Employing BP, graphene, and germanene as modification layers for enhanced Mg₂Ge/Ge broadband SWIR photodetectors

The advancement of Ge-based short-wave infrared (SWIR) photodetectors (PDs) is often hampered by significant interface recombination. To address this problematic issue, we propose a novel interface modification strategy utilizing two-dimensional (2D) materials—black phosphorus (BP), multilayer graphene (MLG), and germanene—to engineer Mg₂Ge/Ge heterojunctions. Through comprehensive technology computer-aided design (TCAD) simulations, we demonstrate that the modified PDs achieve stable broadband detection in the 1150–1550 nm communication band. The Germanene/Mg₂Ge/Ge heterojunction displays optimal performance, with a responsivity of 0.97 A/W at 1400 nm, an external quantum efficiency (EQE) of 97%, and a detectivity ( D ⁎ ) of 1.12×10⁸ Jones—representing enhancements of 20%, 35%, and 18% over the pristine structure. The dark current is reduced to approximately 10⁻¹⁰ A, with a detection performance fluctuation of only 5%, indicating remarkable operational stability. This improvement arises from a quadruple interface modification mechanism: enhanced broadband absorption through the integration of 2D materials, efficient carrier separation attributed to Type-II band alignment, accelerated extraction facilitated by reinforced interface electric fields, and superior carrier transport enabled by the high mobility of 2D materials. Our study not only validates the 2D material interface strategy but also elucidates the underlying "band–field–absorption–transport" optimization mechanism, providing a theoretical foundation for the development of high-performance, chip-integrated, cost-effective, and environmentally friendly broadband SWIR-PDs.