In this paper, we presented a numerical analysis of absorption coefficient, dark current and specific detectivity for InAs/GaAs quantum ring inter-subband photodetector (QRIP). 3D Schrodinger equation was solved using finite difference method and based on effective mass approximation. Dimensions of quantum ring (QR) were considered that inter-subband transition was to be accomplished for radiations of 20 μm. Resonant tunneling (RT) barriers were designed with tunneling probability of unity for electrons with energy of 0.062 meV to lower dark current of conventional QRIP. Numerical analyses show that inclusion of RT barriers can reduce dark current for about two orders of magnitude. Furthermore, specific detectivities for conventional QRIP and RT-QRIP were calculated respectively, and results at different temperatures were compared. It is suggested that specific detectivity for RT-QRIP is one order of magnitude higher than that for conventional QRIP. It is suggested that RT barriers considerably improve the specific detectivity of conventional QRIP at different temperatures.