Miniaturized InSb photovoltaic infrared sensor operating at room temperature

This paper reports the development of a novel InSb infrared photovoltaic sensor (PVS) operating at room temperature. The PVS consists of an InSb p+p−n+ structure grown on semi-insulating GaAs(100) substrate, with a p+-Al0.17In0.83Sb barrier layer between the p+ and p− layers to reduce diffusion of photoexcited electrons. Photodiodes were fabricated by wet etching, and, using a 500-K blackbody, we obtained detectivity D*=2.8×108 cm Hz1/2/W and responsivity RV=1.9 kV/W at room temperature. The SNR was improved with the serial connection of 700 photodiodes patterned on a 600×600-µm2 chip. On increasing the number N of connected photodiodes, the SNR was improved by a factor of N1/2. The responsivity was constant for signals ranging from dc to 500 Hz. From spectral response measurements a cutoff wavelength of 6.8 µm was obtained. The PVS was flip-chip bonded on pre-amplifier IC, allowing the shortest possible connection between the PVS and the pre-amplifier, making the system immune to electromagnetic noise. The system was finally encapsulated in a dual flat nonleaded package with a window, which exposes the back of the GaAs substrate, allowing the infrared light incidence. The device is small (2.2×2.7×0.7 mm3), operates at room temperature, and is able to detect human body radiation in the middle IR range.