Determination of localization of carriers in disordered semiconductors by femtosecond spectroscopy

A new method for determination of the mobility edge in disordered semiconductors by femtosecond pump-supercontinuum probe spectroscopy is presented. The method is based on the determination of the spectral. dependence of a stretched exponential relaxation in a wide spectral range of probing, homega(probe) = 1.6 - 3.2 eV. The method is demonstrated for porous silicon. It is shown that the relaxation parameters for porous silicon have essential spectral dependence. The spectral dependence of stretched exponential index beta(omega) give unique information about existence and position of the mobility edge in disordered materials, and thus may be used as effective tool in manifestation of the transition from localized to delocalized relaxation regime on the femtosecond time scale.