Raman scattering by wavevector-dependent LO phonon-plasmon modes in heavily doped n-type ZnSe
We have studied Raman scattering from heavily n-doped ZnSe:Cl epilayers grown on GaAs substrates by molecular beam epitaxy. The spectrum of the phonon-like component of the coupled plasmon-LO phonon modes is strongly determined by wavevector non-conservation. The degrees of relaxation of the q=O selection rule correspond to two different length scales in real space: the carrier and the impurity spacing. Our experimental results indicate that both length scales are of relevance to the scattering mechanisms that contribute to the observed Raman signal. Using a dye laser tuned in the energy range of the ZnSe bandgap, our measurements show that variations of the carrier density within the epilayer are closely correlated to the local effective impurity concentration extracted from the evaluation of our Raman spectra.