Cientistas do Pacific Northwest National Laboratory descobriram novas propriedades em um material semicondutor usando uma técnica poderosa e não convencional. Crédito: Quardia, Shutterstock.com
Descoberta revela o papel das impurezas de oxigênio nas propriedades dos semicondutores
Uma equipe de pesquisadores investigando as propriedades de um semicondutor combinado com uma nova folha fina de óxido descobriu uma nova e inesperada fonte de condutividade de átomos de oxigênio presos dentro.
Scott Chambers, cientista de materiais do Laboratório Nacional do Noroeste do Pacífico do Departamento de Energia, revelou as descobertas da equipe na reunião de primavera de 2022 da American Physical Society. Os resultados do estudo são detalhados na revista Materiais de Revisão Física.
A descoberta tem implicações de longo alcance para a compreensão da função de filmes finos de óxido no futuro projeto e fabricação de semicondutores. Especificamente, os semicondutores utilizados na eletrônica moderna são classificados em dois tipos básicos: tipo n e tipo p, dependendo da impureza eletrônica introduzida durante a formação do cristal. Ambos os materiais à base de silício do tipo n e p são usados em dispositivos eletrônicos modernos. No entanto, há um interesse contínuo no desenvolvimento de novos tipos de semicondutores. Chambers e seus colegas estavam experimentando germânio em conjunto com uma fina camada cristalina de lantânio-estrôncio-zircônio-óxido de titânio (LSZTO).
Micrografia eletrônica de transmissão de varredura da interface entre germânio (parte inferior) e LSZTO (parte superior). Os átomos individuais são rotulados de ouro: germânio, vermelho: oxigênio, verde: estrôncio e lantânio, azul: titânio e zircônio. Crédito: Scott Chambers, Pacific Northwest National Laboratory
“Estamos relatando uma ferramenta poderosa para testar a estrutura e a função de semicondutores”, disse Chambers. “A espectroscopia de fotoelétrons de raios-X duros revelou neste caso que os átomos de oxigênio, uma impureza no germânio, dominam as propriedades do sistema material quando o germânio é unido a um determinado material de óxido. Esta foi uma grande surpresa.”
Usando o[{” attribute=””>Diamond Light Source on the Harwell Science and Innovation Campus in Oxfordshire, England, the research team discovered they could learn a great deal more about the electronic properties of the germanium/LSZTO system than was possible using the typical methods.
“When we tried to probe the material with conventional techniques, the much higher conductivity of germanium essentially caused a short circuit,” Chambers said. “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.”
Materials Scientist Scott Chambers and his Pacific Northwest National Laboratory colleagues study the properties of semiconductor materials at atomic-level detail. Credit: Andrea Starr, Pacific Northwest National Laboratory
A new role for hard X-rays
The so-called “hard” X-rays produced by the Diamond Light Source could penetrate the material and generate information about 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,” Chambers said. “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. 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 together, is where interesting semiconducting properties often emerge. The challenge, according to Chambers, is to learn how to control the fascinating and potentially useful electric fields that forms at these interfaces by modifying the electric field at the surface. Ongoing experiments at PNNL are probing this possibility.
While the samples used in this research do not likely have the immediate potential for commercial use, the techniques and scientific discoveries made are expected to pay dividends in the longer term, Chambers said. The new scientific knowledge will help materials scientists and physicists better understand how to design new semiconductor material systems with useful properties.
PNNL researchers Bethany Matthews, Steven Spurgeon, Mark Bowden, Zihua Zhu and Peter Sushko contributed to the research. The study was supported by the Department of Energy Office of Science. Some experiments and sample preparation were performed at the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science user facility located at PNNL. Electron microscopy was performed 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 prepared the samples.
Reference: “Mapping hidden space-charge distributions across crystalline metal oxide/group IV semiconductor interfaces” by S. A. Chambers, M. Chrysler, J. H. Ngai, T.-L. Lee, J. Gabel, B. E. Matthews, S. R. Spurgeon, M. E. Bowden, Z. Zhu and P. V. Sushko, 21 January 2022, Physical Review Materials.
DOI: 10.1103/PhysRevMaterials.6.015002
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