Far-infrared transmission studies in disordered and ordered Ga0.52In0.48P

The vibrational properties of both disordered and ordered Ga0.52In0.48P all oys have been studied by room-temperature polarized far-infrared transmissi on at normal incidence. For the disordered alloy, besides the main transver se optical mode at 332 cm(-1), we observe a weak transverse optical mode at 372 cm(-1). The transmission spectrum of the ordered alloy recorded with l ight polarized in the plane containing the ordering axis and the growth dir ection shows, in addition to the transverse modes, an extra band at 354 cm( -1). This is a signature of the reduced trigonal symmetry that we relate to a quasilongitudinal mode. [S0163-1829(99)04128-4].