4TH International Congress on Technology - Engineering & SCIENCE - Kuala Lumpur - Malaysia (2017-08-05)

The Sulfurization Effect On The Nb Doped P-type Layered MoS2
Recently, exfoliated monolayer MoS2 shows a great possibility for n-type FET for next generation due to the ultra-high carrier confinement. It can be used in many kind of application fields, such as low power logic circuits, flexible electronics, sensors, memories and photovoltaic. etc. For integration circuit application, it is important to form n-type and p-type channels in the same MoS2 semiconductor material. Among the group V of transition metals, Nb is the promising candidate for p-type dopant in MoS2 (Mo is group VI) due to the low formation energy of -6.29eV and -0.19eV under the S-rich and Mo-rich conditions, respectively [1]. In our previous works, the Nb doped in MoS2 showed stable p-type characteristics by using co-sputtering to deposit MoOx:Nb and sulfurization in H2S ambient. In this study, we found that the Nb concentration in MoOx, after sulfurized in H2S, would affect the acceptor concentration and mobility. The higher hole concentration in MoS2 show the better mobility as shown in Fig. 1, which is completely contradictory to the silicon semiconductor physics. In addition, as shown in Fig.2, the electrical characteristics examined by transmission line model (TLM) method are strongly dependent on the Nb doping concentration in MoS2. To clarify the effect on Nb activation to be acceptor, the XPS were used to carefully study the chemical characteristics of the NbS2 with various H2S partial pressure during sulfurization. The results show that the formation of NbS2 in MoS2 would be crucial to the p-type characteristic.
Yen-Teng Ho, Yung-Ching Chu, Chao An Jong, Tien-Tung Luong, Chih-Chien Lin