PREPARATION OF THIN POROUS SILICON LAYERS BY STAIN ETCHING

A method of preparation of thin (1000 Angstrom) porous silicon layers by chemical etching of c-Si in HF:HNO3:H2O = 1:3:5 solution is reporte d wherein a thin Al film is deposited by evaporation on the silicon su rface prior to etching. The method is characterized by no ''incubation '' period to the onset of the stain etching. The reaction between Al a nd HNO3 produces the required holes for the very fast start of the che mical etching of Si. Using Al patterns deposited through a mask or pre pared by photolithography it is possible to achieve selective formatio n of porous silicon. The porous silicon layers exhibit visible photolu minescence and when prepared on p-type c-Si and a shallow p-n c-Si hom ojunction the resulting heterostructures also display electroluminesce nce and photovoltaic properties. (C) 1997 Elsevier Science S.A.