Dual-band infrared HgCdTe focal plane array

This paper presents an overview of LETI infrared laboratory activity in the field of dual band infrared focal plane arrays (FPAs). The technology developed uses HgCdTe multi-layer doped heterostructures grown by molecular beam epitaxy (MBE) on lattice matched CdZnTe high quality substrates. The device structure is n+ppn and is spatially coherent. The long wavelength layer is a planar like n(+)/p diode made by ion implantation while the shorter wavelength p-n diode is made in-situ during the MBE growth using Indium impurity doping. The last junction is isolated by mesa etch. The detectors are interconnected by indium bumps to a readout circuit with a yield close to 100%. One or two indium bumps per pixel are used to address sequentially or simultaneously the two wavelengths, the detector pitch being 50mum or 60mum respectively. Elementary detectors exhibit performances in each band that are close to those obtained in single colour detectors with our standard technology. The Si-CMOS readout circuits are specially designed to optimise the performances of the infrared FPAs in both wavelengths. The electro-optical performances of two-colour FPAs with a complexity of 128X128 pixels (pitch of 50mum) operating sequentially within the (2-5mum) middle wavelength infrared range (MWIR) at 77K are presented.