MeV ion damage in GaAs single crystals: Strain saturation and role of nuclear and electronic collisions in defect production

We have reported previously that the perpendicular strain produced in the surface layer (several μm thick) of GaAs(100) crystals under MeV ion irradiation saturates at ∼0.4% regardless of the doping of the specimen, and that the parallel strain is zero within the experimental error. In this paper, the perpendicular strain in GaAs(111) and GaAs(110) crystals is reported to saturate at ∼0.3%. The ionization-induced spontaneous defect recovery is discussed in terms of the activation-energy lowering of the higher-charge-state interstitials. We suggest that inner-shell vacancies which decay by an Auger process may induce most effective self-annealing of defects created by nuclear collisions. We present an ion-lattice single-collision model which describes the production and saturation of the primary defects (interstitial, vacancy, and antisite defect) in GaAs under MeV ion or MeV electron irradiation. The model also shows that at low beam dose the concentration of interstitials and vacancies increases linearly with the product of stopping power and beam dose and is independent of the electronic stopping power. The antisite defect concentration increases initially as the square of the nuclear stopping power times the beam dose, and depends upon the electronic stopping power. The strain measured as a function of beam dose and stopping powers suggests that the strain in the room-temperature irradiated GaAs is controlled by the antisite defects