Determination of Carrier Lifetime in Silicon Using an Ultra-thin Al2O3/SiO2 Dielectric Stack

This work investigates different Al2O3-based dielectric stacks for various applications, including surface passivation of solar cells and photodetectors, replacement of SiO2 gate dielectric in advanced MOSFETs. Ultra-thin Al2O3/SiO2 (3/2 nm) stacks were deposited on silicon by using different techniques. A reference sample with only a single dry-grown SiO2 layer (3 nm) was prepared for comparison purpose. The effective carrier lifetimes were measured by the contactless photoconductance decay method. The lowest surface recombination velocity was calculated to be 34 cm/s in the Al2O3/SiO2 stack. The negative fixed charge density in the stacks was extracted from C–V characteristics. Our results reveal that the effective carrier lifetimes depend on the stacks deposition techniques and conditions, and provide a guideline for optimization.