Far-Infrared Properties of Interacting Donors in Antimony -Doped Germanium

Absorption and photoconductivity of 337-mu m radiation in Sb-doped Ge with excess donor concentrations ranging from 1.2 x 10¹⁶ to 3.6 x 10¹⁷ cm^-3 have been investigated at liquid-He temperatures. The result suggests the existence of a "delocalized" excited state between the conduction band and the donor ground state which arises from the overlapping of donor wave functions.