Zeeman effect in the excitation spectra of shallow acceptors in germanium: experimental

The Zeeman splitting of the D and C lines in the excitation spectra of residual Al acceptors in ultra-pure germanium has been measured using photo-thermal ionisation spectroscopy. The field dependence of the splittings has been studied over the range 0.3-2.5 T, with the magnetic field parallel to the (001), (111) and (110) crystallographic directions. The earlier assignment of a doubly degenerate final state for the C-transition is shown to be inconsistent with the present high-resolution results. The assignment of both the D and C lines to Gamma 8 + to Gamma 8 - transitions is proposed, whereby the ground-state splitting is very small compared with the excited-state splittings at the magnetic field strengths used. From the observed line splittings accurate g-factors for the corresponding excited states are calculated: D-line: ' Gamma 8 - , r=-0.121 to 0.005, g' 1 =+8.4 to 0.4; C-line: 3 Gamma 8 - , r=-1/13 'exact', mod g' 1 mod =3.1+or-0.2. It is suggested that the observed quadratic Zeeman effect cannot be explained within a simple perturbation model, and should be compared with the results of an extensive numerical calculation allowing for many interacting states.