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A surprising new source of conductivity from trapped oxygen atoms has been noted by a research group probing the properties of a semiconductor integrated with a novel thin oxide film.
Scott Chambers, a materials scientist at the Department of Energy’s Pacific Northwest National Laboratory, announced the breakthrough discovery of the group at the Spring 2022 meeting of the American Physical Society. The study's findings have been published in the Physical Review Materials journal.
The findings will have wide impacts in comprehending the role of thin oxide films in future semiconductor design and manufacture. Semiconductors utilized in modern electronics are available in two basic flavors — n-type and p-type — based on the electronic impurity added at the time of the crystal growth.
Modern electronic devices tend to use both n- and p-type silicon-based materials. However, there is continuous interest in developing other kinds of semiconductors. Chambers and his group were testing germanium together with a specialized thin crystalline film of lanthanum-strontium-zirconium-titanium-oxide (LSZTO).
We are reporting on a powerful tool for probing semiconductor structure and function. Hard X-ray photoelectron spectroscopy revealed in this case that atoms of oxygen, an impurity in the germanium, dominate the properties of the material system when germanium is joined to a particular oxide material. This was a big surprise.
Scott Chambers, Materials Scientist, Department of Energy, Pacific Northwest National Laboratory
The researchers discovered they could learn a great deal regarding the electronic properties of the germanium/LSZTO system compared to what was possible using the typical methods. This was done with the help of the Diamond Light Source on the Harwell Science and Innovation Campus in Oxfordshire, England.
When we tried to probe the material with conventional techniques, the much higher conductivity of germanium essentially caused a short circuit. As a result, we could learn something about the electronic properties of the Ge, which we already know a lot about, but nothing about the properties of the LSZTO film or the interface between the LSZTO film and the germanium—which we suspected might be very interesting and possibly useful for technology.
Scott Chambers, Materials Scientist, Department of Energy, Pacific Northwest National Laboratory
“Hard” X-Rays generated by the Diamond Light Source could enter the material and produce data regarding what was going on at the atomic level.
Our results were best interpreted in terms of oxygen impurities in the germanium being responsible for a very interesting effect. The oxygen atoms near the interface donate electrons to the LSZTO film, creating holes, or the absence of electrons, in the germanium within a few atomic layers of the interface.
Scott Chambers, Materials Scientist, Department of Energy, Pacific Northwest National Laboratory
Chambers added, “These specialized holes resulted in behavior that totally eclipsed the semiconducting properties of both n- and p-type germanium in the different samples we prepared. This, too, was a big surprise.”
The interface, where the thin-film oxide and the base semiconductor come into contact, is where interesting semiconducting properties tend to frequently emerge.
According to Chambers, the challenge is to learn how to control the interesting and potentially useful electric fields that develop at these interfaces by altering the electric field at the surface. Experiments in progress at PNNL are probing this possibility.
While the samples utilized in this study are not likely to have immediate commercial potential, the methods and scientific breakthroughs made are anticipated to pay dividends in the longer term, stated Chambers.
The new scientific knowledge gained will aid materials scientists and physicists to better comprehend how to design new semiconductor material systems with beneficial properties.
The PNNL scientists who contributed to the study include Bethany Matthews, Steven Spurgeon, Mark Bowden, Zihua Zhu, and Peter Sushko. The study was financially supported by the Department of Energy Office of Science. Experiments and sample preparation were carried out at the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science user facility located at PNNL.
Electron microscopy analysis was done in the PNNL Radiochemical Processing Laboratory. Collaborators Tien-Lin Lee and Judith Gabel performed experiments at the Diamond Light Source. Additional collaborators included the University of Texas at Arlington's Matt Chrysler and Joe Ngai who made the samples.
Chambers, S. A., et al. (2022) Mapping hidden space-charge distributions across crystalline metal oxide/group IV semiconductor interfaces. Physical Review Materials. doi.org/10.1103/PhysRevMaterials.6.015002
Source: https://www.pnnl.gov/
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