POROSITY SUPERLATTICES - A NEW CLASS OF SI HETEROSTRUCTURES

Porosity superlattices have been investigated by transmission electron microscopy, photoluminescence and reflectance spectroscopy. The super lattices were formed on p-type doped Si using two different techniques . Firstly, for homogeneously doped substrates we have periodically var ied the formation current density and thereby the porosity. Secondly, the current density was kept constant while etching was performed on p eriodically doped Si layers. For the first type of superlattices the l ayer thicknesses were determined by transmission electron microscopy. The results are in good agreement with the values calculated from the etching rate and time. For both types of superlattices, reflectance an d photoluminescence spectra show strong modulation due to the periodic ity of the superlattice.