The effect of oxygen on the properties of evaporated amorphous silicon

The influence on the ESR centres of oxygen incorporation into evaporated amorphous Si is studied. The main effect is not the reduction of the spin density NS, which can be only reduced of a factor 10 after an intitial contamination, but a strong enhancement of the spin–lattice relaxation time T1, which makes the signal very saturable and apparently weak for usual microwave powers. This T1‐ rising is correlated with a slight g‐factor decrease, and lineshape changes from Lorentzian to Gaussian. This was also observed by others with alternative treatments for reducing the spin density, such the rise of the substrate and annealing temperature or hydrogen incorporation. This initial spin density reduction seems always to imply the passivation of the same kind of defects, accessible to the gases and located at the internal surfaces of porous samples. But many other defects with T1‐times in the range 10−5 s at 300 K are not suppressed by this way.