Correlation of Electrical, Structural, and Optical Properties of Erbium in Silicon

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CORRELATION OF ELECTRICAL, STRUCTURAL, AND OPTICAL PROPERTIES OF ERBIUM IN SILICON J. L. Benton, D. J. Eaglesham, M. Almonte, P. H. Citrin, M. A. Marcus, D. L. Adler, D. C. Jacobson and J. M. Poate AT&T Bell Laboratories, Murray Hill, New Jersey 07974 ABSTRACT An understanding of the electrical, structural, and optical properites of Er in Si is necessary to evaluate this system as an opto-electronic material. Extended x-ray absorption fine structure,EXAFS, measurements of Er-implanted Si show that the optically active impurity complex is Er surrounded by an 0 cage of 6 atoms. The Er photoluminescence intensity is a square root function of excitation power, while the free exciton intensity increases linearly. The square root dependence of the 1.541tm-intensity is independent of measurement temperature and independent of co-implanted species. Ion-implantation of Er in Si introduces donor activity, but spreading resistance carrier concentration profiles indicate that these donors do not effect the optical activity of the Er. INTRODUCTION The interest in erbium doping of silicon is an outgrowth of the successful materials science which resulted in the new generation of lightwave communications based on Er-doped fibers and fiber amplifiers. Lightwave networks employing Er doped components offer a new technology with the potential for powerful communications services. It is a natural scientific step, therefore, to introduce Er into silicon in an attempt to invent a compatible silicon optoelectronic device. Light from Si, especially at 1.54gtm, is an important scientific advance, but further work in this area should be measured against technological benchmarks. A careful evaluation of materials parameters has suggested that the erbium-silicon system is not well suited for light emitting diodes, amplifiers or modulators, and that the best chance for its commercial success will reside in lasers. Ell Achievement of a laser based on electroluminescence of Er in Si requires increasing the impurity incorporation beyond the 1 measured solid solubility of lxA 0Icm- 3 and demands, as well, an understanding of the excitation mechanism of the Er defect. With advances on these two fronts, it might be possible to create and maintain the inverted population necessary for stimulated emission. The results presented in this study add some understanding to the issue of Er excitation. The extended x-ray absorption fine-structure (EXAFS) experiments indicate that the optically active Er defect in Si is a complex of Er and six oxygen atoms. The Er luminescence exhibits a square-root function of excitation laser power. This result eliminates exciton bonding as the rate limiting step and suggests that either a back-transfer mechanism or Auger process limits the efficiency of the Er emission. Previous work [2l established that high energy ion implantation of Er into Si introduced donor activity. Although the donor concentration correlates with the Er photoluminescence intensity, this paper shows that the donor defects are not involved in the exc

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