ACTIVATION OF LUMINESCENCE IN POLYCRYSTALLINE SILICON THIN-FILMS BY ULTRASOUND TREATMENT

A dramatic increase of infrared photoluminescence (PL) intensity by a factor of 2 orders of magnitude is observed after a few minutes at 250 degrees C of ultrasound treatment (UST) applied to polycrystalline si licon thin films on glass substrates. In films obtained by solid-phase crystallization of amorphous silicon at 550 degrees C, UST enhances t he 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 t o the amorphous fraction of poly-Si films. Due to similarities in spec tral shape and temperature behavior, this UST activated luminescence i s attributed to a ''defect'' PL band previously observed in hydrogenat ed amorphous Si. This conclusion is confirmed by using a set of films with controlled fractions of the amorphous to crystalline phase. A mec hanism of ultrasound stimulated hydrogen detrapping followed by hydrog en diffusion and passivation of nonradiative centers (e.g., dangling b onds) in polycrystalline and amorphous Si films is discussed. (C) 1996 American Institute of Physics.