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

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-{μ}m-thick amorphous layer was formed containing an almost uniform concentration of Er (10¹⁹/cm³)and O (3×10¹⁹/cm³ or 10²⁰/cm³) or F (10²⁰/cm³). Samples were annealed in nitrogen at 450 ^∘{}C for 30 min (treatment A), treatment A+620 ^∘{}C for 3 h (treatment B), treatment B+900 ^∘{}C for 30 s (treatment C) or treatment B+900 ^∘{}C for 30 min (treatment D). Samples coimplanted to have 3×10¹⁹O/cm³ 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 Er³⁺ in sites with predominantly cubic Td symmetry. Increasing the O concentration to 10²⁰/cm³ produces sharp line EPR spectra the strongest of which are attributed to two Er³⁺ centers having monoclinic C₁ₕ and trigonal symmetry. The principal g values and tilt angle for the monoclinic centers are g₁=0.80, g₂=5.45, g₃=12.60, τ=57.3^∘, g_∥=0.69, and g_⊥=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 3×10¹⁹O/cm³. For the sample containing 10²⁰O/cm³ 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 10²⁰F/cm³ and annealed with either treatment B or C produced an EPR spectrum attributed to Er³⁺in a site of monoclinic C₁ₕ symmetry with g₁=1.36, g₂=9.65, g₃=7.91, and τ=79.1^∘.Tentative models for the structures of Er-impurity complexes are presented and the relationship between the EPR-active and PL-active centers is discussed.