Visible electroluminescence (EL) characteristics of porous Si formed o
n p, n, p(+)-n, and n(+)-p junction substrates are studied under pulse
current regime. We provide experimental proof that porous Si structur
es characterized by highest EL intensity have simultaneously highest p
hotoluminescence (PL) intensity and lowest surface roughness. PL and E
L can be correlated via surface roughness Two types of EL instabilitie
s are observed: fast, with time constant in the milliseconds range and
slow, with time constant in the hours range. The fast EL instability
is affected by the type of ambient and/or sample temperature during el
ectrical excitation and is likely to be associated with the charging o
f the porous network.