Electro-Optic Materials Research

Developing single photon UV detection for compact chemical and biological sensors.

(left) Structure of UV separate absorption, charge, and multiplication (SACM)-APD and (right) measured photoresponse from SACM-APD showing broad UV response at high reverse bias in spectral ranges relevant for chemical/biological detection and identification applications

This report summarizes the main lines of effort for the Electro-Optics Materials Research (EOMR) program including its goals and major accomplishments, focusing on the past 5 years. This EOMR program was an effort within 601102A.31B.1 titled “Optoelectronic and Integrated Photonic Materials and Device Research” for FY16-FY19 and 611102A.AA8.1 titled “Photonic Materials and Device Research” for FY20-FY21. The focus of this EOMR for most of the program was to develop novel semiconductor optoelectronic devices to reduce the size, weight, power, and cost (SWaP-C) of chemical and biological detection and identification systems.

Specifically, the program addressed the need for high sensitivity photodetectors in the near-UV (NUV) spectrum between 300 and 350 nm for biological agent detection using light-induced fluorescence techniques employed by the Tactical Biological (TAC-BIO) detector, developed by the US Army Combat Capabilities Development Command Chemical Biological Center, as well as in the deep UV spectrum (220-240 nm) important for standoff chemical detection based upon fluorescence-free Raman spectroscopy. Late in the program, this effort pivoted to address assured communications challenges relevant to the Army modernization priority for future networks through examining how to improve the efficiency of solar-blind UV LEDs.

One of the four lines of effort for this work includes a focus on Near-UV Avalanche Photodiodes Based upon Silicon Carbide (NUV-SiC APDs). The goal of this effort was to demonstrate high-sensitivity APDs using SiC semiconductors that could replace commercially available photomultiplier tubes in the TAC-BIO detector so as to reduce the cost of the sensor by half as well as improve the overall ruggedness of the system. We demonstrated a separate absorption charge multiplication SiC APD with broad responsivity from 200 to 350 nm and gain greater than 106 by successfully addressing the key technical challenge of improving the collection of NUV photogenerated carriers within the device.

A second line of effort focuses on Deep-UV Avalanche Photodiodes Based upon Silicon Carbide (DUV-SiC APDs). The goal of this effort was to demonstrate high-sensitivity APDs using SiC semiconductors to replace commercially available intensified charge-coupled device (iCCD) detectors used by standoff chemical detections systems, like the PRIED (Portable Raman Improvised Explosive Detector) developed by Alakai Defense System, so as to greatly reduce SWaP-C. SiC APDs demonstrating multiplication gain greater than 5 x 106 at 12 pW of 240-nm illumination and approximately 12-nA/cm2 dark current at gain of 1,000, suitable for single photon counting, were demonstrated by addressing the key technical challenge of suppressing the effects of surface recombination on the collection of DUV photogenerated carrier within the device.

A third line of effort focuses on carrier dynamics in III-Nitride semiconductor LEDs. To help design more-efficient UV devices, this effort researched the carrier dynamics in these materials through time-resolved photoluminescence (TRPL) techniques supported by modeling using a non-equilibrium Green’s function (NEGF) technique. It was shown that the fast photoluminescence (PL) lifetime (how long excited electrons exist before recombining to give off light) observed in these wide bandgap materials could be modeled by a strong excitonic recombination that dominated up to room temperature.

A fourth line of effort focused on non-polar Cubic-III-Nitride semiconductors for LEDs. The idea of this project was to study the relatively unexplored cubic aluminum gallium nitride (AlGaN) material system and investigate its doping properties and radiative emission efficiency to compare its performance against the traditional hexagonal-AlGaN material system. It was learned that heteroepitaxial growth initiation of cubic-AlGaN on the cubic silicon carbide (3C-SiC) using previous processes developed for cubic indium gallium nitride (InGaN) created too many extended defects for useful devices. This problem was attributed to the higher temperature needed for Al incorporations. Possible solutions for future efforts were outlined.

This work was performed by Gregory Garrett and Anand Sampath for the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at mobilityengineeringtech.com/tsp under the Sensors category. ARL-9477

This Brief includes a Technical Support Package (TSP).
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Electro-Optic Materials Research

(reference ARL-9477) is currently available for download from the TSP library.

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