Wet-chemical bromination of Ge (100): A facile surface passivation tool

We demonstrate that wet-chemical surface bromination is an effective and a simple etching method for Ge surface oxide removal, providing excellent reoxidation resistance. Oxide removal and halide passivation for n-type Ge (100) were investigated using time-resolved photoluminescence and X-ray photoemission spectroscopy (XPS). In contrast to HCl, HBr treated Ge surfaces show a strong decrease in minority carrier lifetime, pointing to a surface state spectrum modification. The results from XPS using in situ sample preparation confirm that HBr effectively removes GeO₂ and suboxides, providing an air stable surface. Isopropyl alcohol rinsing after Br passivation maintains the chemical surface composition and the electronic structure. In contrast, during H₂O treatment in an Ar atmosphere, the brominated Ge surface is unstable, evidenced by emerging Ge-OH groups. The distinct observed upward shift of the surface Fermi level indicates an e^- donating behavior of H₂O.