Preferential etching of ion-bombarded GaAs

Ion bombardment of GaAs above fluences of the order of 2 × 10¹³ 400-keV Xe-ions/cm² produces a highly strained surface which is elevated several hundred Angstroms above the adjacent masked surface. The irradiated area etches rapidly to yield circular etch pits ～ 0.3 μ in depth and 0.2 μ in diameter. At lower fluences, observations show much less expansion, slower crystalline etching, and some evidence of triangular etch pits and slip planes. These results are attributed to expansion in the implanted layer which results in high surface strain and the generation of dislocations to accommodate the mismatch of lattice parameters.