Direct Bandgap Ge0.846Sn0.154 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 0.846 Sn 0.154 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 7 cm.Hz 1/2 .W −1 . This detectivity is 60 times better than that of previously reported photodetectors with equivalent Sn content. When such Ge 0.846 Sn 0.154 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 −1/2 .