Abstract

In III-V semiconductors, comparison of femtosecond time scale optical measurements¹ with microscopic carrier dynamic theory² has become direct and quantitative. In Column IV semiconductors, on the other hand, quantitative experiment-theory comparison has been achieved only on a picosecond time scale.³ This paper presents a systematic study of the fs.-time-resolved ellipsometric response of epitaxial Si_1.xGe_x (0≤x≤l) alloys as a first step in measuring and modelling subpicosecond bulk carrier dynamics. Pump and probe beams were derived from either an unamplified CPM laser⁴ (620 nm wavelength) or an unamplified KLM laser(800nm + 400nm second harmonic). The time-dependent optical response is related to free carrier density N_eh(t), reduced effective mass μ^*(t) via a time-varying Drude-Lorentz dielectric function:

© 1994 Optical Society of America