Department of Electrical Engineering, Stanford University , Stanford, California 94305, United States.
IBM T. J. Watson Research Center , Yorktown Heights, New York 10598, United States.
ACS Nano. 2016 Apr 26;10(4):4672-7. doi: 10.1021/acsnano.6b01008. Epub 2016 Apr 5.
A record high current density of 580 μA/μm is achieved for long-channel, few-layer black phosphorus transistors with scandium contacts after 400 K vacuum annealing. The annealing effectively improves the on-state current and Ion/Ioff ratio by 1 order of magnitude and the subthreshold swing by ∼2.5×, whereas Al2O3 capping significantly degrades transistor performances, resulting in 5× lower on-state current and 3× lower Ion/Ioff ratio. The influences of moisture on black phosphorus metal contacts are elucidated by analyzing the hysteresis of 3-20 nm thick black phosphorus transistors with scandium and gold contacts under different conditions: as-fabricated, after vacuum annealing, and after Al2O3 capping. The optimal black phosphorus film thickness for transistors with scandium contacts is found to be ∼10 nm. Moreover, p-type performance is shown in all transistors with scandium contacts, suggesting that the Fermi level is pinned closer to the valence band regardless of the flake thickness.
经 400 K 真空退火后，具有 scandium 接触的长沟道少层黑磷晶体管的电流密度达到了 580 μA/μm 的历史新高。退火有效地将导通电流提高了 1 个数量级，将 Ion/Ioff 提高了 1 个数量级，将亚阈值摆幅降低了约 2.5 倍，而 Al2O3 盖帽则显著降低了晶体管性能，导致导通电流降低了 5 倍，Ion/Ioff 降低了 3 倍。通过分析具有 scandium 和 gold 接触的 3-20nm 厚黑磷晶体管在不同条件下（即制备后、真空退火后和 Al2O3 盖帽后）的滞后现象，阐明了湿气对黑磷金属接触的影响。发现具有 scandium 接触的晶体管的最佳黑磷薄膜厚度约为 10nm。此外，所有具有 scandium 接触的晶体管均表现出 p 型性能，这表明费米能级无论薄片厚度如何都更接近价带。
