Monolithic fabrication of InSb-based photo-pixel for Mid-IR imaging

We present the monolithic fabrication of an active photo-pixel made in InSb on a GaAs substrate that is suitable for large-scale integration into a focal plane array. Pixel addressing is provided by the co-integration of a GaAs MESFET with an InSb photodiode. Various highly selective etch processes for distinct material layers were established. A low temperature annealed Ohmic contact was also achieved so that the processing temperature never exceeded 180 °C and no damage to the InSb detectors was observed. Furthermore, since there is a considerable etch step (> 6 μ) that metal must straddle without breaking, we developed an intermediate step using polyimide to provide a smoothing section between the lower MESFET and upper photodiode regions of the device. This heterogeneous technology creates great potential to realize a new type of monolithic focal plane array of addressable pixels for imaging in the medium wavelength infrared range.