Thermochromic effect with semiconducting layers

A switching of reflectivity with temperature can be achieved in the infrared region, using thermally activated charge carriers in a single semiconductive layer on a reflective base material, when the interference effect between front and back side of the layer is used. We outline, how a surprisingly small change in conductivity - of less than an order of magnitude - changes the reflectivity more than 60% when the semiconductive material is tailored to its task regarding its activation energy and charge carrier density. As a proof of principle, titanium oxynitride layers were prepared on aluminum. A change of reflectivity of 21% was achieved when the sample temperature was increased from 25 °C to 150 °C, and a change of 34% when the sample was heated to 250 °C.