EVALUATION OF ATOMIC DISPLACEMENT IN ION-IMPLANTED GAAS

A Monte Carlo channeling simulation code is applied to defect structur e analysis in weakly damaged [111] GaAs single crystals. Implantation of swift ions (i.e. 325 keV N) into GaAs leads to the formation of def ects consisting mainly of atoms displaced by a certain distance from t heir lattice sites. By means of an analytical method it is possible to evaluate the atomic displacement distance perpendicular to an atomic row and the concentration of displaced atoms from the RBS spectra meas ured at different temperatures. Following this idea Monte Carlo simula tions were performed for crystals with different atom displacements an d defect concentrations for the temperatures 105 K and 295 K. For each defect structure a characteristic pair of channeling spectra was obta ined. The results of simulations are compared with channeling spectra measured at 105 K and 295 K at [111] GaAs single crystals implanted wi th 60 keV H+ ions (dose 3 x 10(16) cm-2). From the experimental result s the existence of heavily displaced atoms could be concluded. The com parison with the Monte Carlo simulations shows that lattice atoms in H + implanted GaAs are displaced to distances in the range from 0.4 up t o 0.7 angstrom.