Black Phosphorus Nanosheets in Field Effect Transistors with Ni and NiCr Contacts

Abstract

Herein, the fabrication and electrical characterization of multilayer black phosphorus (BP)‐based field effect transistors with Ni or NiCr alloy contacts are reported. The devices show p‐type conduction and hysteresis in the transfer characteristics that enable their use as nonvolatile memories. The differences between Ni and NiCr contacts are investigated and the Y‐function method is applied to extract the channel mobility up to 112 cm2 V−1 s−1 and the contact resistances. Ni contacts present specific contact resistance of 6.3 k Ω μm that increases to 18.1 k Ω μm for NiCr. These findings are important for the technological exploitation of multilayer BP in a new class of electronic and optoelectronic devices.

Memory effect and coexistence of negative and positive photoconductivity in black phosphorus field effect transistor for neuromorphic vision sensors

“…The observed transfer characteristics affirm the p-type behavior of the transistor, thereby validating that the Fermi level of the BP transistor fabricated with Ni contacts aligns closely with the valence band of the BP flake, and results in low contact resistance in comparison to other metals or alloys. 34,35 We also observe that the transistor remains in the on-state at zero gate voltage, primarily due to the doping effect of the residual adsorbates, such as O 2 and H 2 O molecules, as well as charges trapped at the BP/SiO 2 interface which serve as p-dopants. Subsequently, we noted a minor modulation in the current and an increase in the hysteresis width, H w , with an increasing sweeping range of V gs .…”

“…Ni contacts were chosen because they yield lower contact resistance in comparison to other metals or alloys. 34,35 To minimize any degradation due to moisture absorption, a poly(methyl methacrylate) PMMA capping layer (80 nm) was placed over the top of the BP thin flake by spin coating at 40 rotations per second for 60 s. 36 Prior to transferring the substrate for electrical measurements, the device was kept in diluted acetone containing 50% deionized (DI) H 2 O for 5 minutes and then cleaned with isopropanol. Dispersion in H 2 O and unavoidable exposure to air during sample handling causes oxidation; H 2 O alone does not seem to react with pristine BP, however, it may act as a catalyst for O 2 oxidation.…”

Black Phosphorus Field-Effect Transistors with Improved Contact via Localized Joule Heating

“…However, the annealing temperature was limited such that the metal-catalytic amorphization or sublimation of the BP would occur at about 300 °C [ 7 , 9 ]. Selecting metals with suitable work functions to form a small Schottky barrier with BP was another approach to reducing the contact resistance [ 10 , 11 , 12 , 13 , 14 , 15 ]. For example, using Ni or NiCr alloy as the contact metal has been reported to achieve a relatively low contact resistance of 6.3 kΩ μm and 18.1 kΩ μm for the BP-FETs, respectively [ 14 ].…”

“…Selecting metals with suitable work functions to form a small Schottky barrier with BP was another approach to reducing the contact resistance [ 10 , 11 , 12 , 13 , 14 , 15 ]. For example, using Ni or NiCr alloy as the contact metal has been reported to achieve a relatively low contact resistance of 6.3 kΩ μm and 18.1 kΩ μm for the BP-FETs, respectively [ 14 ]. However, the obtained contact resistance was still relatively large due to the side-contact nature between the metal and the BP.…”

A Superior Two-Dimensional Phosphorus Flame Retardant: Few-Layer Black Phosphorus

“…Black phosphorus (BP), an emerging allotrope of elemental phosphorus with a two-dimensional (2D) structure, was rediscovered in 2014, and has since become one of the most attractive 2D materials after graphene, and has shown great promise for high-performance electronic and optoelectronic devices, energy storage, and biomedicine applications [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Due to an ultimate phosphorus content (100 wt.%), and good intrinsic thermal stability [ 26 ], few-layer BP is expected as a follow-on high-efficiency flame retardant after RP and organophosphorus.…”