RT&L FOCUS AREA(S): Quantum Sciences TECHNOLOGY AREA(S): Electronics 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 section 3.5 of 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 and demonstrate high-sensitivity at near-room-temperature avalanche photodetector (APD) that operates at low voltage with high gain in the extended short-wave infrared (e-SWIR) spectrum range of 2 to 2.5 m. DESCRIPTION: Photodetectors with high sensitivity operating in high-temperature, low-voltage regime in the e-SWIR spectrum range of ~ 2 to 2.5 m are in high demand [1,2]. A number of approaches have been explored in the recent years in pursue of this goal, but the current performance metrics do not yet meet the stringent requirements for the desired applications. The Army is seeking innovative approaches in next-generation e-SWIR detector technology to significantly improve sensitivity and response time. These innovations include, but are not limited to, novel structures to achieve low-voltage operation and low-dark current APDs covering e-SWIR band for image sensing and communication systems with small size, weight, power and cost (SWaP-C) requirements. A range of APD technologies have been developed in the past and even achieved single photon sensitivity, which explains why the APD is preferred for many applications. However, there are still many application constraints, such as cost, power consumption, reliability, robustness of operating environment and response time. Silicon APD based photoreceivers have state-of-the-art noise-equivalent-power of 40 fW/rt(Hz) with a bandwidth of 140 MHz and proven performance in various applications. However, at wavelengths beyond 1.1 m, silicon becomes transparent to infrared light. Commercially available III-V APDs (e.g. InGaAs APDs) at 1.55 m applicable for fiber communications [3-4] cannot be used in applications beyond 1.7 m. Standard APDs with spectral responsivity to 2 m and beyond show increased dark current and excess noise factor, which limit the gain and hence the signal-to-noise ratio (SNR) of the detection system [5]. In addition, many of these standard technologies (e.g. HgCdTe APDs) are not viable for many field applications due to their need for cryogenic cooling, resulting in high SWaP-C. Furthermore, conventional APDs apply a variable reverse-bias voltage across the device junction to create a variable avalanche gain during APD operation, which in turn optimizes the sensitivity of the receiver. However, to achieve satisfactory levels of avalanche gain, many APDs require high reverse-bias voltages in the 40V to 60V range, and some require voltages exceeding 80V [6]. In addition, the APD avalanche gain depends on temperature and varies with the manufacturing process. Thus, for typical systems in which the APD must operate at constant gain, the high-voltage bias must vary to compensate for the temperature effects. To achieve constant gain in a typical APD supply, the temperature coefficient must be maintained at approximately +0.2%/ C, which corresponds to 100mV/ C. The latter makes the device energy consumption inefficient and incompatible with current CMOS IC technology supply voltages, requiring additional high bias circuit in the read-out. It is highly desirable to design a next-generation APD for e-SWIR photoreceivers to overcome the deficiencies of the standard APD available today. Novel APD solutions are desired that simultaneously enable low-voltage (e.g. <20V) APD operations, reduce dark current, and exhibit low excess noise factor to achieve high gain and enhanced SNR at or near room temperature. Novel APDs technologies focused on structure design, providing high bandwidth, high gain and high quantum efficiency, are sought rather than based on material composition changes. PHASE I: Develop a novel APD device structure with material(s) system enabling detection in extended-SWIR spectral range (2-2.5 m). Theoretically model and simulate APD design, operating at e-SWIR wavelength that is scalable from single element to arrays, e.g. VGA format and beyond. Design, model and simulate essential electrical and optical characteristics for an APD device that meets the performance requirements for low-voltage operation, low excess noise and low dark-current at or near room temperature. A maximum gain is needed at low biasing voltage (e.g. <20V), with low dark current density of a few nA/cm2 at unity gain at or near room temperature. Deliver the simulation and design results. PHASE II: Fabricate, evaluate and optimize a prototype of single element APD as well as an APD array of 4 x 4 elements or larger. Demonstrate low-voltage biased APD operation on single element devices. Demonstrate spectral cut-off wavelengths at e-SWIR wavelength bands as high as 2.5 m. Explore option(s) for readout integration and processing e-SWIR APD. Demonstrate functionality and mechanical integrity over the military temperature range and background-limited infrared photo-response against calibrated illumination. A proof of concept FPA is desirable, but not required. PHASE III DUAL USE APPLICATIONS: Demonstrate APD array integrated into a system for field testing. APD arrays with extended sensitivity to the e-SWIR range are desirable for identifying, tracking, and targeting hostile forces and communicating covertly in applications such as micro air vehicle (MAV) sensors, laser target tracking, laser radar, missile tracking, persistent surveillance and 3D imaging, satellite imaging and interceptors. The detector arrays are also expected to enable measurement and characterization of transient phenomena that have an e-SWIR spectral content, such as a missile signature, flashes, or measuring and characterizing unknown emission signatures in the battlefield. In addition, the commercialization of this technology is expected to provide low cost, high performance imagers for potential uses in variety of commercial applications including automobile, security and surveillance, medical imaging, machine vision, agriculture, scientific imaging including astronomy, mapping, weather monitoring, as well as border patrol and various homeland security applications. REFERENCES: Michael A. Krainak, Xiaoli Sun, Guangning Yang, and Wei Lu, Comparison of linear-mode avalanche photodiode lidar receivers for use at one-micron wavelength , SPIE 7681-34, 2010 Xiaogang Bai, Ping Yuan, etc.; GHz low noise short wavelength infrared (SWIR) photoreceivers Proc. SPIE Laser Radar Technology and Applications XVI, 803717-1 (2011). Achyut. K. Dutta, M. Takechi, R. S. Virk, M. Kobayashi, K. Araki, K. Sato, M. Gentrup, and R. Ragle, IEEE J. Lightwave Technology, 20, pp. 2229-2238(2002). Achyut K. Dutta, Editors: WDM Technology: Active Optical Components , Vol. I, Academic Press, Boston, 2005. R.J. McIntyre, 1966, Multiplication noise in uniform avalanche photodiodes, IEEE Trans. Electron Devices, ED-13:164.R.J. McIntyre, 1999, A new look at impact ionization Part I: A theory of gain, noise, breakdown probability and frequency response, IEEE Trans Electron Devices 46: 1623. Maxim Integrated, Low-Noise APD Bias Circuit, Application Note 1831, 07 Jan, 2003. KEYWORDS: Avalanche Photodiode, APD, multi-color, detectors, extended SWIR, e-SWIR, bias voltage, noise factor, ROIC, sensors, FPA, multispectral sensor; LADAR; High Bandwidth; Dark current, Laser Radar, Imaging, bio-sensing
