Abstract: Infrared photodetectors have extensive applications in military reconnaissance, optical communication, and medical imaging. Higher requirements are placed on their comprehensive performance in terms of high responsivity, low dark current, and fast response. The multiplication SAM structure, which physically separates the carrier absorption and avalanche multiplication processes, has become an important structure for improving the performance of infrared detectors. Based on the Silvaco ATLAS simulation platform, a two-dimensional back-illuminated multiplication SAM detector model was constructed in this paper, and the influence of the thickness and doping concentration was systematically analyzed. The results show that after the GaAs substrate is stripped, the device first shows a photoresponse at a wavelength of 0.6 μm, and the peak responsivity increases from 0 to 0.65 A/W at 1.5 μm. The optimization of the buffer layer reduces the dark current from 1.964×10^-9 A to 7.827×10^-10 A at a bias of -0.4 V. The adjustment of the absorption layer parameters can increase the peak responsivity to 2.44 A/W.