Direct Bandgap Ge _0.846 Sn _0.154 Photodiodes for Gas Sensing in the Mid-Wave Infrared

Recently, all-group-IV (Si)GeSn alloys attracted great attention as materials for Infra-Red optoelectronics monolithically integrated on Si substrates. In this work, we present the fabrication and the electro-optical characterization of direct bandgap GeSn photodiodes with 15.4% of Sn grown on Ge Strain-Relaxed Buffers, themselves on 200 mm Si(001) wafers. The Ge<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.846</sub>Sn<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.154</sub> photodetectors have a cutoff wavelength of 3.5 μm, e.g., they are suitable for methane detection around 3.3 μm. At this wavelength, their specific detectivity D* at room temperature is 3.76 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm.Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup>.W<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup>. This detectivity is 60 times better than that of previously reported photodetectors with equivalent Sn content. When such Ge<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.846</sub>Sn<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.154</sub> photodiodes are placed in a gas cell together with a commercial Light Emitting Diode emitting at 3.3 μm, the system presents a limit of detection for methane of 1 600 parts per million with a noise density of 0.78%.Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1/2</sup>.