Optical-dispersive influence of photo-generated free charge carriers in semiconductors

Optical-dispersive influence of photo-generated free charge carriers in semiconductors. Two experimental arrangements are introduced, with the help of which the optical-dispersive changes caused by photoelectrically produced free charge carriers can be demonstrated very sensitively : (i) Variation of the polarization-dependent reflection coefficient of IR radiation in the angular range of total internal reflection at the air boundary and (ii) Schlieren optical deflection of IR radiation at a modulated refractive index profile. In both cases, the free charge carriers are generated by pulsed light incident on the boundary surface. A CO 2 -laser radiation passing through the semiconductor is the detection probe. The detection sensitivity in silicon and germanium is in the range of 1 E + 16 [cm -3 ] excess carriers corresponding to a change in refractive index of about Δn = 1E-4. The experiments are compared with model calculations which quantitatively take into account the dynamic charge carrier profile. The profile of the corresponding complex refractive index is handled with the help of the matrix calculus.