Interfacial n-Doping Using an Ultrathin TiO2 Layer for Contact Resistance Reduction in MoS2

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• 作者：Naveen Kaushik ; Debjani Karmakar ; Ankur Nipane ; Shruti Karande ; Saurabh Lodha
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：January 13, 2016
• 年：2016
• 卷：8
• 期：1
• 页码：256-263
• 全文大小：579K
• ISSN：1944-8252

文摘

We demonstrate a low and constant effective Schottky barrier height (Φ_B ～ 40 meV) irrespective of the metal work function by introducing an ultrathin TiO₂ ALD interfacial layer between various metals (Ti, Ni, Au, and Pd) and MoS₂. Transmission line method devices with and without the contact TiO₂ interfacial layer on the same MoS₂ flake demonstrate reduced (24×) contact resistance (R_C) in the presence of TiO₂. The insertion of TiO₂ at the source-drain contact interface results in significant improvement in the on-current and field effect mobility (up to 10×). The reduction in R_C and Φ_B has been explained through interfacial doping of MoS₂ and validated by first-principles calculations, which indicate metallic behavior of the TiO₂-MoS₂ interface. Consistent with DFT results of interfacial doping, X-ray photoelectron spectroscopy (XPS) data also exhibit a 0.5 eV shift toward higher binding energies for Mo 3d and S 2p peaks in the presence of TiO₂, indicating Fermi level movement toward the conduction band (n-type doping). Ultraviolet photoelectron spectroscopy (UPS) further corroborates the interfacial doping model, as MoS₂ flakes capped with ultrathin TiO₂ exhibit a reduction of 0.3 eV in the effective work function. Finally, a systematic comparison of the impact of selective doping with the TiO₂ layer under the source-drain metal relative to that on top of the MoS₂ channel shows a larger benefit for transistor performance from the reduction in source-drain contact resistance.