Submicronic Laue diffraction to determine in-depth strain in very closely matched complex HgCdTe/CdZnTe heterostructures with a 10⁻⁵ resolution

Abstract

Cross-sectional submicronic Laue diffraction has been successfully applied to HgCdTe/CdZnTe heterostructures to provide accurate strain profiles from substrate to surface. Combined with chemical-sensitive techniques, this approach allows correlation of lattice-mismatch, interface compositional gradient and strain while isolating specific layer contributions which would otherwise be averaged using conventional X-ray diffraction. The submicronic spatial resolution allowed by the synchrotron white beam size is particularly suited to complex infrared detector designed structures such as dual-color detectors. The extreme strain resolution of 10−5 required for the very low lattice-mismatch system HgCdTe/CdZnTe is demonstrated.

Using 2D integral breadth to study plastic relaxation in a quasi-lattice-matched HgCdTe/CdZnTe heterostructure

“…For this experiment, in order to study intercepted micro-Laue diffraction peaks in fine detail, we have used the same methodology as previously described by Biquard et al (2021). To summarize, first, the CCD camera is placed sufficiently far away from the sample ($290 mm) to induce a peak intensity distribution FWHM larger than 3 pixels.…”

“…Since the two values are almost identical, the critical thickness for the HgCdTe layer with +0.02% compressive mismatch appears to be 2.0 AE 0.25 mm. This seems a reasonable value since the measured critical thickness for the tensile À0.02% mismatch is 2.5 AE 0.3 mm (Biquard et al, 2021). The critical thickness simply corresponds to the depth value of the minimum of the 2D IB, thus providing an elegant way to measure this fundamental value for any kind of epitaxial layer and even without the need for any flexion machine.…”

“…Since the strain gradient extension is only 2 mm on the layer side compared with 10 mm on the substrate side, this probably explains the more than three times greater slope. The presence of a strain gradient inside the 2.0 mm-thick layer interface region and in the 10 mm-thick substrate interface region is quite surprising since there is no measurable strain gradient in the tensile case (Biquard et al, 2021). In the compressive case, a specific mechanism makes the in-plane lattice parameter a k in the substrate interface region increase when getting closer to the interface in order to accommodate the larger relaxed layer lattice parameter.…”

“…In order to experimentally access the onset of relaxation, we decided to carry out a flexion experiment while performing a full micro-Laue investigation of the stress along the growth direction in both layer and substrate. Micro-Laue in crosssection geometry has proved to be very efficient in extracting strain profiles in HgCdTe heterostructures with unprecedented accuracy (Biquard et al, 2021) and also in full mapping of the deformation fields caused by numerous microfabrication steps (Tuaz et al, 2017).…”

In-situ mapping of local orientation and strain in a fully operable infrared sensor

“…Today, the physical origin of defective photodiodes is the core of intense research. The investigation of epitaxial mismatch strain be-tween the MCT layer and CdZnTe (CZT) substrate [4] is of particular interest, as is the impact of the different processing steps throughout device fabrication such as etching, ion implantation, surface passivation, metallization and annealing [5,6] . Moreover, the thermal mismatch between MCT and Si readout circuit in 2D FPAs is another source of the defective photodiodes, since these sensors typically operate at 80 K [7][8][9][10] .…”