Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2022 / Paper 1 / Section B / 9 / i / a / Solution

Use anisotropic alkaline wet etching of a suitably oriented crystalline silicon wafer. A KOH- or TMAH-based process etches crystallographic planes at different rates, leaving slow-etching $\{111\}$ facets as a pyramidal texture on a $\{100\}$ wafer. The facets redirect reflected light towards neighbouring surfaces, increasing the chance of absorption rather than specular escape.

Choose conditions that give a uniform texture without excessive removal or contamination, and clean the wafer before forming the junction. This mechanism depends on crystallinity: a multicrystalline or differently oriented wafer may need another texture process. The drawing alone does not establish the wafer orientation, so the standard pyramidal-texture method carries that explicit assumption.