Defects in bombarded amorphous silicon

Abstract

Luminescence and electron spin resonance are investigated in plasma deposited a-Si: H samples after bombardment with electrons and He⁺ ions. The defects introduced are predominantly singly occupied dangling bonds and act as non-radiative recombination centres. Annealing between room temperature and 300°C decreases the density of these defects, but in some samples annealing apparently leads to the formation of spinless centres. Defect-related luminescence near 0·9 eV is interpreted as a transition between an electron trap and a self-trapped band-tail hole. Disorder induced by the damage broadens the band tails and is observed as a shift of the band-edge luminescence to lower energy. He⁺ ions cause greater damage of this kind than electrons, in accordance with expectations. The annealing of the E.S.R. spin density is sample-dependent and is explained by the differing amounts of hydrogen in the films.