Field-effect passivation of Si by ALD-Al2O3: Second harmonic generation monitoring and simulation

This paper investigates the ability of second harmonic generation (SHG) to probe the passivation quality of atomic layer deposited Al2O3 on Si by estimating the induced interface electric field due to fixed charges in the oxide. Samples with various oxide charges (Qox) and interface state densities (Dit) were fabricated, using different deposition parameters. The samples were characterized by capacitance-voltage (C-V) and microwave photoconductance decay measurements in order to evaluate Qox and Dit, as well as the effective minority carrier lifetime τeff. The SHG results were consistent with Qox, Dit, and τeff values, proving the ability of the technique to monitor the interfacial quality in a contactless and non-destructive way. Optical simulations which use the electric field values obtained from the C-V measurements could reproduce the measured SHG signal. This demonstrates that SHG coupled with optical simulation can give access to the electric field magnitude and thus characterize the electrical properties of oxide/Si interfaces.