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

The optical constants of vacuum deposited SbxSe1-x amorphous thin film s (x = 0.075, 0.15 and 0.20 at%) of different thicknesses (90-150nm) 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 agrees with the optical gap E(0) p redicted theoretically in terms of random bond network proposed by Shi makawa. The relationship between the optical gap and chemical composit ion in SbxSe1-x amorphous system is discussed in terms of the average heat of atomization H-s and the average coordination number m. The res ults of these calculations can be used to rationalize the observed opt ical properties of these materials. (C) 1997 Elsevier Science Ltd.