Computational Study of Spin Injection in 2D Materials

Quantum‐Engineered Devices Based on 2D Materials for Next‐Generation Information Processing and Storage

“…While insulators can offer one such tunneling medium, the lack of precise control over the barrier thickness and the presence of pinhole defects can lead to large device-to-device variability, or low attained ζ s , respectively. Interestingly, 2D-M with the presence of vdW gap along their out-of-plane direction for top-contacts to select metals (Figure 4d) (absence of d-orbitals) can exhibit enhanced spin-injection efficiencies (Figure 4e), [16] thereby lowering device-to-device variability, and offering a distinct advantage over (bulk-) 3D-materials. However, while practically achieving sole top-contacts with pristine interfaces remains difficult, experimental demonstrations with insulating oxides-TiO 2 [65,66] (Figure 4f), SrO, [67] and Al 2 O 3 [68] The presence of a vdW gap along the out-of-plane direction for the top-contact configuration presents an additional TB that increases injected spin-polarization, as seen in (e), where transmission spectrum as a function of energy has been plotted for two contacts.…”

“…Furthermore, the relatively small spin-Hall angle (SHA) of ≈0.1, defined as the ratio of the generated spin-current to the incident chargecurrent, in conventional heavy metals (with a large SOC) like Ta, Pt, [167] limits the maximum achievable energy-efficiency of conventional SOT-MRAMs. This can be also be resolved by the use of low-resistive highly doped 2D-M and its compounds, [16] f) Experimentally reported TMR (blue), and resistance (red) for a Co-h-BN-Fe MTJ at 1.4 K. [182] d,e) Reproduced with permission. [16] Copyright 2019, IEEE.…”

“…In addition, owing to their perfectly ordered crystal structure (no trap states and pristine interface) and low phonon density-of-states (DOS), 2D-M have been shown to possess extremely low Urbach energy, [14] a measure of how quickly the material DOS decays into the bandgap, thereby offering large coherence time in quantum devices and energy-efficient logic computing. [14,15] These beneficial properties of 2D-M are complemented by their strong spin-orbit coupling (SOC) strength, [16] which is orders of magnitude higher than that of Si because of the heavy atomic weight of their constituent transition metal atoms. This results in enhanced Rashba effect, [17] and hence, easier modulation of the electron spin through an externally applied electric field, which is critical for designing energy-efficient spin-based logic devices.…”

“…As already discussed, 2D-layered materials show promise over conventional 3D semiconductors in this aspect because of the presence of intrinsically higher SOC strength and excellent electrostatics, leading to effective spin modulation, while the presence of the vdW gap in their out-of-plane direction can be leveraged to achieve high spin-injection efficiencies, as shown in refs. [16,64]. The next sections discuss the advances made in the field of both spin-injection and transport, and how they can be used to design effective spin-logic and memory devices.…”

One-Dimensional Edge Contacts to Two-Dimensional Transition-Metal Dichalcogenides: Uncovering the Role of Schottky-Barrier Anisotropy in Charge Transport across MoS2 /Metal Interfaces

“…Metal-semiconductor contacts in nature tend to form Schottky barriers (SBs) with rectifying behavior [19]. Although our knowledge of engineering TMD-metal contacts for both charge [20][21][22][23][24] and spin [21,25,26] has undeniably progressed, contact resistance of today's conventional contacts to 2D semiconductors still exceeds that of their CMOS counterparts by at least an order of magnitude [27]. In conventional semiconductor technologies, Schottky contacts are engineered to become ohmic by strong doping of the semiconductor surface [28].…”