Electrical properties of atomic layer deposited Al2O3 with anneal temperature for surface passivation

• Electrical properties of atomic layer deposited Al2O3 vary with anneal temperature.
• Trapped charges in Al2O3 are distinguished by constant voltage stress techniques.
• Positive flatband voltage shifts due to negative charge tunneling are observed.
• Interface density is not useful in predicting recombination after corona charging.

The electrical characteristics of Al2O3 layers prepared by the atomic layer deposition technique using O3, H2O, and plasma O2, as oxidants are investigated through capacitance–voltage measurements of metal–insulator–semiconductor capacitors. Particular emphasis is placed on the properties of thermal annealed Al2O3 for surface passivation. Capacitance measurements at flatband voltage before and after the application of constant voltage stress in the inversion regime indicate that the charge trapping and hysteresis behavior of the capacitors are more dominant at low temperature annealing. Positive flatband voltage shifts due to negative charge tunneling are also observed under both negative and positive bias voltage polarities. The interface trap densities of O3 and plasma O2-based Al2O3 samples at 450 °C decrease by an order of magnitude with increasing annealing temperature, approaching the interface trap density levels in the 1011 eV− 1 cm− 2 range. However, H2O-based Al2O3 doesn't change considerably. The interface trap density distribution shows that H2O-based Al2O3/Si annealed over 400 °C has depassivated defects, similar to those observed in SiO2/Si interfaces. A comparison of the emitter saturation current density and the interface defect density shows that the interface density at the midgap is not so useful in predicting interface recombination after corona charging.