The invention relates to a photodetector for infrared light radiation having a given wavelength (λ), including a stack of layers consisting of: a continuous layer (11) of a partially absorbent semiconductor material, which constitutes the photodetection area; a spacer layer (12) of a material that is transparent to said wavelength and has an index ne; and a structured metal mirror (13), the distance (g) between the top of said mirror and the semiconductor layer being less than (λ)/ne and the mirror surface having a profile corresponding to the periodic repetition, according to period (P), of a basic pattern defined by the alternating series of raised surfaces (131, 132) and slots (133, 134) having the widths (L1, L2) and (L3, L4), respectively, the widths (L1) to (L4) being such that none are equal to zero, and that the sum thereof is equal to P and at least L1≠L2 or L3≠L4.