OPTICAL STUDY OF UNDOPED, B-DOPED OR P-DOPED POLYSILICON

The refractive index n(lambda), and optical absorption coefficient alp ha(lambda), of thin polycrystalline silicon films (Si-poly), undoped o r heavily doped in-situ with boron 8.10(20) cm(-3) or phosphorus 6.10( 20) cm(-3), deposited inside a new kind of reactor, called sector reac tor (a reduced model of an annular reactor). The optical constants of undoped Si-poly are obtained by a simple procedure which is based on t he use of the fringe pattern in the transmission spectrum. For heavily B-or P-doped polysilicon films, the optical absorption coefficient be come not negligible at near infrared and we deduced the optical consta nts from both the measured transmission T(lambda) and reflection R(lam bda) for film-substrate structures. In the infrared, the index of refr action decreases systematically and the absorption coefficient increas es systematically with wavelength. This variation of the optical param eters is attributed to the presence of free carriers. Drude's theory w as used in order to calculate the free-carrier concentration and the m obilities, and these results compared well with those obtained by Hall -effect measurements. (C) 1997 Elsevier Science S.A.