What Are 2D Materials?
2D optoelectronic materials consist of single or few atomic/molecular layers, where atoms within each layer are bonded by strong covalent or ionic bonds, while interlayer interactions are governed by weak van der Waals forces. Their unique structure gives them extraordinary properties and functionalities. Currently, the most prominent 2D materials include graphene (GN), topological insulators (TIs), transition metal dichalcogenides (TMDCs), and black phosphorus (BP).
Graphene (GN)
Graphene is a single layer of carbon atoms arranged in a hexagonal honeycomb lattice through sp² hybridization.
In 2004, Geim and Novoselov isolated graphene using the "scotch-tape method", sparking a global research boom in 2D materials. Their work earned them the 2010 Nobel Prize in Physics.
Graphene boasts exceptional electron mobility—100 times higher than silicon—and a conductivity of up to 10⁶ S·m⁻¹, making it the best-known conductive material at room temperature. It also exhibits ultra-broadband optical responses, spanning from UV to terahertz frequencies, with vast potential in electronics and optoelectronics.
However, its zero bandgap leads to low on/off ratios and short carrier lifetimes, limiting its use in transistors and light-emitting applications.
Topological Insulators (TIs)
TIs are materials that are insulating in their bulk but conductive on their surfaces or edges. Strong spin-orbit coupling causes band inversion, creating a Dirac cone structure similar to graphene.
Experimentally confirmed TIs include Sb₂Se₃, Bi₂Se₃, Bi₂Te₃, and Sb₂Te₃. Their unique bulk-insulating, surface-conducting properties make them ideal for spintronics, topological quantum computing, Majorana fermion research, and laser mode-locking.
Transition Metal Dichalcogenides (TMDCs)
TMDCs, such as MoS₂, WS₂, and WSe₂, are layered materials with a hexagonal crystal structure. In recent years, their unique optoelectronic properties have attracted significant attention.
When reduced to a single atomic layer, TMDCs transition from an indirect to a direct bandgap semiconductor, with tunable bandgaps ranging from 1–2.5 eV. Their strong excitonic effects in the near-infrared range make them promising for LEDs, lasers, and photodetectors.
The broken inversion symmetry and strong spin-orbit coupling in TMDCs enable valleytronics, a cutting-edge field for manipulating electron momentum. As transistor materials, they offer high on/off ratios (up to 10⁶), but their low carrier mobility (0.5–3 cm²·V⁻¹·s⁻¹ at room temperature) restricts broader applications.
Black Phosphorus (BP)
BP is a puckered honeycomb-structured 2D material with phosphorus atoms. Its interlayer spacing (0.53 nm) is larger than graphene’s (0.36 nm), facilitating ion intercalation and making it promising for energy storage (batteries, supercapacitors).
BP is a p-type direct bandgap semiconductor with a layer-dependent bandgap (0.3–2.2 eV), ideal for infrared photonics, photodetection, and optical modulation.
Thanks to its puckered structure, BP exhibits high strain sensitivity, allowing bandgap tuning via mechanical stress—useful for flexible electronics and strain sensors. Its anisotropic electronic properties also enable unique applications in plasmonics and thermal management.
The Future of 2D Materials in Electronics
From graphene’s ultra-conductivity to TMDCs’ tunable bandgaps and BP’s strain adaptability, 2D materials are redefining the limits of chip design. As research advances, these atomically thin materials could soon power next-gen transistors, quantum computers, and ultra-efficient optoelectronic devices, marking the dawn of a post-silicon era.
