Ultrafast absorption in free-standing porous silicon films

Abstract

Ultrafast absorption studies on free-standing porous silicon films have been carried out at room temperature to investigate the carrier dynamics and the luminescence mechanism. Ultraviolet and visible excitations were used on an as-prepared sample and two annealed samples. Transient absorption curves of UV pumped, as-prepared samples contain a fast decay (τf) of 0.8±0.2 ps and a slower decay of ≳30 ps. τf is found to be shorter for both the 500 °C annealed sample with UV excitation and for the as-prepared sample with visible excitation. The faster decay rates suggest that the subpicosecond component of the transient absorption may be due to carrier thermalization rather than core-to-surface state excitation transfer.