Title :
Electrical properties of heavily doped polycrystalline silicon-germanium films
Author :
King, Tsu-Jae ; McVittie, James P. ; Saraswat, Krishna C. ; Pfiester, James R.
Author_Institution :
Dept. of Electr. Eng., Stanford Univ., CA, USA
fDate :
2/1/1994 12:00:00 AM
Abstract :
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
Keywords :
Ge-Si alloys; annealing; boron; carrier mobility; electronic conduction in crystalline semiconductor thin films; energy gap; heavily doped semiconductors; ion implantation; phosphorus; rapid thermal processing; semiconductor materials; semiconductor thin films; work function; 500 C; B activation; Ge mole fractions; P activation; P+ gate-material applications; RTA; SiGe:B; SiGe:P; electrical properties; energy bandgap; heavily doped polycrystalline films; high-dose ion implantation; hole mobilities; metal-oxide-semiconductor technologies; n-type; p-channel TFT applications; p-type; poly-Si1-xGex; resistivity; semiconductors; thin-film transistor applications; work function; Boron; Conductivity; Germanium silicon alloys; Implants; Ion implantation; Photonic band gap; Semiconductor films; Silicon germanium; Temperature; Thin film transistors;
Journal_Title :
Electron Devices, IEEE Transactions on
