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We designed and fabricated narrow-band UV-B AlGaN p-i-n photodiodes (PDs) with a full-width at half-maximum (FWHM) of 8 nm by optimizing the Al composition and thickness of the AlGaN layers. To improve the photoelectric response of the narrow-band PDs, a polarization electric field with the same direction with the applied bias field was introduced to the absorption layer by adjusting the Al composition ratio between the p-type AlGaN layer and i-type AlGaN absorption layer. The polarization enhanced narrow-band PD exhibited a higher external quantum efficiency (EQE) of 82% than the conventional one with an EQE of 67%. Meanwhile, a low dark current density of 1.7 nA/cm² and four orders of magnitude UV-visible rejection ratio were achieved for the enhanced narrow-band PDs with a maximum photocurrent responsivity of 202 mA/W at 304 nm.