Negative charge and charging dynamics in Al2O3 films on Si characterized by second-harmonic generation

Thin films of ${\text{Al}}_2{\text{O}}_3$ synthesized by atomic layer deposition provide an excellent level of interface passivation of crystalline silicon $\left(c\text{-Si}\right)$ after a postdeposition anneal. The ${\text{Al}}_2{\text{O}}_3$ passivation mechanism has been elucidated by contactless characterization of $c{\text{-Si}/\text{Al}}_2{\text{O}}_3$ interfaces by optical second-harmonic generation (SHG). SHG has revealed a negative fixed charge density in as-deposited ${\text{Al}}_2{\text{O}}_3$ on the order of ${10}^{11}{\text{cm}}^{-2}$ that increased to ${10}^{12}–{10}^{13}{\text{cm}}^{-2}$ upon anneal, causing effective field-effect passivation. In addition, multiple photon induced charge trapping dynamics suggest a reduction in recombination channels after anneal and indicate a $c{\text{-Si}/\text{Al}}_2{\text{O}}_3$ conduction band offset of $2.02\pm 0.04\text{eV}$ .