In this paper, we theoretically investigate the influence of randomness in layer thickness and half-wave defect cavities on terahertz (THz) absorption in graphene-based photonic crystals. When these parameters are appropriately changed, it is possible to get the fourwavelength enhanced absorption with values of more than 0.92. In particular, there are three modes with absorption values above 0.99, which indicates the potential applications of the designed model for THz absorbers. Further, we investigated the effect of positional defect cavities on getting multimode absorption. The findings reveal that defect cavities on the leftmost side of the Bragg mirror can support more random structures with near-unity absorption compared to defect cavities on the rightmost layers. In particular, defect cavities at the leftmost layers can be able to achieve 30% of random structures with an absorption value greater than 0.95. We also survey the effects of perpendicular magnetic fields on the absorption characteristics of right-handed polarized (RCP) and left-handed circularly polarized light (LCP). It has been found that when the magnetic bias is increased, the full width at half maximum of the absorption peaks increases for LCP, while it decreases for RCP. However, this behavior can be totally reversed by altering the magnetic field’s direction.
