Deterministic Inverse Design of Lithography-Free, Tamm Plasmon Thermal Emitters with Multi-Resonant Control

<b>Deterministic Inverse Design of Lithography-Free, Tamm Plasmon Thermal Emitters with Multi-Resonant Control </b><br/><br/><b>Mingze He</b>^1,6*, J. Ryan Nolen^2,6, Josh Nordlander³, Angela Cleri³, Nathaniel S. Mcllwaine³, Yucheng Tang⁴, Guanyu Lu¹, Thomas G. Folland^{1, 5}, Bennett A. Landman⁴, Jon-Paul Maria³, Joshua D. Caldwell^{1, 4*}<br/>1. Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee, USA<br/>2. Interdisciplinary Materials Science Program, Vanderbilt University, Nashville, Tennessee, USA<br/>3. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA<br/>4. Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee, USA<br/>5. Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa, USA<br/>6. These authors contributed equally<br/> <br/>* Email: [email protected]; [email protected]<br/> <br/>The development of cheap and effective light sources in the infrared is highly desired for numerous applications, such as non-dispersive infrared (NDIR) gas sensing. Thus, wavelength-selective thermal emitters (WS-EMs) are of particular interest due to the lack of cost-effective light sources in the mid- to long-wave infrared. Yet, most proposed WS-EMs employ patterned nanostructures, thereby requiring high-cost, low-throughput lithographic methods, and are therefore inappropriate for many applications. An alternative solution is Tamm plasmon polariton (TPP) heterostructures composed of a distributed Bragg reflector (DBR) on a conductor, typically a noble metal, resulting in an absorptive resonance with a high quality (Q)-factor at near-normal incident angles. As only thin-film deposition is required for fabrication, TPP-EMs can be grown at wafer-scale with relatively low cost and minimal fabrication steps, offering a promising candidate for WS-EMs.<br/>Despite the broad potential of TPP-EMs, designs of such structures is challenging, as most applications require simultaneous control over both emission frequencies and corresponding Q-factors, and suppression of emission at other frequencies. Although aperiodic TPP-EMs can potentially fulfill those requirements, the large parameter space required makes the design extremely challenging. Furthermore, in experimental reports only noble metals have been used, which due to the fixed plasma frequency that falls in the visible range, severely restricts the spectral control that can be achieved, while also being incompatible with CMOS processing.<br/>Here we present an inverse-design algorithm to efficiently optimize TPP-EMs comprised of an aperiodic DBR grown on an n-type, In-doped cadmium oxide (CdO) film, offering individual control of multi-peak WS-EMs <b>[1]</b>. We experimentally validate our design approach, and realize single-, dual- and triple-band TPP-EMs over a broad spectral range, with all structures exhibiting excellent agreement between experiments and simulations. Furthermore, we illustrate the design capabilities of CdO-based TPP-EMs by demonstrating the ability to match the resonance frequencies, lineshapes, and amplitudes of arbitrarily shaped spectra, including the ability to define Q-factors at any given frequency (e.g., 27 - 10,117 at 2360 cm^-1). Finally, we stress that such functionality is not possible within noble-metal-based TPP-EMs, but instead is enabled by the broadly tunable plasma frequency of CdO. The combination of our efficient inverse-design algorithm with these material advancements facilitates the realization of cost-effective, wafer-scale, CMOS-compatible, and lithography-free TPP-EMs for numerous applications, including multi-gas NDIR and free-space communications.<br/><b>[1] He, M., Nolen, J.R., et al. Deterministic inverse design of Tamm plasmon thermal emitters with multi-resonant control. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-01094-0</b>