Engineering topics

Urbas, Augustine M.

Publications and source records attributed to Urbas, Augustine M..

5 records

NASA NTRS2021

Ni-Silicide Schottky Barrier Micropyramidal Photodetector Array

In attempt to increase the quantum yield of metal/silicide Schottky barrier photodetectors, in this work we fabricated and tested Si micropyramidal arrays which are capable to resonantly trap photons in the photodetector areas. To simplify testing, Ni/silicide Schottky barrier photodetectors were formed on the entire 1.5  1.5 mm areas occupied by the micropyramidal arrays. Preliminary testing results revealed potentially stronger photoresponse of micropiramids with narrow tops, but further studies are required to compare the performance of such novel photodetector arrays with different geometrical parameters of micropyramids.

Astratov, Vasily N.↗

NASA NTRS2021

Anisotropic Wet Etching of Si as a Fabrication Tool Enabling 3-D Microphotonics Structures and Devices

It is shown that due to high speed and large volume of production, anisotropic wet etching of Si is a unique method of manufacturing high quality micropyramidal arrays for silicon photonics. Four types of arrays were fabricated: (i) square pyramids with the 54.7 slope of the sidewall surface, (ii) microcones with the 45 slope of sidewall surface, (iii) inverted square pyramids with 54.7 slope, and (iv) inverted triangular pyramids with different angles of the sidewalls. It is shown that the first type of arrays has a capability to produce tightly focused mid-wave infrared (MWIR) beams at the tips of the pyramids. Other arrays can be also used as light concentrators and various multifunctional microphotonic components.

Astratov, Vasily N.↗

NASA NTRS2021

Light-concentrating microcone array for improving performance of infrared imaging devices

Light-harvesting low-index (n=1.6) microconical arrays are proposed for increasing the sensitivity and the signal-to-noise ratio (SNR) of mid-wave infrared (MWIR) focal plane arrays (FPAs) used in thermal cameras. Numerical modeling showed a 3-D Power enhancement factor ~ 50 in MWIR for 10° tapered microcones with Dt/Db = 60 μm/8μm and h=150μm, where Dt and Db are the top and bottom diameters of microcones, respectively. Such microconical arrays were fabricated in photoresist by using a nanoscribe tool directly on top of the front-illuminated Ni/Si Schottky-barrier, and three-fold enhancement in the photocurrent response was observed. The proposed approach permits increase of the SNR and the operation temperature of the MWIR imaging devices.

Astratov, Vasily N.↗

NASA NTRS2020

Design of Si micro-cone light concentrators for heterogeneous integration with MWIR FPAs

Using 3-D finite difference time domain (FDTD) modeling, it is shown that micro-cone arrays obtained by anisotropic wet etching of Si have high potential for concentrating light on compact photodetector mesas of mid-wave infrared (MWIR) focal plane arrays (FPAs). The proposed structures can be heterogeneously integrated with FPAs possessing high quantum efficiency. They can be used to reduce the thermal noise and, potentially, increase the operating temperature of FPAs while maintaining high sensitivity of the photodetectors.

Astratov, Vasily N.↗

DOE OSTI2020

Design of High Efficient Mid-Wavelength Infrared Polarizer on ORMOCHALC Polymer

While an organically modified chalcogenide (ORMOCHALC) can be used to fabricate a polymeric mid-wavelength infrared (MWIR) polarizer with competitive extinction ratio compared to the commercial wire-grid polarizers, which are composed of fragile inorganic materials, there is still a knowledge gap regarding the systematic design process to obtain high transmission efficiency and extinction ratio. As such, a computational parameter study for design optimization is conducted with the geometric parameters of the bilayer grating ORMOCHALC polarizer. The computational study shows that the Fabry–Pérot cavity is the primary mechanism that determines the transmission behaviors and the extinction ratio. A bilayer grating design, guided by the parameter study, is realized through the thermal nanoimprint and metal deposition processes. The extinction ratios measured with the Fourier-transform infrared are 245, 304, and 351 at the wavelength of 3, 4, and 5 μm, respectively. Compared to the state-of-the-art of the polymeric MWIR linear polarizers, the extinction ratio is improved by 1.4 times, and the transmission efficiency is increased by 2.5 times. Theoretical analysis with the multiple-layer model based on the transfer matrix method predicts a matched transmission behavior with the experiment and a full-wave electromagnetic simulation.

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