Material Perspective on HgTe Nanocrystal-Based Short-Wave Infrared Focal Plane Arrays

Abstract

After the use of nanocrystals as light downconverters, infrared sensing appears to be one of the first market applications where they can be used while being both electrically and optically active. Over recent years, tremendous progress has been achieved, leading to an apparent rise in the technologicalreadiness level (TRL). So far, the efforts have been focused on PbS nanocrystals for operation in the near-infrared. Here, we focus on HgTe since its narrower band gap offers more flexibility to explore the extended short-wave and midwave infrared. We report a photoconductive strategy for the design of short-wave infrared focal plane arrays with enhanced image quality. An important aspect often swept under the rug at an early stage is the material stability. It appears that HgTe remains mostly unaffected by oxidation under air operation. The evaporation of Hg, a potentially dramatic aging process, only occurs at temperatures far beyond the focal plane array's standard working temperature. The main bottleneck appears to be the particle sintering resulting from joule heating of focal plane arrays. This suggests that a cooling system is required, whose first role is to prevent the material from sintering even before targeting dark current reduction.

In Situ Mapping of the Vectorial Electric Field within a Nanocrystal-Based Focal Plane Array Using Photoemission Microscopy

“…It is also worth pointing out that we do not notice any contribution from oxygen even though the film was prepared under air condition. This observation is consistent with the recent report by Zhang et al that concluded with the weak propensity of HgTe NCs for oxidation . This lack of oxidation will leave the state close to the valence band free from oxide contribution, which is critical for photoemission microscopy.…”

“…This observation is consistent with the recent report by Zhang et al that concluded with the weak propensity of HgTe NCs for oxidation. 12 This lack of oxidation will leave the state close to the valence band free from oxide contribution, which is critical for photoemission microscopy. X-ray beam focusing is accomplished by introducing a Fresnel zone plate over the synchrotron beam, which focuses the beam from a conventional level of 100 μm down to 700 nm.…”

“…However, high performance and compatibility with technological developments required by focal plane array (FPA) integration are crucial for the widespread adoption of this technology. Several groups and companies − have been exploring the use of NCs as an active layer for infrared FPAs relying either on PbS , or HgTe − NCs, the latter being the only one to cover both the short- and mid-wave infrared …”

Inside a nanocrystal-based photodiode using photoemission microscopy

“…On the other hand, we observe no contribution coming from oxygen (O 1s state is expected to appear with a 532 eV binding energy) despite the preparation of the sample in air, which confirms the weak oxidation susceptibility of HgTe. 43…”

Bias Reconfigurable Photoresponse of an Infrared Nanocrystal Film Integrated into a Coupled Fabry-Perot Resonator

“…In the infrared, the prospect of bringing cost disruption to a spectral region where detectors and sources are dramatically more expensive than their counterparts operating in the visible range has also spurred interest in colloidal nanomaterials. Some clear successes have been obtained through the design and fabrication of components such as on-chip integrated sensors, , infrared cameras, − spectrometers, and LEDs. , …”