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David S. Sukhdeo

Bio: David S. Sukhdeo is an academic researcher from Stanford University. The author has contributed to research in topics: Germanium & Direct and indirect band gaps. The author has an hindex of 10, co-authored 27 publications receiving 705 citations.

Papers
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TL;DR: In this paper, the authors reported uniaxial tensile strains up to 5.7% along germanium wires on a silicon substrate, measured using Raman spectroscopy.
Abstract: We report uniaxial tensile strains up to 5.7% along 〈100〉 in suspended germanium (Ge) wires on a silicon substrate, measured using Raman spectroscopy. This strain is sufficient to make Ge a direct bandgap semiconductor. Theoretical calculations show that a significant fraction of electrons remain in the indirect conduction valley despite the direct bandgap due to the much larger density of states; however, recombination can nevertheless be dominated by radiative direct bandgap transitions if defects are minimized. We then calculate the theoretical efficiency of direct bandgap Ge LEDs and lasers. These strained Ge wires represent a direct bandgap Group IV semiconductor integrated directly on a silicon platform.

155 citations

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TL;DR: This work presents single-material nanowires which behave exactly like traditional heterostructures, and represents a fundamentally new paradigm for creating nanoscale devices with full heterostructure behavior in photonics and electronics.
Abstract: Semiconductor heterostructures play a vital role in photonics and electronics. They are typically realized by growing layers of different materials, complicating fabrication and limiting the number of unique heterojunctions on a wafer. In this Letter, we present single-material nanowires which behave exactly like traditional heterostructures. These pseudoheterostructures have electronic band profiles that are custom-designed at the nanoscale by strain engineering. Since the band profile depends only on the nanowire geometry with this approach, arbitrary band profiles can be individually tailored at the nanoscale using existing nanolithography. We report the first experimental observations of spatially confined, greatly enhanced (>200×), and wavelength-shifted (>500 nm) emission from strain-induced potential wells that facilitate effective carrier collection at room temperature. This work represents a fundamentally new paradigm for creating nanoscale devices with full heterostructure behavior in photonics ...

122 citations

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TL;DR: In this article, an external stressor technique was employed to introduce a 0.76% bi-axial tensile strain in the active region of a vertical PN junction.
Abstract: We demonstrate room-temperature electroluminescence (EL) from light-emitting diodes (LED) on highly strained germanium (Ge) membranes. An external stressor technique was employed to introduce a 0.76% bi-axial tensile strain in the active region of a vertical PN junction. Electrical measurements show an on-off ratio increase of one order of magnitude in membrane LEDs compared to bulk. The EL spectrum from the 0.76% strained Ge LED shows a 100nm redshift of the center wavelength because of the strain-induced direct band gap reduction. Finally, using tight-binding and FDTD simulations, we discuss the implications for highly efficient Ge lasers.

87 citations

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TL;DR: In this article, a theoretical analysis of unstrained GeSn alloys as a laser gain medium was performed using the empirical pseudopotential method, and the band structure of GeSn was simulated and verified against experimental data.
Abstract: In this paper, a theoretical analysis of unstrained GeSn alloys as a laser gain medium was performed Using the empirical pseudopotential method, the band structure of GeSn alloys was simulated and verified against experimental data This model shows that GeSn becomes direct bandgap with 655% Sn concentration The optical gain of GeSn alloys with 0-10% Sn concentration was calculated with different n-type doping concentrations and injection levels It is shown theoretically that adding Sn greatly increases the differential gain owing to the reduction of energy between the direct and indirect conduction bands For a double-heterostructure laser, the model shows that at a cavity loss of 50 cm-1, the minimum threshold current density drops 60 times from Ge to Ge09Sn01, and the corresponding optimum n-doping concentration of the active layer drops by almost two orders of magnitude These results indicate that GeSn alloys are good candidates for a Si-compatible laser

84 citations

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TL;DR: A silicon-compatible light source is the final missing piece for completing high-speed, low-power on-chip optical interconnects and reduced optical loss in optical cavities formed with germanium under high (>2.3%) tensile strain is found.
Abstract: A silicon-compatible light source is the final missing piece for completing high-speed, low-power on-chip optical interconnects. In this paper, we present a germanium nanowire light emitter that encompasses all the aspects of potential low-threshold lasers: highly strained germanium gain medium, strain-induced pseudoheterostructure, and high-Q nanophotonic cavity. Our nanowire structure presents greatly enhanced photoluminescence into cavity modes with measured quality factors of up to 2000. By varying the dimensions of the germanium nanowire, we tune the emission wavelength over more than 400 nm with a single lithography step. We find reduced optical loss in optical cavities formed with germanium under high (>2.3%) tensile strain. Our compact, high-strain cavities open up new possibilities for low-threshold germanium-based lasers for on-chip optical interconnects.

83 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a direct bandgap GeSn alloy, grown directly onto Si(001), was used for experimentally demonstrating lasing threshold and linewidth narrowing at low temperatures.
Abstract: Lasing is experimentally demonstrated in a direct bandgap GeSn alloy, grown directly onto Si(001). The authors observe a clear lasing threshold as well as linewidth narrowing at low temperatures.

1,027 citations

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TL;DR: The all-printable fabrication of polycrystalline nanowire-based high-performance photodetectors on flexible substrates is demonstrated, showing their ultra-high photoconductive gain, responsivity and detectivity up to 3.3 × 1017 Jones.
Abstract: High-performance photodetectors are critical for high-speed optical communication and environmental sensing, and flexible photodetectors can be used for a wide range of portable or wearable applications. Here we demonstrate the all-printable fabrication of polycrystalline nanowire-based high-performance photodetectors on flexible substrates. Systematic investigations have shown their ultra-high photoconductive gain, responsivity and detectivity up to 3.3 × 10(17) Jones. Further analysis shows that their high performance originates from the unique band-edge modulation along the nanowire axial direction, where the existence of Schottky barriers in series leads to highly suppressed dark current of the device and also gives rise to fast photoelectric response to low-intensity optical signal owing to barrier height modulation. The discovered rationale in this work can be utilized as guideline to design high-performance photodetectors with other nanomaterial systems. The developed fabrication scheme opens up possibility for future flexible and high-performance integrated optoelectronic sensor circuitry.

511 citations

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TL;DR: Zhou et al. as discussed by the authors assess the three main contenders for on-chip light sources: erbium-based light sources, germanium-on-silicon lasers and III-V-based silicon lasers.
Abstract: Hybrid silicon lasers based on bonded III–V layers on silicon are currently the best contenders for on-chip lasers for silicon photonics. On-chip silicon light sources are highly desired for use as electrical-to-optical converters in silicon-based photonics. Zhiping Zhou and Bing Yin of Peking University in China and Jurgen Michel of Massachusetts Institute of Technology assess the three main contenders for such light sources: erbium-based light sources, germanium-on-silicon lasers and III-V-based silicon lasers. They consider operating wavelength, pumping conditions, power consumption, thermal stability and fabrication process. The scientists regard the power efficiencies of electrically pumped erbium-based lasers as being too low and the threshold currents of germanium lasers as being too high. They conclude that III–V quantum dot lasers monolithically grown on silicon show the most promise for realizing on-chip lasers.

448 citations

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TL;DR: Here it is realized and confirmed that a synthetic superlattice of monolayer molybdenum disulphide forms an optoelectronic crystal capable of broadband light absorption and efficient funnelling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei.
Abstract: The isolation of the two-dimensional semiconductor molybdenum disulphide introduced a new optically active material possessing a band gap that can be facilely tuned via elastic strain. As an atomically thin membrane with exceptional strength, monolayer molybdenum disulphide subjected to biaxial strain can embed wide band gap variations overlapping the visible light spectrum, with calculations showing the modified electronic potential emanating from point-induced tensile strain perturbations mimics the Coulomb potential in a mesoscopic atom. Here we realize and confirm this ‘artificial atom’ concept via capillary-pressureinduced nanoindentation of monolayer molybdenum disulphide from a tailored nanopattern, and demonstrate that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funnelling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. Such twodimensional semiconductors with spatially textured band gaps represent a new class of materials, which may find applications in next-generation optoelectronics or photovoltaics.

360 citations

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TL;DR: In this article, the elastic strain field is controlled statically or dynamically by varying the six-dimensional elastic strain as continuous variables, which gives new meaning to Richard Feynman's 1959 statement, "There is plenty of room at the bottom".
Abstract: “Smaller is stronger.” Nanostructured materials such as thin films, nanowires, nanoparticles, bulk nanocomposites, and atomic sheets can withstand non-hydrostatic (e.g., tensile or shear) stresses up to a significant fraction of their ideal strength without inelastic relaxation by plasticity or fracture. Large elastic strains, up to ∼10%, can be generated by epitaxy or by external loading on small-volume or bulk-scale nanomaterials and can be spatially homogeneous or inhomogeneous. This leads to new possibilities for tuning the physical and chemical properties of a material, such as electronic, optical, magnetic, phononic, and catalytic properties, by varying the six-dimensional elastic strain as continuous variables. By controlling the elastic strain field statically or dynamically, a much larger parameter space opens up for optimizing the functional properties of materials, which gives new meaning to Richard Feynman’s 1959 statement, “there’s plenty of room at the bottom.”

230 citations