The compositional profile of the interface between plasma-deposited amorphous silicon (a-Si@B: H) and silicon nitride (a-SiNx:H) thin films has been examined using high depth resolution Rutherford backscattering spectrometry. We have optimized the grazing exit angle geometry of the measurement using a model calculation which predicts a ∼20 Å interface depth resolution. The fundamental noise sources considered in the calculation are the energy straggling and angular divergence of ions traversing the target, detector noise, and geometrical effects. Experimentally, the major compositional change for both Si and N is found to take place within the interface depth resolution which is 18 Å. However, we find a tail of ∼3 at. % nitrogen extending through a 50-Å a-Si:H layer deposited on top of a-SiN x:H. Such a tail is not expected for the reverse order of layer deposition. The compositional asymmetry depending on the order of deposition is presumably associated with the reported asymmetry in the charge density at interfaces. The nitrogen contamination further implies that most a-Si:H/a-SiNx:H quantum well structures are in fact based on nitrogen alloyed a-Si:H layers.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)