Charge transition level of GeP_b1 centers at interfaces of SiO₂/Ge_xSi_1−x/SiO₂ heterostructures investigated by positron annihilation spectroscopy

Abstract

In this work, we address the charge trapping properties of Ge dangling bond (DB) defects – GePb1 centers as typified by electron spin resonance spectroscopy (ESR) – found at the interfaces between condensation‐grown Si1−xGex (0.28 < x < 0.8) alloys and insulating SiO2. The ESR observation of singly‐occupied paramagnetic GePb1 centers, carried out at 4.3 K, is complemented by temperature‐dependent positron annihilation spectroscopy (PAS) in the Doppler broadening mode, which enables observation of the neutral‐to‐negative defect transitions as the temperature increases from 50 to 300 K. Through correlation of this re‐charging behavior with the temperature‐induced shift of the Fermi energy, the energy of the Ge DB −/0 transition in the Si0.27Ge0.73 alloy is inferred to be energetically distributed in a ∼0.1 eV interval above the top of the semiconductor valence band. This result refines previous estimates from capacitance–voltage measurements, thus providing independent affirmation that the energy levels of Ge DBs lie inside the band gap of the Si1−xGex alloys.

Si nanocrystals and nanocrystal interfaces studied by positron annihilation

“…As the atomic structures of Si and Ge are very similar, it is worth to note the studies by Madia et al 24,25 in which GeP b1 centers at interfaces of SiO 2 /Ge x Si 1-x /SiO 2 heterostructures were observed with PAS. A decrease in the positron trapping efficiency of these dangling bond defects was observed there with hydrogen passivation.…”