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Electrical properties of heavily doped polycrystalline silicon-germanium films

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4 Author(s)
T. -J. King ; Dept. of Electr. Eng., Stanford Univ., CA, USA ; J. P. McVittie ; K. C. Saraswat ; J. R. Pfiester

The electrical properties of polycrystalline silicon-germanium (poly-Si1-xGex) films with germanium mole fractions up to 0.56 doped by high-dose ion implantation are presented. The resistivity of heavily doped p-type (P+) poly-Si1-x Gex is much lower than that of comparably doped poly-Si, because higher levels of boron activation and higher hole mobilities are achieved in poly-Si1-xGex. The resistivity of heavily doped n-type (N+) poly-S1-xGex is similar to that of comparably doped poly-Si for x<0.45; however, it is considerably higher for larger Ge mole fractions due to significant reductions in phosphorus activation. Lower temperatures (~500°C), as well as lower implant doses, are sufficient to achieve low resistivities in boron-implanted poly-Si1-xGex films, compared to poly-Si films. The work function of P+ poly-Si1-xGex decreases significantly (by up to ~0.4 Volts), whereas the work function of N+ poly-Si1-xGex decreases only slightly, as Ge content is increased. Estimates of the energy bandgap of poly-Si1-xGex show a reduction (relative to the bandgap of poly-Si) similar to that observed for unstrained single-crystalline Si1-xGex for a 26% Ge film, and a reduction closer to that observed for strained single-crystalline Si 1-xGex for a 56% Ge film. The electrical properties of poly-Si1-xGex make it a potentially favorable alternative to poly-Si for P+ gate-material applications in metal-oxide-semiconductor technologies and also for p-channel thin-film transistor applications

Published in:

IEEE Transactions on Electron Devices  (Volume:41 ,  Issue: 2 )