Radiation-Induced Recombination Centers in Germanium

Abstract

An attempt has been made to provide a better understanding of minority carrier recombination processes in irradiated germanium. To this end, studies have been made of the minority carrier lifetime of both n‐ and p‐type material, following fast neutron and Co⁶⁰ γ irradiations. The effect of carrier concentration and temperature has been determined. The primary conclusion drawn from these investigations is that the recombination process is associated with an energy level located 0.20 ev below the bottom of the conduction band. From measurements of the lifetime in n‐type specimens, the hole capture cross section has been calculated and found to be σ_p=3×10⁻¹⁵ cm² and σ_p=4×10⁻¹⁶ cm² for neutron and γ‐induced centers, respectively. If a second, lower lying level is associated with the second ionization of the defect responsible for recombination, then the effective number of recombination centers is reduced in p‐type material as the Fermi level approaches the valence band, due to this ionization. Such a process is in qualitative agreement with the observed data.