The optical activation, excitation, and concentration limits of erbium in crystal Si are studied. Preamorphized surface layers of Czochralski-grown (Cz) Si(lOO), containing 1.7X lOI O/cm3, were implanted with 250 keV Er at Auences in the range 8X lo"--8X lOI cm-'. After thermal solid-phase epitaxy of the Er-doped amorphous layers at 600 "C, Er is trapped in the crystal at concentrations ranging from 3 X lOI to 7X1019 Er/cm3, as measured by secondary-ion-mass spectrometry. Photoluminescence spectra taken at 77 K show the characteristic Ers+ intra-4f luminescence at 1.54 pm. Photoluminescence excitation spectroscopy shows that Er is excited through a photocarrier-mediated process, Rapid thermal annealing at 1000 "C for 15 s increases the luminescence intensity, mainly due to an increase in minority-carrier lifetime, which enhances the excitation efficiency. Luminescent Er forms clusters with oxygen: the maximum Er concentration that can be optically activated is determined by the 0 content, and is (3 2 1 j X 1017 E&m3 in Cz-Si. The internal quantum efficiency for electrical excitation of Er in Cz-Si is larger than 3X 10e6.

The photoluminescence of erbium-doped semi-insulating polycrystalline and amorphous silicon containing 30 at. % oxygen is studied. The films were deposited on single-crystal Si substrates by chemical vapor deposition, implanted with 500 keV Er to fluences ranging from 0.05 to 6×1015 ions/cm2, and annealed at 300–1000 °C. Upon optical pumping near 500 nm, the samples show room-temperature luminescence around 1.54 μm due to intra-4f transitions in Er3+, excited by photogenerated carriers. The strongest luminescence is obtained after 400 °C annealing. Two classes of Er3+ can be distinguished, characterized by luminescence lifetimes of 170 and 800 μs. The classes are attributed to Er3+ in Si-rich and in O-rich environments. Photoluminescence excitation spectroscopy on a sample with 1×1015 Er/cm2 shows that ∼2% of the implanted Er is optically active. No quenching of the Er luminescence efficiency is observed between 77 K and room temperature in this Si-based semiconductor. The internal quantum efficiency for the excitation of Er3+ via photogenerated carriers is 10−3 at room temperature. A model is presented which explains the luminescence data in terms of trapping of electrical carriers at localized Er-related defects, and subsequent energy transfer to Er3+ ions, which can then decay by emission of 1.5 μm photons.

Soda-lime silicate glass has been locally doped with 0.2-at. % erbium by 3.0-and 5.0-MeV ion implantation. Single-mode fiber-compatible optical waveguides were then fabricated by use of Na 1 $ K 1 ion exchange. Characteristic photoluminescence (PL) of Er 31 centered at 1.54 mm is observed on excitation at 1.48 mm. For low pump intensity the PL decay is nearly single exponential with a lifetime of 7.2 ms. At high intensity it becomes nonexponential as a result of cooperative upconversion, an interaction between excited Er ions. Self-consistent modeling of the PL intensity and decay data yields an upconversion coefficient of 3.2 6 0.8 3 10 224 m 3 ͞s. The effect of upconversion on optical gain is shown and discussed. An extrapolation of measured optical gain shows that 1 dB͞cm of net gain is possible in the present Er-implanted soda-lime glass.

High concentrations (≊1020/cm3) of Er have been incorporated in crystal Si by solid phase epitaxy of Er-implanted amorphous Si. This concentration is some 2 orders of magnitude higher than has previously been achieved. During thermal recrystallization of the amorphous layer, segregation and trapping of Er occurs at the moving crystal/amorphous interface. As long as the concentration of Er trapped in the crystal remains below a critical level, perfect epitaxial regrowth occurs. This concentration limit is temperature dependent, decreasing from 1.2±0.2×1020/cm3 at 600 °C to 6±2×1019/cm3 at 900 °C.

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