UC Berkeley

Large-scale growth of high-quality semiconductors forms the basis of the modern electronics. Growth of high-quality semiconductors such as Si typically requires a high processing temperature, which cannot meet the fabrication thermal budget for the emerging circuit architectures and applications such as three-dimensional (3D) monolithic integration and flexible electronics. Great effort has been devoted to exploration of low temperature material systems with sufficient mobility in last decades. Although low-temperature grown n-type films such as indium gallium zinc oxide (IGZO) with respectable electron mobility have been shown, the development of their p-type thin-film counterpart with sufficiently high hole mobility is still limited. In this report, we identify the elemental p-type semiconductor-Tellurium (Te) as a promising candidate due to its high hole mobility, low processing temperature and possibility for wafer-scale production.Specifically, the wafer-scale growth of Te thin films was realized through thermally evaporated at cryogenic temperatures, field effect transistors (FETs) based on which exhibited respectable electrical properties. 3D monolithic circuits and devices on flexible substrates were fabricated using the evaporated Te thin films, demonstrating that Te is a promising p-type semiconductor processed at low temperatures. After that, we systemically studied the growth mechanism of the thermally evaporated Te thin films, which has an intriguing amorphous to crystalline phase transition at near-ambient temperature. We visualized and modeled the kinetics and dynamics of the crystallization of thermally evaporated Te films and achieved the growth of Te thin films with large grains and patterned Te single crystal arrays by optimizing the crystallization temperature, which possess an enhanced crystallinity and electrical properties. Additionally, orientated growth of ultrathin tellurium was investigated, as Te has attractive orientated and thickness-dependent properties. Two-dimensional (2D) formed Te and SeTe alloys were realized on the three-fold symmetric transition metal dichalcogenides substrates (WSe2, WS2, MoSe2 and MoS2) by van der Waals epitaxy, forming an one-dimensional/2D moiré superlattice, where the chains were aligned to the armchair directions. Further, growth of single-crystal-textured Te film was demonstrated on the low-symmetric surface of WTe2. Finally, we investigated the thermal stability of Te based devices, which is a major drawback for their practical applications. Two failure mechanisms related to the sublimation of Te channel and the degradation of the contacts were raised. To address these issues, we applied graphene contact and SiOx encapsulation, which is able to keep the contacted stable and channel intact at high temperatures. Such devices have the similar effective mobility comparing to the traditional metal contacted ones’, but with an improved thermal stability.