Measurement of the positron lifetime in oxide semiconductors with different concentration of impurities

The effect of the Ni3+ ion concentration on Al2O3 surface on the mechanism of positron annihilation has been investigated, ions being the centers of intensive oxidation of positrons. The lifetimes of positrons in a matter have been measured to get quantitative and qualitative estimates of positron annihilation mechanisms by the delayed coincidence method. Presented is a brief description of a measuring device with the time resolution of 10-9 s and the operating range of 10-7 s. The results of processing the delayed coincidence spectra in the NiO-Al2O3 complex system with concentration of NiO impurity from 0.02 to 3.0 μ molexm-2 are presented. The analysis of the data obtained shows that in the NiO concentration range of 0.02-0.3 μmolexm-2 a dominating production of orthopositronium atoms proceeds in surface layers of Al2O3. At the concentration of about 0.3 μmolexm-2 all the surface of Al2O3 is coated with a Ni2O3 monolayer, and therefore the greater part of orthopositronium atoms undergoes oxidation. In the concentration range of 1.0-3.0 μmolexm-2 the dominating production of orthpositronium atoms proceeds in Ni2O3 polylayers with a loose structure