Characterization of materials for semiconductor devices by means of positron annihilation - Vacancy-type defects in metals, insulators, and semiconductors -

by Prof. Akira Uedono (University of Tsukuba · School of Science and Engineering)

Monday 9 Jul 2018, 14:30 → 15:30 Europe/Berlin

HS 3 (Physics Department)

A positron is an antiparticle of electron. It can be obtained by radio isotopes and pair production from high energy photons. Positrons can be used to a non-destructive probe for investigating defects in materials. Because of its high sensitivity for vacancy-type defects, this technique has been used for studies of materials for semiconductor devices.

When a positron is implanted into solids, it annihilates with an electron and emits two γ-quanta. The energy distribution of the γ-rays is broadened by the momentum component of the annihilating electron-positron pair. A freely diffusing positron may be localized in a vacancy because of Coulomb repulsion from charged ion cores. Because the momentum distribution of the electrons in the defects differs from that of electrons in the bulk material, these defects can be detected by measuring the energy distribution of the annihilation radiation. Because the electron density in vacancies is lower than that in the bulk, the positron lifetime increases in vacancies. Thus, measurements of positron lifetime spectra are also used to detect the defects. In this seminar, applications of positron annihilation to studies of electroplated metals, low dielectric insulators, and wide gap semiconductors will be presented.