The promise of flexible, stretchable, and transparent circuitry has driven intense research in carbon-based and two-dimensional (2D) material-based electronics, such as organic semiconductors, graphene and transition-metal dichalcogenides (TMDs). For integrated circuits applications consisting of CMOS, p-n diodes and other logic components, both n-type and p-type semiconductors are equally important. Controlled doping of two-dimensional semiconductors promises a powerful tool to tailor their electrical and optical properties toward next generation electronic and optoelectronic devices. In this study, solution-processed charge transfer doping of four transition metal dichalcogenides MX2, where M is either Mo or W and X either S or Se, is achieved using molecular reductants and oxidants. Sub-hundred-micron size (ca. 50 to 100 μm) of MX2 were exfoliated via gold-mediated transfer technique.1 The doping type and strength can be conveniently controlled by the redox potential of the metal-organic molecules, the concentration of dopant solutions and treatment time.2 The doping effects are observed through the evolution of electrical characteristics of MX2 field effect transistor devices. I-V characteristics of MX2 field effect transistor (FET) devices treated with both p- and n-dopants are measured, from which the charge carrier densities induced by the doping were estimated. Detailed physical characterizations including photoemission (UPS and XPS), Raman and photoluminescence (PL) spectroscopy are used to study the doping effect and to understand the underlying mechanism. The origin of the doping is attributed to the shift of Fermi level and work function through the charge transfer process between molecular dopants and 2D semiconductors. Overall, we have demonstrated a solution-based charge transfer doping using molecular oxidants and reductants to p- or n-dope several 2D semiconductors. This technique provides a simple yet effective route to tailor the band structure of the 2D materials, and control the resulting electrical and optical properties.
(1) Desai, S. B.; Madhvapathy, S. R.; Amani, M.; Kiriya, D.; Hettick, M.; Tosun, M.; Zhou, Y.; Dubey, M.; Ager, J. W.; Chrzan, D. Adv. Mater. 2016, 28, 4053.
(2) Tarasov, A.; Zhang, S.; Tsai, M. Y.; Campbell, P. M.; Graham, S.; Barlow, S.; Marder, S. R.; Vogel, E. M. Adv. Mater. 2015, 27, 1175.