Raman spectroscopy of heavily doped polycrystalline silicon thin films

Raman backscattering measurements were performed on boron and phosphorous d oped polycrystalline silicon films with an average grain size varying betwe en 150 and 2500 nm. The B- and P-doped samples exhibit free hole and electr on concentrations of up to 5 x 10(20) and 2 x 10(21) cm(-3), respectively. The incorporation of dopants results in a shift of the Raman LO-TO line to smaller wave numbers. At B and P concentrations higher than mid 10(19) cm(- 3) the phonon lines are asymmetric. This is discussed in terms of a resonan t interaction between optical phonons and direct intraband transitions know n as a Fano resonance.