Erbium-Doped Silicon Prepared by UHV/CVD
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ERBIUM-DOPED SILICON PREPARED BY UHV/CVD DAVID B. BEACH, REUBEN T. COLLINS, FRANCOISE K. LEGOUES, AND JACK O. CHU IBM Research Division, Thomas J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598 ABSTRACT Erbium-doped silicon has been prepared using Ultra High Vacuum/Chemical Vapor Deposition (UHV/CVD). An erbium metalorganic compound, tris-I,l,l,5,5,5hexafluoro-2,4-pentanedionato erbium (1II) (Er(HFAC) 3), was used as the erbium source and silane was used as the silicon source. Films were deposited at 650 °C at a total 8 pressure of 3 1 mtorr. Erbium concentrations between 8x10 19 and lxlIO Er atoms/cm were prepared by varying the Er source reservoir temperature. Low temperature photoluminescence measurements showed strong emission at I.54pm. The films are single crystal, but with a high concentration of threading defects. INTRODUCTION The indirect energy band gap in silicon has prevented silicon technology from participating in the increasingly important area of optoelectronics. One possible method for integrating silicon based semiconductor devices and optoelectronic devices is the introduction of rare-earth ions into single crystal silicon. Rare-earth ions emit light via internal transitions involving 4 felectrons. Transitions between 4f states generally result in sharp emission lines since the 4forbitals are well shielded from the 5s and 5p orbitals involved in chemical bonding. In the case of Er 3 + ions, the optical transition between 4I,5/2 and 41/3/1 spin-orbit states results in emission of 1.54 pm wavelength light, essentially independent of the host material. Emission of light at this wavelength, either by a light-emitting diode or a laser, could have great technological importance because the energy of the light emitted is less than the band gap in Si, meaning waveguides could be fabricated within the the substrate and a variety of input/output options would be possible. Also, erbium-doped silica amplifiersi pumped by IR lasers operate at the same wavelength and their use in long distance fiber optic communications may become widespread, making erbium-doped silicon attractive for use in high speed data transmission. Erbium-doped silicon has previously been prepared by either ion implantation3 2 during molecular beam epitaxy or by ion implantation of single crystal silicon. 2 Photoluminescence and electroluminescence 4 have been observed in these samples and electrical measurements have shown that erbium doping introduces donor states into the silicon lattice.3 It has also been observed that both defects and impurities enhance luminescence, 5 although the mechanisms responsible for this enhancement are not known. Indeed, the photoluminescence of erbium implanted into very pure float-zone silicon, after the repair of lattice damage by annealing, is barely discernible, whereas erbium implanted into Czochralski-grown silicon containing 1008 0 atoms/cm3 , shows a two order of magnitude enhancement in the photoluminescence intensity when annealed under the same conditions. Recent studies have
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