Electronic structure and optical properties of Si, Ge and diamond in the lonsdaleite phase

De, Amrit; Pryor, Craig

doi:10.1088/0953-8984/26/4/045801

Cited by 60 publications

(57 citation statements)

References 132 publications

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“…With increasing pressure, contrary to the case of diamond, the band gap is reduced until it finally closes in the vicinity of 1000 GPa. Figure 13 shows the imaginary part of the response function using various approaches along two orientations for the hexagonal lattice structure at q = 0 and [98]. The density range covers 3.5 g/cc to 6.9 g/cc.…”

Section: Lonsdaleitementioning

confidence: 99%

Ab initio dielectric response function of diamond and other relevant high pressure phases of carbon

Ramakrishna

Vorberger

2019

J. Phys.: Condens. Matter

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The electronic structure and dielectric properties of the diamond, body centered cubic diamond (bc8), and hexagonal diamond (lonsdaleite) phases of carbon are computed using density functional theory and many-body perturbation theory with the emphasis on the excitonic picture of the solid phases relevant in the regimes of high-pressure physics and warm dense matter. We also discuss the capabilities of reproducing the inelastic x-ray scattering spectra in comparison with the existing models in light of recent x-ray scattering experiments on carbon and carbon bearing materials in the Megabar range.

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Section: Lonsdaleitementioning

confidence: 99%

Ab initio dielectric response function of diamond and other relevant high pressure phases of carbon

Ramakrishna

Vorberger

2019

J. Phys.: Condens. Matter

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“…As shown in Fig. 1b, for hexagonal Si (Hex-Si) this results in a local CB minimum at the Γ-point, with an energy close to 1.7 eV [11][12][13] . Clearly, Hex-Si remains indirect since the lowest energy CB minimum is at the M-point, close to 1.1 eV.…”

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confidence: 99%

Direct-bandgap emission from hexagonal Ge and SiGe alloys

Fadaly

Dijkstra

Suckert

et al. 2020

Nature

276

332

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Silicon crystallized in the usual cubic (diamond) lattice structure has dominated the electronics industry for more than half a century. However, cubic silicon (Si), germanium (Ge) and SiGe-alloys are all indirect bandgap semiconductors that cannot emit light efficiently. Accordingly, achieving efficient light emission from group-IV materials has been a holy grail 1 in silicon technology for decades and, despite tremendous efforts 2-5 , it has remained elusive 6 . Here, we demonstrate efficient light emission from direct bandgap hexagonal Ge and SiGe alloys. We measure a sub nanosecond, temperature insensitive radiative recombination lifetime and observe a similar emission yield to direct bandgap III-V semiconductors. Moreover, we demonstrate how by controlling the composition of the hexagonal SiGe alloy, the emission wavelength can be continuously tuned in a broad range, while preserving a direct bandgap. Our experimental findings are shown to be in excellent quantitative agreement with the ab initio theory. Hexagonal SiGe embodies an ideal material system to fully unite electronic and optoelectronic functionalities on a single chip, opening the way towards novel device concepts and information processing technologies.Silicon has been the workhorse of the semiconductor industry since it has many highly advantageous physical, electronic and technological properties. However, due to its indirect bandgap, silicon cannot emit light efficientlya property that has seriously constrained potential for applications to electronics and passive optical circuitry 7-9 . Silicon technology can only reach its full application potential when heterogeneously supplemented 10 with an efficient, direct bandgap light emitter.The band structure of cubic Si, presented in Fig. 1a is very well known, having the lowest conduction band (CB) minimum close to the X-point and a second lowest * These authors contributed equally to this work. † Correspondence to E.P.A.M.(e.p.a.m.bakkers@tue.nl).minimum at the L-point.As such, it is the archetypal example of an indirect bandgap semiconductor, that, notwithstanding many great efforts 3-6 , cannot be used for efficient light emission.By modifying the crystal structure from cubic to hexagonal, the symmetry along the 111 crystal direction changes fundamentally, with the consequence that the L-point bands are folded back onto the Γ-point. As shown in Fig. 1b, for hexagonal Si (Hex-Si) this results in a local CB minimum at the Γ-point, with an energy close to 1.7 eV 11-13 . Clearly, Hex-Si remains indirect since the lowest energy CB minimum is at the M-point, close to 1.1 eV. Cubic Ge also has an indirect bandgap but, unlike Si, the lowest CB minimum is situated at the L-point, as shown in Fig. 1c. As a consequence, for Hex-Ge the band folding effect results in a direct bandgap at the Γ-point with a magnitude close to 0.3 eV, as shown in the calculated band structure in Fig. 1d 14 .To investigate how the direct bandgap energy can be tuned by alloying Ge with Si, we calculated the band structures of He...

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“…Experimentally, silicon has been found to have a complicated phase diagram [1]. Many semiconductor silicon structures that have an indirect band gap have been proposed, such as the M phase, Z phase [2], Cmmm phase [3], body-centered-tetragonal Si [4], M 4 phase [5], lonsdaleite phase [6], T 12 phase [7], ST 12 phase [8], C-centered orthorhombic phase [9], C 2/ m -16, C 2/ m -20, Amm 2, I -4 [10], and P 222 1 [11], among others. Many semiconductor silicon structures with a direct band gap have been reported, such as P 2 1 3 phase [12], oF 16-Si, tP 16-Si, mC 12-Si, and tI 16-Si [13].…”

Section: Introductionmentioning

confidence: 99%

Si96: A New Silicon Allotrope with Interesting Physical Properties

et al. 2016

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The structural mechanical properties and electronic properties of a new silicon allotrope Si96 are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations reveal that Si96 is mechanically and dynamically stable at ambient pressure. The conduction band minimum and valence band maximum of Si96 are at the R and G point, which indicates that Si96 is an indirect band gap semiconductor. The anisotropic calculations show that Si96 exhibits a smaller anisotropy than diamond Si in terms of Young’s modulus, the percentage of elastic anisotropy for bulk modulus and shear modulus, and the universal anisotropic index AU. Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si96 quite attractive for applications such as hydrogen storage and electronic devices that work at extreme conditions, and there are potential applications in Li-battery anode materials.

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Electronic structure and optical properties of Si, Ge and diamond in the lonsdaleite phase

Cited by 60 publications

References 132 publications

Ab initio dielectric response function of diamond and other relevant high pressure phases of carbon

Ab initio dielectric response function of diamond and other relevant high pressure phases of carbon

Direct-bandgap emission from hexagonal Ge and SiGe alloys

Si96: A New Silicon Allotrope with Interesting Physical Properties

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