PHOTOLUMINISCENCE OF POROUS SILICON AND POROUS POLYSILICON FILMS (INVITED)

We conducted a series of experiments on porous silicon (PS) and porous polysilicon (PPS) to investigate the origins of photoluminescence in these materials. To study the effect of surface layer, plasma etching for several different durations on the as- anodized samples was conducted. For photoluminescence (PL) study, results show that the intensity decreases rapidly but the peak locations remain fairly unchanged as the surface etching proceeds. In addition, only one band centered at around 680 nm (1.82 eV) is found in PS samples whereas two bands, centered at 400 nm (3.1-eV) and 680 nm, are found in PPS samples. The 400-nm peak disappears when the surface oxide layer was completely removed. These results could not be explained with quantum confinement model of silicon nano structures. We ascribe these PL effects to the radiative centers in the surface oxide layer. Fourier transform infrared (FTIR) measurements on these samples further reveal that the PL peak at 680 nm correlates well with the NBOHCs (non-bridged oxide hole centers or =SiO-) and the 3.1 eV peak can also be attributed to the oxygen vacancy (=Si-Si=) in surface silicon oxide layer.