Infrared reflectivity spectra of the mixed crystal system Ga1-xInxSb

We report measurements of the far-infrared reflectivity spectra for the pseudobinary system Ga1-xInxSb. Data were analyzed with a Kramers-Kronig dispersion analysis and a damped Lorentzian oscillator formalism. For x<0.30, one TO-phonon mode is evident, whereas for x>0.30, two TO modes are observed. The variations of the TO-phonon frequencies and the mode strengths do not conform to the traditional types of behavior previously used to describe the long-wavelength optical phonons in pseudobinary alloy systems. An alternative classification scheme, based on the occurrence of gap and/or local modes, is proposed. It is sufficiently general to encompass the previously defined classes of behavior, as well as the behavior we report here for the Ga1-xInxSb system. © 1970 The American Physical Society.