CMOS-compatible tensile-strained GeSn disk supports continuous lasing

CMOS-compatible tensile-strained GeSn disk supports continuous lasing

Technology News |
By eeNews Europe

Their results published in the Nature Photonics journal under the title “Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys” describes GeSn microdisk lasers fully encapsulated by a stressor layer made of dielectric Silicon Nitride (SiNx) to produce tensile strain. An indirect-bandgap semiconductor as-grown, the 300 nm-thick GeSn layer with 5.4 atomic percent of tin is transformed via tensile strain engineering into a direct-bandgap semiconductor that supports lasing. A specific microdisk cavity design was developed to allow high strain transfer from the stressor layer to the active region, remove the interface defects, and enhanced thermal cooling of the active region.

Scanning Electron Micrographs: (left) A layer of GeSn is transferred onto a silicon substrate and then structured as a microdisk to form an optical cavity. During the transfer, the defective layer in the GeSn, which was at the interface with the Ge/Si substrate, was removed by etching. The transfer also makes it possible to insert a stressed SiNx layer underneath the GeSn layer. An Aluminium layer was used to maintain the cavity while allowing excellent thermal cooling of the laser device through the substrate. (right) A final conformal deposition of a strained film on the microdisk allows to obtain an “all-around” configuration of the stress transfer from the SiNx to the GeSn. The GeSn is then under a tensile strain of 1.6% very homogeneously distributed in its active volume. Credit: C2N / M. El Kurdi & al.

With this approach, the researchers write, 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.

With this device, the researchers observed laser emission in the alloy under continuous-wave (cw) excitation. The laser effect is reached both under continuous wave and pulsed excitations, at temperatures up to 70K and 100K, respectively. The fabricated lasers operated at a wavelength of 2.5μm with a thresholds of 0.8 kW cm−2 for nanosecond pulsed optical excitation and 1.1 kW cm−2 under continuous-wave optical excitation. These thresholds are two orders of magnitude lower than reported in the literature, the researchers highlight, opening a new path toward the integration of group IV laser on a Si-photonic platform.

Centre de Nanosciences et de Nanotechnologies –

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