Fabrication of 15- $\mu$ m pitch $640{\rm ×}512$ InAs/GaSb type-II superlattice focal plane arrays

Abstract

We present the fabrication of large format 640 × 512, 15-μm pitch, mid-wave infrared region (MWIR) InAs/GaSb type-II superlattice (T2SL) focal plane array (FPA). In this report, the details of device design and fabrication processes are withheld adhering to the common practice of most of the manufactures and developers because of the strategic importance; however, information about fabrication processes of T2SLs FPA is presented to a certain extent. Comparison of etching techniques, passivation materials and methods, and substrate thinning (mechanical and chemical) is given besides of details regarding the standard ohmic contact and indium (In) bump formations. Morphological investigations of fabrication step are included. Large area pixels, 220 μm × 220 μm, fabricated by different etching methods and passivation materials/methods are compared in terms of dark current levels. Wet passivation with (NH 4 ) 2 S is discussed in terms of morphological investigations, and dark current results are compared with untreated samples. Large area pixel level characterizations as well as image level benchmarking of mechanical and chemical substrate thinning are reported. Effect of GaSb substrate on device performance and the way of reducing stress of In bumps are revealed. The importance of complete substrate removal is demonstrated through FPA images.