doi:10.1038/nindia.2014.129 Published online 26 September 2014
Researchers have synthesized a versatile semiconducting material that exhibits charge transport and an ultralow thermal conductivity when subjected to controlled temperature changes1. The material is made from highly pure silver, copper and sulfur, and it is promising for fabricating devices such as diodes and transistors.
Semiconductors are essential for making transistors, memory and energy-storage devices, sensors and resistive switches. Previous studies have shown that inorganic semiconducting materials can be tuned by varying their temperature. To explore the semiconducting properties of a single inorganic compound, the researchers synthesized a crystalline metal sulfide semiconductor by heating highly pure silver, copper and sulfur in a quartz tube.
The researchers cut the semiconductor into bar- and coin-shaped samples and en polished them. They used the bar-shaped samples for electrical transport measurements and the coin-shaped samples for thermal conductivity measurements.
The scientists found that the crystalline semiconducting material exhibited ultralow thermal conductivities in the temperature range 300 to 550 kelvin. Using spectroscopic analysis, they detected soft vibrations of disordered silver and copper ions propagating in the crystalline semiconductor; this phenomenon is known as phonon transport and it contributes to the observed low thermal conductivity. In addition, the electronic states of the rigid sulphur sublattice caused the electronic charge transport in the semiconductor.
The researchers say that such decoupling of electronic and phonon transports leads to a unique combination of temperature-dependent conduction switching and ultralow thermal conductivity in the semiconducting material near room temperature. They say that such temperature-dependent changes of the conduction properties open up the possibility of making a new class of temperature-controlled diode or transistor devices based on a single compound.
The authors of this work are from: New Chemistry Unit and Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore and Variable Energy Cyclotron Centre, Bidhannagar, Kolkata, India.