Assessing thermodynamical properties of Al1−xGaxSb alloys and optical modes for Al1−xGaxSb/GaAs epifilms and (AlSb)m/(GaSb)n superlattices

Abstract

A generalized Green's function (GF) theory is adopted in the framework of a realistic rigid-ion-model (RIM) to assess the composition, x-dependent lattice dynamics, and thermodynamical characteristics of ideal random Al1−xGaxSb alloys. For simulating phonons, the alloy parameters are achieved by interpolating the values of the RIM force constants between AlSb and GaSb without requiring any additional interactions. The outcomes of phonon dispersions ωj(q→), Debye temperature ΘD(T), and specific heat Cv(T) compare favorably well with the existing experimental and theoretical data. An established methodology of multilayer optics is also employed for modeling the far-infrared reflectance and transmission spectra of ultrathin GaSb/GaAs, AlSb/GaAs, Al1−xGaxSb/GaAs epilayers, and (AlSb)m/(GaSb)n/GaAs superlattices at near normal (θi = 0) incidence and oblique (θi ≠ 0) incidence. An accurate appraisal of the x-dependent longitudinal-optical [ωLO(Γ)] and transverse-optical [ωTO(Γ)] phonon splitting by Berreman's effect, along with the calculated GF results of localized vibrational mode (GaSb:Al) and gap mode (AlSb:Ga), is carefully integrated into the modified-random-iso-displacement model to validate the two-phonon mode behavior in Al1−xGaxSb ternary alloys.