The voltage response of thermoelectrically coupled nanoantennas (TECNA) to infrared light (IR) is greatly enhanced by suspending them above quasi-spherical cavities. The cavities behave as optical elements that focus the IR radiation onto the nanoantennas. The wavelength response of a cavity depends on its geometrical profile, for which the resonant cavity mode must match the resonant wavelength of the antenna. In this work, TECNAs were designed to detect four different wavelengths in the mid- and long-wave IR and fabricated in a single chip, requiring different cavity profiles. Cavities were fabricated by isotopically etching Si using xenon difluoride (XeF2). XeF2 gas etches the Si substrate through circular windows patterned in resist. The antenna is patterned before the cavity is formed to avoid difficulties in filling and planarizing the supporting layer for antenna patterning and is left suspended over the cavity after etching. The different cavity profiles were formed in a single etch, since subsequent resist patterning and etching of unfilled cavities would destroy previous antennas. This work compares cavity profiles etched using both pulsed and continuous-flow XeF2 etch methods using different etch window sizes to produce variously sized and shaped cavities in a single etch. The cavity profiles were characterized using a laser-scanning confocal microscope. Piecewise equations made up of a torus, a cone, and a cylinder were fitted to the profiles and used in COMSOL simulations of electromagnetic standing-wave patterns within the cavity. Antennas were then chosen to have peak responses at wavelengths that match a simulated cavity’s peak response.
We will present our recent work on achieving a high-quality factor (Q) in microresonators operating in the longwave infrared (LWIR) range of 8 to 14 microns.1 Advances in this area have the potential to drive new developments in integrated non-linear optics and chip-based sensing, due to the availability of powerful integrated light sources such as solid-state quantum cascade lasers and strong demand for sensing applications in the LWIR atmospheric transparency window. However, until recently limitations in low-loss materials and fabrication processes have resulted in Q factors that are only several thousand. We will discuss the use of germanium as a high-quality material and heterogeneous fabrication process that produces ultra-smooth surfaces. By coupling the output of a QCL into a partially suspended Ge-on-glass waveguide, we were able to achieve an intrinsic Q of 2.5 ×105. Our results demonstrate the importance and potential of using high-quality native materials for integrated photonics in the LWIR range and portends new sensor topologies.
Thermoelectrically coupled nanoantennas (TECNAs) are a new class of infrared detectors based on the resonant absorption of freely propagating electromagnetic waves. When IR light illuminates the devices, radiation-induced antenna current heats the nanothermocouples. The temperature difference with respect to the cold junction at the substrate is converted to electrical signals by the Seebeck effect. The physical size of the nanoantenna determines the spectral response of the device. In this work, we show experimentally obtained spectral responses of TECNAs using Fourier-transform infrared spectroscopy (FTIR) and compare the results to simulations.
Thermoelectrically coupled nanoantennas (TECNAs) are fast thermal sensors for the mid- to far-IR regime. TECNAs resonantly absorb EM radiation using a nanoantenna and nanothermocouple, and can be made directionally sensitive using a reflecting cavity. We present TECNAs located above a cavity etched into a substrate to determine angle of incidence of laser beams. The position of the antennas relative to the cavity center provides beam steering capability. We show in simulations that radiation and receiving characteristics of TECNAs are strongly dependent on position above the cavity. Positioning multiple antennas above a cavity provides angle-of-incidence resolution capability in the thermal infrared.
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