Optical Emission in Hexagonal SiGe Nanowires

Cartoixà, Xavier; Palummo, Maurizia; Hauge, Håkon Ikaros T.; Bakkers, Erik P. A. M.; Rurali, Riccardo

doi:10.1021/acs.nanolett.7b01441

Cited by 64 publications

(59 citation statements)

References 48 publications

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“…Applying density-functional theory (DFT) [27,28], a Kohn-Sham (KS) band structure obtained within the localdensity approximation (LDA) or any flavor of the generalized gradient approximation (GGA) is not sufficient, as the system is erroneously predicted to be metallic in this case [13,15,23,29,30]. Moreover, the band gap is extremely sensitive to the value of the lattice constant.…”

Section: Introductionmentioning

confidence: 99%

Accurate electronic and optical properties of hexagonal germanium for optoelectronic applications

Rödl

Furthmüller

Suckert

et al. 2019

Phys. Rev. Materials

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High-quality defect-free lonsdaleite Si and Ge can now be grown on hexagonal nanowire substrates. These hexagonal phases of group-IV semiconductors have been predicted to exhibit improved electronic and optical properties for optoelectronic applications. While lonsdaleite Si is a well-characterized indirect semiconductor, experimental data and reliable calculations on lonsdaleite Ge are scarce and not consistent regarding the nature of its gap. Using ab initio density-functional theory, we calculate accurate structural, electronic, and optical properties for hexagonal Ge. Given the well-known sensitivity of electronic-structure calculations for Ge to the underlying approximations, we systematically test the performance of several exchange-correlation functionals, including meta-GGA and hybrid functionals. We first validate our approach for cubic Ge, obtaining atomic geometries and band structures in excellent agreement with available experimental data. Then, the same approach is applied to predict electronic and optical properties of lonsdaleite Ge. We portray lonsdaleite Ge as a direct semiconductor with only weakly dipole-active lowest optical transitions, small band gap, huge crystalfield splitting, and strongly anisotropic effective masses. The unexpectedly small direct gap and the oscillator strengths of the lowest optical transitions are explained in terms of symmetry and back-folding of energy bands of the diamond structure.

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Section: Introductionmentioning

confidence: 99%

Accurate electronic and optical properties of hexagonal germanium for optoelectronic applications

Rödl

Furthmüller

Suckert

et al. 2019

Phys. Rev. Materials

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show abstract

“…A detailed examination of Figure 7 indicates that Cu-doping of the KCl structure reduces the direct energy bandgap and that the unfolding procedure preserves the same direct character of the energy bandgap ( Figure 5 ). Previous studies suggest that the folded bands fail to reproduce the indirect bandgap character [ 38 , 77 ]. The cutoff of the energy bandgap is attributed to the appearance of empty bands with a dispersionless character located at 1.0 and 2.0 eV.…”

Section: Resultsmentioning

confidence: 99%

“…Particular attention should be paid to the SC method of calculation. This method conveniently allows the folding of the bands into the smaller SC BZ that gives rise to a complicated band structure for which it is difficult to determine whether the bandgap is direct or indirect [ 38 , 39 ]. Moreover, other physical quantities, such as carrier mobility [ 40 ], require knowledge of the PC band structure.…”

Section: Theoretical Methods and Computational Detailsmentioning

confidence: 99%

“…This method gives the probability that an eigenstate of a Hamiltonian, in the SC representation, will have the same character as a PC state. This unfolding procedure of the SC BZ has been successfully employed in several systems, such as SiGe nanowires [ 38 ], graphene [ 54 , 55 ], and ternary alloys [ 56 ].…”

Section: Theoretical Methods and Computational Detailsmentioning

confidence: 99%

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Cu-Doped KCl Unfolded Band Structure and Optical Properties Studied by DFT Calculations

et al. 2020

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The unfolded band structure and optical properties of Cu-doped KCl crystals were computed by first principles within the framework of density functional theory, implemented in the ABINIT software program, utilizing pseudopotential approximation and a plane-wave basis set. From a theoretical point of view, Cu substitution into pristine KCl crystals requires calculation by the supercell (SC) method. This procedure shrinks the Brillouin zone, resulting in a folded band structure that is difficult to interpret. To solve this problem and gain insight into the effect of copper ions (Cu+) on electronic properties, the band structure of SC KCl:Cu was unfolded to make a direct comparison with the band structure of the primitive cell (PC) of pristine KCl. To understand the effect of Cu substitution on optical absorption, we calculated the imaginary part of the dielectric function of KCl:Cu through a sum-over-states formalism and broke it down into different band contributions by partially making an iterated cumulative sum (ICS) of selected valence and conduction bands. Consequently, we identified those interband transitions that give rise to the absorption peaks due to the Cu+ ion. These transitions involve valence and conduction bands formed by the Cu-3d and Cu-4s electronic states.

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“…SiGe is an alloy material which has many advantages for optoelectronic devices, such as high refractive index, high electron mobility, high compatibility, and SiGe material could be used in many optoelectronic devices [3][4][5]. The band gap [6] and refractive index [7] of Si 1-x Ge x alloy material could be changed by adjusting the Ge content.…”

Section: Introductionmentioning

confidence: 99%

Research into Two Photonic-Integrated Waveguides Based on SiGe Material

Feng

Xue

2020

Materials

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SiGe (Silicon Germanium) is a common semiconductor material with many excellent properties, and many photonic-integrated devices are designed and fabricated with SiGe material. In this paper, two photonic-integrated SiGe waveguides are researched, namely the SiGe-SOI (Silicon Germanium-Silicon-On-Insulator) waveguide and the SiGe-OI (Silicon Germanium-On-Insulator) waveguide. In order to verify which structure has the better waveguide performance, two waveguide structures are built, and the effective refractive indexes and the loss characteristics of the two waveguides are analyzed and compared. By simulation, the SiGe-OI optical waveguide has better losses characteristics at a wavelength of 1.55 μm. Finally, SiGe-OI and SiGe-SOI waveguides are fabricated and tested to verify the correctness of theoretical analysis, and the experimental results show that the transmission losses of the SiGe-OI waveguide are respectively decreased by 36.6% and 28.3% at 400 nm and 600 nm waveguide width in comparison with the SiGe-SOI waveguide. The results also show that the SiGe-OI waveguide has better loss characteristics than those of the SiGe-SOI waveguide at the low Ge content.

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Optical Emission in Hexagonal SiGe Nanowires

Cited by 64 publications

References 48 publications

Accurate electronic and optical properties of hexagonal germanium for optoelectronic applications

Accurate electronic and optical properties of hexagonal germanium for optoelectronic applications

Cu-Doped KCl Unfolded Band Structure and Optical Properties Studied by DFT Calculations

Research into Two Photonic-Integrated Waveguides Based on SiGe Material

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