HfO₂ on MoS₂ by Atomic Layer Deposition: Adsorption Mechanisms and Thickness Scalability

Abstract

We report our investigation of the atomic layer deposition (ALD) of HfO2 on the MoS2 surface. In contrast to previous reports of conformal growth on MoS2 flakes, we find that ALD on MoS2 bulk material is not uniform. No covalent bonding between the HfO2 and MoS2 is detected. We highlight that individual precursors do not permanently adsorb on the clean MoS2 surface but that organic and solvent residues can dramatically change ALD nucleation behavior. We then posit that prior reports of conformal ALD deposition on MoS2 flakes that had been exposed to such organics and solvents likely rely on contamination-mediated nucleation. These results highlight that surface functionalization will be required before controllable and low defect density high-κ/MoS2 interfaces will be realized. The band structure of the HfO2/MoS2 system is experimentally derived with valence and conduction band offsets found to be 2.67 and 2.09 eV, respectively.

Transition Metal–MoS2 Reactions: Review and Thermodynamic Predictions

“…[18][19][20][21][22] The electronic properties and reduced dimensionality make single-or fewlayer MoS 2 attractive for field-effect transistors that are largely immune to short-channel effects, have high on-off ratio, and have low switching voltage. 2,7,23 Additionally, the ability to control both the spin and valley polarization of electrons makes MoS 2 a material of interest for novel electronic devices.…”

Air Stable Doping and Intrinsic Mobility Enhancement in Monolayer Molybdenum Disulfide by Amorphous Titanium Suboxide Encapsulation

“…Although several high-κ dielectrics have been investigated, atomic layer deposition (ALD) of alumina and hafnia have been the most common choices. 6,10,15,24,25,26,27 In this letter, we demonstrate an air stable, self-encapsulating, n-type charge transfer doping technique on ML MoS2 utilizing amorphous titanium sub-oxide (ATO) thin films. The ATO can be solution processed in the form of a sol-gel precursor and its application involves a simple spin-coating process, thereby making this approach extremely facile and easily scalable in contrast to the phase engineering or chloride doping schemes which require several hours of treatment with their respective chemical reagents.…”

Improvement in top-gate MoS2 transistor performance due to high quality backside Al2O3 layer

“…16 The combination of the FG anneal and the UV/O 3 functionalization of the MoS 2 surface is anticipated to reduce residual, process-induced contamination from lithography prior to gate dielectric formation. [16][17][18] The final step involved the high-vacuum deposition of a Cr/ Au top gate using the same process as the source/drain, converting the back-gate device into a top-gate 3-terminal FET. The same fabrication flow was used on devices with a SiO 2 backside layer for proper device comparison.…”