WSU team develops van der Waals Schottky junctions with significantly enhanced thermoelectric properties
A team at Washington State University (WSU), with colleagues from the University of Science and Technology of China, Hefei, has developed a multicomponent, multilayered In2Se3composite material van der Waals Schottky diode. Besides ideal diode behaviors and the gate-tunable current rectification, thermoelectric power is significantly enhanced in these junctions by more than three orders of magnitude compared with single-phase multilayer In2Se3, with the thermoelectric figure-of-merit approaching ∼1 at room temperature.
In a paper published in the ACS Journal of Physical Chemistry Letters, the team led by Yi Gu, an associate professor in WSU’s Department of Physics and Astronomy, suggest that these significantly improved thermoelectric properties are not due to the 2D quantum confinement effects but instead are a consequence of the Schottky barrier at the junction interface, which leads to hot carrier transport and shifts the balance between thermally and field-driven currents. While still in an early stage of development, the new diode could eventually provide an extra source of power for everything from smartphones to automobiles.
The ability of our diode to convert heat into electricity is very large compared to other bulk materials currently used in electronics. In the future, one layer could be attached to something hot like a car exhaust or a computer motor and another to a surface at room temperature. The diode would then use the heat differential between the two surfaces to create an electric current that could be stored in a battery and used when needed.—Yi Gu
Schottky diodes guide electricity in a specific direction, similar to how a valve in a water main directs the flow of liquid going through it. They are made by attaching a conductor metal such as aluminum to a semiconductor material such as silicon.
Instead of combining a common metal like aluminum or copper with a conventional semiconductor material like silicon, Gu’s diode is made from a multilayer of microscopic, crystalline Indium Selenide. He and a team of graduate students used a simple heating process to modify one layer of the Indium Selenide to act as a metal and another layer to act as a semiconductor.
The researchers then used a new kind of confocal microscope developed by Klar Scientific, a start-up company founded in part by WSU physicist Matthew McCluskey, to study their materials’ electronic properties.
Unlike its conventional counterparts, Gu’s diode has no impurities or defects at the interface where the metal and semiconductor materials are joined together. The smooth connection between the metal and semiconductor enables electricity to travel through the multilayered device with almost 100 percent efficiency.
When you attach a metal to a semiconductor material like silicon to form a Schottky diode, there are always some defects that form at the interface. These imperfections trap electrons, impeding the flow of electricity. Gu’s diode is unique in that its surface does not appear to have any of these defects. This lowers resistance to the flow of electricity, making the device much more energy efficient.—Matthew McCluskey
Gu and his collaborators are currently investigating new methods to increase the efficiency of their Indium Selenide crystals. They are also exploring ways to synthesize larger quantities of the material so that it can be developed into useful devices.
While still in the preliminary stages, our work represents a big leap forward in the field of thermoelectrics. It could play an important role in realizing a more energy-efficient society in the future.—Yi Gu
Qiaoming Wang, Liangliang Yang, Shengwen Zhou, Xianjun Ye, Zhe Wang, Wenguang Zhu, Matthew D. McCluskey, and Yi Gu (2017) “Phase-Defined van der Waals Schottky Junctions with Significantly Enhanced Thermoelectric Properties”, The Journal of Physical Chemistry Letters 8 (13), 2887-2894 doi: 10.1021/acs.jpclett.7b01089