Silicon-based photodetectors are intrinsically limited in the mid-wave infrared (MWIR) region by the Si bandgap and the Schottky barrier. To overcome these constraints, we employed a CMOS-compatible inverted pyramid structure (IPS) that supports localized surface plasmon resonances (LSPR) and further introduced a composite pyramid formed by embedding an upright pyramid within the IPS. Three device architectures were fabricated and compared: a conventional planar structure, an IPS, and the composite pyramid. At zero external bias under 3.46 µm illumination, the composite pyramid exhibited a responsivity of 17.4 µA/W, corresponding to enhancements of 55.9 times and 266 times relative to the IPS and planar devices, respectively. Notably, at 10 µm, the composite device still outperformed, with a responsivity 75 times higher than that of the IPS, while the planar structure yielded no detectable signal. COMSOL simulations confirmed that the composite design significantly enhances the local electric field, yielding a local optical intensity 1.54 × 1011 times and 120 times higher than that of the planar device and the IPS at 3 µm, respectively. Even at 10 µm, the intensity remains 253 times higher than that of the IPS. These improvements are attributed to the composite configuration, which concentrates and reinforces the resonant electric fields, resulting in a stronger and more confined localized field distribution that sustains robust LSPR at longer infrared wavelengths. Consequently, optical absorption and hot-carrier generation are substantially improved, significantly boosting MWIR responsivity and overall optoelectronic performance. This composite design, thus, provides a promising pathway for efficient, CMOS-compatible silicon-based photodetectors operating in the mid-infrared region.
Chang et al. (2026) studied this question.