Raman analysis of LO phonon-plasmon coupled modes at ZnS : N/(n+,p+)-GaAs interfaces

The activation of p-type doping due to nitrogen incorporation in ZnS layers deposited by MOCVD over both n(+)- and p-GaAs substrates is investigated b y Raman spectroscopy. The study is realized on the substrate side by taking advantage of the high-sensitivity of the substrate-related LO phonon-plasm on (LO-P) lineshape to the carrier density in narrow gap materials. The aim in view is to give evidence for large hole transfer from the layer to the near-interfacial substrate in case of even moderate p-type doping of ZnS. T he Raman response from the space charge region of the substrate remains unc hanged when ZnS is deposited by using precursor diethyl-Zn (DEZn). On the c ontrary deep changes are observed when precursor dimethyl-Zn (DMZn) is used . These are directly related to a high doping efficiency of nitrogen in the layer. It appears indeed that the interfacial hole transfer from the DMZn- based p-ZnS layers to the n(+)- and p-substrates generate LO-P modes, respe ctively inside and outside the optical phonon band. These contrasted behavi ors are qualitatively discussed on the basis of the dispersive and phenomen ological damping approaches. (C) 2000 Elsevier Science S.A. All rights rese rved.