HIGH-ENERGY ION IRRADIATION OF GERMANIUM

Irradiations of n- and p-doped germanium samples have been performed at room temperature at GANIL (Caen) using Ar (1415 MeV), Xe (5510 MeV and 751 MeV), Ca (272 MeV), Zn (691 MeV), O (195 MeV) and Kr (427 MeV) ions. The sample resistance and Hall mobility were measured in situ as a function of the ion fluence. In p-Ge samples the conductivity and the majority carrier density steadily increase up to the maximum fluences used (about 10(12) cm-2). The conductivity-sigma of n-Ge samples first decreases. reaches a minimum at a fluence depending on the initial doping concentration and then increases. At the minimum value of sigma, Hall measurements show a transition from n- to p-type conductivity. These results show that acceptor energy levels are created by irradiation induced defects. At low electronic stopping power values. the creation rate of acceptor levels is approximately a linear function of the calculated number of displacements per atom. This linear dependence becomes invalid at high electronic stopping power values. This last result could be explained by assuming a partial annealing of the defects for the largest electronic stopping power.