Tunable Thermal Emission with Oxides that Undergo Insulator-Metal Transition

Correlated semiconductor materials such as VO₂ and SmNiO₃ display thermally tunable emissivity via insulator-metal transition (e.g. Kats et al, Physical Review X, 3, 041004, 2013). The carrier density can vary by several orders of magnitude across the phase transition boundary while the mobility is largely unaffected. Further, the transition can be triggered both thermally and through electrically driven Joule heating. By suitable choice of dopants on either the cation or anion site, it is possible to tune the insulator-metal transition (IMT) temperature by several tens of degrees as well as the hysteresis. The ability to tune the IMT temperature is of interest to diverse applications such as infrared thermal camouflage, thermochromic coatings for windows and radiative heat transfer in spacecraft. In this presentation, we will discuss our results on Rutherford backscattering spectroscopy of pristine VO₂ and aliovalent cation-doped systems such as (W, V)O₂ and (Nb, V)O₂ thin films on various substrates such as sapphire, SiN and GaAs. We will establish a relation between electron or hole doping density and transition temperature and hysteresis width for tunable thermal emission applications. We will then extend these analyses to the rare-earth nickelates to illustrate Nd-doping of SmNiO₃ to lower the transition temperature near ambient conditions. Finally, we will discuss the use of ion implantation technique to incorporate controlled density of dopants through the depth of a thin film and examine the resulting carrier concentration profile. We anticipate the results to be of broad interest to the community of researchers investigating novel materials for thermal radiation control.