Aluminum-doped lanthanum phosphate (LaPO4:Al) nanoparticles were synthesized using a simple co-precipitation technique. The x-ray diffraction patterns show that all of the collected samples have a monoclinic structure with crystallite size (D) increasing from 13 to 17 nm as the Al-doping concentration increases, whereas the band gap values dropped from 5.46 eV to 3.93 eV with the increased Al-doping concentration. The effect of I–V electrical performance was methodically investigated in 10% Al-doped LaPO4-based metal–insulator–semiconductor (MIS)-type Schottky barrier diodes (SBDs). The experimental results reveal that the changes in the barrier height of 0.772 eV and the lowest ideality factor of 2.95 were both attained under light irradiation. In the comparison of the values of the undoped Cu/LaPO4/n-Si and Cu/Al-LaPO4/n-Si Schottky barrier diodes, the Al-LaPO4/n-Si Schottky barrier diode was found to possess a significantly better barrier height (?B) and ideality factor values (n) than the other. The reported results in this work are among the best to date for 10% Al-doped LaPO4 Schottky barrier diodes.