Electron microscopy and cathodoluminescence (CL) microanalysis
were used for a comparative study of porous layers fabricated
by electrochemical etching of n-GaP and n-InP substrates in aqueous
solutions of sulfuric and hydrochloric acids. Both the CL and
morphology of porous layers were found to depend upon the anodic
current density. At high current density (100 mA/cm2) anodization
leads to the formation of so-called current-line oriented pores
while at low current densities the pores grow along $\langle 111\rangle$
crystallographic directions. The porosity relief was found to
give rise to spatial modulation of the CL intensity. The composition
microanalysis proved the stoichiometry of porous GaP and InP
skeletons, although we found considerable traces of oxygen in
porous GaP layers. Self-induced voltage oscillations giving rise
to a synchronous modulation of the diameter of pores and CL intensity
were evidenced.