<p>Slanted silicon (Si) nanowire (NW) arrays have emerged as a promising platform for high-performance photodetectors due to their large surface-to-volume ratio, intrinsic anti-reflection characteristics and asymmetric geometry that enables diverse optical mode coupling. Although the slanted geometry inherently provides enhanced light trapping capability, its practical implementation has been hindered by challenges in achieving uniform and effective surface passivation, an issue far less problematic in vertically standing NW arrays. Here, we present an effective silicon oxide (SiO_x) passivation strategy for slanted Si NW arrays using spin-on-glass (SOG) technology, leading to an improved optical absorption. The inter-wire gaps were filled with SOG and subsequently annealed to convert the material into SiO_x, thereby uniformly passivating the NW surfaces. Finite-difference time-domain (FDTD) simulations reveal that the uniformly formed SiO_x layer enhances optical absorption by ~ 70% at 1060 nm, attributed to an increased effective refractive index within the NW array, which improves accommodation of the longer-wavelength incident light inside the NW array. Experimentally, the passivated NW array exhibits a markedly reduced dark current of 2.6 µA at 3 V, compared with 133 µA for unpassivated device, along with an improved responsivity of ~ 17 mA/W at 1050 nm, in contrast to ~ 6 mA/W observed in the unpassivated device. This work demonstrates a simple yet effective passivation route for slanted NW architectures, offering a scalable pathway to enhance light absorption and stability in Si-based photodetection applications.</p> Graphical abstract <p></p>