The role of silicon hydride species in the photoluminescence intensity behavior of porous Si has been studied. The surfaces of luminescent porous Si samples were converted to a predominate SiH termination using a remote H plasma. The as-passivated samples were then immersed in various concentrations of hydrofluouric solutions to regulate the recovery of SiH2 termination on the surface. Photoluminescence measurements and transmission Fourier-transform infrared spectroscopy have shown that predominant silicon monohydride (SiH) termination results in weak photoluminescence. In contrast, it has been observed that the appearance of silicon dihydride (SiH2) coincides with an increase in the photoluminescence intensity.

We have developed a new, minimal damage approach for examination of luminescent porous Si (PS) layers by transmission electron microscopy (TEM). In this approach, chemically etched (CE) PS layers are fabricated after conventional plan-view TEM sample preparation. Our TEM studies show that crystalline, polycrystalline, and amorphous phases exist in the same CE sample. The microstructure is believed to gradually change from crystalline to amorphous during chemical etching in a HF-HNO3-H2O solution. The microcrystallites in the polycrystalline region are estimated to be 15–100 Å, while the pore size is on the order of 400 Å.

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