The surface state of Ge epi-ready wafers (such as those used on III–V multijunction solar cells) supplied by two different vendors has been studied using X-ray photoemission spectroscopy. Our experimental results show that the oxide layer on the wafer surface is formed by GeO and GeO2. This oxide layer thickness differs among wafers coming from different suppliers. Besides, several contaminants appear on the wafer surfaces, carbon and probably chlorine being common to every wafer, irrespective of its origin. Wafers from one of the vendors show the presence of carbonates at their surfaces. On such wafers, traces of potassium seem to be present too.
► Ge epi-ready wafers from two different vendors studied using X-ray spectroscopy. ► Oxide layer on all the Ge wafer surfaces formed by GeO and GeO2; layer thickness depending on wafer vendor. ► Probable presence of chlorine at the wafer surfaces. ► Wafer surfaces from one of the vendors contaminated by carbonates.