Spectra analysis of annealed Hg_1-xCd_xTe molecular beam epitaxial films

This letter discusses the analysis of infrared and visible spectra of Hg_1-xCd_xTe thin films deposited by molecular beam epitaxy (MBE) onto a CdTe buffer layer on a GaAs substrate. The spectra were obtained by infrared transmission and spectroscopic ellipsometry. Two mathematical techniques, fast Fourier transform (FFT) of the multiple reflectance spectrum associated with a multilayer system and fractional-derivatives spectra (FDS) were employed. Compared to the conventional fitting procedure, the FFT method directly offers the thickness of individual layers. It can also provide insight into the interfaces. The FDS method, however, gives information of composition and lattice perfection, which is useful in in situ real-time monitoring during the MBE run. The results show that annealing increases the compositional grading of Hg_1-x Cd_xTe MBE films. Furthermore, the crystal microstructure deteriorates due to the irregular arrangement of diffusing atoms in the lattice sites.