High-performance Ge-on-insulator photodetector enabled by thick Ge spacer and tensile-strained GeSi/Ge multiple quantum wells

We have presented PIN Ge-on-insulator (GOI) photodetectors (PDs) incorporating tensile-strained GeSi/Ge multiple quantum wells (MQWs) within the intrinsic layer. To control strain relaxation and reduce dark current, the thickness of the Ge spacer cap above the GeSi/Ge MQWs was systematically optimized. The optimized design yields a dark current density of 2.20 mA/cm² and a responsivity of 1.01 A/W at 1550 nm, corresponding to a specific detectivity of 4.02 × 10¹⁰cm·Hz^1/2·W^-1 under -1 V. The PDs exhibit enhanced responsivity at 1550 nm due to constructive optical interference within the SiO₂ insulator layer. Moreover, the PD with a thicker spacer exhibits an extended cutoff wavelength of 1700nm, as confirmed by photoluminescence and spectral response measurements, which is attributed to the larger tensile strain in Ge-like Ge_0.86Si_0.14. These results demonstrate that GOI PDs with GeSi/Ge MQWs offer significant potential for high-performance, Ge-based extended short-wavelength infrared detection and imaging applications.