Researchers at Cornell University led by Darrell Schlom have developed a sapphire-grown semiconductor film that successfully conducts electricity at a record-breaking bandgap of more than 7 electronvolts (eV). The breakthrough addresses a long-standing challenge in materials science: as semiconductors are engineered with wider bandgaps to handle higher voltages and improve electronic efficiency, maintaining electrical conductivity becomes increasingly difficult.
By adjusting the ratio of aluminum to gallium within thin films of aluminum gallium oxide, the team tuned the material’s bandgap across a range from 5.4 to 8.6 eV, which represents the widest tunable range of any known semiconductor. To overcome the traditional obstacle where aluminum-rich films conduct electricity orders of magnitude more poorly than gallium-rich alternatives, the team used a fabrication technique using a sapphire substrate.
Fabrication and Testing of Colossal-Bandgap Materials
The team utilized molecular-beam epitaxy to construct the oxide films one atomic layer at a time on top of the sapphire. During growth, small amounts of silicon were added to donate spare electrons to the material. Subsequent measurements of the films’ electrical properties revealed that within a range above 6 eV—designated by the researchers as a colossal bandgap
—the material conducted electricity at room temperature over 100 million times better than any previous report, successfully surpassing the previous record held by cubic boron nitride.
To demonstrate practical utility, the researchers tested the films inside two key electronic components, confirming that both a diode and a transistor worked successfully with the colossal-bandgap materials. Researchers noted that sapphire offers distinct manufacturing advantages compared with other ultra-wide-bandgap materials like diamond and cubic boron nitride, as sapphire is abundant, inexpensive, and already produced at high quality on a massive scale. The team expects these developments will enable next-generation power electronics capable of minimizing energy waste as heat during the conversion and control of electricity.