Micro-Raman and photoluminescence characterization of polycrystallization in bulk InxGa1-xAs crystals

Raman and photoluminescence experiments have been performed to characterize the polycrystalline region in the wafers cut from a bulk InGaAs crystal, which was found to be initiating from the inner part of the ingot, unlike the usual observation of polycrystallization starting from the peripheral part of an ingot. This indicates the existence of polycrystallization mechanism other than those relating to the boundary effects. The polycrystalline region was found to have a random fluctuation of composition. The possibility of drastic local fluctuation in composition, which is induced by convection-induced local supercooling, being the main cause of polycrystallization, is investigated here.