AIP Advances (Oct 2016)

The enhanced low resistance contacts and boosted mobility in two-dimensional p-type WSe2 transistors through Ar+ ion-beam generated surface defects

  • Dahye Kim,
  • Hyewon Du,
  • Taekwang Kim,
  • Somyeong Shin,
  • Seonyeong Kim,
  • Minho Song,
  • ChangWon Lee,
  • Jaeung Lee,
  • Hyeonsik Cheong,
  • David H. Seo,
  • Sunae Seo

DOI
https://doi.org/10.1063/1.4966049
Journal volume & issue
Vol. 6, no. 10
pp. 105307 – 105307-10

Abstract

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We intentionally generated surface defects in WSe2 using a low energy argon (Ar+) ion-beam. We were unable to detect any changes in lattice structure through Raman spectroscopy as expected through simulation. Meanwhile, atomic force microscopy showed roughened surfaces with a high density of large protruding spots. Defect-activated Photoluminescence (PL) revealed a binding energy reduction of the W 4f core level indicating significant amounts of defect generation within the bandgap of WSe2 even at the lowest studied 300 eV ion-beam energy. The intensity ratio increase of direct PL peak demonstrated the decoupling of surface layers, which behave like consecutive defective monolayers. Electrical measurements after post-irradiation showed p-type ohmic contacts regardless of the ion-beam energy. The resulting ohmic contact contributed to an increased on/off current ratio, mobility enhancement of around 350 cm2V-1s-1 from a few cm2V-1s-1 in pristine devices and electron conduction suppression. Further increased ion-beam energy over 700 eV resulted in a high shift of threshold voltage and diminished subthreshold slope due to increased surface roughness and boosted interface scattering. The origin of the ohmic contact behavior in p-type WSe2 is expected to be from chalcogen vacancy defects of a certain size which pins the Fermi level near the valence band minimum. An optimized ion-beam irradiation process could provide solutions for fabricating ohmic contacts to transition metal dichalcogenides.