Fast Neutron Bombardment ofp-Type Germanium

Extensive studies of fast neutron bombardment effects in $p$-type Ge have been carried out. Analysis of the initial conductivity behavior indicates the introduction of three vacant states below the middle of the forbidden band: (1) an acceptor state 0.18 ev above the valence band, (2) an occupied (donor) state which acts as a hole trap with a depth of ∼0.07 ev, (3) a second low-lying donor which is a quite shallow hole trap. This distribution of energy levels is consistent with the Frenkel defect model of James and Lark-Horovitz. After prolonged bombardment or room temperature aging, the ionization energy of bombardment-produced acceptors moves to lower values, a behavior which has been attributed to a difference in annealing rate of interstitials and vacancies. The scattering mechanism for holes in bombarded specimens does not appear to be completely describable in terms of ionized impurity scattering. Moreover, the temperature dependence of hole mobility is quite different from electron mobility in bombarded specimens. Extensive bombardments in the range from - 165° to -90°C are described and complex relaxation effects observed on warming are discussed.