Thermal emission of trapped holes in thin SiO2 films

Distributed (∼1.4 eV) and discrete (<∼0.07 eV) hole traps have been detected in thermally grown, pure, thin SiO2 films using the thermally stimulated charge technique from 77 to 594 K. The distribution of hole traps has a U-shaped density of states with a minimum at about 0.7 eV above the SiO2 valence band edge and is attributed to the amorphous band-edge tail states from the SiO2 valence band. The discrete hole trap is located at 1.44±0.20 eV above the SiO2 valence band edge, which was attributed to the oxygen vacancy center. The experimental energy level is consistent with that calculated by Rudra and Fowler [Phys. Rev. B 35, 8223 (1987)] and by O’Reilly and Robertson [Phys. Rev. B 27, 3780 (1993)].