Scientists have discovered a crystalline semiconductor that can produce an exceptionally large electrical voltage from a temperature difference. The finding challenges a decades-old assumption about the maximum thermoelectric response possible in solid crystalline materials.
The unusually high voltage response could open possibilities for ultrasensitive temperature sensors, heat detectors and quantum sensing devices, according to the Ministry of Science & Technology.
Scientists discover semiconductor with exceptionally high thermoelectric response
Scientists have discovered a crystalline semiconductor that can convert a temperature difference into an electrical voltage far beyond the levels traditionally expected in solid materials. The finding challenges a long-standing limit on the Seebeck effect.
The research was carried out by scientists from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute under the Department of Science and Technology (DST), in collaboration with the University of Sydney, Australia, and the Indian Institute of Science (IISc), Bengaluru.
What is the Seebeck effect?
When one side of a junction between two different materials is heated while the other side remains cooler, mobile charge carriers move from the hot region towards the cold region. This movement creates an electrical voltage, a phenomenon known as the Seebeck effect.
The effect, discovered around two centuries ago, forms the basis of technologies such as temperature sensors and thermoelectric generators, which can convert waste heat into electricity.
For decades, crystalline solids were generally expected to have a Seebeck coefficient within a relatively limited range. Metals typically produce only tens of microvolts per Kelvin, while even efficient semiconductor materials generally remain in the hundreds of microvolts per Kelvin range.
The newly reported material shows a response that is several hundred to more than a thousand times higher than values typically observed in inorganic semiconductors.
Scandium nitride used to push thermoelectric performance
The research team, led by Prof Bivas Saha, worked with scandium nitride (ScN), a refractory transition-metal nitride. The scientists produced thin ScN films on magnesium oxide substrates using ultrahigh-vacuum magnetron sputtering.
The material was deliberately doped with magnesium to compensate for naturally occurring free electrons associated with oxygen dopants. This created what researchers describe as a heavily doped, highly compensated (HDHC) semiconductor.
In this type of material, positively and negatively charged dopant atoms are distributed throughout the crystal in nearly equal amounts. The researchers found that this engineered disorder and charge compensation could dramatically alter the material’s electronic transport properties.
X-ray diffraction and atomic-resolution electron microscopy confirmed that the films remained single-crystalline and epitaxial, with the dopants distributed uniformly and without secondary phases or precipitates.
Seebeck response crosses the earlier limit
Measurements of the HDHC ScN films showed a Seebeck coefficient exceeding –124.6 millivolts per Kelvin near room temperature in a film about 200 nanometres thick.
According to the research findings, this is several hundred to more than a thousand times higher than values commonly seen in inorganic semiconductors and nearly 100 times beyond the earlier known ceiling for crystalline solid materials.
Potential applications in sensing and quantum technology
The findings, published in the journal Science, could have applications beyond conventional thermoelectric devices.
The researchers point to potential uses in ultrasensitive temperature sensing, low-noise thermal imaging, high-resolution heat-flux detection and bolometric devices. The technology could also be explored for Internet-of-Things sensors and cryogenic thermoelectric single-photon detectors linked to emerging quantum technologies.
An Indian patent application has also been filed covering thermoelectric thin-film materials and sensors for temperature and photon detection based on the work.