrm{SiC}$ to the shallow P donor at the quasicubic site $({\mathrm{P}}_{\mathrm{k}})$ and the two doublets ${\mathrm{P}}_{1}$ and ${\mathrm{P}}_{2}$ in $6H\text{\ensuremath{-}}\mathrm{SiC}$ to the shallow P donors at two quasicubic sites, ${\mathrm{P}}_{\mathrm{k}1}$ and ${\mathrm{P}}_{\mathrm{k}2}$, respectively.