Mathias Fingerle

Unexpected Pyramid Texturization of n-Type Ge (100) via Electrochemical Etching: Bridging Surface Chemistry and Morphology

We report on the (electro) chemical etching behavior, surface morphology and composition of n-type Ge (100) in acidic halide solutions using various analytical and spectroscopic techniques. The use of an integrated (electro) chemical etching chamber connected to X-ray photoelectron spectroscopy instrument to exclude the effect of oxygen from atmosphere is highlighted.

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.