Stefan Hanna

Numerical Modeling of SRH and Tunneling Mechanisms in High-Operating-Temperature MWIR HgCdTe Photodetectors

A combined experimental and numerical simulation study is presented on two sets of nominally identical

Recent results of two-dimensional LW- and VLW-HgCdTe IR FPAs at AIM

\hbox {Hg}_{1-x}\hbox {Cd}_{x}\hbox {Te}

MCT by MBE on GaAs at AIM: state of the art and roadmap

Hg1-xCdxTe single-color back-illuminated midwave-infrared n-on-p photodetectors grown by liquid-phase epitaxy, p-doped with Hg vacancies and with Au, respectively. The present numerical model includes a novel formulation for band-to-band tunneling, which overcomes the intrinsic limitations of the classical Kane description without introducing numerical issues typical of other approaches. Our study confirms that adopting n-on-p architectures, avoiding metal vacancy doping, and reducing the acceptor density in the absorber region are prerequisites for obtaining high-operating-temperature photodetectors. A significant contribution to the dark current in both sets of devices is attributed to impact ionization, crucial to obtain a satisfactory explanation for the measured characteristics also at low to intermediate bias.

Non-Monochromatic 3D Optical Simulation of HgCdTe Focal Plane Arrays

We present a simulation study of HgCdTe-based long-wavelength infrared detectors, focusing on methodological comparisons between the finite-difference time-domain (FDTD) and ray-tracing optical models. We performed three-dimensional simulations to determine the absorbed photon density distributions and the corresponding photocurrent and quantum efficiency spectra of isolated n-on-p uniform-composition pixels, systematically comparing the results obtained with FDTD and ray tracing. Since ray tracing is a classical optics approach, unable to describe interference effects, its applicability has been found to be strongly wavelength dependent, especially when reflections from metallic layers are relevant. Interesting cavity effects around the material cutoff wavelength are described, and the cases where ray tracing can be considered a viable approximation are discussed.

Towards ultra-small pixel pitch cooled MW and LW IR-modules

In recent years AIM has expanded its portfolio of standard IR focal plane arrays (FPA) in the 3-5μm (MWIR) and 8- 10μm (LWIR) spectral range by 2-dimensional IR detectors, sensitive in the 0.9-2.5μm (SWIR) and especially in the 10- 15μm VLWIR. As far as dark current behavior, homogeneity, and operability are concerned, the VLWIR spectral range constitutes a major challenge for sensor material improvement and device development. This paper reports on the latest technological advancements at AIM. These advancements are not limited to the applications demonstrated in this paper, but a wide range of AIM products will benefit. A reduction of the pixel pitch from 24μm to 15μm is the result of increasing demands for compact detection modules with reduced weight, size, power consumption and improved costefficiency. Performance characterization for such a reduced pitch of 640x512 module in the LWIR (cut-off 9.2μm at 67 K) yields a mean NETD of ~37 mK and an operability of >99.8%. Extending the detection wavelength further into the VLWIR is of major interest for space applications such as Meteosat Third Generation (MTG), which poses challenging requirements for sensor material homogeneity and dark current density. To meet this requirement, an extrinsic doping approach is utilized on a 256x256 HgCdTe Focal Plane Array (FPA) with ~14μm cut-off wavelength at 55K operating temperature, a dark current density of about 1pA/μm2 is demonstrated.

High-performance SWIR/MWIR and MWIR/MWIR bispectral MCT detectors by AIM

We present a modeling technique for the efficient broadband simulation of infrared HgCdTe-based focal plane arrays. The approach performs a single broadband FullWAVETM FDTD optical simulation and a series of discrete Fourier transforms for obtaining absorbed photon density profiles on a set of frequencies. These distributions are then aggregated, through a weighted average, and imported as a generation term into a single Sentaurus Device electrical simulation, which calculates the corresponding photocurrent and inter-pixel crosstalk. This technique can save an order of magnitude in memory and computation time compared to performing multiple monochromatic optical and electrical simulations.

State-of-the-art MCT photodiodes for cutting-edge sensor applications by AIM

In multiple publications over the last years, MCT MBE on GaAs has been shown to be a very versatile and promising material system and indeed may be the prime candidate among the alternative substrates for the fabrication of high-performance detectors across the whole IR composition range. In this paper we report on successful growth of MCT on GaAs over the composition range 0.2 < x(Cd) < 0.8. A single color MWIR 640 × 512, 15 μm pitch detector fabricated from this material with an operability of 99.71% at an operating temperature of 120 K is presented. In the LWIR region, an operability of 99.48% at 65 K has been achieved with a 1280 × 1024, 15 μm pitch detector. Finally we report on preliminary results of a dual-color 640 × 512, 20 μm pitch detector with cutoff wavelengths in the 3 - 4 and 4 - 5 μm range.

State of the art of AIM LWIR and VLWIR MCT 2D focal plane detector arrays for higher operating temperatures

Combined optical and electrical simulations of infrared HgCdTe-based focal plane arrays under broadband, non-monochromatic illumination are critically relevant to the design of small-volume detectors with sub-wavelength pixel pitches. We present an efficient technique, based on a single finite-difference time-domain electromagnetic simulation, that provides the photogeneration rate profile due to realistic, broadband optical sources, avoiding multiple monochromatic simulations. This technique is applied to assess the effects of the temperature of blackbody optical sources on quantum efficiency and inter-pixel crosstalk of planar LWIR arrays.