Dual waveband infrared detectors using MOVPE grown MCT

Mercury Cadmium Telluride (MCT) grown by Metal Organic Vapour Phase Epitaxy (MOVPE) on GaAs substrates is a mature technology at Leonardo MW used for the production of high-performance infrared detectors in the short, mid and long wavebands. Recently reported developments of single waveband devices have seen pixel densities increase by almost an order of magnitude, driven by system requirements for increased resolution together with reduced size, weight and power. High resolution MWIR detectors with 8μm pixels are now in volume production. The mesa structure of MOVPE grown MCT pixels controls most sources of inter-pixel crosstalk with optical scattering, carrier diffusion and other blurring mechanisms reduced to negligible levels, resulting in characteristically sharp infrared images from systems which use these devices. More than a decade ago, Leonardo MW pioneered the development of Dual Waveband Infra-Red (DWIR) technology with devices using 30μm, 24μm and 20μm mesa pixels. Both MWIR-LWIR and MWIR-MWIR devices have been successfully fabricated. These devices use a “back-to-back” diode arrangement in which the waveband is selected by changing the bias polarity across the diode stack. This ensures the spatial correlation between the two wavebands, which is essential for many applications. Such DWIR structures are significantly thicker than single waveband devices, posing challenges to increasing pixel density whilst retaining the highly desirable benefits of mesa isolation. This paper discusses the evolution of the DWIR technology to high density, 12μm MWIR-LWIR pixels, enabling the manufacture of higher resolution, lower cost DWIR devices.