Activation of luminescence in polycrystalline silicon thin films by ultrasound treatment

Abstract

A dramatic increase of infrared photoluminescence (PL) intensity by a factor of 2 orders of magnitude is observed after a few minutes at 250 °C of ultrasound treatment (UST) applied to polycrystalline silicon thin films on glass substrates. In films obtained by solid-phase crystallization of amorphous silicon at 550 °C, UST enhances the PL band intensity at 0.7 eV, and also activates a new luminescence maximum at about 0.9 eV. We prove that the 0.9 eV PL band is related to the amorphous fraction of poly-Si films. Due to similarities in spectral shape and temperature behavior, this UST activated luminescence is attributed to a ‘‘defect’’ PL band previously observed in hydrogenated amorphous Si. This conclusion is confirmed by using a set of films with controlled fractions of the amorphous to crystalline phase. A mechanism of ultrasound stimulated hydrogen detrapping followed by hydrogen diffusion and passivation of nonradiative centers (e.g., dangling bonds) in polycrystalline and amorphous Si films is discussed.