Physics Chat
Type-II Superlattices for MWIR Sensing
Speaker: Dhafer Alshahrani (KesariaM)
Date: Friday 26 February 2021
Time: 15:00
Venue: Zoom
Environmental pollution is one of the greatest challenges confronting humanity globally. Nitric oxide (NO) and nitrogen dioxide (NO2), which are collectively referred to as NOx, are highly poisonous and detrimental to air quality and a primary source of air pollution, contributing to the formation of smog and acid rain [1]. NOx is a toxic gas produced during combustion of fossil fuels in power plants and automobile engines as well as during lightning in thunderstorms and contributes to numerous functions in the human body where it is produced in inflammatory processes [2]. There is an urgent need for highly sensitive photodetectors operating in the 5.1 - 5.5 #m wavelength range at high temperature, for low-cost detection of NOx gas. Although Mercury Cadmium Telluride (MCT) and Quantum Well Infrared Photodetectors (QWIPs) are well-established technologies in mid-wavelength infrared (MWIR) photodetection, they require cryogenic cooling for optimal performance at high temperatures. Type-II superlattices (T2SL) have emerged as a promising alternative due to their flexible and more controllable bandgap engineering through the design of the SL layer thickness/composition and coherency strain. The InAs/GaSb T2SL infrared material is particularly attractive owing to its enormous potential for high device performance at high temperature with significantly reduced dark current [3] and high responsivity [4]. Here, we present the optical and electrical performance of Ga-based, InAs/GaSb T2SL layers and photodiodes operating in the 5.1 - 5.5 #m range which is desirable for NOx detection. A dominant PL peak at around 5.3 #m at 77 K was obtained for the Ga-based samples with an intensity which is less sensitive to changes in temperature compared to a reference Ga-free InAs/InAsSb SL sample. The PL peak intensity of the Ga-based T2SL with an intentional InSb layer was found to be less responsive to changes in temperature and tuned to longer wavelength suitable for NOx sensing. The dark current density and differential-resistance area product (RdA) of the fabricated photodiode were compared with the current state-of-the-art photodetectors and with the ``MCT-Rule 07''. It is found that the dark current density of the device is around three orders of magnitude higher than `'Rule 07'', while the RdA is only a few times close to Rule 07 at high operating temperature (HOT). Current-Voltage modelling of the fabricated photodiode demonstrates that at a temperature of 110 K, generation recombination (G-R) and trap assisted tunnelling (TAT) currents dominate below and above an applied bias of ~0.2 V. However, at higher operating temperature (200-300 K), diffusion current is prevalent at low applied bias while G-R and TAT are dominant at high applied bias.
References [1] R.J. Hargreaves et al., J. Quant. Spectrosc. Radiat. Transf. 232, 35, 2019. [2] J. Wojtas et al., Sensors, 17, 513, 2017. [3] A. Rogalski, Infrared Phys Technol. 54, 136, 2011. [4] M. J. Hobbs et al., Proc. SPIE 8899, 2013.
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