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 report on the CMOS-compatible hybrid III-V/Silicon platform developed in CEA-LETI. In order to follow the large-scale integration capabilities of silicon photonics, already available worldwide in 200mm or 300mm through different foundries, the development of CMOS-compatible process for the III-V integration is of major interest. The technological developments involve not only the hybridization on top of a mature silicon photonic front-end wafer through direct molecular bonding but the patterning of the III-V epitaxy layer, low access resistance contacts, as well as planar multilevel BEOL must also be investigated and optimized. Test vehicles for the process validation based on either distributed feedback (DFB) or distributed Bragg reflector (DBR) laser cavities were designed. A modular approach is proposed in order to minimize the impact on the already qualified silicon photonics devices. Next, a collective III–V die bonding and processing have been successfully developed in this platform. The collective bonding, based on a flexible template holder, allows for large scale die to wafer transfer in both 200 and 300mm. After the III-V substrate removal and III-V patterning relying on optimized dry etching processes, CMOS compatible metallization’s are used to realize ohmic contact on n-InP and P-InGaAs leading to contact resistivity in the range of 10−6 Ω·cm². While first demonstrations have been obtained through wafer bonding, the fabrication process was subsequently validated on III-V dies bonding with a fabrication yield of Fabry-Perot lasers of 97% in 200mm. A planarized two-metal-level BEOL was used to connect the devices, leading to a drastic reduction of series resistance between 5.5 and 7 Ω. Finally, the functionality of DFB and DBR lasers is demonstrated with SMSR up to 50 dB and maximum output power of 3 mW in CW. The overall technological features are expected improve the efficiency, density, and cost of silicon photonics PICs.
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.
Hybrid III-V/Si laser integration on silicon photonic platform has been demonstrated several time using III-V direct bonding on top of patterned silicon [1-3]. Most of these former works have been achieved using small wafer diameter III-V fabrication line for post bonding process steps. The expected low-cost added value of silicon photonics cannot be sustained with such integration scheme. More recently, we present III-V laser integration with a CMOS compatible process using wafer to wafer bonding and 1 level of contact [4]. In this paper, we present the technological progresses on a 200mm fully CMOS compatible hybrid III-V/Si laser technology. We introduced an improved backend of line for hybrid lasers with 2 interconnection levels, W-plugs and fully planarized process offering a state of the art access resistance and a homogeneous current density distribution over the gain material. Second, in order to optimize the use of the costly III-V material and enable the laser large scale integration on silicon we present fabrication process with die to wafer molecular bonding with high bonding yield at wafer scale. These process features will be detailed and the impact of laser performances will be presented. Finally, the scalability towards 300mm for the overall platform will be discussed.
Silicon photonic platforms are becoming more and more mature with competitive devices suitable for increasing needs of HPC (High Performance Computing) systems and datacenters. Compared to bulk III-V technologies, Si photonic technologies are suffering from the lack of integrated light source. Several works have been done in the past years to integrate laser on silicon using III-V direct bonding on top of patterned silicon. These demonstrations were using a CMOS compatible process for the silicon part but all the process steps following the introduction of the III-V material were done with small wafer diameter III-V fabrication lines. With such integrations, the cost advantage of silicon photonics based on the use of CMOS platforms and large wafer format is no more valid.
In this paper we present the integration of a hybrid III-V/Si laser using a fully CMOS compatible 200mm technology. The laser is integrated in a mature photonic platform. The additional process modules required for this integration will be deeply described. These modules are localized silicon thickening using damascene process, Bragg reflector patterning with DUV lithography, III-V patterning and ohmic contact formation with no lift-off and without noble metal. This integration is compatible with a multi metal levels planar BEOL, mandatory for photonic circuit design.
The first DFB lasers fabricated with this new platform are operating at 1310nm with a threshold current around 60mA, a SMSR larger than 45dB and more than 1.5mW optical power in the output waveguide. New laser designs, specifically adapted for this new process, will be introduced and fabricated.
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