Wet Chemical Etching of Antimonide-Based Infrared Materials

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 (C₆H₈O₇) 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 R₀A value of 466 Ω?cm² and a detectivity of 1.43×10¹¹ cm?Hz^1/2W^?1. Crystallographic orientation selectivity is seen in InAs etching, and also is seen in the InAs/GaSb superlattice wet chemical etching process.