An investigation was made of paramagnetic defects and the structure of magnetron-sputtered amorphous SiO2 films containing 3.8at%Ge (a-SiO2:Ge), annealed at 500 to 1000C, using electron paramagnetic resonance, Fourier-transform infra-red absorption and transmission electron microscopy. The electron paramagnetic resonance spectra of as-grown a-SiO2:Ge films revealed 3 different defects: Si-E’ centers with g|| = 2.0019 and g┴ = 2.0004, •Ge≡Si3 dangling bonds with g|| =2.001 and g┴ = 2.024, and •Si≡Si2O or •Si≡SiO2 defects with g = 2.004. While the Si-E’ and g = 2.004 lines were removed by heat treatments at 500C, the signal from •Ge≡Si3 dangling bonds persisted up to annealing temperatures of 700C. The structural changes induced upon annealing on the a-SiO2:Ge films were studied by monitoring the frequency and line-width of the asymmetrical stretching vibration of the Si–O–Si linkage using Fourier transform infra-red. It was found that the rearrangement of the amorphous oxide network occurred mainly at 500 to 700C and no further significant recovery occurred upon annealing at above 700C; in line with the electron paramagnetic resonance results. Transmission electron microscopy images revealed the formation of Ge nanocrystals (Ge ncs) with diameters of 2 to 4nm already upon heat-treatment at 500C. Moreover, it was shown that the mean size of the Ge ncs increased quite significantly as the temperature of the heat treatments increased. The mean diameter of Ge ncs observed after annealing at temperatures above 600C was above that expected for Ge ncs with efficient photoluminescence properties. The implications of the experimental results for the understanding of the quenching of the photoluminescence from quantum-confined excitons within Ge ncs were explored.

Paramagnetic Defects and Amorphous Network Reconstruction of Magnetron Sputtered a-SiO2:Ge Films. R.N.Pereira, J.S.Jensen, J.Chevallier, B.B.Nielsen, A.N.Larsen: Journal of Applied Physics, 2007, 102[4], 044309