Thickness-Dependent Bandgap and Atomic Structure in Elemental Tellurium Films

Elemental tellurium electrical switch, relying on a transient crystal-liquid-crystal phase transition, has recently been proposed as a promising selector candidate for the next-generation 3D high-density memory, bridging performance gap in today's computer. Further miniaturization of the switch cell to increase memory density strongly depends on the scalability of the tellurium film, which, however, has not been experimentally studied. Herein, the tellurium films are prepared with the thickness downscaled from 400 to 2 nm and a significant increase is found in the bandgap from 0.29 to 0.91 eV, as predicted by ab initio molecular dynamics. Interestingly, the as-deposited tellurium films with a thickness above 3 nm are in the crystalline trigonal phase, whereas 2 nm thick film suddenly becomes amorphous, observed by both Raman and transmission electron microscopies. In this finding, since the leakage current of the elemental tellurium switch is determined by both the Schottky barrier between tellurium/electrode interface and the bandgap of the tellurium film, a reduction in leakage current is predicted with further miniaturization. In this research, with the help of ab initio molecular dynamics calculation, a low-cost and feasible approach is proposed to effectively increase the bandgap of Te films via thinning the thickness. This increase of bandgap further suppresses the leakage current of elemental Te switching devices, and paves the way for future application in large-array-scale 3D high-density phase-change memory.image (c) 2024 WILEY-VCH GmbH