FREE-CARRIER ABSORPTION IN MICROCRYSTALLINE SILICON THIN-FILMS PREPARED BY VERY-HIGH-FREQUENCY GLOW-DISCHARGE

The optical properties of heavily phosphorus- and boron-doped microcrystalline silicon thin films prepared at 70 MHz in a silane glow discharge have been measured in the visible and near infrared. The experimental data have been analysed in terms of the classical Drude model for free-carrier absorption. Excellent agreement between the carrier concentration deduced from the dispersion of the refractive index and that obtained by Hall-effect measurements has been obtained. A self-consistent analysis of (an)(-1) against lambda(-2) led to the determination of a Drude mobility of 9-15 cm(2) V-1 s(-1) in n-type material. The possible reasons for the deviation from room-temperature Hall values mu(H) of about 1-3 cm(2) V-1 s(-1) are discussed.