THE RELATIONSHIP BETWEEN OPTICAL GAP AND CHEMICAL-COMPOSITION IN SBXSE1-X SYSTEM

The optical constants of vacuum deposited SbxS1-x amorphous thin films (x = 0.075, 0.15 and 0.20 at%) of different thicknesses (90-150 nm) w ere studied in the wavelength range 550-800 nm. It was found that both the refractive index n and the absorption index k are independent of the film thickness, whilst there is a distinct dependence of n and k o n the Sb content. The allowed optical transition was found to be non-d irect, the corresponding optical gaps E(g)(opt) are determined. The wi dth of the band tail E(e) is also determined. As a result, E(g)(opt) d ecreases while E(e) increases with increasing Sb contents. The variati on of E(g)(opt) with x for SbxSe1-x agree with the optical gap E(o) pr edicted theoretically in terms of random bond network proposed by Shim akawa. The relationship between the optical gap and chemical compositi on in SbxSe1-x amorphous system is discussed in terms of the average h eat of atomization H-s and the average coordination number m. The resu lts of these calculations can be used to rationalize the observed opti cal properties of these materials.