Raman scattering in InGaAlP layers grown by molecular-beam epitaxy

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Abstract
Raman scattering from InGaAlP layers on (100) GaAs substrates grown by molecular‐beam epitaxy (MBE) is studied. Compositional dependencies of Raman shifts show two‐mode behavior for InAlP and partial three‐mode behavior for InGaAlP. The empirical expressions for the compositional variations of LO and TO phonon frequencies are presented. Enhancement of the Raman peak intensities for AlP‐ and InP‐like LO phonons is observed for the composition range when the direct band‐gap E0 is close to the photon energy of the excitation light source. The ratio of valley depth to InP‐like LO phonon peak height in the Raman spectrum of InGaP ranges from about 0.5 to 0.43, and correlates with the room‐temperature photoluminescence peak energy (1.9–1.88 eV). The relationship between these is the same as for the metalorganic vapor‐phase epitaxy (MOVPE) samples, although the depth‐to‐peak height ratios for the MBE samples coincide with the higher side values. The growth temperature dependence is also observed. These results indicate that the InGaP layers grown under the appropriate MBE‐growth conditions show the ordered state, although the degree of the order is low. The InAlP layers show Raman spectra having well‐resolved InP‐like LO and TO phonon peaks. This differs from most of the reported results for MOVPE‐grown InAlP layers, and suggests that the MBE‐grown InAlP layers are very close to the disordered state alloy.