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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ASISA (Advanced Superlattice Infrared detectors for Space Applications)

Teaser

Summary

Crucial information from our environment is in the infrared spectral domain, which we can not see with our eyes, infrared detectors are therefore essential to go beyond human capacity. In particular for specific applications, the needs for high performance photodetectors with low dark-current and high quantum efficiency are increasingly relevant. ASISA was intended to demonstrate photodetectors based on Type-II InAs/GaSb Superlattice (T2SL) material system for space applications such as space-based astronomy, Earth observations and climate monitoring. At the end of the project, the platform to access T2SL detectors was built and photodiode with dark-current at the state-of-the art was demonstrated.

Work performed

\"During this project, we developed the growth by molecular beam epitaxy (MBE) of T2SL material on GaSb substrate. By investigating the optimal growth conditions with a focus on the shutter sequence at the interfaces between the InAs and GaSb layers (Figure 1), nearly strain compensated T2SL on GaSb were obtained with a relatively smooth surface. The samples exhibited a cut-off wavelength from midwave (MW, 3 â€“ 5 um) to longwave (LW, 8 -12 um) infrared spectral domain (Figure 2). From epitaxial layer, single-pixel devices (mesa type) obtained via wet etching and standard photolithography process were fabricated in the cleanroom of the Institute for Compound Semiconductor at CU. For detector array fabrication, we carried out initial investigations on dry etch processes by inductively coupled plasma (ICP) and on different passivation method. Note that this work is still being carried at CU. After the fabrication in cleanroom, single pixel characterizations were performed in the newly established optics lab of the SÃªr Cymru research group. The electrical characteristic (current-voltage) was routinely measured as a function of temperature from 77K to room temperature (Figure 3). Our devices consisted of a p-i-n structure having an absorption region made of 1 Âµm of an undoped T2SL layer. Dark-current levels of 8.3 x 10-3 and 3.1 x 10-3 A/cm2 were obtained for an energy band gap of the T2SL of 240 and 110 meV, respectively. These results are at the state-of-the-art for T2SL-based p-i-n photodiode grown on GaSb substrate. Finally, to complete the platform, we developed advanced simulation tools for the material properties of the T2SL and for the device performance simulation by using Nextnano3 and TCAD Silvaco software. Using these tools, an optimized structure has been proposed to achieve high performance with an improved electron-hole wavefunction overlap of 74% and a dark-current lower by a factor of 0.77 than the Rule07 (MCT benchmark).

During the project, the fellow published 3 papers as first-author, 2 in international peer-reviewed journals and 1 is a conference paper. She presented her work in 4 international conferences.
Papers in international peer-reviewed journals:
* M. Delmas, D. C. M. Kwan, B. L. Liang, D. L. Huffaker, Flexibility of Ga-containing Type-II superlattice for long-wavelength infrared detection, Journal of Physics D: Applied Physics, Submitted
* M. Delmas, M. C. Debnath, B. L. Liang, D. L. Huffaker, Material and device characterization of Type-II InAs/GaSb superlattice infrared detectors, Infrared Physics and Technology, 94, 286-290 (2018).
Oral and Poster communications, conference papers:
* D. C. M. Kwan, M. Delmas, B. Liang, D. Huffaker, A comparative study of period composition and thickness of type-II InAs/GaSb superlattices for long-wavelength detectors, UK Semiconductors conference (Sheffield), Submitted for oral presentation.
* D. C. M. Kwan, M. Delmas, B. Liang, D. Huffaker, Growth and characterization of long-wavelength Type-II InAs/GaSb superlattice infrared detectors (oral), Semiconductor and Integrated OptoElectronics (SIOE) conference 2019, Cardiff, 16-18th April 2019.
* M. Delmas, D. C. M. Kwan, M.C. Debnath, B. L. Liang, D. L. Huffaker, Long wavelength Type-II InAs/GaSb superlattice with interface layers grown by migration-enhanced epitaxy (poster), 44th Freiburg IR colloquium (Freiburg), 19th â€“ 20th March (2019).
* M. Delmas, B. L. Liang, D. L. Huffaker, A comprehensive set of simulation tools to model and design high performance Type-II InAs/GaSb superlattice infrared detectors (oral), Photonics West SPIE Conference \"\"Quantum sensing and Nano Electronics and Photonics XVI\"\", San-Francisco, 2nd â€“ 7th February 2019; Proc. of SPIE vol. 10926, 109260G (2019).
* M. Delmas, M. C. Debnath, B. L. Liang, D. L. Huffaker, Material and device characterization of Type-II InAs/GaSb superlattice infrared detectors (oral), Quantum Structure Infrared Photodetector Conference, Stockholm, 17th â€“ 21st\"

Final results

This project attracted a lot of attention within the host institution CU and from the scientific community in the UK and in the EU. As a matter of fact, although, the fellow has left the host institution the T2SL project is still being carried out at CU and few research members including a PhD student, are still working on this topic. Note that this work also contributed to the EPSRC The Future Compound Semiconductor Manufacturing Hub (CS Hb).
ASISA helped the fellow to strengthen her expertise in this research topic by increasing her knowledge and understanding on T2SL detectors. The fellow also strengthened her position as independent researcher by giving presentations at international conferences and by building her own network and collaborations in this field. At the end of the project, she has been recruited by IRnova, European manufacturers of T2SL detectors.