TEM AND PHOTOLUMINESCENCE CHARACTERIZATION OF POROUS-SILICON LAYERS FROM [111]-ORIENTED P(+) SILICON SUBSTRATES

A first structural investigation, carried out by transmission electron microscopy on porous-silicon samples from p(+), [111]-oriented substr ates is presented. The samples, which show intense visible room temper ature luminescence, ape composed by an interconnected network of cryst alline nanostructures. Evidences of the pores propagation along the [1 00] directions are provided. The optical and morphological characteris tics of the investigated samples are found to be much similar to those of samples coming from p-type, non-degenerate, [100]-oriented substra tes rather than those obtained from [100] substrates with comparable r esistivity. This striking effect is explained by invoking different et ch-limiting mechanisms during pore formation. Their relative weights a re proposed to depend on the crystallographic orientation of the silic on specimen subjected to etching.