We demonstrate two short-wavelength infrared avalanche photodiodes based on InAs/GaSb superlattice grown by metal-organic chemical vapor deposition.The difference between the two devices,namely,p+nˉn+ and p+nnˉn+,is that the p+nnˉn+ device possesses an additional middle-doped layer to separate the multiplication region from the absorption region.By properly controlling the electric field distribution in the p+nnˉn+ device,an electric field of 906 kV/cm has been achieved,which is 2.6 times higher than that in the p+nˉn+ device.At a reverse bias of-0.1 V at 77 K,both devices show a 100％ cut-off wavelength of 2.25 pm.The p+nˉn+ and p+nnˉn+ show a dark current density of 1.5x 10-7 A/cm2 and 1.8 × 10-8 A/cm2,and a peak responsivity about 0.35 A/W and 0.40 A/W at 1.5 pm,respectively.A maximum multiplication gain of 55 is achieved in the p+nnˉn+ device while the value is only less than 2 in the p+nˉn+device.Exponential nature of the gain characteristic as a function of reverse bias confirms a single carrier hole dominated impact ionization.