First Principles Study of Si/Ge Core-Shell Nanowires ---- Structural and Electronic Properties

Peng, Xihong; Tang, Fu; Logan, Paul

doi:10.5772/16298

Cited by 5 publications

(4 citation statements)

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“…17,18,[27][28][29][30] More interesting in Figure 4(b) is the E CB- shift with strain, which is maximized at 0% strain and drops at both tensile and compressive uniaxial strains, demonstrating a non-linear behavior. To understand this unique behavior which essentially determines the band gap transition, we further explored the detailed wavefunction and electron density of the state CB at with different values of strain.…”

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confidence: 96%

“…29 However, the anti-bonding characteristics suggests that the nodal surfaces of the positive and negative values of the wavefunction are perpendicular to the z-direction and a compressive uniaxial strain reduces the distance between the nodal surfaces, therefore kinetic energy associated with the electron transportation between atoms increases. [30][31][32] In contrast, a tensile strain increases the nodal surfaces thus reducing the associated kinetic energy.…”

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confidence: 99%

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Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain

Copple

Ralston

Peng

2012

Applied Physics Letters

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Electronic structures of wurtzite GaAs nanowires in the [0001] direction were studied using first-principles calculations. It was found that the band gap of GaAs nanowires experience a direct-to-indirect transition when the diameter of the nanowires is smaller than ~28 Å. For those thin GaAs nanowires with an indirect band gap, it was found that the gap can be tuned to be direct if a moderate external uniaxial strain is applied. Both tensile and compressive strain can trigger the indirect-to-direct gap transition. The critical strains for the gap-transition are determined by the energy crossover of two states in conduction bands. etc. In particular, GaAs has been considered as a promising channel material for the high speed NMOS beyond Si based technology. GaAs has two different crystal structures zinc blende (ZB) and wurtzite (WZ) phases. In bulk GaAs, ZB phase is energetically more favorable than WZ. In nanoscale, however, WZ phase was observed more often experimentally. Theoretical work,8 including abinitio calculations, has shown that at small size WZ structure is energetically more favorable, [8][9][10] and the interface energy may also facilitate the growth of WZ structure. 11Recent experiments have shown it is possible to grow GaAs nanowires in ZB, 12 WZ, 13 and mixed crystal phases. 14 While bulk GaAs (both ZB and WZ) has a direct band gap, GaAs nanowires may demonstrate an indirect gap when the diameter of nanowire is sufficiently small. 15,16 This band gap transition could fundamentally alter the electronic properties of nanowires. In addition to size, strain has become a routine factor to engineer band gaps of semiconductors in the field of microelectronics. Researchers have theoretically demonstrated the modulated band gap by external strains in a variety of systems such as pure Si 17 and Ge 18and Si/Ge Core-shell nanowires. 19It would be very interesting to investigate strain effects on the band structure of WZ GaAs nanowires and examine if the direct-indirect band gap transition can be engineered for applications.The ab-initio density functional theory (DFT) 20 calculations were carried out using VASP code 21,22 . The DFT local density approximation and the projector-augmented wave potentials 23,24 were used along with plane wave basis sets. The kinetic energy cutoff for the plane wave basis set was chosen to be 300.0 eV. The energy convergence criteria for electronic and ionic iterations are 10 -4 eV and 0.03 eV/Å, respectively. The GaAs nanowires were generated along the [0001] direction (i.e. z-axis) from bulk WZ GaAs with different diameters in the wire cross section (see Figure 1). The dangling bonds on the wire surface are saturated by hydrogen atoms.

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confidence: 99%

Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain

Copple

Ralston

Peng

2012

Applied Physics Letters

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“…Various approaches are proposed to tailor the electronic properties of 2D materials and their corresponding nanostructures, which is crucial for their applications in electronics. By virtue of the advantages such as maintaining the materials' properties and effective for single layers, strain engineering is visualized as one of the best possible candidates [14][15][16] and has attracted substantial attention [17][18][19][20][21][22][23][24][25] . Since graphene and plentiful postgraphene 2D materials emerged, studies revealed 2D layered materials have superior mechanical flexibility compared to their bulk counterparts 21,26 .…”

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Superior mechanical flexibility and strained-engineered direct-indirect band gap transition of green phosphorene

Yang

Peng

2018

Applied Physics Letters

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Most recently, a phosphorus allotrope called green phosphorus has been predicted, which has a direct band gap up to 2.4 eV, and its single-layer form termed green phosphorene shows high stability.Here the mechanical properties and the uniaxial strain effect on the electronic band structure of green phosphorene along two perpendicular in-plane directions were investigated. Remarkably, we found that this material can sustain a tensile strain in the armchair direction up to a threshold of 35% which is larger than that of black phosphorene, suggesting that green phosphorene is more puckered. Our calculations also show the Young's modulus and Poisson's ratio in the zigzag direction are four times larger than those in the armchair direction, which confirm the anisotropy of the material. Furthermore, the uniaxial strain can trigger the direct-indirect band gap transition for green phosphorene and the critical strains for the band gap transition are revealed. arXiv:1803.06495v2 [cond-mat.mtrl-sci]

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“…cập [34][35][36][37][38][39][40][41][42][43] . Ứng suất nhiệt và sự mất ổn định của Si/Ge NWs cũng đã được D. Suvankar và đồng nghiệp 44 khảo sát bằng phương pháp mô phỏng động lực học phân tử.…”

Section: Giới Thiệuunclassified

Investigate the mechanical properties of Si/Ge (Ge/Si) core-shell nanowires: A molecular dynamics study

Thanh¹,

Hung²,

Huy³

et al. 2020

Sci. Tech. Dev. J.- Eng. Tech.

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Nanowires (NWs) have been used increasingly in practice due to their outstanding mechanical, physical, and chemical properties. In this paper, we use the molecular dynamics (MD) method to investigate the mechanical properties of NWs (Si/Ge, Ge/Si) with a core-shell structure under the axial tensile strain along the <100>/{100} direction. Our results show that the strength and elastic modulus of Ge/Si and Si/Ge NWs depend on the composition and size of the core/shell crosssection. The strength and strain of Ge/Si NW decrease with increasing the size of the core crosssection because of the lattice mismatch between two layers of core/shell materials. The elastic modulus of Ge/Si NWs increases with the increasing the size of the core cross-section, while the elastic modulus of the Si/Ge NW decreases. In addition, the theoretical strength and elastic modulus of Ge/Si NWs reduce with the growth of the temperature. Furthermore, we also investigate the effect of strain rate on the mechanical properties of the Ge/Si NWs. The obtained results of the study provide the intrinsic properties of the core-shell NWs and also help in the design and fabrication of electronic and optical devices based on the Ge/Si NWs.

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First Principles Study of Si/Ge Core-Shell Nanowires ---- Structural and Electronic Properties

Cited by 5 publications

References 61 publications

Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain

Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain

Superior mechanical flexibility and strained-engineered direct-indirect band gap transition of green phosphorene

Investigate the mechanical properties of Si/Ge (Ge/Si) core-shell nanowires: A molecular dynamics study

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