Investigation of Energy Levels of Small Vacancy Clusters in Proton Irradiated Silicon by Laplace Photoinduced Transient Spectroscopy

Laplace photoinduced transient spectroscopy has been applied to determine the electronic properties and concentrations of deep traps in high purity n-type silicon irradiated with high fluences of 23-MeV protons. From the temperature dependence of thermal emission rates of excess charge carriers obtained by the analysis of the photocurrent relaxation waveforms measured at temperatures of 30-320 K, eight deep traps with activation energies ranging from 255 to 559 meV have been resolved. The dependence of these trap's concentrations on the proton fluence are demonstrated for the fluence values ranging from 1 x 10(14) to 5 x 10(15) n(eq)/cm(2). In comparison to the previously reported results of theoretical and experimental studies on the electronic properties of small vacancy clusters in irradiated silicon, we tentatively attribute four detected traps with activation energies of 255, 367, 405, and 512 meV to the energy levels related to the 2-/- charge state changes of divacancy (V-2), trivacancy (V-3), tetravacancy (V-4), and pentavacancy (V-5), respectively. Simultaneously, we propose the attribution of four deep traps with higher activation energies of 415, 456, 526, and 559 meV to the energy levels related to the -/0 charge state changes of these small vacancy clusters, respectively.