This contribution presents several new experimental results provided by the
techniques of X-ray diffraction at grazing incidence, photoluminescence at
6 K, C-Q-V and charge version of deep level transient spectroscopy on poro
us silicon (thickness similar to 1 mu m)/crystalline silicon structures pre
pared by the standard electrochemical etching process. An existence of new
XRGI distinct reflection at 2 theta = 38.5 degrees, coming from the polycry
stalline structure of the porous silicon layer, has been confirmed. For the
first time we revealed a reversible metastability feature of two groups of
gap states with the thermal activation energies of similar to 0.53 and sim
ilar to 0.70 eV, respectively. The metastable properties are related to the
changes of both the water and hydrogen contents in the porous silicon laye
r induced by a low temperature annealing process. (C) 1999 Elsevier Science
S.A. All rights reserved.