Er 3+ -Doped Silicon Prepared by Laser Doping
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Er 3 +-DOPED SILICON PREPARED BY LASER DOPING T. ASATSUMA*, P. DODD, J. F. DONEGAN, J. G. LUNNEY, AND J. HEGARTY Department of Pure and Applied Physics, Trinity College, Dublin 2, Ireland * Present address : Corporate Research Laboratories, Sony Corporation, 6-7-35 Kitashinagawa, Shinagawa-Ku, Tokyo, 141, Japan ABSTRACT
We have carried out an investigation of the laser doping of Si with rare-earth ions. In this technique a silicon surface coated with a thin layer of the rare-earth metal is melted with a pulsed laser, the dopant is mixed in the molten layer, and incorporated in the crystal during regrowth. Er was chosen for the main part of our work as it is the best characterized of the rare-earth ions in Si. Luminescence is observed around 1.541tm and is assigned to optical transitions on Er 3+ ions. This preliminary study shows that this new technique is viable for the production of optically active Er 3รท in Si. INTRODUCTION
Silicon has dominated the world of electronic devices for the last 30 years. Despite its indirect bandgap the simplicity of this elemental semiconductor means that Si still accounts for over 95% of all electronic devices. Until recently it was expected that Si would not make a significant contribution to the newer generation optoelectronic devices due to the weak radiative recombination processes at its indirect bandgap. However, the discovery of highly luminescent porous silicon and the incorporation into silicon of luminescent rare-earth ions now places silicon optoelectronics in the forefront of optical materials research. Rare-earth ions have been very interesting and attractive candidates for laser sources when incorporated into insulating host materials. The characteristics of rare-earth ion emission in insulating hosts are sharp luminescence lines in the visible and near infra-red, whose spectral position and emission intensity are essentially temperature independent. The recent development of diode-laser (semiconductor) pumped Nd:YAG (insulator) lasers with efficiencies of greater than 10% shows the technological importance of the rare-earth ions. A rare-earth doped semiconductor-diode laser would combine the pumping and the emission in the same material structure thereby greatly simplifying these lasers and potentially increasing the overall electrical efficiency much further. In this and other ways, rare-earth ion doped semiconductor materials have tremendous potential 1-6* Among the rare-earth ions, Er is interesting because the emission occurs mainly around 1.541im, which is very close to the wavelength of the least transmission loss of silica optical fibre. Therefore there have been several reports on the properties of Er in semiconductor host lattices 7-15. In those reports, several processes to dope the semiconductor with the rare-earth ion were reported ; MBE 7,8,11, MOCVD 9, and ionimplantation followed by annealing 10,12-15. To date all of these techniques have failed to produce silicon with significant concentrations of rare-earth ions which can be electrically excited at
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