The use of the electron accelerator in solid state physics

Abstract

Abstract Among the many processes by which electrons in the energy range 300 keV to 3 MeV interact with matter, two are important for the physics of crystalline solids: ionization and nuclear recoils. The processes and their secondary effects are reviewed. Examples are given of their importance: 1. 1. The ionization creates in semiconductors electron-hole pairs in large excess; these extra carriers relax, their recombination laws are studied by various means, such as “electron-voltaic” effect, excess conductivity decay, emission and decay of fluorescent light. 2. 2. The nuclear recoils are the cause of radiation damage in most materials. The energy transfer in an electron collision is small, and the incident electron energy has to be greater than a certain threshold to produce permanent displacements, thus creating lattice defects. In electron irradiation these defects are simple point defects (vacancies and interstitials at low temperature, which can combine into simple associations by warming). Electron irradiation can then be used to obtain knowledge of interatomic forces to test the laws of displacement of atoms by radiation, or to introduce in a crystal point defects in a controllable way. Examples are given such as measurement of threshold in metals, and study of lifetime in semiconductors. A curious phenomenon is the failure of the reciprocity law: the magnitude of damage in germanium is dependent not only on the total dose, but also on the dose rate. Some emphasis is put on the experimental requirements for electron irradiation of solids: energy and intensity stability, beam steering and controlling, large range of beam currents, including pulsed operation. The design and mounting of samples are also discussed, specially for low temperature irradiation.