Tensile-strained germanium microdisks with circular Bragg reflectors

Kurdi, M. El; Prost, Mathias; Ghrib, A.; Elbaz, Anas; Sauvage, S.; Checoury, X.; Beaudoin, G.; Sagnes, I.; Picardi, Gennaro; Ossikovski, Razvigor; Bœuf, F.; Boucaud, P.

doi:10.1063/1.4942891

Cited by 22 publications

(31 citation statements)

References 31 publications

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“…n>>m. In this case the resonant wavelength , can be approximated into an analytical expression only depending on the index (n,m), the disk radius and the effective index of vertically confined waves propagating in the Ge layer. From Equation 1 of [23] we obtain resonant wavelengths at 1772 nm, 1789 nm and 1830 nm, that can be associated to TE 0 (16,1), TE 1 (10,2) and TE 0 (15,2) respectively in quite good agreement with the experimentally observed mode positions. Note that these mode positions may vary by typically only +/-10nm for different combinations of (n,m) providing that the 2n+m value is kept constant.…”

Section: Methodssupporting

confidence: 82%

“…We consider TE polarization since it should be preferentially collected in the setup configuration, i. e. collection of emission from the top surface of the disk. The analysis in [23] is performed in a 2D analytical model considering quasi-radial modes, exhibiting small azimuthal index (m) with respect to radial index (n) i.e. n>>m. In this case the resonant wavelength , can be approximated into an analytical expression only depending on the index (n,m), the disk radius and the effective index of vertically confined waves propagating in the Ge layer.…”

Section: Methodsmentioning

confidence: 99%

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Solving thermal issues in tensile-strained Ge microdisks

Elbaz¹,

Kurdi²,

Aassime³

et al. 2018

Opt. Express

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We propose to use a Ge-dielectric-metal stacking to allow one to address both thermal management with the metal as an efficient heat sink and tensile strain engineering with the buried dielectric as a stressor layer. This scheme is particularly useful for the development of Ge-based optical sources. We demonstrate experimentally the relevance of this approach by comparing the optical response of tensile-strained Ge microdisks with an Al heat sink or an oxide pedestal. Photoluminescence indicates a much reduced temperature rise in the microdisk (16 K with Al pedestal against 200 K with SiO 2 pedestal under a 9 mW continuous wave optical pumping). An excellent agreement is found with finite element modeling of the temperature rise. This original stacking combining metal and dielectrics is promising for integrated photonics where thermal management is an issue.

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Section: Methodssupporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

Solving thermal issues in tensile-strained Ge microdisks

Elbaz¹,

Kurdi²,

Aassime³

et al. 2018

Opt. Express

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“…In contrast to the conventional geometry in which the strained Ge gain medium is suspended in air 29 – 32 , our laser structures hold the strained Ge nanowire in close contact with silicon dioxide (SiO 2 ), which provides superior thermal conduction to the air gap while confining optical fields within the Ge layer (Supplementary Fig. 3 ).…”

Section: Resultsmentioning

confidence: 99%

Low-threshold optically pumped lasing in highly strained germanium nanowires

et al. 2017

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The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system. Here we demonstrate a low-threshold, compact group IV laser that employs a germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently overcome optical losses at 83 K, thus allowing the observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm−2. Our demonstration opens new possibilities for group IV lasers for photonic-integrated circuits.

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“…The same laser threshold is obtained as for the smaller 9 µm diameter disks and increases with temperature reaching about 5 mW at 72 K (details in SI). Estimation of the disk heating under optical pumping, using Finite Element Modeling (FEM) 30,36 , can be found in the SI.…”

Section: /12mentioning

confidence: 99%

Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys

et al. 2020

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GeSn alloys are the most promising semiconductors for light emitters entirely based on group IV elements. Alloys containing more than 8 at. % Sn have fundamental direct band-gaps, similar to conventional III-V semiconductors and thus can be employed for light emitting devices. Here, we report on GeSn microdisk lasers encapsulated with a SiN x stressor layer to produce tensile strain. A 300 nm GeSn layer with 5.4 at. % Sn, which is an indirect band-gap semiconductor as-grown with a compressive strain of −0.32 %, is transformed via tensile strain engineering into a truly direct band-gap semiconductor. In this approach the low Sn concentration enables improved defect engineering and the tensile strain delivers a low density of states at the valence band edge, which is the light hole band. Continuous wave (cw) as well as pulsed lasing are observed at very low optical pump powers. Lasers with emission wavelength of 2.5 µm have thresholds as low as 0.8 kW cm −2 for ns-pulsed excitation, and 1.1 kW cm −2 under cw excitation. These thresholds are more than two orders of magnitude lower than those previously reported for bulk GeSn lasers, approaching these values obtained for III-V lasers on Si. The present results demonstrate the feasabiliy and are the guideline for monolithically integrated Si-based laser sources on Si photonics platform. arXiv:2001.04927v1 [physics.app-ph] 14 Jan 2020 at an Sn concentration of 8 at. % 3 . The lattice mismatch between Sn-containing alloys and the Ge buffer layer, the typical virtual substrate for their epitaxial growth, generates compressive strain in the grown layer, which counteracts the effect of Sn incorporation, decreasing the directness ∆E L−Γ = E L − E Γ . On the contrary, applying tensile strain will increase the directness. Finding a proper balance between a moderate Sn content to minimize crystal defects and to maintain thermal stability of the GeSn alloy on one hand and making use of tensile strain on the other hand are the keys to bring lasing threshold and operation temperature close to application's requirements. The mainstream research to increase ∆E L−Γ focuses on high Sn content alloys 5, 12 , obtained by epitaxy of thick strain-relaxed GeSn layers. A large directnesss is obtained, leading to higher temperature operation, although at the expense of steadily increasing laser threshold 13 . We have recently theoretically proposed an alternative approach, which is based on two key ingredients: employing moderate Sn content GeSn alloys, and inducing tensile strain in them 14 . This study indicated that, if a given directness is reached via tensile strain rather than by increasing Sn content, the material can provide a higher net gain. The underlying physics originates in the valence band splitting and lifting up of the light hole, LH, band above the heavy hole, HH, band. Its lower density of states (DOS) reduces the carrier density required for transparency, hence reduces the lasing threshold, as will be shown below. GeSn alloys with a moderate Sn content offer a couple of ...

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Tensile-strained germanium microdisks with circular Bragg reflectors

Cited by 22 publications

References 31 publications

Solving thermal issues in tensile-strained Ge microdisks

Solving thermal issues in tensile-strained Ge microdisks

Low-threshold optically pumped lasing in highly strained germanium nanowires

Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys

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