This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Semiconductors with wider bandgaps could pave the way for smaller, more efficient electronics that can handle far higher voltages, but the wider this gap becomes, the harder it is to control how well a material conducts electricity. Now, a team led by Darrell Schlom at Cornell University has shown that adding silicon to thin films of aluminum gallium oxide can keep this control intact at bandgaps wider than any semiconductor before it.
Their research has been published in Nature. In a semiconductor, electrons occupy two distinct ranges of energy. In the lower "valence band," they are bound tightly to their atoms and can't carry a current.
If they gain enough energy, however, they can jump into the higher "conduction band," where they move freely. A semiconductor's bandgap describes the energy required for an electron to make this leap and allows semiconductors to be switched between insulating and conducting states. Since wider bandgaps let materials withstand stronger electric fields, wide-bandgap semiconductors like gallium nitride and silicon carbide are already used in everything from fast phone chargers to electric vehicles.
Aluminum gallium oxide is an especially promising material. By adjusting its ratio of aluminum to gallium, its bandgap can be tuned anywhere from 5.4 to 8.6 electronvolts (eV), the widest range of any known semiconductor. But as the aluminum content rises, it becomes far harder to supply the material with free electrons.
Until now, aluminum-rich films have conducted electricity several orders of magnitude more poorly than gallium-rich ones, which has made them impractical for electronics. Schlom's team tackled this challenge through a careful fabrication approach involving a sapphire substrate. To grow the oxide films, they applied a technique called molecular-beam epitaxy, which builds up a material one atomic layer at a time.
As each film grew on top of the sapphire, they added small amounts of silicon, whose atoms donate spare electrons to the material. Finally, they measured the films' bandgaps and electrical properties and tested how the films behaved inside two key electronic components: a diode and a transistor. The silicon-doped films conducted electricity at bandgaps of more than 7 eV, beating the previous record held by cubic boron nitride.
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