THE BAND GAP OF GLOW-DISCHARGE-PRODUCED AMORPHOUS SiOx

Amorphous films of composition SiOx (H,N) were prepared in a gas discharge of suitable mixtures of SiH4 with N2O or O2 (Ar). The photoluminescence of these films showed two bands, one of which shifts to higher energy with increasing oxygen content similar to the optical absorption edge. As x increases this luminescence band broadens, and the absorption edge becomes less steep. - This increase of the band gap and the tailing can be understood with a simple model which deals with the role of the Si-Si and Si-O bonds in SiOx. The band gap of SiOx is chiefly determined by the Si-Si bonding and antibonding bands. Oxygen bridges withdraw electronic states from them and produce new states further below in the SiO2 valence band region. The effect on the Si-Si bands is, therefore, mainly indirect in that the Si-Si bond coordination number is reduced. The bands become narrower and the gap widens