Raman scattering studies of (GaP)_n/(InP)_n (n = 1, 1.7, 2) short-period superlattice structures

We report Raman scattering from (GaP)_n/(InP)_n (n = 1, 1.7, 2) short-period superlattice (SPS) structures to study the effect of lateral composition modulation (LCM) on the behavior of optical phonons. Cross-sectional transmission electron microscope images revealed that LCM was formed with complex pattern in the n = 1.7 and n = 2 samples grown at 490°C. Interestingly, both the InP- and the GaP-like longitudinal optical (LO) phonon energies increased systematically as the number of monolayers was increased from n = 1 to n = 2. A significant broadening of the phonon line shapes was also observed for the n = 1.7 and n=2 samples. In contrast, for samples grown at 425°C, both the increase of the LO phonon energies and the broadening of the phonon line shapes were observed only when n = 1.7. Our results demonstrate that the optical phonons in the (GaP)_n/(InP)_n SPS structures are significantly affected in the occurrence of LCM related to the growth temperature and the number of monolayers.