Infrared dielectric function and phonon modes of highly disordered (AlxGa1-x)0.52In0.48P -: art. no. 155206

Dielectric function spectra and phonon modes of highly disordered (AlxGa1-x)(0.48)In0.52P, i.e., solid solutions with nearly randomly distributed cations, lattice matched to GaAs, are studied for Al compositions x = 0, 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 (AlxGa1-x)(0.48)In0.52P 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 AIP-like with TO-LO splitting) bands are present in Ga0.52In0.48P and Al0.52In0.48P, respectively, (ii) three (one weak GaP-like, one weak Alp-like, and one strong InP-like) bands dominate the quaternary compounds for x<0.5, (iii) the GaP-like band is absent for x>0.5, and (iv) three additional modes (AM's) with low polarity occur with small composition dependencies at AM(1)similar to 313 cm(-1), AM(2)similar to 351 cm(-1), and AM(3)similar to 390-405 cm(-1), respectively. Results from polarized Raman measurements agree excellently with the mode scheme developed from the ellipsometry study. Modes AM, and AM(2) coincide with CuPt-type superlattice-ordering-induced lattice modes, predicted recently for Ga0.52In0.48P from first-principles calculations [V Ozolins 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.