Drastic structure changes in pre-damaged GaAs crystals irradiated with swift heavy ions

We have studied structural transformations in pre-damaged GaAs crystals irradiated with high-energy Bi ions (710 MeV, 4.3 × 1012 cm−2). The pre-damage has been created via irradiation with swift electrons (4 MeV, 4 × 1017 cm−2). A structural disorder in irradiated samples has been investigated by means of selective chemical etching (SCE) and X-ray diffraction (XRD) in combination with the material layer-by-layer removal. Character of lattice deformation in the double-irradiated sample gives an evidence of subsurface region's swelling. Strong lattice distortion has been found in the region of Bi ion ranges at the depth of about 30 μm. The nature of this effect is discussed.