Gradient etching of silicon-based thin films for depth-resolved measurements: The example of Raman crystallinity

An etching procedure was applied to microcrystalline silicon (μc-Si:H) thin films in order to obtain a wedge-shaped profile for depth-resolved characterization. A microfluidic flow cell that merges deionized water with a potassium hydroxide solution (KOHaq) was utilized. The samples consisted of texture-etched ZnO:Al on a Corning Glass substrate, a microcrystalline p-doped layer serving as seed layer and the investigated intrinsic microcrystalline or amorphous silicon (a-Si:H). Along the etched profiles, microscopic Raman spectroscopy was used to estimate the crystalline volume fraction Xc for samples deposited with intentionally varied silane concentration to investigate the a-Si:H/μc-Si:H and μc-Si:H/a-Si:H transition.