POROUS SILICON HOST MATRIX FOR DEPOSITION BY ATOMIC LAYER EPITAXY

Atomic layer epitaxy (ALE) is known to provide uniform layer-by-layer growth controlled by the chemisorption of the precursors on a substrat e regardless of geometry. Uniform distribution of ALE deposited tin ox ide and gallium oxide in porous silicon (PS) was detected by Rutherfor d backscattering spectrometry and secondary ion mass spectrometry when the deposition conditions were properly selected. However, the nuclea tion of macroscopically uniform SnO2 in PS was detected by cross-secti onal high resolution scanning electron microscopy. The nanosize partic les of different lattice constant inside the silicon matrix can be ass ociated with crystallites of the deposited material, i.e. SnO2. 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 crysta llites are embedded in a thin amorphous phase. It is also possible tha t the macroscopically 'conformal' coating on a nanometre scale is an a gglomeration of SnO, nanocrystallites. Evidence of nucleation was also confirmed on hat silicon surfaces by lateral force microscopy. (C) 19 97 Elsevier Science S.A.