A 7-eV bandgap semiconductor based on silicon-doped α-(Al_xGa_1-x)₂O₃

In rectifying power electronics, wider-bandgap (E_g) semiconductors allow higher efficiency and power density with the Baliga figure of merit proportional to E_g^5.5 (refs. ^1,2). Unfortunately, the unique ability of semiconductors to have their conductivities controllably modulated over orders of magnitude by equilibrium doping methods becomes increasingly elusive as the bandgap increases. Increasing demand for wider-bandgap semiconductors has led to many materials previously considered insulators-including GaN, SiC, AlN, Ga₂O₃ and GeO₂-to emerge as useful semiconductors after decreasing defect densities and finding appropriate dopants. Here we report silicon-doped α-(Al_xGa_1-x)₂O₃ films with bandgaps exceeding 7.0 eV grown by suboxide molecular-beam epitaxy, surpassing that of cubic boron nitride, the next-widest-bandgap semiconductor known^3-5. In the colossal-bandgap regime, >6 eV, our silicon-doped α-(Al_xGa_1-x)₂O₃ films have room-temperature conductivities over 100 million times higher than all previous reports⁶. We fabricate a Schottky diode and a field-effect transistor (the AlphaFET) with colossal-bandgap channels. These α-(Al_xGa_1-x)₂O₃ films and devices use sapphire, an abundant, inexpensive substrate with excellent quality that is produced at massive scale, facilitating the development and adoption of colossal-bandgap electronics. Our achievement breaks the trend of increasing synthesis difficulty, cost and small size of ever-wider-bandgap semiconductors, for example, diamond and cubic boron nitride.