Infrared detectors based on II–VI semiconductors are cooled from room temperature (RT) to cryogenic temperatures between 80 K and 150 K in order to operate with strong requirements regarding sensor performances for infrared detection. At these cryogenic temperatures, the mechanical properties of II–VI alloys have to be known in detail to improve handling, use and lifetime of infrared sensors. We have developed a cryogenic indentation tool and in situ measured the mechanical properties of CdZnTe alloys at both RT and 90 K. CdZnTe hardness increases by a factor of about 3 when cooling from RT to 90 K, from 0.6 GPa to 1.6 GPa. The plastic flow driving mechanism shows at least two different domains with activation energies around 0.01 eV at low temperatures and around 0.05 eV at RT, showing an increase by a factor of about 5. These two domains might be ‘connected’ by an intermediate domain in the 235 K–290 K temperature range. Radial cracks can be in situ detected. Toughness of CdZnTe alloys also increases dramatically by a factor of about 2 with cooling down to cryogenic temperature from 0.13 MPa.m1/2 at RT to 0.25 MPa.m1/2 at 90 K.

SOFRADIR is a worldwide leader on the cooled infrared (IR) detector market for high-performance space, military and security applications thanks to a high maturity Mercury Cadmium Telluride (MCT) technology, and III-V technology: InGaAs, and QWIP quantum detectors. As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. The current trend in quantum IR detector development is the design of very small pixel, operating at higher temperatures. In this context, keeping high image quality is a key challenge. This paper discusses the relevant criteria to quantify image quality: the Modulation Transfer Function (MTF) and the Residual Fixed Pattern Noise (RFPN). State of the art relevant performances for IR detection and imaging will be presented for Daphnis MW product, 10μm pitch XGA/HD720 extended MW matrix (cut-off wavelength 5.3μm) operating at 110K: range improvement, digital ROIC optimization, NUC (Non Uniformity Correction) table stability. Projections and results for smaller pixel pitch are also detailed.

HgCdTe (MCT) is a widely used semiconductor material used for manufacturing high-quality infrared detectors. At Sofradir, HgCdTe is grown by liquid phase epitaxy on lattice-matched CdZnTe substrates. Low threading dislocation densities (TDD) in the low 1 × 104 dislocations/cm2 are routinely obtained. Despite these low TDD levels, these dislocations are known to affect the electrical properties of photodiodes. Dislocation electrical behavior needs a deeper understanding in order to improve the manufacturing technology and the photodiode performance. In this study, we use Vickers micro-indentations to inject extra dislocations into dedicated areas of n on p mid-wave infrared photodiodes. The photodiodes were then characterized and analyzed theoretically thanks to I(V) and I(t) measurements under F/3 flux conditions (typical focal plane array illumination) at 110 K. Microindentations were performed close to the photodiodes in order to inject controlled high to very high dislocation densities. The effect of such an injection was then studied in depth on photodiodes. The electrical results have shown that the temporal variation of the current I(t) is mostly affected by the generation of extra dislocations. The same type of degradation of I(t) was observed in focal plane arrays, which confirms that dislocations play an important role in the generation of noise defects.

Both low-frequency noises and electrically active defects have been investigated for two technological variants, i.e. optimized and non-optimized, of the HgCdTe p on n technology applied to the mid-wave infrared blue band with a cut-off wavelength of 4.2 μm. This has been achieved using electro-optical characterizations and the deep level transient spectroscopy (DLTS) technique. The results show that the impact of extra 1/f and random telegraph signal noises has been reduced with the optimization of the technology. Furthermore, a broadened DLTS peak, probably related to dislocations in the material, has been found for both variants, the relative amplitude of which is reduced in the optimized case. The potential correlation between low-frequency noises and this broadened peak is discussed.

Extended electrically active defects have been investigated in Short Wave InfraRed (SWIR) HgCdTe n on p photodiodes, using the Deep Level Transient Spectroscopy (DLTS) technique. Three localized defects have been found in the dislocations core or in their close environment. DLTS studies have also been performed before and after indentation, a technique which generates dislocations in the material. DLTS spectra are discussed and dislocations generated by indentation have been found to be electrically active only after annealing.