HgTe Colloidal Quantum Dot Imagers for Longwave Infrared Wavelengths

Conventional shortwave infrared (SWIR), midwave infrared (MWIR), and long-wave (LWIR) III-V (e.g. gallium indium antimonide, or GaInSb) and II-VI (e.g. mercury cadmium telluride, or HgCdTe) epitaxial semiconductor materials show useful performance for various infrared photodetection applications, but their high-cost and substantial cooling requirements seriously limit the wide field deployment of infrared imaging sensors on mobile military platforms. To fabricate a focal plane array (FPA) with these materials, the manufacturer must physically bond the detector array to a ROIC, typically at die level, by flip-chipping a single detector array die to a single ROIC die, using bump bonding, an expensive and time-intensive process which requires specialized tooling. Recently, several low-dimensional materials, including quantum dots, nanowires, and 2D semiconductors have been identified as promising enabling technologies for SWIR, MWIR, and LWIR critical applications. In particular, mercury telluride (HgTe) colloidal quantum dots (CQDs) have attracted interest for their unique advantages as detector materials. Monolithic thin films of HgTe CQD materials can be patterned directly on a CMOS ROIC using solution processing techniques, enabling the development of low-cost, large-area imagers which can be produced without the need for expensive hybridization steps. HgTe colloidal quantum dots are capable of infrared detection from about 1 micron out into the LWIR, depending on the diameter of the quantum dot. Quantum confinement in HgTe CQDs enables wide spectral tunability from 1 micron to the LWIR by controlling the size of the dimensions of the nanoparticle, greater absorption coefficients, and lower Auger coefficients that may offer high temperature or uncooled operation for infrared imaging. The combination of all these factors motivates further study of HgTe colloidal quantum dots for imagers, particularly towards the development of novel, uncooled focal plane arrays (FPAs) at LWIR wavelengths. The objective of this program is to develop a low-cost, large-format LWIR imager targeting uncooled operation and cost-effective fabrication using HgTe CQDs as the detector material. In this Phase II effort, a custom ROIC will be designed and tested to complement the HgTe CQDs, development of the materials chemistry for preparing high quality LWIR HgTe CQDs will continue, and the manner of fabricating large format focal plane arrays with these materials will be developed. By the end of the Phase II, we will evaluate a prototype small-format HgTe CQD LWIR FPA, demonstrating LWIR imaging capabilities and TRL 5 readiness level, and establish a trajectory for producing >2K x 2K large format imaging for high volume deployment in military operations.