Studies of picosecond carrier dynamics in polysilane alloys: evidence for geminate recombination in small hydrogenated amorphous silicon clusters

The ultrafast photocarrier dynamics in polysilane alloys amorphous (SiH2)n' has been studied using the picosecond photoinduced absorption (PA) technique. For excitation below the optical gap, the PA response decays exponentially and is faster at low temperatures. This is interpreted in terms of e-h geminate recombination in the small clusters (~ 10 A) of αSi:H embedded in the polysilane matrix. The PA response with above-gap excitation t-ß (ß<1), independent of spectral range between 1.4 and 2.2 eV. This shows that the e-h distance after above-gap photogeneration is larger than the size of the αSi:H clusters.