Decay Features of Positrons in Semiconductors

Positron lifetime measurements in some typical semiconductors are reported. In every case the decay displays two components, the longer one being of the order of ${\tau }_2={10}^{-9\mathrm{}}$ sec and having an intensity of a few percent. Measurements on neutron-damaged samples show that both components are sensitive to the presence of lattice defects. Moreover, at least in the case of silicon, the long-lifetime component is lacking when a high electric field is applied to the sample. Also, the presence of a high oxygen concentration in gallium arsenide and in silicon is effective in preventing annihilations through the ${\tau }_2$ lifetime.