= Solution
\b[Diffuse a donor such as <phosphorus> into the textured p-type surface, then control the thermal drive-in to form the shallow n-type emitter.] A phosphorus-containing vapour source can supply the donor over the exposed area. Diffusion and activation create an n-on-p <p-n junction>; remove the phosphorus-rich surface glass and isolate the rear and wafer edges as required to avoid shunts.
An alternative is <ion implantation> followed by an activation and damage-repair anneal. The diffusion route is particularly convenient for large-area coverage of a textured wafer. The indicated roughly $1\,\mu\mathrm m$ layer is a depth target for process control, not an instruction to grow an undoped film and assume that it becomes n-type.
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