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TRANSCRIPT
Phosphorene – Can it be Effectively Passivated?
Jim Hwang [email protected]
US-‐EU Workshop on 2D Layered Materials and Devices Wednesday, April 25, 2015
• IntroducJon • Passivated phosphorene FETs
• Temporal and thermal stability
• Mechanical stability
• Mobility enhancement
• Conclusion
Outline
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Phosphorene Surface
• Highly puckered structure allowing permanent out-‐of-‐plane dipole moment • Hydrophilic surface reacJve with O2 and H2O especially when lit • Surface roughens with water droplets in air within hours
A. Castellanos-‐Gomez et al (2014) Y. Du et al (2010)
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Top Gate vs. Back Gate
H. Liu et al (2014) High-‐Resis)vity Si
• High-‐resisJvity substrate to reduce parasiJc capacitance • High-‐k gate insulator to reduce Coulomb scaYering
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Phosphorene Surface Passivation
• PassivaJon appears adequate for environmental protecJon • Need to reduce interface state density and defect scaYering
Authors University Gate PassivaJon Ambient Stability
Thermal Stability
J. Na et al KIST Back Al2O3 2 mo
J. D. Wood et al Northwestern Back AlOx 2 wk
X. Luo et al Lehigh Top Al2O3 3 mo −50 oC─ 150 oC
J.-‐S. Kim et al UT AusJn Back Al2O3 3 mo
N. Gillgren et al UC Riverside Back hBN 2 wk
A. Avsar et al Singapore Top hBN 2 mo −263 oC─ 25 oC
X. Chen et al HKUST Back hBN 1 wk
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Al2O3-‐Passivated Phosphorene MOSFETs
Annealing in dry nitrogen at 200o C for 1 h increases on/off and linear/saturated drain currents by orders of magnitude
X. Luo et al (2014)
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Temporal/Thermal Stability
Stable to at least 2000 h and 150 oC
X. Luo et al (2014)
Al2O3-‐Passivated Phosphorene MOSFET
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Mechanical Stability Sandwiched between Al2O3
Stable up to 5000 1.5% strain cycles
Ti-‐Au
W. Zhu et al (2015)
phosphorene
polyimide
Al2O3
Al2O3 Ti-‐Pd
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Record Mobility Sandwiched between hBN
Polymer-‐free interfaces and annealing at 500 oC in Ar2 for 8 h
X. Chen et al (2015)
Room Air
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Summary of State of Art
• “Can it be stable?” to “How stable?” in less than a year
• Passivated phosphorene FETs environmentally stable
• Phosphorene FETs adequate for flexible electronics
• ReducJon of interface state density and hence subthreshold slope for high-‐speed electronics
• Opportunity for enhancing carrier density and mobility
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Technical Challenges
• Understand effect of passivaJon and annealing on carrier density, mobility, interface roughness, interface state density … • Validate theory and experiment on nano-‐FETs with opJmized gate stack • Evaluate long-‐term stability beyond a few months and invesJgate failure mechanism
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References • Y. Du, C. Ouyang, S. Shi, and M. Lei, “Ab iniJo studies on atomic and electronic structures of black phosphorus,” J. Appl. Phys., vol. 107, pp. 093718-‐1−093718-‐4, May 2010. • A. Castellanos-‐Gomez, L. Vicarelli, E. Prada, J. O. Island, K. L. Narasimha-‐Acharya, S. I. Blanter, D. J. Groenendijk, M. Buscema, G. A. Steele, J. V. Alvarez, H. W. Zandbergen, J. J. Palacios, and H. S. J. van der Zant, “IsolaJon and characterizaJon of few-‐layer black phosphorus,” 2D Mater., vol. 1, no. 2, pp. 025001-‐1−025001-‐19, Jun. 2014. • H. Liu, A. T. Neal, M. Si, Y. Du, and P. D. Ye, “The effect of dielectric capping on few-‐layer phosphorene transistors: Tuning the SchoYky barrier heights,” IEEE Electron Device Le<., vol. 35, no. 7, pp. 795−797, Jul. 2014. • J. Na, Y. T. Lee, J. A. Lim, D. K. Hwang, G. T. Kim, W. K. Choi, and Y. Song, “Few-‐layer black phosphorus field-‐effect transistors with reduced current fluctuaJon,” ACS Nano, vol. 8, no. 11, pp. 11753–11762, Nov. 2014. • J. D. Wood, S. A. Wells, D. Jariwala, K. S. Chen, E. Cho, V. K. Sangwan, X. Liu, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “EffecJve passivaJon of exfoliated black phosphorus transistors against ambient degradaJon,” Nano Le<., vol. 14, no. 12, pp. 6964–6970, Dec. 2014. • X. Luo, Y. Rahbarihagh, J. C. M. Hwang, H. Liu, Y. Du, and P. D. Ye, “Temporal and thermal stability of Al2O3-‐passivated phosphorene MOSFETs,” IEEE Electron Device Le<., vol. 35, no. 12, pp. 1314–1316, Dec. 2014. • J. S. Kim, Y. Liu, W. Zhu, S. Kim, D. Wu, L. Tao, A. Dodabalapur, K. Lai, and D. Akinwande, “Toward air-‐stable mulJlayer phosphorene thin-‐films and transistors,” Sci. Rep., vol. 5, pp. 8989-‐1−8989-‐7, Mar. 2015. • N. Gillgren, D. Wickramaratne, Y. Shi, T. Espiritu, J. Yang, J. Hu, J. Wei, X. Liu, Z. Mao, K. Watanabe, T. Taniguchi, M. Bockrath, Y. Barlas, R. K. Lake, and C. N. Lau, “Gate tunable quantum oscillaJons in air-‐stable and high mobility few-‐layer phosphorene heterostructures,” 2D Mater., vol. 2, no. 1, pp. 011001-‐1−011001-‐7, Mar. 2015. • A. Avsar, I. J. Vera-‐Marun, T. J. You, K. Watanabe, T. Taniguchi, A. H. Castro Neto, and B. Ozyilmaz, “Electrical characterizaJon of fully encapsulated ultra thin black phosphorus-‐based heterostructures with graphene contacts.” Available: hYp://arxiv.org/abs/1412.1191. • X. Chen, Y. Wu, Z. Wu, S. Xu, L. Wang, Y. Han, W. Ye, T. Han, Y. He, Y. Cai, and N. Wang, “High quality sandwiched black phosphorus heterostructure and its quantum oscillaJons.” Available: hYp://arxiv.org/abs/1412.1357.
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Acknowledgment
Xi Luo Kuanchen Xiong Yaghoob Rahbarihagh
Han Liu Yuchen Du Peide Ye
Grant N00014-‐14-‐1-‐0653
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