Evaluation of compositional depth profiles in mixed-phase (amorphous + crystalline) silicon films from real time spectroscopic ellipsometry

摘要

The ability to characterize the phase of the intrinsic (i) semiconductor layers incorporated into amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) thin film solar cells is critically important for device optimization. In this study, a new method has been developed to extract the thickness evolution of the μc-Si:H volume fraction in mixed-phase amorphous + microcrystalline silicon [(a + μuc)-Si:H] i-layers. This method applies real time spectroscopic ellipsometry (RTSE) performed using a rotating-compensator multichannel ellipsometer during r.f. plasma-enhanced chemical vapor deposition of the films, in conjunction with a two-layer virtual interface analysis of the RTSE data. In this analysis, the depth profile of the μc-Si:H volume fraction in the mixed-phase growth regime can be determined simultaneously with the evolution of the surface roughness layer thickness. From this information, the microcrystallite nucleation density and cone angle can be estimated, the latter describing the preferential growth of the silicon microcrystallites. The results from RTSE analysis correlate well with structural and p-i-n solar cell device measurements.