Atomic Layer Deposition of Al-Doped MoS₂: Synthesizing a p-type 2D Semiconductor with Tunable Carrier Density

Abstract

Extrinsically doped two-dimensional (2D) semiconductors are essential for the fabrication of high-performance nanoelectronics among many other applications. Herein, we present a facile synthesis method for Al-doped MoS 2 via plasma-enhanced atomic layer deposition (ALD), resulting in a particularly sought-after p -type 2D material. Precise and accurate control over the carrier concentration was achieved over a wide range (10 17 up to 10 21 cm –3 ) while retaining good crystallinity, mobility, and stoichiometry. This ALD-based approach also affords excellent control over the doping profile, as demonstrated by a combined transmission electron microscopy and energy-dispersive X-ray spectroscopy study. Sharp transitions in the Al concentration were realized and both doped and undoped materials had the characteristic 2D-layered nature. The fine control over the doping concentration, combined with the conformality and uniformity, and subnanometer thickness control inherent to ALD should ensure compatibility with large-scale fabrication. This makes Al:MoS 2 ALD of interest not only for nanoelectronics but also for photovoltaics and transition-metal dichalcogenide-based catalysts.

Thermal Stability and Decomposition Pathways in Volatile Molybdenum(VI) Bis-Imides

“…For example, bis(tert-butylimido)bis(dimethylamido)molybdenum(VI) (A) has been used as a precursor for the ALD of MoNx, [11,12] MoO3, [13,14] MoS2, [15][16][17] MoCxNy, [18,19] TiMoxNy, [20] and Al:MoS2. [21] N,N'-chelating ligands have also been used to prepare volatile bis(tert-butylimido)molybdenum(VI) compounds, such as amidinates (B), [22] pyrazolates (C), [10] guanidinates (D), [23] and diazabutadienyls (E). [24] However, only the amidinate B has been used for ALD to prepare MoO3 films with O3.…”

High Hole Mobility Polycrystalline GaSb Thin Films

“…The same heterostructure implemented on a GaAs substrate had the opposite effect on mobility, which increased from 76.8 to 218.57 cm 2 /Vs. Room temperature Hall effect measurements were obtained (Table 1), with the nominally 250 nm GaSb film returning an impressive hole mobility figure of 66.5 cm 2 /Vs, which far exceeds the reported values for metal oxide semiconductors [14,24,25] and 2D materials [26,27] grown at <500 °C on amorphous substrates. There was no significant difference between the hole mobility results for the 50 nm and 150 nm films (24.2 and 22.9 To investigate this surprising result from the 50 nm GaAs + 50 nm GaSb sample and to gain further knowledge of the actual thickness and structure of other films, XTEM was performed.…”

“…Room temperature Hall effect measurements were obtained (Table 1), with the nominally 250 nm GaSb film returning an impressive hole mobility figure of 66.5 cm 2 /Vs, which far exceeds the reported values for metal oxide semiconductors [14,24,25] and 2D materials [26,27] grown at <500 • C on amorphous substrates. There was no significant difference between the hole mobility results for the 50 nm and 150 nm films (24.2 and 22.9 cm 2 /Vs respectively), suggesting that complete film continuity was achieved somewhere between the nominal 150 and 250 nm thicknesses.…”

Thermal Decomposition Mechanisms of Volatile Molybdenum(VI) Bis-Imides

“…For example, the amide A 11,14 and the amidinate C 20 have been used to prepare MoO3 thin films by ALD. The amide A has also been used as a precursor for the ALD of MoNx, 37,38 MoS2, 21,25,26 MoCxNy, 16,24 Al:MoS2, 32 and TiMoxNy. 34 Finally, the thiolate G has also been used for the ALD of Mo2N films with H2 plasma.…”