Identification of bandgap states in semiconductors by transmutation of implanted radioactive tracers

Bandgap levels in semiconductors are frequently detected and characterized by spectroscopic techniques that reveal their electronic or optical properties, but not the chemical identity of the observed defect. This problem is overcome by using radioactive isotopes to create bandgap states and by repealing the measurements during the elemental transmutation: Defects containing the parent isotope of the decay will vanish on a well defined timescale given by the nuclear half life and correspondingly daughter element related defects will arise. Thus a definite chemical identification of the observed bandgap states is possible. The key to this kind of experiments is the doping with radioactive isotopes, The paper compares the techniques used up to now and presents some experiments by various authors to illustrate this kind of 'radiotracer spectroscopy'. In greater detail, radiotracer experiments on recoil implanted radioisotopes (Se-75, V-48, Cr-51) in silicon and SIC are described. The bandgap levels of these elements are identified.