In this paper we present an overview of the very recent developments of the HgCdTe infrared detector technology developed by CEA-LETI and industrialized by Sofradir in France.
Today Sofradir uses in production for more than 15years a very mature, reproducible, well mastered and fully understood, planar n on p ion implanted technology. This process that allows very high yields to be achieved in all infrared bands from SWIR to LWIR uses the very conventional approach of LPE growth of MCT on lattice-matched CdZnTe substrates. Progress in this field is continuous from 20years and has recently leaded to the fabrication of high performance VLWIR FPA (320x256 with cut off wavelengths as high as 20μm). Moreover, thanks to the design of the epitaxial structure and to the substrate removal step MCT FPAs present the unique features to have very high quantum efficiency (above 70%) from the cut off wavelength down to the UV. This effect, which opens new application fields, was recently demonstrated in SWIR 320x256 FPAs with cut off wavelength of 2.5μm.
Very high quality FPAs (1280x1024) with pitches as small as 15μm have already been demonstrated last year using the MBE growth of MWIR MCT epilayers on 4 inches germanium substrates, n on p ion implanted photodiodes and the hot welding indium bump hybridization technique. At the same time, with the MBE growth, bicolor and dual band FPAs which uses more complex multi hetero-junctions architectures (both 4 layers npn and 'pseudo planar' structures and extrinsically doped MCT layers) were fabricated with formats of 320x256 and pitches as small as 25μm.
A very new area of development concerns avalanche photodiodes (APD) made with MCT. This semiconductor presents a unique feature among all the over semiconductors. Extremely high avalanche gains can be obtained on n on p photodiodes without absolutely any noise excess (F(K)=1): MCT APDs act as perfect amplifiers. These results open new interesting fields of investigation for low flux applications and fast detectors (including hyper spectral imaging and active imaging).