Type-I Ge∕Ge1−x−ySixSny strained-layer heterostructures with a direct Ge bandgap
TL;DR: In this paper, the electronic properties of Ge∕Ge1−x−ySixSny strained-layer heterostructures are predicted theoretically and the required level of tensile strain in the Ge layers is compatible with Si-Ge technology.
Abstract: The electronic properties of Ge∕Ge1−x−ySixSny strained-layer heterostructures are predicted theoretically It is found that a lattice-matched system with fully strained Ge layers and relaxed Ge1−x−ySixSny alloys can have a direct fundamental bandgap with spatial localization in the Ge layers (type I) The Si and Sn concentrations for which such a direct bandgap obtains are close to those that have already been experimentally demonstrated [M Bauer, C Ritter, P A Crozier, J Ren, J Menendez, G Wolf, and J Kouvetakis, Appl Phys Lett 83, 2163 (2003)] The required level of tensile strain in the Ge layers is compatible with Si–Ge technology The predicted direct bandgap values are as high as 06eV
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TL;DR: In this paper, the state-of-the-art CMOS silicon-on-insulator (SOI) foundries are now being utilized in a crucial test of 1.55mum monolithic optoelectronic (OE) integration, a test sponsored by the Defense Advanced Research Projects Agency (DARPA).
Abstract: The pace of the development of silicon photonics has quickened since 2004 due to investment by industry and government. Commercial state-of-the-art CMOS silicon-on-insulator (SOI) foundries are now being utilized in a crucial test of 1.55-mum monolithic optoelectronic (OE) integration, a test sponsored by the Defense Advanced Research Projects Agency (DARPA). The preliminary results indicate that the silicon photonics are truly CMOS compatible. RD however, lasing has not yet been attained. The new paradigm for the Si-based photonic and optoelectric integrated circuits is that these chip-scale networks, when suitably designed, will operate at a wavelength anywhere within the broad spectral range of 1.2-100 mum, with cryocooling needed in some cases
1,789 citations
TL;DR: In this paper, a scaling behavior for the electronic properties that is the analog of the scaling behavior found earlier for the vibrational properties was found for the optical transitions in the alloys, which is not predicted by electronic structure calculations within the virtual crystal approximation.
Abstract: The ${E}_{0}$, ${E}_{0}+{\ensuremath{\Delta}}_{0}$, ${E}_{1}$, ${E}_{1}+{\ensuremath{\Delta}}_{1}$, ${E}_{0}^{\ensuremath{'}}$, and ${E}_{2}$ optical transitions have been measured in ${\mathrm{Ge}}_{1\ensuremath{-}y}{\mathrm{Sn}}_{y}$ alloys $(yl0.2)$ using spectroscopic ellipsometry and photoreflectance. The results indicate a strong nonlinearity (bowing) in the compositional dependence of these quantities. Such behavior is not predicted by electronic structure calculations within the virtual crystal approximation. The bowing parameters for ${\mathrm{Ge}}_{1\ensuremath{-}y}{\mathrm{Sn}}_{y}$ alloys show an intriguing correlation with the corresponding bowing parameters in the ${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Si}}_{x}$ system, suggesting a scaling behavior for the electronic properties that is the analog of the scaling behavior found earlier for the vibrational properties. A direct consequence of this scaling behavior is a significant reduction (relative to prior theoretical estimates within the virtual crystal approximation) of the concentration ${y}_{c}$ for a crossover from an indirect- to a direct-gap system.
299 citations
TL;DR: It is demonstrated that mechanically stressed nanomembranes allow for the introduction of sufficient biaxial tensile strain to transform Ge into a direct-bandgap material with strongly enhanced light-emission efficiency, capable of supporting population inversion as required for providing optical gain.
Abstract: Silicon, germanium, and related alloys, which provide the leading materials platform of electronics, are extremely inefficient light emitters because of the indirect nature of their fundamental energy bandgap. This basic materials property has so far hindered the development of group-IV photonic active devices, including diode lasers, thereby significantly limiting our ability to integrate electronic and photonic functionalities at the chip level. Here we show that Ge nanomembranes (i.e., single-crystal sheets no more than a few tens of nanometers thick) can be used to overcome this materials limitation. Theoretical studies have predicted that tensile strain in Ge lowers the direct energy bandgap relative to the indirect one. We demonstrate that mechanically stressed nanomembranes allow for the introduction of sufficient biaxial tensile strain to transform Ge into a direct-bandgap material with strongly enhanced light-emission efficiency, capable of supporting population inversion as required for providing optical gain.
228 citations
Cites background from "Type-I Ge∕Ge1−x−ySixSny strained-la..."
...Similarly, SiGeSn has been proposed as a suitable growth template for the same purpose (10, 16), but its epitaxy is quite challenging and still under development....
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TL;DR: In this article, a new class of Sn-containing group IV semiconductors are described, which exhibit unprecedented thermal stability, superior crystallinity and unique optical and strain properties such as adjustable bandgaps, and controllable strain states.
Abstract: ▪ Abstract New classes of Sn-containing group IV semiconductors are described. Novel CVD routes lead to growth of a broad range of Ge1−ySny alloys and compounds directly on Si substrates. The direct bandgap (E0) and optical transitions E0+Δ0, E1, E1+Δ1, E0′, and E2 of Ge1−ySny exhibit strong nonlinearities in the compositional dependence, and their bowing parameters correlate with those in Ge1 −xSix, suggesting a scaling behavior for the electronic properties. The Ge1−ySny films can be used as “virtual substrates” for the subsequent growth of Ge1−x−ySixSny ternaries. These are created for the first time and exhibit unprecedented thermal stability, superior crystallinity and unique optical and strain properties such as adjustable bandgaps, and controllable strain states (compressive, relaxed, and tensile). The synthesis of Ge1−x−ySixSny makes it possible to decouple strain and bandgap and adds new levels of flexibility to the design of group IV devices. The Ge-Si-Sn system also represents a new class of “d...
224 citations
TL;DR: In this paper, the authors investigated the band structure of tensile-strained germanium using a 30 band k⋅p formalism and obtained that the crossover from indirect to direct band gap occurs for a tensile in-plane strain of 1.9%.
Abstract: We have investigated the band structure of tensile-strained germanium using a 30 band k⋅p formalism. This multiband formalism allows to simultaneously describe the valence and conduction bands, including the L, Δ, and Γ valleys. We calculate the energy band variation as a function of strain and obtain that the crossover from indirect to direct band gap occurs for a tensile in-plane strain of 1.9%. The effective masses of density of states are deduced from the calculated conduction and valence band density of states. Significant deviations are observed as compared to the effective masses of density of states values of unstrained bulk germanium. We finally calculate the optical gain that can be achieved with tensile-strained bulk germanium. An optical gain larger than 3000 cm−1 is predicted for a carrier density of 1×1018 cm−3 and a 3% in-plane biaxial strain. This optical gain is larger than the one of GaAs calculated with the same formalism and is much larger than the experimental free-carrier absorption ...
206 citations
References
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IBM1
TL;DR: In this paper, a theoretical model is presented to predict the band offsets at both lattice-matched and pseudomorphic strained-layer interfaces, based on the local density functional pseudopotential formalism and the ''model solid approach'' of Van de Walle and Martin.
Abstract: Semiconductor heterojunctions and superlattices have recently shown tremendous potential for device applications because of their flexibility for tailoring the electronic band structure. A theoretical model is presented to predict the band offsets at both lattice-matched and pseudomorphic strained-layer interfaces. The theory is based on the local-density-functional pseudopotential formalism and the ``model-solid approach'' of Van de Walle and Martin. This paper is intended as a self-contained description of the model, suitable for practical application. The results can be most simply expressed in terms of an ``absolute'' energy level for each semiconductor and deformation potentials that describe the effects of strain on the electronic bands. The model predicts reliable values for the experimentally observed lineups in a wide variety of test cases and can be used to explore which combinations of materials and configurations of the strains will lead to the desired electronic properties.
1,807 citations
PARC1
TL;DR: A theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides.
Abstract: We present a theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides. The self-consistent calculations, based on the local density functional and ab initio pseudopotentials, determine the atomic structures and strains of minimum energy, and the lineup of the Si and Ge band structures. The presence of the strains causes significant shifts and splittings of the bulk bands. We derive values for the band discontinuities for (001), (111), and (110) interfaces under different strain conditions, and discuss the validity of the density-functional methods for the analysis of the interface problem. Spin-orbit splitting effects in the valence bands are included a posteriori. We express our results in terms of discontinuities in the valence bands, and deformation potentials for the bulk bands, and compare them with recent experiments on Si/${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ge}}_{\mathrm{x}}$ heterostructures.
1,108 citations
TL;DR: La photoluminescence pres de la bande interdite a basse temperature des alliages est etudiee sur l'intervalle entier de composition ainsi que les expressions analytiques pour les bandes X et L.
Abstract: The low-temperature near-band-gap photoluminescence of ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ge}}_{\mathrm{x}}$ is studied over the whole composition range 0\ensuremath{\le}x\ensuremath{\le}1. We identify free- and bound-exciton processes and determine the properties of momentum-conserving phonons. From our results we determine the low-temperature band gap of the alloys. Analytical expressions are derived for the X and L bands: ${E}_{\mathrm{gx}}^{X}$(x) =1.155-0.43x+0.206${x}^{2}$ eV; ${E}_{\mathrm{gx}}^{L}$(x)=2.010-1.270x eV. The intensity and the linewidth of the various excitonic transitions are found to depend only on the statistical alloy fluctuations. No preferential clustering of Si and Ge atoms is detected.
502 citations
TL;DR: In this paper, the effects of static uniaxial compression along [001] and [111] on the Schottky-barrier electroreflectance spectrum of the ${E}_{0]-ensuremath{-}{E}-0+{\ensureMath{\Delta}}_{0}$ transitions in Ge and GaAs were investigated.
Abstract: We have investigated the effects of static uniaxial compression along [001] and [111] on the Schottky-barrier electroreflectance spectrum of the ${E}_{0}\ensuremath{-}{E}_{0}+{\ensuremath{\Delta}}_{0}$ and ${E}_{1}\ensuremath{-}{E}_{1}+{\ensuremath{\Delta}}_{1}$ transitions in Ge and GaAs. From the stress-induced splittings and shifts of these optical structures we have obtained deformation potentials, spin-exchange parameters and reduced interband masses. For the ${E}_{0}\ensuremath{-}{E}_{0}+{\ensuremath{\Delta}}_{0}$ transitions orbital (${b}_{1}$ and ${d}_{1}$), spin-dependent (${b}_{2}$ and ${d}_{2}$), and hydrostatic deformation potentials have been determined. In GaAs these are the first measurements reported for ${b}_{2}$ and ${d}_{2}$. The other parameters were found to be in good agreement with previous works. Interband reduced masses for the ${E}_{0}$ transition in Ge were determined at high stresses, in which case the degenerate valence band is split and the constant-energy surfaces are parabolic. Conclusive evidence for the existence of the electron-hole Coulomb interaction at 300\ifmmode^\circ\else\textdegree\fi{}K as well as 77\ifmmode^\circ\else\textdegree\fi{}K in the ${E}_{1}\ensuremath{-}{E}_{1}+{\ensuremath{\Delta}}_{1}$ transitions has been obtained from the polarization-dependent stress-induced splittings for [001] stress. The observed splitting is not explained by one-electron theory but is accounted for by including the electron-hole exchange interaction. By including exciton effects at 300\ifmmode^\circ\else\textdegree\fi{}K the systematic discrepancy between theory and experiment for the intensity and line shape of this structure should be resolved. In addition, deformation potentials due to shear (${D}_{1}^{5}$), hydrostatic (${D}_{1}^{1}$), and intraband (${D}_{3}^{3}$) effects were determined for the ${E}_{1}\ensuremath{-}{E}_{1}+{\ensuremath{\Delta}}_{1}$ transitions. The values obtained for ${D}_{1}^{5}$ in GaAs and Ge were found to be almost a factor of 2 larger than those previously reported. The reason for this is believed to be the higher resolution of the present experiments. Other parameters agree with prior works.
251 citations