INVESTIGATION OF THE KINETICS OF CRYSTALLIZATION OF AL A-GE BILAYER BY ELECTRICAL-CONDUCTIVITY MEASUREMENT/

The kinetics of aluminium-induced crystallisation of thin amorphous ge rmanium layers have been studied by electrical conductivity measuremen ts. Al/a-Ge bilayers (5/50 nm) were prepared by thermal evaporation on to NaCl substrate at constant temperature (220 degrees C) in a high va cuum (10(-6) Torr), between two electrical contacts, previously prepar ed on the substrate. The changes in the electrical conductivity due to deposition and phase transformation of amorphous germanium to polycry stalline germanium were recorded as a function of time. Crystallisatio n starts from aluminium/amorphous germanium interface forming a polycr ystalline germanium layer. Using a model of conductors connected in pa rallel for the system formed by amorphous germanium, polycrystalline g ermanium and aluminium layers, the time dependence of the crystallisat ion front motion was calculated. The experiment resulted in a paraboli c dependence of the thickness of polycrystalline germanium layer on th e annealing time, suggesting that crystallisation of amorphous germani um induced by aluminium is diffusion-controlled. Aluminium concentrati on profile in depth as measured by AES depth profiling supports furthe r this conclusion. (C) 1998 Elsevier Science S.A.