EAGER: Lateral Heterojunctions: Fabrication & Characteristics of a Novel Concept in 2D Materials Electronics

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Non-technical Description: Two-dimensional materials such as graphene and molybdenum disulfide have attracted considerable attention because they may offer a facile way of fabricating electronic devices at the ultimate limit of miniaturization, i.e., based on an inert, stable atomic sheet that is only a single layer thick. Within this framework, this EAGER research project intends to develop the concept of lateral continuous transitions between different single-layer materials, in which the composition of the material is controlled by chemical means to transition rapidly, e.g., from molybdenum disulfide to molybdenum diselenide. The ultimate goal is to develop a procedure by which well-defined patterns of material composition and ensuing electronic properties can be "woven" into a single atomic sheet like a pattern in a plaid cloth. If successful, this approach will provide for significantly more facile fabrication of device structures than the conventional approach. This project is conducted at a Hispanic Serving institution and directly benefits multiple Hispanic undergraduate and graduate students in the lab. It synergizes with a Research Experience for Undergraduate students site directed by the principle investigator.Technical Description: This project intends the development of methods for the preparation of lateral compositional heterojunctions in transition metal dichalcogenide single-layer films utilizing a modified chemical vapor deposition approach. It builds on findings in the principle investigator's lab that permit the preparation of alloys between molybdenum disulfide and molybdenum diselenide at any composition. Preliminary data show that compositional gradients on the meV/micrometer scale can be fabricated. This research project investigates whether these gradients can be made sufficiently sharp and controlled so that they can set up quantum wells or other functional elements for single-layer devices. To this end, researchers apply both dedicated control of the chalcogen injection during the film growth and post-growth processing of films by sulfur-selenium exchange. Characterization proceeds primarily by optical spectroscopy augmented by electrical testing where promising results are achieved. If the project has success, the resultant structures will permit transfer of many materials and device concepts of current GaAs/GaAlAs heterojunction technology, which is the base of much of modern optoelectronics, to the world of two-dimensional films.