Phosphorus-doped carbon quantum dots for broadband self-powered n-Si Schottky photodetectors with enhanced quantum efficiency and detectivity

The interfacial energetics of metal–semiconductor junctions critically determine the carrier transport behavior and overall performance of Schottky-based optoelectronic devices. In this work, unmodified carbon quantum dots (CQDs) and phosphorus-doped carbon quantum dots (P-CQDs) were synthesized and comprehensively characterized through transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, UV-Vis spectroscopy (UV-Vis), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS). The engineered quantum dots were subsequently integrated into n-Si heterojunction architectures to investigate the influence of heteroatom-induced band structure modulation on broadband self-powered photodetection. Under zero-bias operation, the P-CQD/n-Si photodetector demonstrated markedly enhanced optoelectronic performance compared to the undoped CQD/n-Si device. The photocurrent increased from 2.22 × 10−5 A (CQD/n-Si) to 9.66 × 10−5 A (P-CQD/n-Si) under 100 mW cm−2 illumination. The maximum responsivity reached 0.386 A W−1, while specific detectivity achieved 6.99 × 1010 Jones, accompanied by a low noise-equivalent power of 1.46 × 10−12 W Hz−1/2. Broadband spectral sensitivity spanning 351–1600 nm was achieved, with pronounced enhancement in the visible–NIR region. Notably, the external quantum efficiency (EQE) was significantly enhanced from ∼3.34% in the undoped device to ∼22.88% after phosphorus doping, corresponding to an approximately sevenfold improvement in photon-to-charge conversion efficiency. Overall, phosphorus doping provides an effective strategy for tailoring interfacial barrier properties and quantum dot electronic structure, enabling high-responsivity, low-noise, and high-efficiency self-powered photodetectors suitable for next-generation wide-band optoelectronic applications.