Planar-type 2.2 μm wavelength-extended InGaAs photodetectors (PDs) using the sealed-ampoule diffusion method was reported. The zinc arsenide powder was used as the dopant source, which was driven into the cap of the In_0.75Al_0.25As/In_0.75Ga_0.25As/In_0.75Al_0.25As hetero structure materials grown by molecular beam epitaxy (MBE), using a SiN_x as diffusion mask deposited by ICP-CVD. The junction depth, the lateral collection width of photogenerated carriers, the I-V characteristics, the spectral response and the detectivity of the detector at different temperatures were analyzed. The results indicate that the PD exhibits a low dark current density of 0.69×10^-9 A/cm² at -10 mV at 150 K. The cutoff wavelength and peak wavelength were 2.12 μm and 1.97 μm. The peak detectivity, peak responsivity and quantum efficiency was 1.01×10¹² cm·Hz^1/2/W, 1.29 A/W and 82% respectively. These results suggest that the planar-type InGaAs can reach high performance.