Localized energy levels generated in Magnetic Czochralski silicon by proton irradiation and their influence on the sign of space charge density

Abstract

The microscopic damage produced in diodes made of n-type Magnetic Czochralski (MCz) silicon by 24 GeV and 26 MeV protons, up to the fluence of 1.3 × 10 15 cm - 2 1 MeV equivalent neutrons, has been investigated and results are compared to the damage produced in devices made of standard Floating Zone (STFZ) silicon. It is found by means of Thermally Stimulated Currents (TSC) that the production of a radiation induced charged defect is enhanced in MCz, and might be in part responsible for the differences observed in the two materials at room temperature. The influence of defects on the sign of the space charge density has been studied by current transients at constant temperature i ( T , t ) and by Transient Current Technique (TCT). Type inversion is not revealed up to the highest investigated fluence. Full depletion voltage V dep measurements versus fluence exhibits a minimum close to 2 × 10 14 cm - 2 1 MeV equivalent neutrons; at the same fluence, V dep measured as a function of annealing time changes its initial slope from positive to negative. It is shown by numerical simulations that these features can be accounted by the formation of a double junction, even in absence of type inversion.