Electron paramagnetic resonance and photoluminescence study of Er-impurity complexes in Si

Abstract

Electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy have been used to examine the structure and optical properties of erbium-impurity complexes formed in float-zone Si by multiple-energy implants at 77 K of Er together with either O or F. After implantation a 2-\ensuremath{\mu}m-thick amorphous layer was formed containing an almost uniform concentration of Er ${(10}^{19}/{\mathrm{cm}}^{3})$and O $(3\ifmmode\times\else\texttimes\fi{}{10}^{19}/{\mathrm{cm}}^{3}$ or ${10}^{20}/{\mathrm{cm}}^{3})$ or F ${(10}^{20}/{\mathrm{cm}}^{3}).$ Samples were annealed in nitrogen at 450 \ifmmode^\circ\else\textdegree\fi{}C for 30 min (treatment A), treatment A+620 \ifmmode^\circ\else\textdegree\fi{}C for 3 h (treatment B), treatment B+900 \ifmmode^\circ\else\textdegree\fi{}C for 30 s (treatment C) or treatment B+900 \ifmmode^\circ\else\textdegree\fi{}C for 30 min (treatment D). Samples coimplanted to have $3\ifmmode\times\else\texttimes\fi{}{10}^{19}{\mathrm{O}/\mathrm{c}\mathrm{m}}^{3}$ and subject to treatment C show a broad line anisotropic EPR spectrum. These samples have the most intense low-temperature PL spectrum containing several sharp peaks attributed to ${\mathrm{Er}}^{3+}$ in sites with predominantly cubic ${T}_{d}$ symmetry. Increasing the O concentration to ${10}^{20}/{\mathrm{cm}}^{3}$ produces sharp line EPR spectra the strongest of which are attributed to two ${\mathrm{Er}}^{3+}$ centers having monoclinic ${C}_{1h}$ and trigonal symmetry. The principal g values and tilt angle for the monoclinic centers are ${g}_{1}=0.80,$ ${g}_{2}=5.45,$ ${g}_{3}=12.60,$ $\ensuremath{\tau}=57.3\ifmmode^\circ\else\textdegree\fi{},$ ${g}_{\ensuremath{\parallel}}=0.69,$ and ${g}_{\ensuremath{\perp}}=3.24$ for the trigonal centers. The low-temperature PL spectrum from this sample showed additional sharp lines but the total intensity is reduced when compared to the sample with $3\ifmmode\times\else\texttimes\fi{}{10}^{19}{\mathrm{O}/\mathrm{c}\mathrm{m}}^{3}.$ For the sample containing ${10}^{20}{\mathrm{O}/\mathrm{c}\mathrm{m}}^{3}$ at least four distinct centers are observed by EPR after treatment B but after treatment D no EPR spectrum is observed. The PL spectra are also observed to change depending on the specific anneal treatment but even after treatment D, Er-related PL is still observed. Samples containing ${10}^{20}{\mathrm{F}/\mathrm{c}\mathrm{m}}^{3}$ and annealed with either treatment B or C produced an EPR spectrum attributed to ${\mathrm{Er}}^{3+}$in a site of monoclinic ${C}_{1h}$ symmetry with ${g}_{1}=1.36,$ ${g}_{2}=9.65,$ ${g}_{3}=7.91,$ and $\ensuremath{\tau}=79.1\ifmmode^\circ\else\textdegree\fi{}.$Tentative models for the structures of Er-impurity complexes are presented and the relationship between the EPR-active and PL-active centers is discussed.