Abstract
Antimonide heterojunction phototransistors (HPTs) have shown significant potential for extended short-wave infrared (SWIR) detection owing to their intrinsic internal gain mechanism. However, in the 2 μm spectral region, the rapid decrease in the intrinsic absorption coefficient of the material, together with the limited absorber thickness of the device, restricts further improvement in quantum efficiency. In addition, the collector region, which serves as the core absorption region, is deeply buried beneath the relatively thick emitter and base regions, posing a significant challenge for efficient photon coupling and capture. In this work, an enhanced HPT architecture integrated with a high-refractive-index all-dielectric silicon nanopillar metasurface is proposed and systematically designed. To overcome the optical absorption limitation without increasing the epitaxial absorber thickness, a periodic silicon nanopillar array is introduced onto the top surface of the device, approximately 470 nm above the 500-nm-thick core collector region. Through finite-difference time-domain (FDTD) simulations and multidimensional parameter optimization, the metasurface-integrated device achieves pronounced resonant absorption enhancement at 2 μm. Compared with the conventional planar structure, the absolute absorptance in the deeply buried collector region increases from 0.19 to 0.34, corresponding to an absolute absorptance gain of 0.15. Multipole decomposition and near-field distribution analyses reveal the underlying physical mechanism: the metasurface excites a dominant bright-state toroidal dipole resonance (TDR), while the asymmetric dielectric environment breaks the symmetric radiation profile of the TDR mode and induces efficient directional forward scattering. The forward-scattered photons are then coherently coupled into the waveguide mode supported by the underlying heterojunction, exciting a laterally propagating guided-mode resonance (GMR) and thereby significantly extending the effective optical path length of photons within the core absorption region. Furthermore, angle-dependent analysis indicates that oblique-incidence-induced mode degeneracy lifting can broaden the absorption response and provide good robustness under small-angle oblique illumination. This TDR–GMR synergistic enhancement mechanism provides a new design strategy for developing efficient SWIR photodetectors.