N232-104 TITLE: Mid-Wave Infrared Detectors with Tunable Narrow-Band Spectral Response

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a mini-array of optical detectors that combine narrow spectral response (= 200 nm) with enhanced specific detectivity for all polarizations, and which can be tuned across at least 500 nm of the 3 � 5 �m midwave infrared (MWIR) spectral band.

DESCRIPTION: Navy requirements for advanced MWIR and longwave infrared (LWIR) detectors have typically been subdivided into two application classes. The first is broadband thermal imaging by a focal plane array (FPA), to provide high-resolution vision and identification in near or total darkness. This requires a broad spectral bandwidth that maximizes the net signal within a given atmospheric window such as the MWIR (3-5 �m) or LWIR (8-12 �m). Cryogenics are generally required to reach background-limited performance (BLIP). The second application class requires high sensitivity only within a narrow spectral bandwidth. This occurs when the signal to be detected is produced by an infrared (IR) laser or for passively detecting optical emission at known spectral lines. Examples include active imaging, multispectral/hyperspectral imaging, target designation, free-space communications, laser spectroscopy for chemical/biological/explosives sensing, laser/beacon detection, and Light Detection and Ranging (LiDAR).

The goal of this SBIR topic is to combine the benefits of both applications by enabling the development of larger format MWIR detector arrays that have high sensitivity within a dynamically tunable narrow spectral bandwidth. To achieve this goal, the Navy is seeking MWIR detectors that display enhanced specific detectivity (D*) within a narrow spectral bandwidth. This is in direct contrast to the state-of-the-art approach that lowers detectivity through the use of a narrow bandpass filter placed in front of a broadband detector. A further goal is to provide the ability to tune the peak response wavelength while maintaining enhanced D* for applications such as hyperspectral imaging.

One potential approach that could be used to address this problem involves placing a very thin detector absorber region within a resonant cavity tuned to the wavelength bandwidth of interest [Ref 1]. High quantum efficiency is retained due to numerous passes of the incident light through the cavity, while clutter associated with wavelengths outside the spectral region of interest is rejected. The resonant cavity infrared detector (RCID) architecture can also enhance the frequency response, since photogenerated carriers are collected much more rapidly from the very thin absorber. RCIDs are relatively mature at telecommunication wavelengths, where the primary motivation is to maximize the speed for high data rate [Ref 1]. However, RCIDs operating at MWIR wavelengths beyond 3 microns have previously performed poorly compared to conventional broadband detectors. Only quite recently have more encouraging results been reported [Refs 2,3], which confirm a promising pathway to substantial reduction of the dark current noise while maintaining high peak quantum efficiency for enhanced sensitivity within the resonance bandwidth.

A second potential approach is to incorporate a plasmonic metamaterial grating [Refs 4,5]. These architectures can also maintain high quantum efficiency when the absorber is very thin by redirecting the normal-incidence IR signal to propagation in the plane. For grating resonance wavelength in the LWIR, this has led to enhancement of D* in type-II superlattice nBn devices at operating temperatures in the thermoelectric cooler range [Ref 5].

Both RCIDs and plasmonic gratings can enhance D* within a narrow spectral bandwidth by reducing the diffusion current noise generated in the very thin absorber. This may allow both laser detectors and multi-spectral imagers to display background-limited performance at higher operating temperatures than is currently possible, leading to substantial reduction of the size, weight, and power (SWaP) of Navy systems. Both architectures are also suitable for fabricating devices displaying different resonance wavelengths on the same chip, which may potentially provide multi-spectral imaging by scanning a 1D array. Other architectures may allow simultaneous dynamic tuning of the resonance wavelengths of all devices in a 2D array.

Overall goals of this SBIR topic are to: (1) Enhance the sensitivity and overall performance of single-element narrow-band IR detectors for all polarizations of the incident radiation; (2) Demonstrate small arrays with nominal dimensions of at least 4 � 4 or 16 � 1 by the end of Phase II, which can be scaled to a 64 � 64 format mini-camera in a Phase II option and higher format wavelength tunable cameras in Phase III; and (3) Demonstrate controlled tuning of the resonance wavelength over at least 500 nm and return back to the initial wavelength within 0.1 ms, for an effective hyperspectral revisit rate of = 5 kHz.

PHASE I: Develop a proof of principle approach to fabricating narrow-band (= 200 nm) detectors with tunable resonance wavelength. The design should be capable of reaching D* > 4 x 1011 [cm � sqrt(Hz) / Watt] for a resonance wavelength of 4.5 �m and all polarizations when operated at 200 K. Process and deliver a single fixed-wavelength narrow-band detector for evaluation by the Offeror and/or NRL.

In the Phase I Option, if exercised, demonstrate via experiment and/or modeling the feasibility of a tunable narrow-band mini-array for development in Phase II. The mini-array will have dimensions at least 4 � 4 or 16 � 1, and variable resonance wavelength spanning at least 500 nm of the MWIR band.

In Phase I, MWIR detector wafer materials can be provided by the Naval Research Laboratory (NRL), or the awardee may employ its own source of material.

PHASE II: In the first 18 months of Phase II, optimize D* of the narrow-band MWIR detectors. By the end of Year 2, fabricate and deliver a narrow-band mini-array with dimensions of at least 4�4 or 16�1, and which provides variable resonance wavelength spanning at least 500 nm of the MWIR band. The spectral bandwidth should be = 200 nm, but may be much narrower and its value is optional because different widths are optimal for different applications. Delivery will include a cooler/dewar as needed, electronic controls, and input/output optics. If the awardee chooses to employ detector wafer materials from NRL, those materials can be provided as needed.

PHASE III DUAL USE APPLICATIONS: Fabricate and deliver a narrow-band camera with array dimensions of at least 128 � 128 and resonance wavelength spanning = 500 nm of the MWIR at a rate = 5 kHz. Delivery will include a cooler/dewar, read-out integrated circuit (ROIC), and input/output optics, with input lens providing = 8� field of view. The manufacturing technology for producing the array should be at least MRL 4 [Ref 6]. The narrow-band arrays should be suitable for hyperspectral imaging, remote chemical and biological detection, or free space optical communications for DoD missions.

REFERENCES:

1. Meyer, Jerry et al. "Resonant-Cavity Infrared Photodetectors with Fully-depleted Absorbers." US Patent No. 10062794 B2 (2018). https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/10062794
2. Li, et al., "Room temperature detection of N2O using a resonant cavity mid-IR detector and interband cascade LED," Laser Applications to Chemical, Security & Environmental Analysis, (11-15 July 2022, Vancouver), paper LM3B.2, https://opg.optica.org/abstract.cfm?uri=LACSEA-2022-LM3B.2.
3. Canedy, Chadwick L. et al. "Resonant-cavity infrared detector with five-quantum-well absorber and 34% external quantum efficiency at 4 �m." Opt. Express 27, 2019, pp. 3771-3781. https://opg.optica.org/oe/fulltext.cfm?uri=oe-27-3-3771
4. Jackson, E.L. et al. "Two-dimensional plasmonic grating for increased quantum efficiency in midwave infrared nBn detectors with thin absorbers." Opt. Express 26, 2018, pp. 13850-13864. https://opg.optica.org/oe/fulltext.cfm?uri=oe-26-11-13850&id=389666
5. Nordin,L. et al."High operating temperature plasmonic infrared detectors." Appl. Phys. Lett. 120, 101103, 2022. https://aip.scitation.org/doi/10.1063/5.0077456
6. Wikipedia. "Manufacturing readiness level." https://en.wikipedia.org/wiki/Manufacturing_readiness_level

KEYWORDS: MWIR, resonant cavity devices, plasmonic metamaterials, laser detection, spectroscopy, remote sensing

---