In this paper, we focus on the influence of thermal treatment on the passivation of silicon nitride (SiN<sub>x</sub>) film of p-i-n InGaAs detector. In our experiment, the perimeter/area (P/A) test diodes are fabricated by using two different device processes, and the relationship between the dark current density and P/A is investigated. The results indicate that the thermal treatment in the vacuum can be able to improve the passivation SiN<sub>x</sub> film effect and thus suppress the perimeterrelated current with the decrease of two orders of magnitude. Then the analysis of dark current source is carried out. The result shows that the sample with SiN<sub>x</sub> film through thermal treatment is composed of diffusion current and ohmic current, on the contrary, the other mainly consists of surface leakage current and diffusion current. It is illustrated that the passivation effect of SiN<sub>x</sub> was strengthened after thermal treatment and surface leakage current can be suppressed.
Nanowire grating is designed within the wavelength range from 1μm to 3μm according to the sensitive wavelength of InGaAs short wave infrared (SWIR) detector. The polarization performance is analyzed on the basis of finite difference time domain (FDTD) method. In order to improve the polarization performance, we insert a SiO<sub>2</sub> dielectric grating between metal grating and substrate to form Au-SiO<sub>2</sub> hybrid grating. The numerical study shows transmittance of hybrid grating is almost 88％which is 18％ higher than monolayer metal grating at 1.8μm. In addition, the hybrid grating with the grooved- SiO<sub>2</sub> layer has higher transmittance efficiency than those with smooth SiO<sub>2</sub> layer for special wave band. By optimizing the specific parameters of the hybrid grating such as period, thickness and the groove depth of SiO<sub>2</sub>, finally we obtain the optimal parameters of the designed hybrid grating: the grating period is 0.4 μm, the thickness and groove depth of SiO<sub>2</sub> are 0.4μm and 0.1μm respectively. Numerical study shows that the designed grating has advantages of wide band, high transmittance efficiency and high extinction ratio.