ANOMALOUS BEHAVIOR OF OPTICAL PHONON MODES IN ZNSE EPITAXIAL LAYERS

Raman measurements on ZnSe/GaAs heterostructures show unusual behaviou r of the optical phonon modes from ZnSe. High epitaxy rates are respon sible for both poor structural quality at the interface and Fermi leve l pinning by carrier traps, The first effect gives rise, beyond a crit ical thickness, to polycrystalline growth associated with the activati on of a theoretically forbidden TO-ZnSe mode, The second effect induce s a spectacular enhancement of the interfacial LO-ZnSe mode strength, The competition between the latter local electric field effect and abs orption in the upper disoriented part of the layer may result in the q uasi-total extinction of the LO-ZnSe mode. (C) 1997 John Wiley & Sons, Ltd.