Ultra-Wide Bandgap Semiconductors Research

NREL's materials discovery and design work on ultra-wide bandgap (UWBG, E.g. > 3.4 eV) semiconductor focuses on epitaxial growth, high-performance device fabrication, and modeling from the materials to the package level.

Our research covers group III nitrides (GaN, AlGaN, AlN), gallium oxide (Ga₂O₃ and alloys) and related oxide and nitride compounds (such as ZnGeN₂, InBO₃, In₂Ge₂O₇), and next-generation materials and includes wide bandgap (WBG, Eg > 2.7) semiconductors.

UWBG materials discovery and design research at NREL aims to develop materials and devices that can handle large power loads with low loss, often in extreme environments such as high temperatures, chemically aggressive atmospheres, and under significant radiation. These devices include power devices such as transistors, diodes, and next-generation extreme environment sensors.

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 (MBE) and pulsed laser deposition. We have three MBE tools dedicated to nitride discovery, group III-N growth, and UWBG oxides (including Ga₂O₃, NiO, and others). These growth techniques enable high-quality materials and interfaces between functional semiconductor/insulator/metal layers, which are critical for reliable material and device performance.  

An example is given below, where MBE was used to grow a series of Al-substituted Ga₂O₃ thin films up to 21% Al. Substituting Al into Ga₂O₃ is used to increase the bandgap, decrease leakage current, and create modulation-doped field effect transistors. Another focus area is heteroepitaxial growth of p-type oxide semiconductors used in conjunction with n-type Ga₂O_3, which is not able to be p-type doped. Examples of these compounds include NiO and Mg:Cr₂O₃, among others.

For more information, see:

Epitaxial (Al_xGa_1−x−yIn_y)₂O₃ Alloys Lattice Matched to Monoclinic Ga₂O₃ Substrates,  Applied Physics Letters (2024)

Rapid Screening of Molecular Beam Epitaxy Conditions for Monoclinic (In_xGa_1−x)₂O₃ Alloys, Journal of Materials Chemistry A  (2024)

Structure, Defects, and Optical Properties of Commensurate GaN/ZnGeN₂/GaN Double Heterojunctions, Journal of Materials Chemistry C (2023)

Growth and Characterization of Homoepitaxial β-Ga₂O₃ Layers, Journal of Physics D: Applied Physics (2020).

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, metallization, and dielectric deposition capabilities.

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

Using this device expertise, we are exploring a variety of applications, including long-term characterization of an oxide p-n heterojunction consisting of Mg:Cr₂O₃ on Ga₂O₃ that operated in a stable manner after exposure to 500°C for hundreds of hours and tens of cycles.

For more information, see:

NiGa₂O₄ Interfacial Layers in NiO/Ga₂O₃ Heterojunction Diodes at High Temperature,  Applied Physics Letters (2024)

Ultrathin Stable Ohmic Contacts for High-Temperature Operation of β-Ga₂O₃ Devices, Journal of Vacuum Science & Technology A (2023)

Gallium Oxide Heterojunction Diodes for 400 °C High-Temperature Applications,  Physica Status Solidi (a) (2023)

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 materials discovery and design researchers are solving this issue through novel carbide, nitride, and boride substrates and buffer layers which are lattice-matched to a wide range of III-N materials. These materials can eliminate the need for costly and thick metamorphic buffer layers, which result in poor device quality and cracks due to thermal mismatch.

For more information, see Designing TaC Virtual Substrates for Vertical AlGaN Power Electronics Devices, PRX Energy (2024).

Computational Predictions and Experimental Validation of New Ultra-Wide Bandgap Materials

In collaboration with the Colorado School of Mines, we are predicting new UWBG semiconductors and experimentally validating their structure and properties. Recent examples include InBO₃, In₂Ge₂O_7, and related materials.

For more information, see:

Computational Identification of Ternary Wide-Band-Gap Oxides for High-Power Electronics, PRX Energy (2022)

Defect Chemistry and Doping of Ultrawide Band Gap (III)BO₃ Compounds, Chemistry of Materials (2023)

A Computational Survey of Semiconductors for Power Electronics, Energy & Environmental Science (2020)

Electrothermal Modeling and Technoeconomic Analysis

We are collaborating with other directorates at NREL in simulating the expected power electronic device performance, designing device packaging for its reliability, modeling thermal performance of the packages, and evaluating future cost reduction potential of UWBG materials.

For more information, see:

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

Projected Cost of Gallium Oxide Wafers from Edge-Defined Film-Fed Crystal Growth, Crystal Growth & Design (2022)

Computational Insights into Phase Equilibria between Wide-Gap Semiconductors and Contact Materials, ACS Applied Electronic Materials (2024)

Modeling and Analysis of Gallium Oxide Vertical Transistors, ECS Journal of Solid (2019).

Projects

Ultra-wide bandgap material and device research at NREL has been funded by the U.S. Department of Energy's (DOE) Office of Energy Efficiency and Renewable Energy (EERE) through the Advanced Materials and Manufacturing Technology Office (AMMTO),  the DOE Office of Science (SC) and NREL's Laboratory Directed Research and Development (LDRD) Program.

Research Collaborators

Contacts