MICROSTRUCTURE AND PHOTOLUMINESCENCE OF POROUS SI FORMED ON N-TYPE SUBSTRATES IN THE DARK

The microstructure, from the general morphology to the lattice structu re, of porous Si layers produced by electrochemical etching of highly doped n-type Si substrates in obscurity conditions was studied by scan ning and transmission electron microscopies. Scanning electron microsc opy revealed that the porous layer consists of two distinctive layers, characterised by the size of the observed structural features: an upp er mesoporous layer and a lower macroporous layer. High resolution ele ctron microscopy showed the presence of thin crystalline Si platelets held at various depths within the pores of the mesoporous layer, in co ntrast to the Si nanocrystallites and nanowires identified in previous studies. In spite of the different geometry of the nanoparticles resu lting from the obscurity conditions, the observed photoluminescence wa s that of the typical red band. (C) 1997 Elsevier Science S.A.