A study of silicon MBE on porous silicon substrates

Abstract

The defect structure of Si MBE layers grown on porous silicon substrates depends critically on the technique for cleaning the substrate surface. Cross-sectional TEM studies demonstrate that a combined sputter-clean and thermal cycle markedly reduces the density of microtwins and dislocations in the epitaxial layer when compared with simple thermal cleaning. X-ray diffraction studies show the porous silicon layer to be lattice-matched to the underlying (100) bulk silicon substrate in the plane of the wafer so that misfit dislocations are not expected in the epitaxial layer. However, both the lattice parameter of the porous layer in the direction normal to the wafer and the thermal stability of the porous layer in vacuum, depend upon the resistivity of the starting wafer. The photoluminescence of a 4-μm MBE layer grown on a sputter-cleaned, high resistivity substrate is still dominated by recombination at dislocations.