Nature of Bombardment Damage and Energy Levels in Semiconductors

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Abstract
The different effects of Co60 gamma ray and fast neutron bombardment on the electrical behavior of germanium are discussed in terms of different local distributions of lattice defects expected for these two types of radiation. For the first of these, which is expected to introduce randomly distributed pairs of interstitials and vacancies, the state at 0.20 ev below the conduction band has been found to increase the concentration of ionized scattering centers on becoming occupied with conduction electrons. This state has been ascribed to a mobile interstitial because of its annealing behavior at moderate temperatures. Energy levels in p‐type Ge and their annealing behavior are also discussed. In neutron irradiated n‐type germanium the behavior of Hall mobility and the apparent energy distribution of defect levels are discussed in terms of a tentative model for the potential distribution around regions of high local lattice disorder expected to result from neutron bombardment. This model postulates that the disordered region is p type and is surrounded by a positive space charge region in the n‐type matrix which insulates it from the matrix. This configuration of electrostatic potential around the disordered region in effect produces an insulating region whose radius is ∼10 times that of the disordered region itself. The behavior of Hall mobility in irradiated n‐type specimens is consistent with the predictions of this model.

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