ORIGIN OF 2 DISTINCT SURFACE OPTICAL PHONON MODES ON AN N-TYPE POLAR SEMICONDUCTOR SURFACE

We investigate surface optical phonons on a doped polar semiconductor surface for the case of heavy doping where carrier electrons are well degenerate and where plasmon energies are higher than phonon energies. Our theoretical analysis asserts that there exist two distinct surface optical phonon modes, which form two energy dispersion branches, and our analysis clarifies the origin of these two distinct surface optical phonon modes. On the basis of our analysis the energy dispersion of the surface phonon on an n-type GaAs surface which was recently observed by electron energy loss spectroscopy can be interpreted as switching from one dispersion branch to the other. © 1990.