Contacts to Layered Dichalcogenide Semiconductors

非技术描述：二维层状半导体最近吸引了科学家和工程师的想象力，因为它们具有不同寻常的物理性质和许多应用的潜力。例如，用这些材料制造的晶体管可以用于消费电子产品；从这些材料衍生的光伏可以提供更大的能源独立性；使用这些材料的分子传感可以帮助国土安全。为了实现这些新材料的潜力并在各种设备中有效地使用它们，了解和开发允许电流流入和流出设备而不会造成重大损失的电触点是至关重要的。一名研究生和本科生正在接受科学和工程研究方法方面的直接培训，以解决这一科学问题。首席研究人员还在获得经验，为高级材料科学和工程课程以及针对代表性不足的初中生和高中生的外联活动提供信息。技术描述：该项目解决了二维层状二卤化物半导体的低电阻欧姆接触的需求，包括二硫化钼和二硒化钽。研究人员正在使用热力学计算和相图来选择金属触点，这些金属触点在退火时可能会表现出不同类型的反应。反应的情景包括金属扩散到半导体中，用其他过渡金属取代钼或钨，以及形成具有不同带隙的不同层状半导体。这种反应提供了掺杂半导体或改变金属/半导体界面的肖特基势垒高度的可能性，因此它们可以降低接触的电阻。这些反应正在使用透射电子显微镜(包括像差校正的扫描/透射电子显微镜)进行研究，这非常适合于检测金属/半导体界面上或附近原子排列的变化。研究人员还使用互补的方法来测量特定的接触电阻，并更深入地了解通过触点的电流传输。该项目有助于更深入地了解与二维层状二卤化物半导体的接触，更广泛地说，有助于处理层状材料的科学。

Non-technical Description: Two-dimensional layered semiconductors have recently captured the imagination of scientists and engineers because of their unusual physical properties and potential for many applications. For example, transistors fabricated from these materials could be used in consumer electronics; photovoltaics derived from the materials could offer greater energy independence; and molecular sensing using these materials could aid homeland security. To realize the potential of these new materials and use them efficiently in a variety of devices, it is critical to understand and develop electrical contacts that allow current to flow in and out of the devices without significant losses. A graduate student and undergraduate students are receiving direct training in science and engineering research methods as they address this scientific problem. The principal investigator is also gaining experience that informs upper-level material science and engineering courses, as well as outreach activities for underrepresented middle- and high-school students.Technical Description: This project addresses the need for low-resistance Ohmic contacts for two-dimensional layered dichalcogenide semiconductors, including molybdenum disulfide and tantalum diselenide. Investigators are using thermodynamic calculations and phase diagrams to select metal contacts that are likely to exhibit different types of reactions upon annealing. The scenarios for reaction include diffusion of the metal into the semiconductor, substitution of other transition metals for molybdenum or tungsten, and formation of a different layered semiconductor with a different band gap. Such reactions offer the potential to dope the semiconductor or alter the Schottky barrier height at the metal/semiconductor interface, and they could therefore reduce the resistance of the contacts. The reactions are under study using transmission electron microscopy (including aberration-corrected scanning/transmission electron microscopy), which is well suited to detecting changes in the arrangement of atoms at or near the metal/semiconductor interface. Researchers also employ complementary approaches to measure specific contact resistance and gain greater insight into current transport through the contacts. The project contributes to a deeper understanding of contacts to two-dimensional layered dichalcogenide semiconductors and more generally to the science of processing layered materials.