Few-layer Tellurium: one-dimensional-like layered elementary semiconductor with striking physical properties (1707.09888v4)

Abstract: Few-layer Tellurium, an elementary semiconductor, succeeds most of striking physical properties that black phosphorus (BP) offers and could be feasibly synthesized by simple solution-based methods. It is comprised of non-covalently bound parallel Te chains, among which covalent-like feature appears. This feature is, we believe, another demonstration of the previously found covalent-like quasi-bonding (CLQB) where wavefunction hybridization does occur. The strength of this inter-chain CLQB is comparable with that of intra-chain covalent bonding, leading to closed stability of several Te allotropes. It also introduces a tunable bandgap varying from nearly direct 0.31 eV (bulk) to indirect 1.17 eV (2L) and four (two) complex, highly anisotropic and layer-dependent hole (electron) pockets in the first Brillouin zone. It also exhibits an extraordinarily high hole mobility (~10$^5$ cm$^2$/Vs) and strong optical absorption along the non-covalently bound direction, nearly isotropic and layer-dependent optical properties, large ideal strength over 20%, better environmental stability than BP and unusual crossover of force constants for interlayer shear and breathing modes. All these results manifest that the few-layer Te is an extraordinary-high-mobility, high optical absorption, intrinsic-anisotropy, low-cost-fabrication, tunable bandgap, better environmental stability and nearly direct bandgap semiconductor. This "one-dimension-like" few-layer Te, together with other geometrically similar layered materials, may promote the emergence of a new family of layered materials.

• The paper demonstrates that few-layer tellurium exhibits covalent-like inter-chain bonding, enabling tunable bandgaps and robust stability.
• It employs density functional theory to reveal near-direct bandgap transitions and exceptional hole mobility (~10^5 cm²/Vs) compared to black phosphorus.
• The analysis highlights FL-α-Te’s superior environmental stability and promising potential for high-performance optoelectronic and thermoelectric devices.

Few-layer Tellurium: A High-Mobility, Layered Semiconductor with Covalent-Like Interactions

The research paper focuses on the exploration of few-layer Tellurium (Te) as an elementary semiconductor, offering significant promise due to its remarkable physical properties and synthesis convenience. Similar in its advantages to black phosphorus (BP), few-layer Tellurium (FL-α-Te) is evaluated through theoretical predictions of its structural, electronic, and transport properties, using methods such as density functional theory (DFT).

Structural Insights

Tellurium, in its α-phase, forms a layered structure composed of helical chains stabilized through covalent-like quasi-bonding (CLQB). These inter-chain interactions are pivotal, as their strength is comparable to intra-chain covalent bonds, providing formidable stability to the material across various phases. This stability paves the way for a tunable bandgap that transitions from a direct 0.31 eV in its bulk form to an indirect 1.17 eV in the bilayer form. The CLQB observed introduces pronounced anisotropic behavior and complexity in the electronic band structures, significantly affecting its electronic properties.

Electronic Band Structure

FL-α-Te’s electronic band structure is characterized by its nearly direct bandgap in bulk form, highly dependent on the inclusion of spin-orbit coupling (SOC). This bandgap evolution, defined by layer thickness, is notably controlled by inter-chain covalent-like interactions, leading to complex valence and conduction band surfaces that influence the charge carrier dynamics significantly. Noteworthy is FL-α-Te's high hole mobility (~10^5 cm²/Vs), which remarkably exceeds that seen in other 2D materials like black phosphorus, attributed to the pronounced quasi-bonding interactions.

Transport Properties

The carrier mobility of FL-α-Te, driven by phonon-limited scattering mechanisms, shows exceptional values, particularly for holes along the non-covalently bonded y-direction. These values, reaching up to ~10^4 cm²/Vs for electrons, suggest the promising potential of FL-α-Te for high-performance electronic applications, outperforming known 2D semiconductors like phosphorene.

Optical and Mechanical Attributes

Despite the intrinsic anisotropy in its structure, FL-α-Te exhibits layer-dependent isotropic optical absorption with elevated absorbance rates, marking it as a notable candidate for optoelectronic applications. Mechanically, the material exhibits high elastic moduli and tensile strengths, particularly along the z-direction, suggesting it can withstand and possibly exploit substantial strain before phase transitions occur.

Environmental Stability and Potential Applications

FL-α-Te showcases superior environmental stability in comparison to black phosphorus, with a notable resistance to oxidation, attributed to a high barrier energy for the chemisorption of oxygen. This stability, coupled with its other intriguing properties, suggests various potential applications, ranging from photodetectors to thermoelectric devices, due to its high mobility and tunable optoelectronic properties.

Implications and Future Directions

The exceptional properties of FL-α-Te, ranging from its anisotropic carrier mobility to robust environmental stability, illustrate its potential as a versatile semiconductor material. Its resemblance to BP yet easier synthetization through solution-based methods further underlines its attractiveness for both theoretical research and practical applications. Future research can be directed towards experimental validations, exploring FL-α-Te’s integration into device architectures, and further understanding the role of covalent-like interactions in 2D and quasi-1D layered materials.