Dual-band infrared detectors made on high-quality HgCdTe epilayers grown by molecular beam epitaxy on CdZnTe or CdTe/Ge substrates

In this paper, we present all the successive steps for realizing dual-band infrared detectors operating in the mid-wavelength infrared (MWIR) band. High crystalline quality HgCdTe multilayer stacks have been grown by molecular beam epitaxy (MBE) on CdZnTe and CdTe/Ge substrates. Material characterization in the light of high-resolution x-ray diffraction (HRXRD) results and dislocation density measurements are exposed in detail. These characterizations show some striking differences between structures grown on the two kinds of substrates. Device processing and readout circuit for 128×128 focal-plane array (FPA) fabrication are described. The electro-optical characteristics of the devices show that devices grown on Ge match those grown on CdZnTe substrates in terms of responsivity, noise measurements, and operability.     

Resistance changes in thin film integrated circuits caused by interdiffusion

The resistance changes in the thin film Au/Pd and Al/Au systems are investigated at a temperature of 350°C (Au/Pd) and in the range 100–200°C (Al/Au). Except for the original Au/Pd and Al/Au data, the experimental Au/Pd values published in the paper by Hall et al. are evaluated. The correct mathematical solutions for lateral diffusion from grain boundaries into grains and for interdiffusion in two-film samples are used in interpreting the experimental data. The evaluated values of the diffusion coefficient D satisfy the Arrhenius relationships and yield reliable information on the activation enthalpies H of the interdiffusion processes. However, the values of the frequency factors D₀ are less reliable, owing to their direct dependence on the grain size (Au/Pd) or on the film thicknesses (Al/Au).     

Single-scan extraction of two-dimensional parameters of infrared focal plane arrays utilizing a Fourier-transform spectrometer

We present what is believed to be a novel experimental method to measure the technological parameters (spectral response and quantum yield) of an infrared focal plane array. This method makes original use of a Fourier transform spectrometer, which allows us to simultaneously extract the spectral performances of all pixels from one single set of measurements. The methodology used and the principle of the experimental setup are detailed. A Fourier analysis is shown to provide various optogeometrical information on the detector microstructure. A demonstrator based on the HgCdTe technology was designed, and satisfactory experimental results were obtained.     

Neutron field characterisation at mixed oxide fuel plant

A neutron field characterisation was conducted at the AREVA Melox Plant to determine the response of passive and active neutron dosemeters for several stages in the mixed oxide fuel manufacturing process. Landauer Europe provides radiation dosimetry to many contractors working at the Melox site. The studies were conducted to assist in determining the neutron radiation fields the workers are exposed to routinely, evaluate the need for specific neutron correction factors and to ensure that the most accurate neutron dose is reported for the Melox Plant workers.     

Status of the MBE technology at leti LIR for the manufacturing of HgCdTe focal plane arrays

This paper presents recent developments that have been made in Leti Infrared Laboratory in the field of molecular beam epitaxy (MBE) growth and fabrication of medium wavelength and long wavelength infrared (MWIR and LWIR) HgCdTe devices. The techniques that lead to growth temperature and flux control are presented. Run to run composition reproducibility is investigated on runs of more than 15 consecutively grown layers. Etch pit density in the low 10⁵ cm⁻² and void density lower than 10³ cm⁻² are obtained routinely on CdZnTe substrates. The samples exhibit low n-type carrier concentration in the 10¹⁴ to 10¹⁵ cm⁻³ range and mobility in excess of 10⁵ cm²/Vs at 77 K for epilayers with 9.5 μm cut-off wavelength. LWIR diodes, fabricated with an-on-p homojunction process present dynamic resistance area products which reach values of 8 10³ Ωcm² for a biased voltage of −50 mV and a cutoff wavelength of 9.5 μm at 77 K. A 320 × 240 plane array with a 30 μm pitch operating at 77 K in the MWIR range has been developed using HgCdTe and CdTe layers MBE grown on a Germanium substrate. Mean NEDT value of 8.8 mK together with an operability of 99.94% is obtained. We fabricated MWIR two-color detectors by the superposition of layers of HgCdTe with different compositions and a mixed MESA and planar technology. These detectors are spatially coherent and can be independently addressed. Current voltage curves of 60 × 60 μm² photodiodes have breakdown voltage exceeding 800 mV for each diode. The cutoff wavelength at 77 K is 3.1 μm for the MWIR-1 and 5 μm for the MWIR-2.     

Extended X-Ray Absorption Fine Structure Study of Arsenic in HgCdTe

Extended x-ray absorption fine structure (EXAFS) experiments using the As K-edge have been carried out at the European Synchrotron Radiation Facility on two molecular beam epitaxy (MBE) grown arsenic-doped HgCdTe samples. Arsenic (As) is provided by a radio-frequency plasma cell and was incorporated to a level of a few 10¹⁸ at·cm⁻³. Both samples were analyzed as grown and after a high-temperature anneal (410°C/1 h) under saturated mercury pressure. The EXAFS signature of as-grown and annealed samples are strikingly different, indicating a drastic change in the environment of the As atom. In any case, the EXAFS signal originates from at least two different contributions and is found to be dominated by As clusters. The other contribution for as-grown samples comes from tellurium neighbors indicating that As incorporates partially in the (Cd,Hg) site.