Abstract
Transition-metal dichalcogenides (TMDs) are promising nanoscale materials with a wide range of applications. Chemical doping is a powerful tool for tailoring the physical and chemical properties of TMDs for targeted functionalities. As one of the most important TMDs, WSe2 has great potential for applications in field effect transistor and complementary metal oxide semiconductor technologies for its bipolar dopability. However, precise control over the type and density of free carriers remains challenging. First-principles calculations are performed to study intrinsic defects and transition-metal (TM) dopants in WSe2. Our results show that TM doping can effectively control the Fermi level in WSe2 with no significant compensation by intrinsic defects. Nb and Ta are effective p-type dopants capable of generating a high free hole density in WSe2. While n-type doping is possible by Re (under the Se-rich condition) and Cu (under the W-rich condition), the doping efficiency is reduced due to the lower attainable dopant concentration and higher ionization energies. The chemical trend in the attainable concentration of various substitutional TM dopants in WSe2 is largely determined by the competition between the dopant incorporation in WSe2 and the formation of the secondary phase TMSe2. Such a competition is strongly affected by the different crystal environments of the TM ion in TMSe2 and WSe2, which determine the crystal field splitting and electron filling of TM d levels and consequently the formation energy of the TM dopant.