High resolution photoconductivity studies of residual shallow donors in ultrapure Ge

High resolution photoconductivity studies of residual shallow donors in ultrapure (n = 2 x 10¹⁰cm^-3) germanium have revealed absorption corresponding to transitions to higher lying levels not previously observed because of spectrometer limitations and/or line broadening due to impurity-impurity interactions. In this paper we list the results of our studies of four residual donors in high purity material, compare these results with a theoretical calculation for higher lying energy level spacings, and examine the temperature dependence of the two step photothermal photoconductivity process.