Ultrafast Metasurface-Integrated Pyroelectric Photodetectors

Abstract

Pyroelectric photodetectors offer robust detection mechanisms for infrared and thermalradiation. However, conventional designs suffer from intrinsically slow response times (mi- crosecond to millisecond scale) and a lack of spectral selectivity, limiting their applicability in high-speed optical systems and spectrally discriminative sensing applications. To address these critical challenges, this dissertation introduces an innovative class of ultrafast, compact, and spectrally selective pyroelectric photodetectors enabled by the in- tegration of plasmonic metasurface absorbers with thin-film pyroelectric materials. Specif- ically, metasurfaces—two-dimensional arrays of engineered plasmonic nanostructures—are meticulously designed to achieve near-perfect absorption at targeted near-infrared wave- lengths, converting incident photons to heat on femtosecond timescales. These metasur- faces are combined intimately with an aluminum nitride (AlN) thin film, which generates measurable electrical currents in response to transient temperature changes induced by pho- tothermal conversion. The metasurface’s tailored nanogap cavity structure ensures strong spectral selectivity and efficient local heating. Simultaneously, careful electrical and ther- mal engineering of the device structure reduces RC time delays, enhancing the temporal response. Leveraging this integrated metasurface-pyroelectric platform, the developed devices achieve unprecedented performance metrics for thermal photodetectors, including a record- high 3dB bandwidth of up to 2.8 GHz, rise time ~125 ps assuming an ideal low pass filter, a nearly thousand-fold improvement over conventional pyroelectric detectors. This remarkable speed improvement effectively narrows the performance gap traditionally ex- isting between thermal detectors and semiconductor photodiodes. Moreover, the devices exhibit competitive sensitivity, demonstrated by noise-equivalent power (NEP) on the or- der of 10^(-10) W(Hz)^(-1/2), and intrinsic spectral selectivity and polarization sensitivity. By engineering anisotropic metasurface elements, polarization extinction ratios as high as 19:1 are achieved, allowing direct, integrated on-chip polarization state measurements without external power. In summary, this dissertation demonstrates that the integration of nanophotonic meta- surfaces and pyroelectric detection substantially overcomes the traditional limitations of speed and spectral selectivity in pyroelectric photodetection. The result is an ultrafast, wavelength-selective, and polarization-sensitive optical sensing platform ideal for compact, room-temperature, and power-free operation in advanced photonic systems.