NREL Theory Establishes a Path to High-Performance 2D Semiconductor Devices
April 27, 2016 | NRELEstimated reading time: 2 minutes
Researchers at the Energy Department's National Renewable Energy Laboratory (NREL) have uncovered a way to overcome a principal obstacle in using two-dimensional (2D) semiconductors in electronic and optoelectronic devices.
2D semiconductors such as molybdenum disulfide are only a few layers thick and are considered promising candidates for next-generation devices. Scientists first must overcome limitations imposed by a large and tunable Schottky barrier between the semiconductor and a metal contact. The barrier, at the metal/semiconductor junction, creates an obstacle for the flow of electrons or holes through the semiconductor.
The NREL team discovered that the height of the Schottky barrier can be adjusted-or even made to vanish-by using certain 2D metals as electrodes. Such adjustments are not possible with conventional three-dimensional metals because of a strong Fermi level pinning (FLP) effect occurring at the junction of metal and semiconductor, due to electronic states in the semiconductor band gap that are induced by the metal. Increasing the flow of electrons or holes through a semiconductor reduces power losses and improves the device performance.
The NREL theorists considered a family of 2D metals that could bind with the 2D semiconductors through van der Waals interaction. Because this interaction is relatively weak, the metal-induced gap states are suppressed and the FLP effect is negligible. This means that the Schottky barrier becomes highly tunable. By selecting an appropriate 2D metal/2D semiconductor pair, one can reduce the barrier to almost zero (such as H-NbS2/WSe2 for hole conduction).
They noted that using a 2D metal as an electrode would also prove useful for integrating into transparent and flexible electronics because the 2D metal is also transparent and flexible. They also noted that the junction of 2D metal and 2D semiconductor is atomically flat and can have fewer defects, which would reduce carrier scattering and recombination.
The work by Yuanyue Liu, Paul Stradins, and Su-Huai Wei, "Van der Waals metal-semiconductor junction: weak Fermi level pinning enables effective tuning of Schottky barrier," appears in the new issue of Science Advances.
The trio of researchers predicts that hexagonal phase of niobium disulfide (NbS2) is the most promising for hole injection into a 2D semiconductor, and heavily nitrogen-doped graphene can enable efficient electron injection.
This research was funded by the Department of Energy's Office of Energy Efficiency and Renewable Energy. The work used computational resources at NREL and the National Energy Research Scientific Computing Center.
NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.
Suggested Items
Water Management in a Large Printed Circuit Board Manufacturer
04/15/2024 | Charles Nehrig, TTM TechnologiesTTM’s environmental management is grounded in its Environmental Statement and Environmental Policy, which promote measures that make for a more responsible environmental management process. Our management system helps TTM work toward minimizing its environmental footprint and increasing the sustainability of its operations. TTM monitors its environmental performance just as it monitors its operational performance, and provides the resources required to adhere to the Company’s environmental responsibilities.
Happy’s Tech Talk #27: Integrated Mesh Power System (IMPS) for PCBs
04/08/2024 | Happy Holden -- Column: Happy’s Tech TalkA significant decrease in HDI substrate production cost can be achieved by reducing the number of substrate layers from conventional through-hole multilayers and microvia multilayers of eight, 10, 12, and more to only two layers. Besides reducing direct processing steps, the yield will increase as defect-producing operations are eliminated. The integrated mesh power system (IMPS) was invented in the latter years of MCM-D use for thin-film fabrication. Those geometries fit today into our use of ultra HDI.
Trouble in Your Tank: Supporting IC Substrates and Advanced Packaging, Part 5
03/19/2024 | Michael Carano -- Column: Trouble in Your TankDirect metallization systems based on conductive graphite or carbon dispersion are quickly gaining acceptance worldwide. Indeed, the environmental and productivity gains one can achieve with these processes are outstanding. In today’s highly competitive and litigious environment, direct metallization reduces costs associated with compliance, waste treatment, and legal issues related to chemical exposure. What makes these processes leaders in the direct metallization space?
Indium Corporation Experts to Present at SEMI THERM
03/07/2024 | Indium CorporationIndium Corporation Global Account Manager and Senior Thermal Technologist Tim Jensen and Product Development Specialist for Thermal Interface Materials Miloš Lazić will present on thermal interface material (TIM) technology at SEMI-THERM, taking place March 25–28 in San Jose, California, U.S.
Indium Corporation to Showcase Proven EV Products and High-Reliability Alloys at Productronica China
02/28/2024 | Indium CorporationAs a materials pioneer and trusted partner in electric vehicle (EV) and e-Mobility manufacturing, Indium Corporation is proud to showcase its high-reliability alloys and soldering solutions at Productronica China, March 20-22, in Shanghai.