Cathodoluminescence depth profiling by electron beam energy variation

For investigation of luminescent centre profiles cathodoluminescence (CL) measurements are used by means of variation of the primary electron (PE) energy from Eo = 0.5 to 3 keV. Applying a constant incident power regime Eo x jo = const, the depth profiles of luminescent centres are deduced im comparable magnitude from the electron energy transfer profiles dE/dx.
Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+-ions of energy 350 keV and doses 5x1015 to 5x1016 ions/cm2. Thus Ge profiles with a concentration maximum at the depth of about dm = 240 nm are expected. Afterwards the layers have been investigated partially "as implanted" and after different thermal annealing up to Ta = 1100 °C for one hour in dry nitrogen.
After thermal annealing, not only the typical violet luminescence (at 400 nm) of the Ge centers is strongly increased but also the luminescent centre profiles are sharpened and shifted in a characteristic manner from about 250 nm to 170 nm depth towards the surface.
In Ge-doped SiO2 layers the red (R) luminescence due to non-bridging oxygen hole centres (NBOHC) of the silica matrix is preserved, but the huge violet (V) band at 400 nm is attributed to twofold co-ordinated =Ge: centres as observed also in rutile-like GeO2 crystals. These centres in Ge+ implanted silica layers are especially developed during thermal annealing accompanied by Ge nanocluster formation, probably embedded in a GeO2 (or GeOx) surrounding within the silica matrix.