Dielectric function spectra and phonon modes of highly disordered (formula presented) i.e., solid solutions with nearly randomly distributed cations, lattice matched to GaAs, are studied for Al compositions (formula presented) 0.33, 0.48, 0.7, 0.82, and 1 using far-infrared ellipsometry and Raman scattering. An anharmonic oscillator model approach is employed for line-shape analysis of the (formula presented) dielectric function. A complex phonon mode behavior for the random-alloy solid solutions is found: (i) two (one weak GaP-like and one strong InP-like or one weak InP-like and one strong AlP-like with TO-LO splitting) bands are present in (formula presented) and (formula presented) respectively, (ii) three (one weak GaP-like, one weak AlP-like, and one strong InP-like) bands dominate the quaternary compounds for (formula presented) (iii) the GaP-like band is absent for (formula presented) and (iv) three additional modes (AM’s) with low polarity occur with small composition dependencies at (formula presented) (formula presented) and (formula presented) respectively. Results from polarized Raman measurements agree excellently with the mode scheme developed from the ellipsometry study. Modes (formula presented) and (formula presented) coincide with CuPt-type superlattice-ordering-induced lattice modes, predicted recently for (formula presented) from first-principles calculations [V. Ozoliņš and A. Zunger, Phys. Rev. B 57, R9404 (1998)] and may be used to identify small degrees of ordering in AlGaInP by far-infrared ellipsometry.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 2001|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics