PL and PR measurements have been performed on a set of silicon samples p-type doped between 1018 cm−3 and 1020 cm−3. Both optical methods are shown to be complementary as the bandgap narrowing effect is clearly evidenced from PL results, whereas low temperature PR results rather show the filling effect of the valence band, in good agreement with theoretical determinations. We observe an increase of E′0 transition as p-type doping level is increased.
PR spectra of Si and SiGe alloys at low temperature are presented together with theoretical fitting using the third derivative functional form of the unperturbed dielectric function of both direct optical transitions involved in the main PR feature : E′0 and E1.
This characterisation work will be discussed by pointing out that PL and PR results are closely connected, allowing the measurement of the effect of heavy doping on the Si and SiGe band structures.This study is fully relevant to high speed bipolar transistor development.