Infrared dielectric function and phonon modes of highly disordered(AlxGa1−x

Abstract

Dielectric function spectra and phonon modes of highly disordered (Al x Ga 1Ϫx ) 0.48 In 0.52 P, i.e., solid solutions with nearly randomly distributed cations, lattice matched to GaAs, are studied for Al compositions x ϭ0, 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 (Al x Ga 1Ϫx ) 0.48 In 0.52 P dielectric function. A complex phonon mode behavior for the random-alloy solid solutions is found: ͑i͒ two ͑one weak GaP-like and one strong InP-like or one weak InP-like and one strong AlP-like with TO-LO splitting͒ bands are present in Ga 0.52 In 0.48 P and Al 0.52 In 0.48 P, respectively, ͑ii͒ three ͑one weak GaP-like, one weak AlP-like, and one strong InP-like͒ bands dominate the quaternary compounds for xϽ0.5, ͑iii͒ the GaP-like band is absent for xϾ0.5, and ͑iv͒ three additional modes ͑AM's͒ with low polarity occur with small composition dependencies at AM 1 ϳ313 cm Ϫ1 , AM 2 ϳ351 cm Ϫ1 , and AM 3 ϳ390-405 cm Ϫ1 , respectively. Results from polarized Raman measurements agree excellently with the mode scheme developed from the ellipsometry study. Modes AM 1 and AM 2 coincide with CuPt-type superlattice-ordering-induced lattice modes, predicted recently for Ga 0.52 In 0.48 P from first-principles calculations ͓V. Ozoliņš and A. Zunger, Phys. Rev. B 57, R9404 ͑1998͔͒ and may be used to identify small degrees of ordering in AlGaInP by far-infrared ellipsometry.

Polaron and phonon properties in proton intercalated amorphous tungsten oxide thin films

“…The DF obtained from the point-by-point analysis needs to be further compared to physical line-shape models in order to obtain physically relevant parameters such as phonon mode frequencies and polaron parameters. 44 The number of unknown parameters in the regression analysis can be reduced considerably if appropriate parametric-model lineshape functions are used to describe the DF for the layer material of interest. Thereby, all measured spectral data points are simultaneously involved in the regression analysis.…”

“…67 Both approaches were described in detail previously. 44 Table I summarizes the best-match IR DF model parameters. We emphasize the excellent agreement between the point-bypoint inverted DF spectra and the model DF.…”

Dielectric anisotropy and phonon modes of ordered indirect-gap Al0.52In0.48P studied by far-infrared ellipsometry

“…In a previous work on disordered ͑Al x Ga 1−x ͒ 0.52 In 0.48 P, we identified AM 2 as likely ordering induced, but the origin of AM 3 remained unclear. 12 It is evident now from Fig. 3 that AM 3 is caused by long range atomic ordering, but might also be observed in highly disordered samples due to residual ordering.…”

“…As expected from studies of disordered AlInP 2 samples, TO and LO resonances of the InP-and AlP-like lattice and two additional modes ͑AM 2 and AM 3 ͒ which do not descend from the binary lattice constituents in AlInP 2 can be identified. 12 In contrast to disordered AlInP 2 , differences can be observed between the two sample orientations, reflecting the anisotropic character of the ordered AlInP 2 layer. The difference between ⌿ A and ⌿ B is most notably in the region of 400 cm −1 ഛ ഛ 460 cm −1 were the AlP͑TO,LO͒ and AM 3 ͑TO, LO͒ modes occur.…”

“…Hence, the dielectric tensor ⑀͑ , ͒ may be diagonalized and ordinary and extraordinary dielectric functions for polarization perpendicular and parallel to the ordering direction can be assigned, denoted here by ⑀ Ќ and ⑀ ʈ , respectively. 12 For perfect ordering, lattice modes split into those with A 1 -and E-type symmetries, with lattice displacement pattern parallel and perpendicular to the trigonal axis, respectively.…”