Absorption cross sections in the far-IR spectrum of elemental shallow donors and acceptors in germanium

The integrated absorption cross section of the main lines in the far-IR spectrum of the group-V donors Sb, P, and As and the group-III acceptors B, Al, Ga, and In in germanium has been determined for impurity densities in the range of 1012–1014 atoms/cm3. The cross sections and consequently the experimental oscillator strengths for transitions from the ground state, decrease gradually with increasing ground-state energy. In compensated samples the electric field due to the ionized impurities strongly affects the relative line strengths; neutralizing by band-gap illumination allows one to minimize the effect of the electric field and to observe simultaneously the majority and minority impurities, allowing one to calculate the compensation.