Copper in Germanium: Recombination Center and Trapping Center

Abstract

The time-dependent photoconductivity of copper-doped $n$-type and $p$-type germanium bridges has been measured between 130°K and 293°K. Temporary hole traps were found in the $n$-type samples at the lower temperatures but no traps were observed in the $p$ type. Trap concentrations agreed with the density of copper atoms to within a factor of two and were at least 100 times higher than undoped crystals. The trappings levels are 0.2 ev above the valence band; the capture cross section for holes, ${\sigma }_p$, is ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ and independent of temperature while the capture cross section for electrons, ${\sigma }_n$, is temperature-dependent with an activation energy greater than 0.1 ev. As a result of this temperature dependence of ${\sigma }_n$, the 0.2-ev copper level changes from a recombination center at room temperature to a hole trap at lower temperatures.