Long-wavelength lattice dynamics of In1−xGaxAsyP1−y alloys

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Abstract
The first investigation of the lattice dynamics of In1−xGaxAsyP1−y quaternary semiconductor alloys lattice matched to GaAs has been made by Raman scattering. The spectra in the optical frequency range consist of two separate bands, each having a peak at the high‐frequency end. These two peaks are shown to be GaP‐like and GaAs‐like, respectively. The cell‐isodisplacement theory for the long‐wavelength lattice dynamics by Zinger, Ipatova, and Subashiev [Sov. Phys. Semicond. 1 0, 286 (1976)] is reexamined in detail. It is improved upon by consistently treating the renormalization of the intracell force constants and then applied to InGaAsP. This improvement gives remarkably better fitting of the calculated phonon frequencies to the existing experiments in the entire composition range 0≤x, y≤1 and enables the construction of a coherent model for the long‐wavelength lattice dynamics of InGaAsP. The results of the Raman measurements are discussed in the light of the calculation. The oscillator strengths are also calculated and compared with the infrared experiment.