Molecular Dynamics Simulations and Experimental Evidence for Deep Penetration by Channeled Ions During Low-Energy Ion Bombardment of III-V Semiconductors

Molecular dynamics simulations are used to investigate the formation of deep crystalline damage during the low-energy ion bombardment of semiconductor crystals. The trajectories of primary ions are calculated as they propagated through a model crystal lattice. Energy losses by nuclear recoil and and by electronic excitation are included. For beams of heavy ions at energies below 1 keV, the average penetration range of the simulated trajectories is only a few nanometers. However, a small, but, significant fraction of the ions are found to scatter into <011= axial channels through which they propagate tens of nm below the surface. This effect is used to explain high-resolution secondary ion mass spectrometry and photoluminescence data which reveal deep ion penetration and optical damage on the same length scale. Our results suggest that unintentional ion channeling is a major factor in the extensive degradation of optical and electrical properties of semiconductor surfaces which are exposed to low energy ion bombardment during device fabrication.