Effect of high electronic energy deposition in semiconductors

Abstract

Track formation due to high electronic energy deposition during swift heavy ion irradiation is well known in insulating materials as well as in some intermetallic compounds and metals. In semiconductors the physical situation was much less clear, and only during the last few years several experimental results on the effect of high electronic energy deposition were published, which are summarised and discussed in the present paper. Like in insulators, swift heavy ion irradiation may cause amorphous tracks in some semiconductors, such as InP, InSb, InAs, GaSb and Ge, if a certain value of the electronic energy deposition ε e per ion and unit length characteristic for the material and the ion is exceeded. The critical values of ε e are much higher than in the other materials, and the corresponding ion energies are close to the maximum ion energies available with the existing high energy accelerators. On the other hand, with cluster ions, as e.g. C 60, tracks are easily formed in Si, Ge and GaAs with ion energies of several tens of MeV. Beside damage and track formation, annealing of damage was observed in the semiconductors, and it can be concluded that the effect of high electronic energy deposition represents itself as a competition between damage formation and annealing. Which of the two processes dominates is mainly determined by the electronic energy deposition. Qualitatively the observed behaviour can be explained in the framework of the thermal spike model. However, a quantitative description of all data available is not successful in the framework of this concept. This is obviously due to the fact that the effects are influenced not only by the electronic energy deposition, but also by a variety of other parameters, such as the ion velocity, the ion mass, the charge state of the impinging ions and the radial distribution of the electronic energy around the ions' path. All these parameters have to be taken into account within a theoretical description. However, the present situation is characterised by a lack of sufficient experimental data, and further systematic work is required to make progress in this interesting field.