From Event: SPIE Optical Engineering + Applications, 2016
Group-IV semiconductors have the opportunity to have an equivalent or better temperature coefficient of resistance (TCR) than other microbolometer thermistor materials. By using multiple-quantum-well (MQW) structures, their TCR values can be optimized due to a confinement of carriers. Through two approaches – an activation energy approximation and a custom Monte Carlo transfer matrix method – we simulated this effect for a combination of Group-IV semiconductors and their alloys (e.g., SiGe and GeSn) to find the highest possible TCR, while keeping in mind the critical thicknesses of such layers in a MQW epitaxial stack. We calculated the TCR for a critical-thickness-limited Ge0.8Sn0.2/Ge MQW device to be about -1.9 %/K. Although this TCR is lower than similar SiGe/Si MQW thermistors, GeSn offers possible advantages in terms of fabricating suspended devices with its interesting etch-stop properties shown in previous literature. Furthermore, using finite element modeling of heat transport, we looked at another key bolometer parameter: the thermal time constant. The dimensions of a suspended Ge microbolometer’s supporting legs were fine-tuned for a target response time of 5 ms, incorporating estimations for the size effects of the nanowire-like legs on thermal conductivity.
Matthew Morea, Kevin Gu, Victoria Savikhin, Colleen S. Fenrich, Eric Pop, and James S. Harris, "Optimization of TCR and heat transport in group-IV multiple-quantum-well microbolometers," Proc. SPIE 9974, Infrared Sensors, Devices, and Applications VI, 99740M (Presented at SPIE Optical Engineering + Applications: September 01, 2016; Published: 19 September 2016); https://doi.org/10.1117/12.2236166.
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