Photoacoustic spectra for porous silicon using piezoelectric transducer and microphone

Photoacoustic (PA) spectra are measured for porous Si (PS) using piezoelect ric detectors (PPT) and compared with the microphone PA (MPA) spectra to ex amine the nonradiative properties of PS that has complicated nanostructures . Three peaks (peaks 1 and 2, and a small peak at 600 nm) are observed in s amples 2 and 3 with porosities p = 60 and 70%, respectively, while only a s ingle peak (peak 1) is observed in sample 1 with p = 30%. Peak 2 is related to the band gap of the Si substrate. In Contrast. peak 1 seems to be due t o the absorption change at the band gap unique to the PS. This band gap shi fts to higher energy for PS samples with higher porosity. We propose that t his band gap is defined by the largest size nanocrystals. where PS has nano crystallite size distribution. The small peak at 600 nm is related to the P L peak and it is observed only in PPT spectra. These results suggest that d ifferent mechanisms are operating in PPT spectra and NIPA ones for the enha ncement of the PA spectra.