Transport in Complex Crystalline Materials Based on van der Waals Heterostructures

A dearth of high-quality 2-D semiconductors and the difficulty of scaling down 3-D semiconductors have severely limited the prospects for the development of next-generation energy efficient electronic devices. To overcome these challenges, we have developed a technique to integrate van der Waals 2-D and conventional 3-D semiconductors. Our resultant novel 2-D3-Dheterostructure consists of molybdenum disulfide as the 2-D component encapsulated between 3-D gallium nitride in a vertical configuration. This ultra-thin structure is a promising material system as a component of an improved heterojunction bipolar transistor HBT. High-quality, defect-free interfaces between the 2- and 3-D systems, a critical criterion for efficient HBT device operation, was achieved through chemical powder vaporization, metal-organic chemical vapor deposition, and molecular beam epitaxy. We also synthesized a trilayer 3-D2-D3-D semiconductor structure the first demonstration of itskind, validated all major critical aspects of the design, and performed a feasibility study of our design and microfabrication process for a functional HBT model. In particular, 2-D3-D diode behavior was demonstrated for the fully synthesizedheterostructures built without mechanical transfer. The outcomes of this basic research effort could pave the way for explorations into the novel physics of 2-D materials for energy-efficient electronics devices and systems.