Optical Structural and Phonon Characteristics of Epitaxially Grown II–VI/III–V Films and Superlattices

This chapter focuses on providing a systematic analysis of the far-infrared (FIR) reflectivity/transmission, Raman scattering, spectroscopic ellipsometry (SE), and high-resolution synchrotron extended x-ray absorption spectroscopy (HR-SXAS) data for comprehending film thickness, optical, structural, and phonon traits of several epitaxially grown II–VI/III–V epilayers and superlattices (SLs). The structural and electronic properties are acquired by employing phonon Raman scattering, induced by deformation potential, as well as coupled plasmon LO-phonon modes. Experimental FIR line shapes and transverse optical modes (ωTO) have offered information on epilayer alignment to the substrates. A traditional methodology of multilayer optics (ambient/ film/substrate) is exploited for analyzing the FIR reflectivity/transmission spectra at both near normal incidence (θa = 0°) and oblique incidence (θa = 45°), i.e., using the Berreman effect, for extracting film thickness d of binary/ternary epilayers and layered structures of SLs. A clear distinction of the transverse optical (ωTO) in the s-polarization, longitudinal optical (ωLO), and ωTO modes in the p-polarization has established an effective way of assessing the long wavelength optical phonons in ultrathin materials. Model dielectric functions derived from the SE data are meticulously incorporated to fit the reflectivity and transmission spectra of thin binary and ternary alloys in the range of ~1.0 to 6 eV. Comprehensive analyses of the HR-SXAS data on the structural characteristics of epilayers have provided accurate values of the bond lengths and coordination numbers in very good agreement with the existing appropriate data of the bulk materials. Examples of epitaxially grown semiconductor materials considered here included the CdZnTe/GaAs(001), CdTe/InSb(001) epilayers, and heavily strained (ZnSe)m/(BeSe)n/GaAs(001) SLs.