Fabrication of InAs photodiodes with reduced surface leakage current

Abstract

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 AlAs_0.16Sb_0.84 was developed using molecular beam epitaxy. A photodiode structure was designed, grown and characterized using an AlAs_0.16Sb_0.84 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.