Scientists at UCLA have developed a new process for assembling semiconductor devices that could lead to more energy-efficient transistors in future electronics and computer chips
The breakthrough is also said to help create diodes for solar cells and light-emitting diodes in the future that use far less energy than they do currently.
A paper about the research has been published in the journal Nature and was led by professor of chemistry and biochemistry in the UCLA College, Xiangfeng Duan, alongside professor of materials science and engineering at the UCLA Samueli School of Engineering, and Yu Huang.
The new method consists of joining a semiconductor layer and a metal electrode layer without the atomic-level defects that typically occur when other processes are used to build semiconductor-based devices.
Usually, when building such devices, those defects are minuscule. But even so, they can trap electrons traveling between the semiconductor and the adjacent metal electrodes, which makes the devices less efficient than they could be. The defects trap electrons traveling across them, and the electrons need extra energy to get through those spots.
However, the fresh method discovered by the UCLA prevents the defects from forming, by joining a thin sheet of metal atop the semiconductor layer through a simple lamination process.
So instead of using chemical bonds to hold the two components together, the new procedure uses van der Waals forces, which are weak electrostatic connections that are activated when atoms are very close to each other.
These keep the molecules 'attached' to each other even though their forces are weaker than chemical bonds. They are strong enough to hold the materials together because of how thin they are, with each layer is around 10 nanometers thick or less.
"Even though they are different in their geometry, the two layers join without defects and stay in place due to the van der Waals forces," Huang explained.
Using this theory, the engineers should be able to select the metal that allows electrons to move across the junction between metal and semiconductor with the smallest amount of energy. But because of those tiny defects that have always occurred during manufacturing, semiconductor devices have always needed electrons with more energy than the theoretical minimum.
The UCLA team is the first to test the theory in real-life experiments with different combinations of metals and semiconductors, and because the electrons didn't have to overcome the usual defects, they were able to travel with the minimum amount of energy.
"Our study for the first time validates these fundamental limits of metal-semiconductor interfaces," Duan added.
"It shows a new way to integrate metals onto other surfaces without introducing defects. Broadly, this can be applied to the fabrication of any delicate material with interfaces that were previously plagued by defects."
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