THE LOCAL-STRUCTURE OF POROUS SILICON STUDIED BY EXAFS

X-ray absorption measurements at the K-edge of silicon have been done in transmission mode on three powdered samples of porous silicon (p-Si) with 50, 65 and 80% porosity, prepared by decreasing the HF content in the anodic solution. The analysis of EXAFS reveals a crystal-like structure of p-Si at least up to the 3rd coordination shell. A slight progressive reduction of coordination numbers and an increase of Debye-Waller factors with respect to c-Si is found in passing from the Ist to the 3rd coordination shell; this behaviour is connected to the limited range of homogeneous structural regions in p-Si. The Debye-Waller factors increase with decreasing porosity, indicating a more ordered local structure in samples prepared with lower HF content.