Peculiarities of the track formation in InP and GaAs crystals

Track formation processes in InP and GaAs crystals irradiated with swift Bi and U ions to fluences in the range 5×1010-1×1012 cm−2 have been investigated by means of selective chemical etching (SCE), atomic force microscopy (AFM) and computer simulation. SCE data on the InP crystals show the formation of the two-layer system of tracks differing by the matrix disorder degree under the Bi ion irradiation. Transition from an individual track embedded in an unchanged solid (single tracks) to a modified solid (consisting of partial overlapping tracks) is observed at the fluence of 1×1012 Bi/cm2. Ion tracks in GaAs samples irradiated with U and Bi ions to the fluence of 5×1010 cm−2 were registered by means of AFM and SCE. The density of the tracks obtained from AFM data coincides well with the irradiation fluence. Fluence growth up to 1×1012 cm−2 leads to the annealing of the tracks formed in GaAs on the early stages of irradiation. The results of the computer simulation of the track formation processes in InP and GaAs crystals are also presented. Simulation was based on the modified thermal spike model, including thermal dependencies of thermophysical properties and containing no free parameters. Calculated diameters of molten regions near the surface of the crystal are 20.6 and 17.4 nm for InP and GaAs crystals, respectively, irradiated with 710 MeV Bi ions. The comparison of the calculation results with the experimental data has been made.