Study of LWIR and VLWIR Focal Plane Array Developments: Comparison Between p-on-n and Different n-on-p Technologies on LPE HgCdTe

Abstract

The very long infrared wavelength (>14 lm) is a very challenging range for the design of mercury cadmium telluride (HgCdTe) large focal plane arrays (FPAs). The need (mainly expressed by the space industry) for very long wave FPAs appears very difficult to fulfil. High homogeneity, low defect rate, high quantum efficiency, low dark current, and low excess noise are required. Indeed, for such wavelength, the corresponding HgCdTe gap becomes smaller than 100 meV and each step from the metallurgy to the technology becomes critical. This paper aims at presenting a status of long and very long wave FPAs developments at DEFIR (LETI-LIR/Sofradir joint venture). This study will focus on results obtained in our laboratory for three different ion implanted technologies: n-on-p mercury vacancies doped technology, n-on-p extrinsic doped technology, and p-on-n arsenic on indium technology. Special focus is given to 15 lm cutoff n/p FPA fabricated in our laboratory demonstrating high uniformity, diffusion and shot noise limited photodiodes at 50 K.

Enhanced numerical analysis of current-voltage characteristics of long wavelength infrared p-on-n HgCdTe photodiodes

“…In comparison with p-on-n photodiodes, the vacancy doped photodiodes (n-on-p structure) exhibit higher dark currents [2]. Despite this fact, n-on-p technology is a viable solution for operation in a high flux configuration where the dark current is not an issue.…”

“…Generally, n-on-p vacancy doped diodes give rather high diffusion currents but leads to a robust technology as photodiode performance weakly depends on the doping level and absorbing layer thickness. Simple modelling manages to describe dark current behaviour of V Hg doped n-on-p junctions over a range of at least eight orders of magnitude [2]. In the case of extrinsic doping, Cu, Au, and As are often used.…”

HgCdTe detectors for space and science imaging in France: general issues and latest achievements

“…The evaluated structure was based on n/p diodes and ended up to fully functional 320x256 arrays with cutoffs close to 19µm at 50K [ 16 ]. This activity was followed by an ESA contract to target more specifically the 14.5µm cutoff required by the MTG needs [ 3 ], using the classical n/p diode configuration. Arrays showed very good performances in terms of QE, noise and defectivity.…”

Latest Developments in Long-Wavelength and Very-Long-Wavelength Infrared Detection with p-on-n HgCdTe

“…CEA-LETI and SOFRADIR have a good background in this band with a variety of achievements in terms of results 13,14 with up to 20 lm cutoff wavelength with n-on-p technology. These detectors serve as a reference for the production of VLWIR flight models for Meteosat Third Generation (MTG) program by SOFRADIR.…”