Enhanced Response of Si-Based PbSe Thin Film MSM Photodetectors by Photon-Trapping Hole Array in the Surface

A Si-based PbSe thin film metal–semiconductor–metal (MSM) photodetector with enhanced efficiency in a wide spectral range is demonstrated with an integrated photon-trapping hole array in the surface. Based on the finite difference time domain method, the effects of film thickness, substrate, hole structure (diameter, period, and depth), and top electrodes on the infrared absorption of the photodetector are studied to optimize the device structure. The photon-trapping hole array effectively reduces the surface reflection and induces laterally slow propagating modes of the vertically incident light within the device, thereby achieving enhanced absorption. Additionally, the peak absorption wavelength can be tuned by changing the period of the holes. Several Si-based PbSe thin film MSM photodetectors with various hole structures are fabricated, and the measured efficiency agrees well with the theoretical prediction of infrared absorption. The photodetector with a hole array in a square lattice with a diameter/period ratio (d/p) of 700/1000 nm achieves a responsivity of 0.449 A/W at 808 nm. Compared to the device without hole structures, the responsivities at 808, 1064, 1310, and 1550 nm show significant enhancements of 225%, 267%, 334%, and 357%, respectively. The specific detectivity reaches 1.474 × 10⁹ Jones at 808 nm and 9.3 × 10⁸ Jones at 1550 nm. This study provides a new approach for the Si-based single-chip-integrated photodetectors with high efficiency over a broad spectral range, which makes the microhole-enabled Si-based PbSe MSM photodiodes promising to cover C, L, and even wider bands for low-cost infrared sensing and communication applications.