Engineers at Rensselaer Polytechnic Institute have developed a method that uses a one-degree change in temperature to alter the color of light that a semiconductor emits.

The process, which uses a thin-film semiconductor layered on top of a heat-sensitive substrate material, may offer a path to electronically triggering changes in the properties of semiconductor materials.

“If you can manipulate a material through temperature, you can also potentially manipulate it with voltage and make an electronic device, and that is significant. Now you can control emission wavelengths electronically,” says Jian Shi, assistant professor of materials science and engineering.

Jian Shi of RPI.Scientists like Shi develop materials with properties that can enable new or improve current technologies. In essence, three major options exist for changing the properties of a material: change its composition, change its temperature, or change the pressure on the material. Each has advantages and drawbacks, and a material suitable for commercial applications must be economical and exhibit the necessary properties under relatively common conditions.

In the research, Shi focuses on pressure to alter the electron-lattice composition, or symmetry, of cadmium sulfite to change its properties. The use of bulk pressure has potential pitfalls: it takes a lot of energy to change the electron-lattice interaction of a material through pressure; generating that energy may require the use of a bulky apparatus that renders the material inaccessible for applications; and many materials have little tolerance for deformation and can shatter before they are deformed sufficiently to provoke new properties.

To overcome those challenges, Shi’s approach uses a thin film of the semiconductor—which can tolerate greater deformation than the bulk material—deposited onto a substrate material that deforms substantially when subjected to only a slight temperature change. The thin film of cadmium sulfite can tolerate at least 1% deformation without shattering, an advantage over the bulk material. The substrate material, vanadium dioxide, undergoes a phase transformation from metal to insulator between 6 and 8 degrees Celsius, changing the volume of the material and exerting pressure on the thin-film semiconductor deposited on its surface.

By combining the robust thin-film semiconductor with the temperature-sensitive substrate, Shi can subject the semiconductor to great strain.

The method could be extended to a variety of thin-film semiconductors and to substrates that undergo phase transition from pressure, temperature or electrostatic doping. Significantly, the results also hint at the potential for producing a voltage from thermal energy, which could lead to thermal energy harvesting.