Northwestern University researchers are investigating the possibility of vertical heat transport for better cooling devices.
A new paper published in Physical Review Letters by researchers at Northwestern University in Illinois explores the idea of using materials in which heat flows perpendicular to an electric current to develop better devices for cooling electronics.
Traditional solid state cooling devices make use of an electric current to induce heat flow in the same or opposite direction as the current. While the thermoelectric effect in metals occurs because the electrons that carry charge also transport heat, the situation is different in semiconductors.
“In semiconductors, electrons populate distinct ranges of energy levels called bands. Holes, where electrons are missing from otherwise-filled bands, act as positive charges that carry energy in the opposite direction from the current-carrying electrons.” Under normal circumstances, the heat transported by electronics and holes partially cancels out, Physics explains.
However, according to Matthew Grayson of Northwestern University and his colleagues, the situation changes when electrons and holes do not move in directly opposite directions. They present an example “where an electric current along one axis of a crystal is carried mostly by electrons, whereas current in the perpendicular directions consists mostly of holes. When the current runs at an intermediate angle, a “transverse” thermoelectric effect that moves heat perpendicular to this current [was identified].”
Because the charge and heat move in perpendicular directions, Grayson explains, the potential area available for vertical heat transport is much larger than if it were confined to the same traditional dimensions as the electric current.
“That’s the essence of what you can make these structures [work],” Grayson said.
Grayson proposes that such a possibility could be achieved in artificial “heterostructures” consisting of alternating ultrathin layers of indium arsenide and gallium antimonide, but admits that heterostructure-based devices may be difficult to make, in part because “such materials are grown with the layers parallel to the substrate.” He suggests several possibilities for further investigation, including using natural materials with related effects and experimenting with non-planar devices.
For more information, visit Physics.