Direct determination of impact-parameter-dependent stopping powers for million-electron-volt He ions penetrating Er-doped GaAs.

Abstract

We have directly determined the impact-parameter-dependent stopping powers for 2.0- and 2.5-MeV He ions passing through GaAs single crystals. The points reside in the preparation of the single-crystal sample with a dopant of a heavy element located in some definite interstitial site at definite depth and in synthesis of a Monte Carlo program to simulate accurately the ion trajectories. Er-doped homoepitaxial GaAs layers grown by molecular-beam epitaxy and by metal-organic chemical-vapor deposition were used for this purpose. As previously reported, fine single-crystal clusters of ErAs are formed in the GaAs host and Er takes the position exactly equivalent to the tetrahedral interstitial site. The present Monte Carlo simulation has revealed the fact that some definite impact-parameter region dominates the backscattering Er peak position and this region shifts continuously by tilting the incident beam axis slightly from a major crystal axis. The results obtained are compared with the Oen-Robinson [Nucl. Instrum. Methods 132, 647 (1976)] model and other theoretical predictions and clearly show that inner-shell excitations and ionizations contribute significantly to the stopping power even for large impact parameters. \textcopyright{} 1996 The American Physical Society.