Si-Based Graded GeSn Waveguide Photodetectors With 2.61 μm Cutoff Wavelength for Mid-Infrared Silicon Photonics

The pursuit of highly efficient mid-infrared (MIR) photodetectors (PDs) for electronic photonic integrated circuits (EPICs) has spurred extensive research, with GeSn alloys emerging as promising candidates due to their tunable bandgaps and compatibility with complementary metal-oxide-semiconductor (CMOS) processes. Herein, we present the first demonstration of vertical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</i> GeSn ridge waveguide photodetectors (WGPD) exhibiting cutoff wavelength of λ = 2.61 μm suitable for MIR EPICs on Si. These WGPDs incorporate thick graded GeSn layers with 4.85% and 10.41% Sn content, achieving a narrow direct bandgap that facilitates efficient light absorption in the MIR range up to λ = 2.61 μm. A theoretical analysis using finite element method (FEM) simulation reveals optical confinement factors (OCF) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Gamma = 60.03\% $</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Gamma = 30.37\% $</tex-math></inline-formula> for the 1<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> and 2<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i>-GeSn layers, respectively, indicating enhanced light–matter interactions. Key parameters such as dark current, optical response, and specific detectivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$({{D}^*})$</tex-math></inline-formula> are thoroughly discussed, providing insights into the functionality of these GeSn WGPDs operating in the MIR regime. The proposed device exhibits a room-temperature <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{D}^*}$</tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{D}^*} = 3.05 \times {{10}^6}\;\text{cmH}{{\mathrm{z}}^{{\rm{1/2}}}}{{\mathrm{W}}^{{\rm{ - 1}}}}$</tex-math></inline-formula> at λ = 2 μm, comparable to the operational range of commercially available E-InGaAs PD, affirming its versatility across MIR applications. The integration of the proposed WGPD into EPICs opens avenues for advanced operations in the MIR region, with potential applications across diverse industries and scientific fields that require MIR photodetection capabilities.