Porous SiGe Nanostructures Formed by Electrochemical Etching of Thin Poly-SiGe Films

Abstract

We have studied the effect of the current density (J) and etching time in the formation of porous poly-SiGe (pp-SiGe) layers, with Ge fractions in the 0 to 0.55 range, by electrochemical etching. The starting material was unintentionally doped polycrystalline SiGe thin films, deposited in amorphous state by low-pressure chemical vapor deposition and subsequently crystallized. pp-Si structures were found to be homogeneous at large scale and show nanocrystalline of around 5 nm for low J values. The pp-SiGe structures show nonuniformities in their structure; the nanocrystal size is around 10 nm for low J and decreases for high J values and increasing etching times, reaching values of 2-4 nm. The composition of the pp-SiGe films, for low to moderate J values, shows a slight Ge enrichment. For high J values, in samples with all the Si was etched and the composition of the porous layer is pure Ge. This effect is not so strong for samples with high Ge fractions The dominant radiative recombination mechanism is not excitonic; we associate it with recombination via defects in the crystalline structure of the porous film or states at the interface nanocrystals/native © 2004 The Electrochemical Society. All rights reserved.