µ-ATOMS Center Established to Understand Fundamentals of Atomic Ordering in Semiconductors
The newly established Manipulation of Atomic Ordering for Manufacturing Semiconductors (µ-ATOMS) Energy Frontier Research Center aims to discover the fundamental principles determining the ordering of atoms in semiconductor alloys and how ordering affects material properties. Semiconductors are widely used in electronic devices such as transistors in smartphones and computers, solar cells, and light-emitting diodes (LEDs) due to their unique electronic properties. The performance of these devices is closely related to the atomic-level structure of the semiconductors. By understanding and manipulating the atomic ordering of semiconductors, researchers at the µ-ATOMS Center ultimately aim to enable improved performance of electronic and optoelectronic devices through fundamental discoveries achieved in the EFRC. The Center employs a multi-disciplinary approach, using a variety of techniques through four research thrusts to achieve its goals. The Center is expected to make significant contributions to the field of semiconductor manufacturing, with the potential to enable a "synthesis by design" approach for creating semiconductor alloys with specific properties by manipulating the atomic ordering. This approach could lead to new, low-cost, and reliable microelectronics technologies.
Specifically, µ-ATOMS will be investigating the effects of short-range order (SRO) on the properties of semiconductor alloys, such as electronic band structures, electronic transport properties, and thermal conductivity. SRO has emerged as a hot research topic in recent years. It refers to the non-random distribution of atoms over a short distance, usually only a few nanometers (about 10,000 times smaller than the width of human hair!). Figure 1 illustrates the difference between a random distribution and a SRO distribution: a random distribution has no restriction/preference on its nearest neighbors, while a SRO distribution has restriction/preference on its nearest neighbors. Using state-of-art computational modeling, the Center's team discovered that silicon germanium tin (SiGeSn) alloys—promising semiconductor materials for microelectronics and optoelectronics—are not as random as previously assumed, but instead display a SRO hidden beneath the nominal randomness. A remarkable finding is that the subtle change in atomic ordering can lead to significant changes in the underlying electronic structure that are sufficient to enable new functions and devices that are hard to achieve through conventional approaches . This finding generated excitement in the SiGeSn community and pointed to the tantalizing prospect that material properties in semiconductor alloys could be designed and fabricated by manipulating the order of atoms. The Center thus has a vision to precisely manipulate the spatial correlation among atoms, enabling a new way of tuning semiconductor properties of SRO quantum wells, wires, or dots using only one composition, with possible SRO band switching, novel interfaces, lateral heterostructure, new memory, and transistors (Fig. 1). The new way of tuning semiconductor properties is different from the conventional approaches that manipulate composition, dopants, or defects. While the finding is exciting, significant challenges and fundamental knowledge gaps exist in understanding and controlling SRO.
To address challenges and fundamental knowledge gaps, the µ-ATOMS Center will employ a multi-disciplinary approach through a synergistic team effort that covers the full spectrum of materials research including materials theory, growth, characterization, and device prototyping. The µ-ATOMS Center has 18 principal investigators from 10 institutions, including University of Arkansas, Sandia National Laboratory, George Washington University, Dartmouth College, Stanford University, Rensselaer Polytechnic Institute, Arizona State University, University of Delaware, University of Arkansas at Pine Bluff, and University of California, Berkeley. The team’s expertise spans physics, materials science and engineering, electrical engineering, and metallurgy. The Center focuses their efforts through four research thrusts: Theory and Modeling (Thrust-1), Synthesis and Control of SRO (Thrust-2), Determination of Degree and Type of SRO (Thrust-3), and Transformative Opportunities (Thrust-4), enabled by new optical, electrical, quantum, and SRO structure transition properties. Specifically, the Theory and Modeling Thrust will model the underlying physics and materials science that govern growth of materials and impact on material properties and will provide guidelines for other thrusts and get feedback from them. The Synthesis and Control of SRO Thrust will develop new synthesis methods and techniques to control and prepare Group IV SiGeSn semiconductors with different types and degrees of SRO, with the goal of achieving growth of different degrees of SRO and control over the spatial arrangement of SRO domains. The Determination of Degree and Type of SRO Thrust will characterize the SRO in semiconductor alloys by using a variety of techniques that include advanced methods such as atom probe tomography (APT), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), scanning tunneling microscopy (STM), Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), optical probes, and electrical transport measurements. These techniques will be used in combination to provide a comprehensive understanding of the degree and type of SRO and its connection to material properties. The Transformative Opportunities Thrust will crosscut Thrusts 1–3, utilizing the new knowledge base to uncover the connection between SRO and semiconductor properties and to synthesize SRO functional structures to demonstrate these properties (see also Fig. 1).
In summary, the newly established µ-ATOMS Center aims to understand the fundamental scientific principles that determine the short-range ordering (SRO) of atoms in semiconductor alloys, using a combination of modeling, simulation, synthesis, characterization, and measurement techniques. The fundamental research of µ-ATOMs may eventually enable the development of reliable, economical, environmentally friendly, and transformative approaches to the manufacturing of semiconductors for efficient smart devices and innovative technologies.
 X. Jin, S. Chen, and T. Li, “Coexistence of two types of short-range order in Si–Ge–Sn medium-entropy alloys,” Communications Materials 3, 66 (2022).