Status of HgCdTe Bicolor and Dual-Band Infrared Focal Arrays at LETI

Abstract

In this paper we show the latest achievements of HgCdTe-based infrared bispectral focal plane arrays (FPAs) at LETI infrared laboratory. We present and compare the two different pixel architectures that are studied now in our laboratory, named ''NPN'' and ''pseudo-planar''. With these two technologies, a wide range of system applications in dual-band detection can be covered. Advantages of both architectures will be pointed out. We also review performances obtained with these different architectures. The first one has been studied for several years in our laboratory, and we review results obtained on FPAs of size 256 · 256 pixels on a 25 lm pitch, in the MWIR/MWIR (3 lm/5 lm) range. Very high noise equivalent temperature difference (NETD) operability is obtained, at 99.8% for the k c = 3 lm band and 98.7% for the k c = 5 lm band. The second one has been developed more recently, to address other applications that need temporal coherence as well as spatial coherence. We show detailed performances measured on pseudo-planar type FPAs of size 256 · 256 pixels on a 30 lm pitch, in the MWIR/LWIR (5 lm/9 lm) range. The results are also very promising for these prototypes, with NETD as low as 15 mK for an integration time as short as 1 ms, and good operability. The main manufacturing issues are also presented and discussed for both pixel architectures. Challenging process steps are, firstly, molecular beam epitaxy (MBE) HgCdTe heterostructure growth, on large substrates (cadmium zinc telluride) and heterosubstrates (germanium), and, secondly, detector array fabrication on a nonplanar surface. In particular, trenches or hole etching steps, photolithography and hybridization are crucial to improve uniformity, number of defects and performances. Some results of surface, structural and electrical characterizations are shown to illustrate these issues. On the basis of these results, the short-term and longterm objectives and trends for our research and development are presented, in terms of pixel pitch reduction, wavelengths, and dual-band FPA size.

New material systems for third generation infrared photodetectors

“…Both HgCdTe photodiodes [25][26][27][28][29][30] and QWIPs [31][32][33][34][35][36][37] offer the multicolour capability in the SWIR, MWIR and LWIR range. The performance figures of merit of state-of-the-art QWIP and HgCdTe FPAs are similar because the main limitations come from the readout circuits.…”

“…A variation on the original back to back concept was implemented using HgCdTe at Rockwell [112] and Santa Barbara Research Center [113]. Following the successful demonstration of multispectral detectors in LPE-grown HgCdTe devices [113], the MBE and MOCVD techniques have been used for the grown of a variety of multispectral detectors at Raytheon [27,[114][115][116][117], BAE Systems [118], Leti [28,30,[119][120][121], Selex and QinetiQ [29,122,123], DRS, [26,124,125] Teledyne and NVESD [126,127]. For more than a decade a steady progression have been made in a wide variety of pixel size (to as small as 20 µm.…”

Two-colour HgCdTe infrared detectors operating above 200 K

“…In recent years, the realization of dual-band HgCdTe infrared detectors has been the core of intensive research and technological developments [3][4][5][6][7][8][9]. The detection in two different infrared bands or at two different wavelengths within the same band, allows the absolute temperature determination of an infrared scene, assuming a constant emissivity over the spectral range.…”

“…Previously, the multilayer approach has been usually fabricated using molecular beam epitaxy (MBE) [4][5][6]9]. However, an alternative growth technique, metaloorganic chemical vapour deposition (MOCVD), also allows the growth of multilayer structures with excellent control of composition and doping profiles [8].…”

Simulation and analysis of grating-integrated quantum dot infrared detectors for spectral response control and performance enhancement

“…Multispectral detectors, which can provide spectral resolution and enable multiband detection, are highly beneficial for these applications and are being actively studied. [8][9][10][11][12][13] Usually, a broadband IR camera is used to obtain the spatial distribution of IR radiation (i.e., IR images), together with dispersive elements (such as spinning filter wheels or prisms), to get the spectral information. However, these mechanical parts increase the cost and complexity of IR cameras significantly.…”