Far infrared phonon spectroscopy of In/sub 1-x/Ga/sub x/As epilayers on InP[100]

Polarized far infrared reflectance was measured at oblique incidence for a large number of strained In/sub 1-x/Ga/sub x/As epilayers grown on InP wafers. From these measurements the concentration dependence of the zone-center optical phonon frequencies has been obtained for strained In/sub 1-x/Ga/sub x/As epilayers grown by chemical beam epitaxy on InP[100]. With the method used the reflectance spectra contain sharp Berreman peaks precisely at the optical phonon frequencies. To resolve the contributions of the individual phonon modes, curve fitting of the measured spectra was used. With this analysis it was observed that the modes included GaAs-like longitudinal and transverse optic (LO and TO), a disorder induced (TO-like), and InAs-like LO and TO phonons. The concentration dependence of these phonon frequencies, determined for 0.31