Highly strained Ge micro-blocks bonded on Si platform for mid-infrared photonic applications
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Research Letter
Highly strained Ge micro-blocks bonded on Si platform for mid-infrared photonic applications A. Gassenq, K. Guilloy, and N. Pauc, Univ. Grenoble Alpes, CEA, INAC, PHELIQS, F-38000 Grenoble, France D. Rouchon, J. Widiez, J. Rothman, J.-M. Hartmann, A. Chelnokov, and V. Reboud, CEA-LETI, Univ. Grenoble Alpes, 38000 Grenoble, France V. Calvo, Univ. Grenoble Alpes, CEA, INAC, PHELIQS, F-38000 Grenoble, France Address all correspondence to A. Gassenq at [email protected] (Received 12 May 2017; accepted 28 June 2017)
Abstract Applying sufficient tensile strain to Ge leads to a direct bandgap group IV semiconductor, which emits in the mid-infrared (MIR) wavelength range. However, highly strained-Ge cannot be directly grown on Si because of its large lattice mismatch. In this work, we have developed a process based on Ge micro-bridge strain redistribution intentionally landed to the Si substrate. Traction arms were then partially etched to keep locally strained-Ge micro-blocks. Large tunable uniaxial stresses up to 4.2% strain were demonstrated in Ge, which was bonded on Si. Our approach allows envisioning integrated strained-Ge on Si platform for MIR-integrated optics. Silicon photonics merge optical and electronic components that can be integrated together onto a single microchip.
Since the greatest interest in Si photonics have been demonstrated for telecommunication application, more applications have now emerged in the MIR wavelength range (2–5 µm) like gas sensing.[1] Since SiO2 is transparent up to 3.5 µm wavelength,[2] silicon-on-insulator MIR spectrometers have been successfully demonstrated.[3] For longer wavelength, Ge on Si platform is used.[4,5] However, the monolithical integration of active devices (sources and photodetector) are still missing in MIR Si photonics. The current solution consists of growing[6,7] or bonding III–V materials[8,9] on Si, which are not considered as complementary metal oxide semiconductor (CMOS) compatible by industrial foundries. For the group IV material sources, doped-Ge[10] and GeSn alloys[11] are envisioned to obtain a CMOS compatible laser source. Note that GeSn devices are also studied for photo-detection applications on Si substrate.[12,13] Strained-Ge structures also exhibits a MIR direct bandgap[14,15] but their integration remains challenging. Such integration on a Si platform would open the way to MIR fully-integrated active devices (source and detectors), which are CMOS compatible. The availability of such approach would have many applications for sensing systems[2] or on-chip optical interconnects for high-performance computing.[16] In this work, we propose to bond highly-strained Ge directly on Si using a specific processing based on micro-bridge landing followed by the traction arm etching. Compared with free standing membranes, our landing approach will greatly facilitate the next process steps needed to go toward electrically pumped laser sources or integrated photodetectors based on
strained-Ge for mid-infrared (MIR) applications. We measure a
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