Unique Hyperspectral Response Design Enabled by Periodic Surface Textures in Photodiodes

The applications
of hyperspectral imaging across disciplines such
as healthcare, automobiles, forensics, and astronomy are constrained
by the requirement for intricate filters and dispersion lenses. By
utilization of devices with engineered spectral responses and advanced
signal processing techniques, the spectral imaging process can be
made more approachable across various fields. We propose a spectral
response design method employing photon-trapping surface textures
(PTSTs), which eliminates the necessity for external diffraction optics
and facilitates system miniaturization. We have developed an analytical
model to calculate electromagnetic wave coupling using the effective
refractive index of silicon in the presence of PTST. We have extensively
validated the model against simulations and experimental data, ensuring
the accuracy of our predictions. We observe a strong linear relationship
between the peak coupling wavelength and the PTST period along with
a moderate proportional relation to the PTST diameters. Additionally,
we identify a significant correlation between inter-PTST spacing and
wave propagation modes. The experimental validation of the model is
conducted using PTST-equipped photodiodes fabricated through complementary
metal-oxide-semiconductor-compatible processes. Further, we demonstrate
the electrical and optical performance of these PTST-equipped photodiodes
to show high speed (response time: 27 ps), high gain (multiplication
gain, M: 90), and a low operating voltage (breakdown
voltage: ∼ 8.0 V). Last, we utilize the distinctive response
of the fabricated PTST-equipped photodiode to simulate hyperspectral
imaging, providing a proof of principle. These findings are crucial
for the progression of on-chip integration of high-performance spectrometers,
guaranteeing real-time data manipulation, and cost-effective production
of hyperspectral imaging systems.