THE EFFECT OF COMPOSITION AND SUBSTRATE-TEMPERATURE ON THE OPTICAL-ENERGY GAP OF SIOX/SNO AMORPHOUS THIN-FILMS

The fundamental absorption edge of co-evaporated SiOx/SnO thin films of various compositions has been investigated. The results have been analysed by assuming optical absorption by non-direct electronic transitions. The optical energy gap is seen to decrease with increase in the molar content of SnO which increases the level of disorder of the complex system. The effect of substrate temperature during deposition on the optical absorption is also studied. The optical energy gap increases with the substrate temperature. This is attributed to the annealing of some of the dangling bonds and hence to an increase in the order of the system. The Urbach tail is related to the broadening of the absorption edge as a result of charged defects present in the films and related to the Franz-Keldysh effect. © 1990 Chapman and Hall Ltd.