Owing to their direct band gaps, (Si)GeSn all-group-IV alloys are promising candidates for light sources, photodetectors and modulators monolithically integrated onto a CMOS-compatible mid-infrared photonic platform. Several research teams have demonstrated optically pumped GeSn lasers, and, more recently, an electrically pumped GeSn laser at low operating temperature. Here, we studied Ge0.85Sn0.15-based light emitting diodes (LEDs) and photodiodes (PDs) operating at room temperature. The stack was grown on a p-doped Ge strain-relaxed buffer at low growth temperatures (below 350°C) in a 200 mm chemical vapor deposition tool. Fabricated GeSn devices were characterized at room temperature with a Fourier-transform infrared spectrometer (FTIR) and an InSb detector. The spectral response of the FTIR InSb detector was calibrated with respect to a Deuterated Triglycine Sulfate detector (DTGS). This spectral response was then used to correct Ge0.85Sn0.15 LEDs emission spectra with emission maximum at 3.3 μm. The cutoff wavelength at 3.7 μm of the GeSn photodiode was finally obtained (at 0V bias) after correction of the Globar incident light spectrum. Such emission and detection open up promising perspectives for all-group-IV LEDs and PDs in applications such as gas sensing.
We investigated at room temperature the Franz-Keldysh effect in GeSn layers with Sn concentrations up to 13%. Several p-i-n stacks with indirect and direct band-gaps were grown by Reduced Pressure Chemical Vapor Deposition (RPCVD) with Ge2H6, Si2H6 and SnCl4 precursors. Direct band-gap energies and absorption coefficient were determined in transmission by electro-absorption measurements. The direct band-gap position was consistent with our k.p model. A maximum modulation of 1% was obtained at the direct band gap for a 0.5 V bias.
Lasing in bulk GeSn alloys have been reported lately with relatively high thresholds in the range of several hundreds of kW/cm². This can be mainly attributed to high defect densities of high Sn content alloy thick layers grown on relaxed Ge-VS. Indeed the use of high Sn contents in Ge(1-x)Snx alloy to reach direct band gap alignment (with xSn>10%) consequently results in large lattice mismatches with Ge and therefore produces large defect densities in partially relaxed thick layers. We show here that GeSn alloys with low Sn content exhibit strongly reduced lasing thresholds densities, in the 10 kW/cm² range, in microdisk cavities. We developed a layer transfer technology enabling management of the GeSn/Ge defect interface thus allowing to further reduce lasing thresholds in the kW/cm² range. The layer transfer additionally allows tensile strain engineering using silicon nitride stressor layer to increase the band structure directness as required for RT-laser operation.
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