Fast-Neutron Bombardment ofn-Type Ge

The effect of fast-neutron bombardment on the electrical properties of $n$-type Ge has been extensively studied by a variety of experiments. The initial rate of carrier removal, the shape of the bombardment curve, and the temperature dependence of electron concentration in bombarded specimens all indicate the production of two vacant states, one located below the middle of the forbidden energy band and the other located ∼0.2 ev below the conduction band. These two vacant states are consistent with predictions of the model of James and Lark-Horovitz. Studies of mobility reveal that the additional scattering associated with bombardment-induced lattice disorder is more complex than charged impurity scattering in that it exhibits a much greater temperature dependence and is markedly dependent on electron concentration. Low-temperature exposure and subsequent warming experiments indicate that appreciable photoconductivity associated with minority-carrier trapping results from fast-neutron bombardment. The important minority-carrier traps appear to anneal during warming below room temperature.