SURFACE-MORPHOLOGY OF GE(001) DURING ETCHING BY LOW-ENERGY IONS

The roughening of a crystalline semiconductor during etching by low-en ergy ions is characterized using in situ scanning tunneling microscopy . Ge(001) surfaces are bombarded by 240-eV Xe ions using a wide range of exposure times and temperatures. Ge dimers are resolved for surface s etched at T greater than or equal to 165 degrees C and imaged at roo m temperature. For fixed ion exposure, the roughness increases with in creasing temperature; a maximum surface roughness is reached for etchi ng at similar or equal to 250 degrees C. At T similar or equal to 270 degrees C the character of the surface morphology changes from a relat ively disordered arrangement of mounds to a more regular pattern of pi ts. The isotropy of this pattern formation and the dependence of the i n-plane length of the roughness on exposure time suggest that asymmetr ic kinetics for the attachment of dimer vacancies at ascending versus descending steps drives roughening during etching.