Efficient Photodetector Based on Sub-Bandgap Transition in Silicon-ITO Distributed-Heterojunctions

An efficient photodetector based on the sub-bandgap transition in Silicon-Indium Tin Oxide (ITO) distributed heterojunctions in form of a grating is demonstrated. The barrier height of 0.45 eV across n: Si - n: ITO heterojunction is sufficient to knock out the electrons to be photoexcited from ITO to Si for a wide wavelength around 1550 nm without using any plasmonic interaction.  The n: Si - n: ITO grating structure with high refractive index contrast provides enhanced light-matter interaction and improved absorption efficiency. A large amount of photoexcitation resulting from the distributed heterojunctions leads to an improved responsivity as compared to the single planar heterojunction. We report a responsivity of 0.28 A/W at 1550 nm wavelength in a sub-bandgap regime which is higher than that of photodetectors with metal/2D materials using plasmonic interactions. The responsivity remains acceptably high for a wide wavelength range of 1530 nm-1570 nm.