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Behavior of the Si/SiO2 interface observed by Fowler-Nordheim tunneling

Thin-oxide (40-50 A) metal oxide semiconductor (MOS) structures are shown to exhibit, before large levels of electron tunnel injection, the near-ideal behavior predicted for a uniform trapezoidal barrier with thick-oxide properties. The oscillatory field dependence caused by electron-wave interference at the Si/SiO2 interface suggests an abrupt, one-monolayer barrier transition (approximately 2.5 A) consistent with earlier work. After tunnel injection of 10 to the 17th - 5 x 10 to the 18th electrons/sq cm, the barrier undergoes appreciable degradation, leading to enhanced tunneling conductance. Reproducible behavior is observed among different samples. This effect is found to be consistent with the generation of positive states in the region of the oxide near the Si/SiO2 interface (less than 20 A), where the tunneling electrons emerge into the oxide conduction band.

Maserjian, J.↗

Oscillations in MOS tunneling

Oscillatory deviations from Fowler-Nordheim tunneling currents were measured in MOS capacitors with oxide thicknesses ranging from 30 to 75 A. The observed variation of oscillation phases and amplitudes with oxide thickness indicates that the Si-SiO2 interface is independent of oxide thickness only for thicknesses greater than 65 A. At lower thicknesses, the barrier height at the interface decreases gradually with oxide thickness at a rate on the order of 10 mV/A. At higher thicknesses, the barrier height is 4.08 eV. The energy dispersion relation with the SiO2 conduction band is parabolic. The mean free path within the SiO2 conduction band is on the order of 13 A.

Lewicki, G.↗

Tunneling in thin MOS structures

Recent results on tunneling in thin MOS structures are described. Thermally grown SiO2 films in the thickness range of 22-40 A have been shown to be effectively uniform on an atomic scale and exhibit an extremely abrupt oxide-silicon interface. Resonant reflections are observed at this interface for Fowler-Nordheim tunneling and are shown to agree with the exact theory for a trapezoidal barrier. Tunneling at lower fields is consistent with elastic tunneling into the silicon direct conduction band and, at still lower fields, inelastic tunneling into the indirect conduction band. Approximate dispersion relations are obtained over portions of the silicon-dioxide energy gap and conduction band.

Maserjian, J.↗