Working with scientists in Texas and Warsaw, researchers at Finland’s Aalto University have made a breakthrough in revising methods largely discarded 15 years ago (‘Amphoteric Be in GaN: Experimental Evidence for Switching between Substitutional and Interstitial Lattice Sites’, Physical Review Letters (2017) volume 119, p196404).
Experiments with beryllium doping of gallium nitride were conducted in the late 1990s in the hope that beryllium would prove more efficient as a doping agent than the prevailing magnesium used in LED lights. However, the work proved unsuccessful, and research on beryllium was largely discarded.
The researchers have now discovered a microscopic mechanism that can allow GaN-based semiconductors to be used in electronic devices that distribute large amounts of electric power. To be useful in devices that need to process considerably more energy than in everyday home entertainment, gallium nitride needs to be manipulated in new ways on the atomic level, they add.
“There is growing demand for semiconducting gallium nitride in the power electronics industry,” notes professor Filip Tuomisto of Aalto University. “To make electronic devices that can process the amounts of power required in, say, electric cars, we need structures based on large-area semi-insulating semiconductors with properties that allow minimizing power loss and can dissipate heat efficiently.” To achieve this, doping gallium nitride with beryllium shows great promise, he adds.
Due to advances in computer modelling and experimental techniques, the researchers have managed to show that beryllium can actually perform useful functions in gallium nitride. Depending on whether the material is heated or cooled, beryllium atoms exhibit amphoteric behavior in GaN, involving switching between substitutional and interstitial positions in the lattice, changing their nature of either donating or accepting electrons.
“Our results provide valuable knowledge for experimental scientists about the fundamentals of how beryllium changes its behaviour during the manufacturing process,” says Tuomisto. “During it – while being subjected to high temperatures – the doped compound functions very differently than the end result.”
If the beryllium-doped gallium nitride structures and their electronic properties can be fully controlled, power electronics could move to a new realm of energy efficiency, it is reckoned.
“The magnitude of the change in energy efficiency could as be similar as when we moved to LED lights from traditional incandescent light bulbs,” says Tuomisto. “It could be possible to cut down the global power consumption by up to 10% by cutting the energy losses in power distribution systems,” he concludes.
Moreover, the similarity of this behavior to that found for sodium (Na) and lithium (Li) dopants in zinc oxide (ZnO) suggests that this could be a universal property of light dopants substituting for heavy cations in compound semiconductors.
