Gallium-related defects in <i>p</i> -type silicon irradiated with electrons and protons. Anisotropy of conductivity due to boron- and gallium-related defects in irradiated silicon

Abstract

Hall effect and conductivity measurements over a wide temperature range of 20–300 K are carried out on gallium-doped silicon subjected to 3.5 MeV electron and 15 MeV proton irradiation at room temperature. Electrical data obtained provide convincing evidence that impurity atoms are involved in interactions with intrinsic point defects during irradiation. As a result, heavy losses of the shallow acceptors in the irradiated samples are found. Then, to shed light on the electrical properties of the radiation-produced defects, these samples are subjected to annealing. Two kinds of defects, Ga–vacancy pairs and substitutional Ga−–interstitial Ga+ ion pairs, are earlier discussed in the literature. However, a new kind of Ga-related radiation defects that are electrically neutral in p-type materials makes its appearance as well. In fact, under our irradiation conditions, they turn out to be dominant and stable up to 450 °C. Interstitial Ga-related defects in the irradiated samples are believed to be responsible for the anisotropic effects observed for the hole mobility at cryogenic temperatures. Similar anisotropic effects are also observed in boron-doped silicon subjected to electron and proton irradiation. Some interesting peculiarities in the formation processes of interstitial Ga-related defects are discussed.