Selenium double donors in neutron transmutation doped, isotopically controlled germanium

Far infrared photoconductivity and absorption measurements were performed o n isotopically controlled Ge-76 samples that were neutron irradiated to pro d;ce Se-77 through double beta decay. The spectra exhibit ground state to b ound excited state transitions which place the first ionization level of Se at E-c-0.2688 eV. Hall effect measurements on compensated Ge:Se single cry stals yield the second ionization level in the lower half of the band gap a t E-nu+0.17 eV. Our experiments offer the first unambiguous identification of the deep donor level formed by single Se atoms on Ge lattice sites and v erify earlier findings. (C) 1998 Elsevier Science Ltd. All rights reserved.