Miniaturized InSb photovoltaic infrared sensor operating at room temperature

Abstract

This paper reports the development of a novel InSb photovoltaic infrared sensor (InSb PVS) operating at room temperature. The InSb PVS consists of an InSb p⁺/p^-/n⁺ structure grown on semi-insulating GaAs (100) substrate, with a p⁺ Al_0.17In_0.83Sb barrier layer between p⁺ and p^- layers to reduce diffusion of photo-excited electrons. Photodiodes were fabricated by wet etching process and, using a 500K blackbody, we obtained D* of 2.8x10⁸ cmHz^1/2/W and R_V of 1.9 kV/W at room temperature. S/N was improved with the serial connection of 700 photodiodes patterned on a 600x600 μm² chip. Increasing the number (N) of connected photodiodes, S/N ratio was improved by a factor of N^1/2. RV was constant for signals ranging from DC to 500Hz. From spectral response measurements a cut-off wavelength of 6.8 μm was obtained. The InSb PVS was flip-chip bonded on a pre-amplifier IC, allowing the shortest connection between the InSb PVS and the pre-amplifier, making the system immune to electromagnetic noise. The system was finally encapsulated by a Dual Flat Non-leaded (DFN) package with a window, which exposes the backside of the GaAs substrate allowing the infrared light incidence. The device external sizes are 2.2 mm x 2.7 mm x 0.7 mm and to our knowledge is the smallest uncooled sensor for the middle-infrared range reported until now.