Some regularities of ion-beam interactions with semiconductors

During the last few years, various regularities of ion interaction with crystals have been studied, and a number of effects, caused by the regular arrangement of the target atoms, have become apparent. It is interesting that a suitable interpretation of the observed crystal lattice effects can be produced on the basis of the perfect crystal. At first glance this is surprising, since it is known that ion bombardment causes radiation damage, thereby disturbing the regular arrangement of the lattice atoms. The success of the concept of the ideal crystal is determined by the fact that the conditions of many experiments permit rapid annealing of the defects caused by the ion bombardment. In order to prove this assumption, it was necessary to make measurements over a wide temperature range, including the annealing temperature. Semiconductor crystals are the most suitable materials, because their annealing temperatures are high enough. These temperatures are easily obtained and controlled under usual ion-bombardment conditions. Germanium and silicon monocrystalline targets were chosen. The targets were bombarded by 30-keV ions of the noble gases. The temperature range studied was from about 100 to 700 °C. The influence of temperature on the angular regularities of the secondary electron-emission coefficient and on the energy distributions of the scattered ions was investigated. Two strongly different types of ion–electron emission and of scattering regularities were established. At comparatively high temperatures, there are typical anisotropies of the secondary electron-emission coefficient and the "double"-scattering peaks in energy distributions, caused by regular arrangement of the target atoms. At lower temperatures, the normal polycrystalline dependences are observed, i.e., the secondary electron coefficient increases monotonically with increasing incident angle, and the "double"-scattering peak is smoothed out. It has been established that the dependences usually observed with polycrystals change sharply to those observed with single crystals within a small temperature range around the defect annealing temperature. Thus, the concept of the ideal crystal may be used for interpreting the results of ion interactions with crystals, provided the measurements are made at temperatures higher than the annealing temperature of the defects.