Ultra-Wide Bandgap Semiconductors Research

NREL’s wide bandgap (WBG, Eg > 2.7) and ultra-wide bandgap (UWBG, Eg > 3.4 eV) semiconductor research focuses on epitaxial growth, high-performance device fabrication, and modeling from the materials to the package level.

Epitaxial Growth

We perform thin-film growth and characterization of homoepitaxial and heteroepitaxial layers of WBG and UWBG semiconductors for applications in electronic devices that can operate at extreme conditions. Growth methods include molecular beam epitaxy and pulsed laser deposition.

NREL's UWBG capabilities cover many material systems from the relatively established aluminum gallium nitride (AlGaN) material system and emerging and promising candidate gallium oxide to novel and unexplored material system.

For more information, see Growth and Characterization of Homoepitaxial ß-Ga2O3 Layers, J. Phys. D: Appl. Phys. (2020).

Chart measuring thin-film growth and characterization

Device Fabrication

NREL's research in this area includes fabrication and characterization of first-of-a- kind device prototypes based on new ultra-wide bandgap semiconductor materials. Our extensive clean room fabrication capabilities include photolithography mask aligners, wet and dry etching stations, metalization, and dielectric deposition capabilities.

Device characterization efforts feature conventional probe stations with suitable electronics, as well as low-temperature and high-temperature measurement capabilities.

For more information, see Performance and Reliability of β-Ga2O3 Schottky Barrier Diodes at High Temperature, Journal of Vacuum Science and Technology A (2021).

Chart showing device characterization temperatures

Novel Substrates

A key limitation in the establishment of any UWBG system is the availability of lattice-matched substrates or templates for epitaxial layer growth. Some promising material systems, such as high-aluminum content AlGaN alloys, have yet to realize their full potential due to a lack of lattice matched substrates.

NREL is solving this issue through novel carbonitride substrates and buffer layers which are lattice-matched to a wide range of III-N materials, eliminating the need for costly and thick metamorphic buffer layers, which result in poor device quality and cracks due to thermal mismatch. Even more exciting, these novel buffers and substrates have tunable lattice constants, enabling lattice-matched epitaxy across the entire III-N alloy space.

Chart measuring novel substrates

Modeling

We also collaborate with several modeling groups on predicting new ultra WBG semiconductors, simulating the expected device performance, designing device packaging for its reliability, modeling thermal performance of the packages and evaluating future cost reduction potential.

For more information, see the following publications:

A Computational Survey of Semiconductors for Power Electronics, Energy & Environmental Science (2019)

How Much Will Gallium Oxide Power Electronics Cost? Joule, (2019).             

Chart modeling UWBGs

Projects

The UWBG semiconductor research has been funded by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office and by NREL’s Laboratory Directed Research and Development Program.

This project explores concepts in the substrates by design space, leveraging rapid material prototyping through combinatorial (and epitaxial) sputtering, high temperature annealing, high quality nitride  growth by molecular beam epitaxy, and state-of-the-art characterization facilities.
The goal of this project is to demonstrate oxide electronic materials and devices suitable for operation at high temperature (600⁰C) in extreme environments (corrosive atmosphere, mechanical stress) by improving manufacturing of Ga2O3 single-crystal wafers, using them to fabricate oxide electronic devices and sensors, and evaluating the device performance and reliability under extreme conditions.

The objective of this LDRD was to demonstrate oxidation-resistant wide-bandgap semiconductor materials for electronic devices that can operate at high temperature. The specific goals were to fabricate and characterize Ga2O3 diodes during operation at 500 °C in ambient atmosphere, and to demonstrate proof-of-concept transistors based on new oxide semiconductors.

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