We report the findings of work undertaken to develop InAs photodiodes with low reverse leakage current, for detection of mid-wave infrared wavelengths up to 3.5 mu m. Good quality epitaxial growth of InAs and the lattice matched ternary AlAs0.16Sb0.84 was developed using molecular beam epitaxy. A photodiode structure was designed, grown and characterized using an AlAs0.16Sb0.84 layer to block the diffusion of minority electrons. Further reductions in the reverse leakage current were achieved through studies of wet etching using a range of etchants. A sulphuric acid based etchant provided the lowest surface leakage current for a single etch step, however the surface leakage current was further reduces when a two steps etching process was employed, starting with a phosphoric acid based etchant and finishing off with a sulphuric acid based etchant. Surface profile analysis showed that higher etching rates were obtained in the direction parallel to the (100) direction. The atomic composition of the etched surface was investigated using Auger analysis. By etching a test pixel array, the potential for fabricating small pitch focal plane arrays by wet etching was evaluated.