Origin of a Shallow Acceptor in Quenched Germanium

The origin of a quenched-in shallow acceptor (SA), a t E, + 9 meV is studied by investigating the effect of copper and iron dopings via their diffusion on the density of this acceptor. Hall-effect measurements are done in the range 5 to 150 K to determine the energy and density of the SA, level. A defect pair model consisting of mobile and immobile constituents is proposed for the SA, acceptor. The iron interstitial as the mobile constituent suggested recently by Broeckx et al. is not favored by the present doping experiments. Neither is a vacancy plausible in view of the authors recent electron-irradiation experiments. It is likely due to another unknown interstitial impurity. The immobile constituent, which is left behind when the SA, acceptor disappeared at 320 °C, has an acceptor level near E, + 40 meV. It is very probably attributable to substitutional copper as suggested by Broeckx et al., but the other possibility that it is due to any other impurity or defect giving rise to a similar acceptor level is still remaining.