Raman studies of carbon-doped GaAs layers grown by a metallic-arsenic-based metalorganic chemical vapor deposition system

High-quality p type GaAs epilayers were grown by metalorganic chemical vapor deposition using trimethylgallium and metallic arsenic as gallium and arsenic sources, respectively. The range of hole concentration analyzed goes from 10(17) to 10(19) cm(-3), as measured by the Hall-van der Pauw method. For controlling the hole concentration, a mixture of hydrogen and nitrogen was used as the carrier gas. Raman scattering spectra show transversal optical mode at 270 cm(-1) for low-doped samples and a longitudinal optical (LO) mode at 292 cm(-1) produced by phonon-hole-plasmon coupling for high-doped samples. The relative intensity of the LO mode for the doped samples correlates very well with the hole concentration. As the carrier concentration increases, the LO phonon-plasmon-coupled mode increases. The corresponding decrease of the intensity of the LO mode is interpreted as the decrease in the depletion layer as the carrier concentration increases.