Study of photoexcited carriers in semi-insulating InP by means of Raman spectroscopy

We present a study of photoexcited plasmons in semi-insulating, Fe-doped InP at room temperature and at 80 K by means of Raman spectroscopy. Two peaks are detected in the frequency region of the LO mode. Whereas the low-energy peak does not change with incident laser power, the high-energy peak shifts to higher energies with increasing laser power, and therefore is assigned to the L⁺ branch of the LO-plasmon coupled mode. The LO and the L⁺ modes could be resolved at room temperature for high incident power, and were clearly resolved at 80 K for all the incident powers studied. The Raman spectra were fitted using a L⁺ lineshape model based on the Lindhard-Mermin dielectric function, in which contributions from electron, heavy-hole and light-hole intraband transitions as well as heavy-hole-light-hole interband transitions were taken into account. The fitting procedure allows us to determine the photoexcited plasma density as a function of the incident laser power