Chapter 5 Positron Annihilation Spectroscopy of Defects in Semiconductors

Abstract

This chapter discusses the positron annihilation spectroscopy of defects in semiconductors. There are many techniques to identify defects in semiconductors on an atomic scale. The role of positron annihilation is in its ability to detect vacancy-type defects. An energetic positron that has penetrated into a solid rapidly loses its energy and then lives a few hundred picoseconds in thermal equilibrium with the environment. The sensitivity of positron annihilation spectroscopy to vacancy-type defects is easy to understand. The free positron in a crystal lattice feels strong repulsion from positive ion cores. The main advantages of positron spectroscopy can be listed as follows: (1) the identification of vacancy-type defects is straightforward, (2) the technique is strongly supported by theory, because the annihilation characteristics can be calculated from first principles, and (3) positron annihilation can be applied to bulk crystals and thin layers of any electrical conduction type. The increase of the average positron lifetime under illumination indicates that some vacancies are converted to more efficient positron traps by capturing electrons.