LO-PHONON PLASMON MODES IN N-GAAS AND N-INP UNDER PRESSURE

We have investigated the effect of hydrostatic pressure on coupled longitudinal optical (LO)-phonon-plasmon modes and Fermi energies in heavily doped n-GaAs and n-InP using Raman scattering and photoluminescence (PL) spectroscopy at T = 6 K. The combined Raman and PL data allow us to determine both the free carrier density and electron effective mass of the Gamma conduction band minimum as a function of pressure. Near the pressure-induced Gamma-X conduction band crossover both materials exhibit striking changes in the coupled mode frequencies, which are caused by the transfer of electrons from Gamma to X minima. The onset pressure of the electron transfer in n-InP is used to determine the Gamma-X crossover pressure P-c = 11.1 +/- 0.4 GPa, in undoped InP.