Refractive index dependence on optical gap in amorphous silicon—part II. Si prepared by chemical vapour deposition

Abstract

In the present study, we essentially attempt to extrapolate our earlier studies (1) to amorphous silicon films prepared by chemical vapour deposition using a slightly different approach. This work assumes significance especially in view of a rather dangerous trend prevailing today to generalize model calculations without attributing any importance to the method of preparation of the films. (2–4) Here, we adopt a spectroscopic approach to analyse the various properties of the a-Si films. Some of these films are doped with boron and most of them have been subjected to post-hydrogenation. This study leads us to conclude that the Moss formula (5) is again a fairly good representative of the optical gap-refractive index variation. The scheme developed by Ravindra et al. (6) is shown to be valid for these CVD films. In the passing, we attempt to analyse the properties of films prepared at different temperatures and at different rates of deposition. The model of Revesz (7) is utilised to explain the variation in the density. Our study leads us to believe that for the CVD technique (a high temperature technique with temperatures close to that of crystallisation (8), the rate of deposition seems to be very important in determining the surface conditions of the films. Further, it is seen that on post-hydrogenation, the spectroscopic parameters as have been defined in the Wemple-Didomenico model (9) behave randomly. The study has been carried out on a large number of samples.