Radiation-produced defects in germanium: experimental data and models of defects

The problem of radiation-produced defects in $n$-Ge before and after $n\to p$ conversion is discussed in the light of electrical data obtained by means of Hall effect measurements as well as Deep Level Transient Spectroscopy. The picture of the dominant radiation defects in irradiated $n$-Ge before $n\to p$ conversion appears to be complicated, since they turn out to be neutral in $n$-type material and unobserved in the electrical measurements. It is argued that radiation-produced acceptors at $\approx E_{C}$-0.2 eV previously ascribed to vacancy-donor pairs ($E$-centers) play a minor role in the defect formation processes under irradiation. Acceptor defects at $\approx E_{V}$+0.1 eV are absolutely dominating in irradiated $n$-Ge after $n\to p$ conversion. All the radiation defects under consideration were found to be dependent on the chemical group-$V$ impurities. Together with this, they are concluded to be vacancy-related, as evidenced positron annihilation experiments. A detailed consideration of experimental data on irradiated $n$-Ge shows that the present model of radiation-produced defects adopted in literature should be reconsidered.