OPTICAL-ABSORPTION OF A-B AND A-B1-XSIX FILMS PREPARED BY LPCVD METHOD

A series of a-B films with substrate temperature T(s) ranging from 300 to 800-degrees-C and two series of a-B1-xSix films (0.1 less-than-or-equal-to x less-than-or-equal-to 0.9) with T(s) = 460 and 620-degrees-C were prepared by LPCVD method. Optical absorption spectra of these films from visible to near infrared region are measured in order to study the influence of T(s) and the effect of Si incorporation into boron. Functions for density of states are constructed to fit the curves. When T(s) increases from 300-degrees-C to 800-degrees-C, the optical gap of a-B films decreases from congruent-to 1.2 to congruent-to 0.8eV, while the width of the tail states decreases. It is found that Si incorporation into boron introduces additional sub-gap states.