Silicon (Si) photodiodes play a crucial role in complementary metal-oxide-semiconductor (CMOS) image sensors, particularly in visible cameras, and are increasingly in demand for infrared or short-wavelength (SWIR) cameras in modern autonomous vehicles operating under various weather conditions. However, the bandgap energy of 1.12eV in Si limits its capability to detect light in the infrared range, only allowing visible light detection. In this study, we propose transparent, quantum-thickness, Schottky-junction photodiodes on Si for light detection from visible to SWIR wavelengths. We employ an atomically thin TiO2 interfacial layer between an n-type Si substrate and a nanometer-thick metallic layer, which is positioned beneath a transparent conductive oxide (TCO) layer, to create n-Si/TiO2/TiN/ITO multilayered Schottky-junction photodiodes. Without the typical p-n junction in Si, we observed photocurrents through interband transitions by incident photons in the wavelength range of 400 ~ 1,100nm. Additionally, small but noticeable amounts of photocurrent were also measured by internal photoemission (IPE) via hot carrier generation even at the wavelength of 1,310nm. The embedded TiO2 layer significantly reduced dark current by two orders of magnitude with little change in photocurrent or quantum efficiency. This can be attributed to the low conduction band offset of the TiO2 semiconductor, which contributes to a quantum tunneling barrier without changing the Schottky barrier height and disturbing the internal photoemission process.
Biomolecular detection using Localized Surface Plasmon Resonances (LSPR) has been extensively investigated
because these techniques enable label-free detection. The high-density metal nanopatterns with tunable LSPR
characteristics have been used as refractive index sensing because LSPR property is highly sensitive to refractive index
change of surroundings. Meanwhile, Colloidal lithography is a robust method for fabricating regularly ordered
nanostructures in a controlled and reproducible way using spontaneous assembly of colloidal particles. In this study,
nanopatterns on UV-curable polymer were prepared via colloidal lithography. Then, metallic nanograil arrays with high
density were fabricated by sputtering noble metals such as gold and subsequent removal of residual polymers and
colloidal particles. From Finite-Difference Time-Domain Method (FDTD) simulations and reflectance spectra, we found
that multiple dipolar plasmon modes were induced by gold nanograil arrays and each mode was closely related with
structural parameters. LSPR characteristics of gold nanograil arrays could be tuned by varying the fabrication conditions
to obtain optimal structures for LSPR sensing. Sensing behavior of gold nanograil arrays was tested by applying various
solvents with different refractive indices and measuring the variations of LSPR dips. Finally, gold nanograil arrays as
LSPR sensors were integrated in optofluidic devices and used to achieve real-time label-free monitoring of biomolecules.
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