Ultra-Violet Detector Innovation for Raman Exploration and CharacTerization (UV-DIRECT) of Ocean Worlds

Ultra-Violet Detector Innovation for Raman Exploration and CharacTerization (UV-DIRECT) enables the identification of minerals, volatiles, organic molecules, biopolymers, water, and other hydrous phases in planetary materials with the added bonus of Raman spectroscopic imaging. UV-DIRECT accomplishes this by utilizing time-gated SiC avalanche photodiode (APD) detector technology. Our goal is to develop a compact, energy efficient, ruggedized linear detector array for UV-NUV (266 nm-340 nm) - Raman spectroscopy and spectroscopic imaging. The development of UV-DIRECT will be guided by recent efforts by Army Research Laboratory to design a compact and wavelength-specific SiC Avalanche Photodiode (APD) detector for the identification of chem-bio compounds in the field. SiC APD detectors have advantages over the Si Single Photon Avalanche Diodes (SPADs) that have been developed for time resolved Raman spectroscopy in recent years. SiC substrates are more tolerant to radiation and temperature extremes and do not require cooling, moreover these detectors provide a higher signal-to-noise than their Si based detector counterparts in the UV region. Yet, the benefits of SiC detectors have not been taken advantage of in planetary science. The successful demonstration of our novel approach on fabricating a single 35 µm square pixel device using e-beam lithography to reduce the sidewall widths from ~ 10 microns for beveled mesa to ~2 microns, will lay the groundwork for developing large format, high fill factor SiC APD arrays in the future. Our team will build on our wealth of experience in spectroscopic science and detector technology to develop a SiC APD specifically targeted for the identification of ocean world-relevant compounds utilizing UV/NUV-Raman spectroscopy. We will develop our UV focal plane with an entry level maturity of TRL-2 to an exit of TRL-3. In this PICASSO we will fabricate a two-pixel array with a single pixel as the fallback depending on the first-year progress. Task phasing has been selected to first extend the UV response of a single SiC APD to the performance levels comparable to single Si APD (SPAD) response. This involves 1) Modifications to the sensor structure to accommodate the 266-340 nm spectral window, and the fabrication process commensurate with the 35 micron pixel size with a 20 micron spacing for a future array; 2) E-beam lithographic techniques to reduce the sidewall thickness from 10 microns to 2 microns permitting the higher fill factors; 3) Characterization of dark current, gain uniformity, impact of dislocation densities, single photon detection efficiency using a single photon counting set-up in the laboratory; 4) Evaluation of the single pixel device with the fast-pulsed 340 nm LED source; 5) Integration with laboratory optical bench breadboard assembly; 6) Testing the breadboard system in time-gated mode using ocean worlds-relevant samples. We have identified a selected development and characterization work effort appropriate for the PICASSO time scale. This proposal is directly relevant to the Planetary Science Division’s strategic goals “to develop new technologies that significantly improve measurement capabilities for planetary science missions”. We will be leveraging technologies in use by the military to detect chemical and biological agents that have not yet been proven for a planetary science context, satisfying the PICASSO requirement of low TRL instruments, “developing new proof-of-concept instruments or instrument components, including sampling technologies, that enable new science by significantly improving measurement capabilities for planetary science missions…”. UV-DIRECT addresses the needs of the NASA Astrobiology Strategy, including “…process samples from their native solid and liquid matrices, characterize potential biopolymers, detect ultralow concentrations of microorganisms, and detect chemical processes indicative of potential life”. More »