Electron capture kinetics at AlF3/SiO2 interfaces

Charge deep-level transient spectroscopy (Q-DLTS) was applied to study the mechanism of capturing electrons at the AlF3/SiO2 interfaces of AlF3-coated oxidized p-type Si. The process may be viewed as comprising three consecutive steps: (i) formation of an inversion layer in p-Si; (ii) electron tunneling through the ultra-thin SiO2 interlayer; and (iii) capture of electrons at F-vacancies in AlF3 after surmounting a potential barrier Eb. A semi-empirical model of non-exponential kinetics of the charge transients has been developed and compared with experiment. Three discrete electron traps of a quasi-discrete spectrum of traps in AlF3 could be resolved. The thermal activation energy of a Q-DLTS peak (0.6-0.7 eV) seems to reflect Eb, while the full-width at half-maximum (FWHM) corresponds to thermal activation of minority carriers over the band gap of p-Si (∼1.1 eV). Coulomb-blockade effects may be responsible for the temperature dependence of the capture cross-section σn=σn0 exp(-Eb/kT)