Development of the surface morphology of germanium upon irradiation with gallium ions

Experimental studies of the germanium surface morphology development under irradiation with a focused gallium ion beam at different angles of incidence and fluences are presented. It is shown that a nanoporous structure formes in the near-surface layer starting with a dose of 5·10¹⁵ cm^‒2.This leads to the formation of a sponge-like morphology with a wall thickness of about 20 nm and a depth up to 150 nm with an increasing dose. Changing the ion beam incidence angle with respect to the surface normal leads to a tilt of the pores walls in the collinear direction.