High-Performance Back-Illuminated Ge0.92Sn0.08/Ge Multiple-Quantum-Well Photodetector on Si Platform For SWIR Detection

Recently, high-performance GeSn photodiodes (PDs) with external light illuminated on the device's top surface have been demonstrated on various platforms. However, for image sensing systems with a focal-plane array (FPA), the front-illuminated sensors usually suffer from area limitations. Here, we report high-performance back-illuminated Ge_0.92Sn_0.08/Ge multiple-quantum-well (MQW) p-i-n PD on 300-mm silicon substrate, which was realized entirely by complementary metal-oxide-semiconductor (CMOS) compatible processes. A broadband photoresponse between 1,000-2,100 nm was observed, and the responsivity is 0.2850 and 0.0085A/W at 1,550 and 2,000 nm, respectively. A specific detectivity larger than 10⁹ cm·Hz^1/2/W was achieved between 1,050 and 1,900 nm, covering all the conventional telecommunication bands (O to U band). Furthermore, the influence of the anti-reflective layers also was studied in detail. The result shows the black Si (b-Si) surface enhances more photocurrent between 1,000-1,500 nm while the SiO₂ layer (400-nm-thickness) increases more current beyond 1,500 nm. The 3-dB bandwidth was calculated to be up to 8 GHz for a mesa with a diameter of 20 μm at −2 V. Our experiments demonstrated the high-detectivity and high-speed back-illuminated GeSn/Ge MQW PD with the potential applications in image sensing systems operated in the short-wave infrared (SWIR) range.