Microstructured silicon doped with selenium beyond the equilibrium solid solubility limit was formed by picosecond pulsed laser mixing of a 20-nm Se film with the underlying p-Si wafer. The effects of pulse fluence varying from 0.40 to 0.72 J cm−2 on the structural and electronic properties of this material were investigated. It was found that the surface roughness in the laser-irradiated regions increases with increasing pulse fluence, and a phase transition from the crystalline to the amorphous occurs at a pulse fluence of 0.72 J cm−2. Silicon microstructures were doped with selenium of the order of 1018 cm−3 within a depth of 100 nm below the surface, and n+p junctions were formed between the Se-doped layers and the silicon substrates. The current–voltage as well as spectral response characteristics of the photodiodes fabricated from microstructured silicon were also analyzed and discussed. The leakage currents and responsivities of these photodiodes strongly depend on the pulse fluence, presumably due to the effects of picosecond laser modification on the crystal structure and electronic structure of the surface Se-doped layers.