Ultra-Sensitive Cubic-ITO/Silicon Photodiode via Interface Engineering of Native SiO_x and Lattice-Strain-Assisted Atomic Oxidation

A highly orientated cubic indium tin oxide (c-ITO)/native SiO_x/n-Si Schottky photodiode with negligible electronic noise is demonstrated. This extraordinary property is achieved via simple interface engineering, which combines native SiO_x, facile air-annealing, and the resulting ITO-lattice-strain-assisted oxidation of proximal underlying Si atoms. An exceptionally well-passivated ITO/n-Si interface is realized, which leads to a heretofore unreported single-atom-thin inversion layer observed via transmission electron microscopy imaging. The device exhibits a record-low dark current density of ≈3 × 10^–8 A cm^–2 at −5 V, a tenfold reduction over the lowest reported value. Additional excellent optoelectronic properties achieved include self-powered operation, high quantum efficiency, fast time response, and ultra-high sensitivity for low illumination signals. Interface characterization reveals that ITO-lattice relaxation and oxygen diffusion during annealing create a highly ordered c-ITO crystal and an extended ≈2.2 nm SiO_x interlayer formed via atomic oxidation of the underlying pristine Si, thus rendering a high-quality interface. Moreover, the Schottky barrier is further enhanced by the presence of negatively charged sub-stoichiometric silicon oxide interlayer. These results bring forth new insights in the surface atomic oxidation process and the significance of natively grown SiO_x which together contribute to the realization of economic highly sensitive photodetectors.