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-μm-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