Trapping in Germanium and Silicon

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Abstract
Various analyses have been performed in the past for transient photoconductivity decay in the presence of trapping. One which is potentially of great use, performed by Baicker, yields both trap concentration and energy-level position from transient decay measurements performed at a single temperature. (With the usual analyses, temperature variation measurements are required to determine energy-level position.) Comparison between this and other analyses is performed, and criteria are developed to determine the validity of Baicker's solution. Several sets of data are presented, of which those for one trapping level meet the stated criteria, while the others do not. The discrepancy arises because of the use by Baicker of the condition of thermal equilibrium between the traps and the minority carrier band. The most interesting data presented are probably those for certain irradiated and unirradiated silicon samples which display trapping above room temperature, and show an apparent activation energy of ∼1.6 eV, substantially larger than the silicon bandgap. Such a strong dependence is partially explained using Baicker's analysis. Data for irradiated silicon and germanium are also given, including trap annealing for gamma-irradiated Sb-doped germanium.