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.