Technical. This collaborative project addresses materials science growth/processing research of InGaAs/GaAsSb multiple quantum wells (MQW) with related investigations aimed toward mid-IR wavelength detector applications. The nature of the band alignment allows tuning of the en-ergy gap by varying layer thickness, strain, and composition. Emphasis is placed on gaining greater understanding of the trap formation in GaInAs/GaAsSb MQWs and correlation of their formation with prototype device performance. The approach involves the use of InP to provide advantages: these include the use of compressive and tensile strained materials for flexible device design options; mature wafer foundry capabilities for processing InP-based structures; the ability to leverage advances in InP-based epi-growth over the past decade; and the ability to leverage fu-ture advances driven by InP electronics. Currently, device performance apppears limited by mid-gap traps in the absorption region; hence this work is focused on providing a more complete un-derstanding of these traps and correlating them with device performance. While the MIR photo-diode test structure used in this work has its merit from device perspectives, the basic under-standing of trap states in GaInAs, GaAsSb, and GaInAs/GaAsSb MQWs will improve our fun-damental understanding of these materials. In turn, this will help to better understand the nature of the Sb-based MQW structure. Additionally, these MQWs also impact other important devices such as heterojunction bipolar transistors and mid-IR semiconductor lasers. Non-Technical. The project addresses fundamental research issues in a topical area of elec-tronic/photonic materials science having technological relevance. Societal benefits of the pro-posed research of these materials are potentially broad since the materials and prototype devices being studied support civilian and military applications including pollution detection, medical di-agnostics, night vision, and missile tracking. At present, the best detectors are based on band-to-band transitions in HgCdTe or quantum-well infrared photodetectors (QWIPs) using III-V com-pound semiconductors. Neither technology is well-suited for operation at or near room-temperature. An important advantage of InGaAs/GaAsSb MQW detectors is the potential for high detectivity at relatively high temperatures (200-300K). Through their participation in state-of-the-art research both graduate and undergraduate students will gain invaluable skills and better understand the connection between materials growth, characterization, device design, and device fabrication. To show the impact of mid-IR photodiodes on applications, the photodiodes devel-oped will be used in a trace-gas monitoring demonstration platform. This platform will be used in outreach programs (Engineering Open House; a summer program called Introduction to Engi-neering (ITE); and ENGR 162 (UVA) and EG EG10111/10112 (Notre Dame) required first year engineering courses) designed to illustrate the societal benefits of Electrical Engineering. The goals of these outreach activities are to (i) educate the public about engineering, (ii) recruit pre-college students to pursue engineering as a career, and (iii) motivate first-year engineering students to remain in the major after their first year.
Light with a wavelength beyond what our eyes can "see" (called the infrared regime) has a number of important properties. These include a transmission window in the Earth’s atmosphere, the fact objects emit infrared photons via black body radiation that are strongly wavelength and temperature dependent, and that many organic compounds can be detected with infrared light. These properties can positively impact commercial and military applications. On the commercial side, these applications include high resolution molecular spectroscopy, trace gas monitoring, air pollution analysis, and non-invasive medical diagnostics. On the military side, applications include night vision, target identification and detection, infrared thermal sensors, and remote sensing. Our main goal is to create photodetectors (devices that covert light into an electrical signal) for these applications. Our approach is to use an InP-based platform since this platform provides advantages such as flexible device design options and mature wafer foundry capabilities for processing InP-based structures. Such a solution to infrared detection is transformative in that it couples infrared optoelectronics to a technology platform that has been well developed in industry but does not currently allow use of this wavelength range. The approach we have used is to develop GaInAs/GaAsSb quantum wells for infrared detection and to understand how defects in these quantum wells affect device performance. In collaboration with research at the Notre Dame, we have accomplished the following in this work: Characterization of defects that exists within the GaInAs and GaAsSb layers that make up the quantum well structures Identification of defects that exists at the interfaces between GaInAs and GaAsSb in these quantum well structures Initial experimental evidences that suggest device design that employ epitaxial strain (important for extending the detection wavelengths possible) do not add additional defects Correlation of experimental device performance with the above findings These results have also lead to collaborations with small businesses (though Small Business Innovation Research and Small Business Technology Transfer programs) and federally funded research and development centers (through joint collaborative research funding).
