Observation of phonon confinement in SiGe nanocrystals and preferential etching of Si in porous Si1-xGex films

The structure of porous Si1-xGex films was characterized using Raman spectroscopy. As the film porosity increases the sizes of Si1-xGex nanocrystals decrease, and also the film composition slightly modifies in favor of Ge. The Si1-xGex nanocrystals were estimated to be 12.0 rim, 16.1 DID and 19.3 nm average diameter in three porous samples prepared from undoped Si0.87Ge0.13 films with 20 min, 10 min and 2 min etch times, respectively, at the same current density 22 mA cm(-2). The final Ge fractions were determined for the samples as 17.4%, 14.5% and 13.0%, respectively. It is seen by this study that Raman spectroscopy is, as it has always been for bulk Si1-xGex alloys, a very useful technique for characterizing the structure of porous Si1-xGex films.