We investigate the formation of submonolayer InN quantum sheets and their embedment into GaN to form (In,Ga)N/GaN superlattices. While supplying InN on GaN(0001), we have monitored in-situ the formation of an In adlayer manifesting itself by the (1 × 3) reflection high-energy electron diffraction pattern, that is thought to be established by a third of a monolayer of In adatoms consistent with a (√3 × √3)R30° structure. We have utilized this In adsorbate structure on GaN(0001) as a template for the synthesis of laterally ordered InGaN quantum sheets with a self-limited thickness of 1 monolayer and an In content expected to be 0.33 as defined by the (√3 × √3)R30° structure. Repeatedly inserting these quantum sheets into GaN, we have synthesized (In,Ga)N/GaN shortperiod superlattices with abrupt interfaces and high periodicity, as concurrently determined ex-situ by X-ray diffractometry. The embedded …