Band Alignment of Grafted Si/Ge 0.89 Sn 0.11 Heterojunction Determined by X‐Ray Photoelectron Spectroscopy

ABSTRACT We investigate the band alignment of a monocrystalline grafted p‐type Si/Ge 0.89 Sn 0.11 heterostructure using X‐ray photoelectron spectroscopy (XPS). The bandgap of the Ge 0.89 Sn 0.11 epilayer of 0.50 eV was first determined and cross‐verified using photoluminescence spectroscopy, infrared transmission, and theoretical calculation. The band offsets values at the grafted Si/Ge 0.89 Sn 0.11 interface were determined using Kraut's method via a top‐down interface approach with multiple core‐level combinations, yielding a valence band offset (VBO) of −0.43 ± 0.031 eV and a conduction band offset (CBO) of +0.19 eV. The band alignment was also constructed based on Anderson's rule by using work function values extracted from secondary electron cutoff (SECO) measurements. The effective band alignment extracted from Kraut's method shows good agreement with the Anderson‐rule estimate, suggesting that interface‐state‐induced Fermi‐level pinning is not dominant in the grafted Si/Ge 0.89 Sn 0.11 ​ heterostructure. This buffer‐free, oxide‐mediated grafted interface offers a promising integration strategy for high‐Sn‐content GeSn directly on Si for future optoelectronic applications.