Direct Bandgap Light Emission from Strained Germanium Nanowires Coupled with High-Q Nanophotonic Cavities

Petykiewicz, Jan; Nam, Donguk; Sukhdeo, David S.; Gupta, Shashank; Buckley, Sonia; Piggott, Alexander Y.; Vučković, Jelena; Saraswat, Krishna C.

doi:10.1021/acs.nanolett.5b03976

Cited by 83 publications

(62 citation statements)

References 34 publications

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“…Increasing the tensile strain or Sn concentration lowers the Γ energy at a greater rate than the L-valley, therefore leading to a transition to a direct bandgap material. [5] High tensile strain has been demonstrated in Ge with suspended micro and nano-wires [6][7][8], which locally amplify the residual tensile strain in the epilayer, and through application of high stress silicon nitride (SiN) layers to optical cavities [9][10][11][12][13], amongst other techniques [14,15]. Both these methods have induced levels of strain required for a transition to direct bandgap, however lasing has not been demonstrated from such devices.…”

Section: Introductionmentioning

confidence: 99%

Mid-infrared light emission > 3 µm wavelength from tensile strained GeSn microdisks

et al. 2017

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GeSn alloys with Sn contents of 8.4 % and 10.7 % are grown pseudomorphically on Ge buffers on Si (001) substrates. The alloys as-grown are compressively strained, and therefore indirect bandgap. Undercut GeSn on Ge microdisk structures are fabricated and strained by silicon nitride stressor layers, which leads to tensile strain in the alloys, and direct bandgap photoluminescence in the 3-5 µm gas sensing window of the electromagnetic spectrum. The use of pseudomorphic layers and external stress mitigates the need for plastic deformation to obtain direct bandgap alloys. It is demonstrated, that the optically pumped light emission overlaps with the methane absorption lines, suggesting that GeSn alloys are well suited for mid-infrared integrated gas sensors on Si chips.

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Section: Introductionmentioning

confidence: 99%

Mid-infrared light emission > 3 µm wavelength from tensile strained GeSn microdisks

et al. 2017

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“…Lastly, we note that a tensile axial strain above 2% in the 20nm Ge core can be achieved at a GeSn shell thickness larger than 60nm (Fig.4d), which could eventually induce an indirect to direct band gap transition in the Ge core, thus enriching the physical properties of a fully-integrated group-IV semiconductor opto-electronic platform. [33][34][35] In conclusion, the growth of GeSn alloys in a Ge/GeSn core/shell NW heterostructure shows few striking differences with respect to conventional planar growth. In the latter, the uniform plastic relaxation allows for enhanced Sn incorporation beyond the dislocated region while keeping a limited surface roughness (<10nm).…”

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confidence: 99%

Strain engineering in Ge/GeSn core/shell nanowires

Assali

Albani

Bergamaschini

et al. 2019

Applied Physics Letters

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Strain engineering in Sn-rich group IV semiconductors is a key enabling factor to exploit the direct band gap at mid-infrared wavelengths. Here, we investigate the effect of strain on the growth of GeSn alloys in a Ge/GeSn core/shell nanowire geometry. Incorporation of Sn content in the 10-20 at.% range is achieved with Ge core diameters ranging from 50nm to 100nm. While the smaller cores lead to the formation of a regular and homogeneous GeSn shell, larger cores lead to the formation of multi-faceted sidewalls and broadened segregation domains, inducing the nucleation of defects. This behavior is rationalized in terms of the different residual strain, as obtained by realistic finite element method simulations. The extended analysis of the strain relaxation as a function of core and shell sizes, in comparison with the conventional planar geometry, provides a deeper understanding of the role of strain in the epitaxy of metastable GeSn semiconductors.Strained semiconductor heterostructures provide a rich playground for investigating the epitaxy of lattice-mismatched materials. 1 In the last decades SiGe alloys grown with a graded composition on Si were extensively studied to relieve strain by nucleating misfit dislocations in the buffer layers. [2][3][4] Recently, direct band gap and metastable GeSn alloys gained tremendous interest as a 2 platform for Si-compatible photonics operating at mid-infrared wavelengths. [5][6][7][8][9] In unstrained GeSn the direct band gap is achieved at Sn contents higher than 10at.%, hence well above the ~1at.% equilibrium solubility of Sn in Ge. The incorporation of Sn is highly sensitive to the inplane strain that the GeSn layer experiences during growth. 10,11 Due to the large lattice mismatch between Ge and α-Sn (>10%), the growth of GeSn layers has been developed on high-quality Gevirtual substrates (Ge-VS) on Si. 12,13 Partial strain relaxation can induce a compositional grading in GeSn, 8,14-16 eventually leading to segregation and precipitation of Sn, compromising material quality. [17][18][19] In GeSn layers grown on Ge-VS, the compressive strain is reduced in a multi-layer buffered heterostructure grown with different Sn contents by controlling the growth temperature 20,21 and precursors flows. 22 The high amount of strain induces nucleation of dislocations in the low (7-11at.%) Sn content buffer layers, 11,23 and the resulting uniform (plastic) strain relaxation enhances the Sn incorporation above 16at.% in the GeSn layers grown on top. 8,11,14,19 One-dimensional nanowires(NWs) provide additional degrees of freedom in tuning the effect of strain in the growth of lattice-mismatch heterostructures 24,25 when using a core/shell NW geometry. 26 The shell displays an increasing strain relaxation with thickness provided by the free surfaces at the sidewalls, while the elastic compliance of the NW core allows for enhanced strain relaxation in the shell, accommodating the lattice mismatch of the system and avoiding bending. 26,27 Recent studies on Ge/GeSn core/shell NWs 15,16,28,29...

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“…Bragg reflectors were also integrated to complete the resonator structure, as shown in Fig. 2(a) [34]. Because of the small features of Bragg reflectors, we use electron beam lithography, followed by anisotropic dry etching.…”

Section: Fabrication Processmentioning

confidence: 99%

Strained Ge Light Emitter with Ge on Dual Insulators for Improved Thermal Conduction and Optical Insulation

Kim¹,

Petykiewicz²,

Gupta³

et al. 2015

IEIE Transactions on Smart Processing and Computing

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Abstract:We present a new way to create a thermally stable, highly strained germanium (Ge) optical resonator using a novel Ge-on-dual-insulators substrate. Instead of using a conventional way to undercut the oxide layer of a Ge-on-single-insulator substrate for inducing tensile strain in germanium, we use thin aluminum oxide as a sacrificial layer. By eliminating the air gap underneath the active germanium layer, we achieve an optically insulating, thermally conductive, and highly strained Ge resonator structure that is critical for a practical germanium laser. Using Raman spectroscopy and photoluminescence experiments, we prove that the novel geometry of our Ge resonator structure provides a significant improvement in thermal stability while maintaining good optical confinement.

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Direct Bandgap Light Emission from Strained Germanium Nanowires Coupled with High-Q Nanophotonic Cavities

Cited by 83 publications

References 34 publications

Mid-infrared light emission > 3 µm wavelength from tensile strained GeSn microdisks

Mid-infrared light emission > 3 µm wavelength from tensile strained GeSn microdisks

Strain engineering in Ge/GeSn core/shell nanowires

Strained Ge Light Emitter with Ge on Dual Insulators for Improved Thermal Conduction and Optical Insulation

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