As wide-bandgap GaN-based RF materials approach commercialization and deployment, a new generation of ultra-wide bandgap materials has come of interest. These materials could enable two- to ten-fold improvement in voltage handling as a consequence of their bandgaps in the 4.5-6 eV range, leading to improved RF output power, efficiency, and thermal management. Specific materials of interest include diamond and cubic boron nitride (c-BN) which possess bandgaps from 5.5-6.4 eV, the potential for heterostructure engineering, and some of the highest known thermal conductivities. AlN, with a bandgap of 6.2 eV, together with pesudobinary alloys of a family of novel nitride semiconductors including ScN, YN, and LaN in additional to traditional InN and GaN, forms a promising material system with attractive electronic, piezoelectric, and optical properties. Additional nitride materials which complement the capabilities of these ultra-wide bandgap materials are also of interest.

The objective of this research will be to understand the relationship between the epitaxial growth process and resulting point/extended defects, and morphology in these novel materials to achieve electrical, acoustic, and optical performance required for the next-generation of RF technology. Close collaboration with device scientists at NRL will enable correlation of materials properties with electronic properties through early-stage fabrication and testing of test structures and full devices. Extensive facilities exist to enable epitaxial growth and characterization of ultra-wide bandgap semiconductors, including two modern nitride molecular beam epitaxy systems including integrated multi-pocket e-beam evaporators for refractory source materials, a full suite of materials characterization tools (X-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, deep-UV photoluminescence, and Hall, CV, pulsed IV, and RF electrical test benches), and both an in-house and campus-wide state-of-the art cleanroom.

Eligible candidates with experience in epitaxial growth, ultra-high vacuum hardware, and materials characterization are encouraged to apply.

References:

M.T. Hardy, A.C. Lang, E.N. Jin, N. Nepal, B.P. Downey, V.J. Gokhale, D.S. Katzer, and V.D. Wheeler, “Nucleation Control of High Crystal Quality Heteroepitaxial Sc0.4Al0.6N Grown by Molecular Beam Epitaxy,” J. Appl. Phys. 134, 105301 (2023).

M. B. Tahhan, J. A. Logan, M.T. Hardy, M.G. Ancona, B. Schultz, B. Appleton, T. Kazior, D.J. Meyer, E.M. Chumbes, “Passivation Schemes for ScAlN-based mm-Wave High Electron Mobility Transistors,” IEEE Trans. Electron Dev. 69, 962 (2022).

D.F. Storm, S.I. Maximenko, A.C. Lang, N. Nepal, T.I Feygelson, B.B. Pate, C.A. Affouda, and D.J. Meyer, “Mg-Facilitated Growth of Cubic Boron Nitride by Ion Beam-Assisted Molecular Beam Epitaxy” Phys. Status Solidi RRL 16, 2200036 (2023).

key words

ultra-wide bandgap semiconductor; AlN; BN; molecular beam epitaxy; transition metal nitride; III-nitride; RF electronics; energy efficiency; materials science; transistor

Citizenship:  Open to U.S. citizens and permanent residents

Level:  Open to Postdoctoral applicants