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The effect of thickness, temperature, and source-drain bias voltage, VDS, on the subthreshold slope, SS, and off-state properties of black phosphorus (BP) field-effect transistors is reported. Locally back-gated p-MOSFETs with thin HfO2 gate dielectrics were analyzed using exfoliated BP layers ranging in thickness from ∼4 to 14 nm. SS was found to degrade with increasing VDS and to a greater extent in thicker flakes. In one of the thinnest devices, SS values as low as 126 mV/decade were achieved at VDS = -0.1 V, and the devices displayed record performance at VDS = -1.0 V with SS = 161 mV/decade and on-to-off current ratio of 2.84 × 103 within a 1 V gate bias window. A one-dimensional transport model has been utilized to extract the band gap, interface state density, and the work function of the metal contacts. The model shows that SS degradation in BP MOSFETs occurs due to the ambipolar turn on of the carriers injected at the drain before the onset of purely thermionic-limited transport at the source. The model is further utilized to provide design guidelines for achieving ideal SS and meet off-state leakage targets, and it is found that band edge work functions and thin flakes are required for ideal operation at high VDS. This work represents a comprehensive analysis of the fundamental performance limitations of Schottky-contacted BP MOSFETs under realistic operating conditions.
Bibliographical noteFunding Information:
This work was supported primarily by the National Science Foundation (NSF) through the University of Minnesota MRSEC under Award No. DMR-1420013 (N.H., S.-H.O., S.J.K.). This work also received partial support from the Air Force Office of Scientific Research under Award No. FA9550- 14-1-0277 (S.N., S.J.K.). Device fabrication was performed at the Minnesota Nanofabrication Center at the University of Minnesota, which receives partial support from the NSF through the National Nanotechnology Coordinated Infrastructure (NNCI). Portions of this work were also carried out in the University of Minnesota Characterization Facility, which received capital equipment from the NSF.
© 2016 American Chemical Society.
- black phosphorus
- subthreshold slope
How much support was provided by MRSEC?
Reporting period for MRSEC
- Period 3
PubMed: MeSH publication types
- Journal Article
- Research Support, U.S. Gov't, Non-P.H.S.
11/1/14 → …
Project: Research project