Transmission electron microscopy study of chemically etched porous Si

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.