Ultra-Short Pulsed Laser Annealing Effects on MoS2 Transistors with Asymmetric and Symmetric Contacts

Abstract

The ultra-short pulsed laser annealing process enhances the performance of MoS2 thin film transistors (TFTs) without thermal damage on plastic substrates. However, there has been insufficient investigation into how much improvement can be brought about by the laser process. In this paper, we observed how the parameters of TFTs, i.e., mobility, subthreshold swing, Ion/Ioff ratio, and Vth, changed as the TFTs’ contacts were (1) not annealed, (2) annealed on one side, or (3) annealed on both sides. The results showed that the linear effective mobility (μeff_lin) increased from 13.14 [cm2/Vs] (not annealed) to 18.84 (one side annealed) to 24.91 (both sides annealed). Also, Ion/Ioff ratio increased from 2.27 × 10 5 (not annealed) to 3.14 × 10 5 (one side annealed) to 4.81 × 10 5 (both sides annealed), with Vth shifting to negative direction. Analyzing the main reason for the improvement through the Y function method (YFM), we found that both the contact resistance (Rc) and the channel interface resistance (Rch) improves after the pulsed laser annealings under different conditions. Moreover, the Rc enhances more dramatically than the Rch does. In conclusion, our picosecond laser annealing improves the performance of TFTs (especially, the Rc) in direct proportion to the number of annealings applied. The results will contribute to the investigation about correlations between the laser annealing process and the performance of devices.

Large-Area, Two-Dimensional MoS2 Exfoliated on Gold: Direct Experimental Access to the Metal–Semiconductor Interface

“…Given our findings that the 1L-MoS 2 work function depends on the area in direct contact with the Au substrate, it is likely that the previously observed reduction of contact resistance by introduction of energy or particles ,− is related to a shift of the Fermi level toward the conduction band, probably due to thermally induced sulfur vacancies at the interface. However, since any surface treatment can induce several changes not only at the interface but also at the MoS 2 surface , (see the Supporting Information, Figure S8, for 1L-MoS 2 on Au), further studies on this important topic are certainly needed, in particular because the origin of such treatment-mediated surface changes is not yet understood.…”

Electron Irradiation of Metal Contacts in Monolayer MoS2 Field-Effect Transistors

“…We note that the reduction of contact resistance by chemical reactions between the metal contacts and MoS 2 channel has been reported for the metal deposited under ultrahigh vacuum 47 and contact laser annealing. 48 A disordered, compositionally graded layer, composed of Mo and Ti x S y species, forms on the surface of the MoS 2 crystal following the deposition of Ti, and thermal annealing in the 100–600 °C temperature range can cause Ti diffusion inducing further chemical and structural changes at the Ti–MoS 2 interface. 49 , 50 It is also possible that diffusion of Au atoms to the interface with MoS 2 occurs under the energetic electron beam irradiation.…”

Molybdenum Disulfide Field Effect Transistors under Electron Beam Irradiation and External Electric Fields

“…The energy release in the metal contacts can modify the chemistry of the metal/MoS2 interface or create stress and defects that can lead to a lowering of the barrier and a consequent contact resistance reduction. We note that the reduction of the contact resistance by chemical reactions between the metal contacts and MoS2 channel has been reported for metal deposited under ultrahigh vacuum [42] and contact laser annealing [43]. A disordered, compositionally graded layer, composed of Mo and Ti x S y species, forms at the surface of the MoS2 crystal following the deposition of Ti, and thermal annealing in the 100-600 °C temperature range can cause Ti diffusion inducing further chemical and structural changes at the Ti/MoS2 interface [44,45].…”