4‑inch AlN on Patterned Sapphire Substrate (PSS) Epitaxial Wafer is a high‑quality undoped AlN thin‑film epitaxially grown on micro‑patterned C‑plane sapphire substrate. The periodic micro‑nano patterns effectively suppress threading dislocation propagation, improve crystal quality of subsequent AlGaN/GaN epitaxial layers and greatly boost light‑extraction efficiency for ultraviolet emitters. With wide band‑gap, excellent deep‑ultraviolet transmittance, high thermal conductivity and epi‑ready ultra‑smooth surface, this large‑size template is ideal for mass‑production of high‑performance UVC‑LED, UV laser diodes, ultraviolet detectors, RF‑HEMT and nitride‑based semiconductor research. Custom‑available options include PSS pattern geometry, pattern pitch, AlN film thickness, sapphire substrate thickness and cleaning grade.