Improved model for the analysis of FTIR transmission spectra from multilayer HgCdTe structures

This paper reports the further development of the model for the analysis of FTIR transmission spectra from the dual-color Hg1−xCdxTe (MCT) structures for the constituent layer thickness and alloy composition. The previously reported model1 was shown to suffer from excessively high uncertainty in the provided individual layer thickness and low convergence rate for some types of structures, attributed primarily to inaccuracies in the model representation of the MCT dielectric function. Since last report, we have substantially improved the FTIR analysis accuracy by developing a better MCT dielectric function approximation, which is based on the interpolation of the measured spectroscopic ellipsometry (SE) experimental spectral dielectric functions at few discrete alloy compositions. Based on this, the optical model for graded layers was also created and calibrated against the traditional FTIR data reduction technique. The new model was shown to produce the most accurate fits to the experimental FTIR transmission spectra from single- and two-color detector structures, and has demonstrated a better convergence rate. The new model was tested to predict both band cutoff wavelengths for the actual two-color MWIR/LWIR SUMIT detectors.15 We have demonstrated that the model prediction from as-grown structures was in good agreement with the actual two-color device data, as measured on performance evaluation chips (PECs), thus validating the modeling technique for routine postgrowth wafer screening.