A new approach utilizes high-mobility, 2D electron gas to boost thermoelectric conversion efficiency. More than 60 percent of the energy produced by fossil fuels is lost as heat. Thermoelectric energy conversion has attracted attention as a way to convert waste heat from power plants, factories and cars into electricity. But currently, available technology needs improvement to become viable on industrial scales.
Researchers from Hokkaido University in Japan have proposed the use of high-mobility electrons generated at a semiconductor interface called 2D electron gas (2DEG), which can improve the ability of thermoelectric materials to convert heat energy into electricity.
The researchers made a transistor on the 2DEG at the interface between two semiconducting materials, aluminum gallium nitride and gallium nitride. When an electric field was applied, concentrations of 2DEG could be modulated without reducing its high mobility. The 2DEG’s “power factor," which is a measure of electric power, is two to six times higher than most of the state-of-the-art thermoelectric materials.
Efficient thermoelectric energy requires materials with high electrical conductivity, low thermal conductivity and a large thermopower, which is high voltage produced in response to the difference in temperature across the material.
Current nanostructuring techniques have managed to significantly reduce the thermal conductivity of these materials. This improves their performance. A high power factor is also necessary for efficient power generation, but improving it has been limited because it necessitates simultaneously increasing a material’s thermopower and its electrical conductivity, which is difficult. Electrical conductivity has remained low due to ionized impurities in the material that suppress the mobility of electrons.
Applying an electric field to the transistor fabricated by researchers from Hokkaido University allows modulating the material’s thermopower and its electrical conductivity without suppressing its high mobility.
"Although the device cannot be used as a thermoelectric generator because it is too thin, the 2D electron gas approach should open avenues for further improving the performance of state-of-the-art thermoelectric materials," says Hiromichi Ohta, the lead author of the study.
The study on this research was published in Advanced Science.