The roughness and the crystallographic orientation selectivity of etched antimonide-based infrared materials are examined and are used to optimize the chemical mesa etching process of the InAs/GaSb superlattice photodiode with the goal of reducing the dark current.The etchant used is based on phosphoric acid (H3PO4),citric acid (C6HsO7) and hydrogen peroxide (H2O2).The roughness of the mesa sidewalls and etching rates are compared and used to find an optimized etchant,with which we obtain optimized mid-wavelength infrared photodiodes possessing an RoA value of 466 Ω·cm2 and a detectivity of 1.43 × 1011 cm·Hz1/2 W-1.Crystallographic orientation selectivity is seen in InAs etching,and also is seen in the InAs/GaSb superlattice wet chemical etching process.