Contact Engineering and Doping Techniques for 2D Semiconductors

This chapter provides an in-depth analysis of advanced contact and doping techniques to optimize the performance of two-dimensional (2D) semiconductors, which are promising candidates for next-generation electronic and optoelectronic devices. Contact engineering techniques, including top and bottom contacts, transferred contacts, van der Waals (vdW), edge contacts, and semi-metallic contacts, are systematically explored. These approaches address critical issues such as Schottky barrier formation, Fermi level pinning, and interface damage caused by conventional deposition techniques. For instance, bottom and transferred contacts minimize interfacial defects, while vdW, edge, and semi-metallic contacts mitigate metal-induced gap states and ensure clean, defect-free interfaces, enhancing charge injection efficiency and device performance. In parallel, the chapter examines doping strategies to modulate the electronic properties of 2D materials. Oxidation doping introduces oxygen atoms to substitute sulfur vacancies, enabling p-type doping with controlled structural integrity. Laser-induced doping leverages precision energy delivery to tailor carrier concentration and reduce contact resistance, while charge transfer doping achieves either n-type or p-type behavior through surface-adsorbed dopants like benzyl viologen, Magic Blue, and metal oxides without compromising the crystal structure. Each method is discussed with its mechanisms, advantages, and challenges, including issues like contamination, scalability, and stability.