Study of the spatial response of reduced pitch Hg1−xCdxTe dual-band detector arrays

Self Cite

Extrinsic p-type doping during molecular-beam epitaxy (MBE) growth represents an essential generic toolbox for advanced heterostructures based on the HgCdTe material system: PiN diodes, mesa avalanche photodiodes (APD) or third-generation multispectral focal-plane arrays. Today, arsenic appears to be the best candidate to fulfill this role and our group is actively working on its incorporation during MBE growth, using an original radio frequency (RF) plasma source for arsenic. Such a cell is supposed to deliver a monatomic As flux, and as expected we observed high As electrical activation rates after annealing short-wave (SW), mid-wave (MW), and long-wave (LW) layers. At last, a couple of technological runs have been carried out in the MW range in order to validate the approach on practical devices. p-on-n focal-plane arrays (FPA) have been fabricated using a mesa delineated technology on an As-on-In doped metallurgical heterojunction layer grown on a lattice-matched CdZnTe layer (320 9 256, 30 lm pitch, 5 lm cutoff at 77 K). Observed diodes exhibit very interesting electro-optical characteristics: large shunt impedance, high quantum efficiency, and no noticeable excess noise. The resulting focalplane arrays were observed to be very uniform, leading to high operabilities. Noise equivalent temperature difference (NETD) distributions are very similar to those observed with the As ion-implanted p-on-n technology, fabricated in our laboratory as well. In our opinion, those excellent results demonstrate the feasibility of our MBE in situ arsenic doping process. Good electrical activation rates and high-quality layers can be obtained. We believe that such an approach allows precise control of the p-doping profile in the HgCdTe layer, which is necessary for advanced structure designs.

Section: Validation On Single Photodiodesmentioning

confidence: 99%

HgCdTe p-on-n Focal-Plane Array Fabrication Using Arsenic Incorporation During MBE Growth

Gravrand

Ballet

Baylet

et al. 2009

Self Cite

“…First, there is not much field penetrating the intertrench space confirming the fact that mesa walls offer high reflection and thus do not degrade the optical filling factor of such a device. 7 Secondly, due to the presence of the trenches, diffraction occurs, resulting in strong interference fringes close to the mesa walls. The spot-scan experiment can also be reproduced by introducing an Airy profile on the incident boundary, namely…”

Section: Examples Of Computationmentioning

confidence: 99%

Electromagnetic Modeling of n-on-p HgCdTe Back-Illuminated Infrared Photodiode Response

Gravrand

Gidon

2008

Self Cite

The mercury cadmium telluride (MCT) photodiode is a well-known detector for infrared (IR) sensing. Its growth (mainly liquid phase epitaxy (LPE)) and photovoltaic technology (ion implantation planar technology for instance) for second-generation IR detectors (linear and 2D monospectral arrays) now appear to be mature, well mastered, and understood, and allow optimal detection in a wide range of spectral bands. However, the next generation of IR detectors is supposed to use more sophisticated structures and technologies (such as mesa technology for dual-band detection or advanced heterostructures for high-operating-temperature detectors). Such structures are usually grown by molecular beam epitaxy (MBE) and consist of a layered stack of different thicknesses, HgCdTe (MCT) compositions, and doping levels. Moreover, pitches accessible today with advanced hybridization techniques (20 lm or less) tend to approach the diffraction limit, especially for long-wave (LWIR) and very long-wave (VLWIR) devices. Hence, the physical understanding of these third-generation pixels from an electromagnetic (EM) point of view is not straightforward as it will have to take into account diffraction effects in the pixels. This paper will focus on EM simulation of advanced MCT detectors, using finite element modeling (FEM) to solve MaxwellÕs equations in a twodimensional (2D) configuration and calculate absorption in the pixel. The corresponding collected current is then estimated by introducing a simple diffusion modeled diode and is compared to spot-scan experiments and/or experimental spectral responses to validate the method.

“…Previous measurements have demonstrated the fact that even if the geometrical fill factor of the upper band is low, the pixel optical size can be higher than its geometrical size because of internal reflections on the trench edges. 16 Performances of a Dual-Band NPN MWIR/MWIR 256 · 256 Pixel FPA Laboratory Prototype with a Pitch of 25 lm Readout Circuit Architecture CEA-LETI has designed a 256 · 256 pixel, twocolor, readout integrated circuit (ROIC) with a 25 lm pitch suited to the stacked dual-band detectors. It makes use of a high performance direct injection (DI) input circuit.…”

Section: Individual Npn Pixel Performancesmentioning

confidence: 99%

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

Destéfanis

Baylet

Ballet

et al. 2007

Self Cite

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.