FROM AMORPHOUS TO POLYCRYSTALLINE THIN-FILMS - DEPENDENCE ON ANNEALING TIME OF STRUCTURAL AND ELECTRONIC-PROPERTIES

Some new results about the amorphous to polycrystalline transition of silicon thin films obtained by low pressure chemical vapor deposition (LPCVD) at 550 degrees C are presented. From in situ (monitored during the crystallization annealing) conductance, electron spin resonance, photoluminescence and modulated photocurrent experiments, the density of states is shown to increase in the so-called nucleation regime and reach a maximum just before crystal grain growth starts. These results indicate that crystallization needs the creation of a defected materi al with large dangling bond densities and wide band-tails. It appears that the electronic quality of the final polycrystalline material is l inked to the maximum density of states reached just at the end of the nucleation phase. This level may be associated to a viscous structure. (C) 1998 Elsevier Science B.V. All rights reserved.