Porous silicon host matrix for deposition by atomic layer epitaxy

Abstract

Atomic layer epitaxy (ALE) is known to provide uniform layer-by-layer growth controlled by the chemisorption of the precursors on a substrate regardless of geometry. Uniform distribution of ALE deposited tin oxide and gallium oxide in porous silicon (PS) was detected by Rutherford backscattering spectrometry and secondary ion mass spectrometry when the deposition conditions were properly selected. However, the nucleation of macroscopically uniform SnO 2 in PS was detected by cross-sectional high resolution scanning electron microscopy. The nanosize particles of different lattice constant inside the silicon matrix can be associated with crystallites of the deposited material, i.e. SnO 2. Their size, up to 12 nm, is smaller than the average pore size deduced from BET measurements. Nevertheless, it cannot be ruled out that the crystallites are embedded in a thin amorphous phase. It is also possible that the macroscopically `conformal' coating on a nanometre scale is an agglomeration of SnO 2 nanocrystallites. Evidence of nucleation was also confirmed on flat silicon surfaces by lateral force microscopy. © 1997 Elsevier Science S.A.