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 – 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 Sêr 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 µm 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 – 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 – 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 – 21st June 2018.
* M. Delmas, Y. Rawal, B. Liang, D. Huffaker, Growth and material characterizations of Type-II InAs/GaSb Superlattice (oral), Semiconductor and Integrated OptoElectronics (SIOE) conference 2018, Cardiff, 27-29th March 2018.
In addition, results from this project have also been presented by people involved in this project at SIOE conference 2019 in Cardiff and an abstract has been submitted for UK Semiconductor 2019 in Sheffield (UK). Other activity also includes an invited presentation at the All Wales MSCA Summer School at Swansea University 2017.
