OPTICAL PHONONS AND ORDERING OF THE CRYSTAL-LATTICE OF INXGA1-XAS SOLID-SOLUTIONS

Optical phonons of three types are seen in the Raman scattering spectr a and the IR reflection spectra of the two-component solidsolutions In xGa1-xAs (x = 0.1 -0.3). The oscillator strengths S(p) and the Faust-H enry coefficients C(p) of the optical phonons of InxGa1-xAs (x almost- equal-to 0.2) are found from the Raman spectra. Analysis of the values of S(p) and C(p) and also of the polarization state in the spectra sh ows that optical phonons with the frequencies of transverse components , 236 and 260 cm-1, stem from vibrations of a spontaneously ordered ph ase. This phase has the structure of a monolayer (InAs)1(GaAs)1 superl attice in the (100) plane. The analysis also shows that the optical ph onons with 267 cm-1 stem from vibrations of the GaAs phase with the zi nc blende structure. The conclusion that there is a partial ordering o f the InxGa1-xAs crystal lattice, accompanied by the formation of a mo nolayer (InAs)1(GaAs)1 superlattice, is supported by calculations of t he transverse-response function in a linear-chain model. (C) 1994 Amer ican Institute of Physics.