Interface State Density Profiles Research Articles

Interface Characteristics of Metal‐Oxide‐Semiconductor Capacitors with Ultrathin Oxides

MOS structures were fabricated on single‐crystal as well as polycrystalline silicon. Oxidation was carried out in dry oxygen at 1000 and 1100°C. No annealing was performed either after oxidation or after metallization. The oxide thickness ranged between 35 and 490 Å. Admittance‐voltage‐frequency measurements were made on a large number of nonleaky structures to obtain the interface charge density at flatband and the interface state density vs. bandgap energy profile. As the oxide thickness increased, both the interface state density and the flatband interface charge density first decreased and then went through a maximum. The oxidation rate was also found to undergo a changeover at the same value of the oxide thickness. The observed correlation between the oxidation rate and the interface defects underscores the need to take into account the influence of the interface charge density and the built‐in interfacial potential, while formulating a model for the oxidation kinetics of the initial phase.

An investigation of optically activated Si—SiO2interface states in metal-oxide-silicon structures

Transparent gate structures were fabricated by electron-beam evaporation of Sn-doped In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> on oxidized p-Si substrates. The samples were oxidized at 1100°C in dry oxygen. No post-oxidation or post-electrode-deposition annealing was carried out. Admittance-voltage-frequency measurements were made under optical illumination. Interface state density distributions and hole and electron capture cross sections were obtained using the recently developed optical metal-oxide-semiconductor admittance technique. The experimental interface state density profile contained two peaked distributions, one near the valence band edge E <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</inf> , and the other near the conduction band edge E <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , Overlying a concave background. The peak near E <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> was sharper and the peak density was higher than in the Case of the peak near E <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</inf> . The capture cross section versus bandgap energy profile also displayed a peaked distribution for interface states under each of the peaks. With increasing illumination, the state density at the peak increased, the peak energy location moved closer to the respective band edge, and the capture cross section decreased. The experimental results show the presence of defects at unpassivated Si-SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> interfaces, which exchange electrons/holes with the silicon bands under illumination.

Dependence of Si-SiO2 interface state density on oxide thickness in structures with ultrathin (79–227 Å) oxides

Admittance voltage characteristics of Si/79–227 Å SiO2/metal structures were measured in dark and under optical illumination in the frequency range of 30 Hz–100 kHz. For fabricating the structures, thermal oxidation was carried out in dry oxygen at 900 °C at 1 atm. The interface state versus band-gap energy profiles of the unannealed samples exhibited peaked distributions near the valence and conductance-band edges, overlying a concave background. The interface state density versus oxide thickness profile was observed to go through a minimum and a maximum instead of decreasing in a monotonic fashion.