Abstract
Raman measurements on ZnSe/GaAs heterostructures show unusual behaviour of the optical phonon modes from ZnSe. High epitaxy rates are responsible for both poor structural quality at the interface and Fermi level pinning by carrier traps, The first effect gives rise, beyond a critical thickness, to polycrystalline growth associated with the activation of a theoretically forbidden TO-ZnSe mode, The second effect induces a spectacular enhancement of the interfacial LO-ZnSe mode strength, The competition between the latter local electric field effect and absorption in the upper disoriented part of the layer may result in the quasi-total extinction of the LO-ZnSe mode. (C) 1997 John Wiley & Sons, Ltd.