Nucleation and growth of germanium islands during layer exchange metal-induced crystallization

Al-induced layer exchange crystallization of amorphous Ge thin films has been demonstrated recently, and provides a suitable system to characterize, model and control Ge crystal growth on non-crystalline substrates. Direct observation of Ge transfer to the surface of Al through an interposed GeOx interfacial layer allows independent measurement of the density and average area of crystalline Ge islands formed on the surface. Based on these experimental observations, the Johnson-Mehl-Avrami-Kologoromov phase transformation theory is extended to model nanoscale nucleation and growth of Ge islands in two dimensions. The Ge island growth mechanism switches from atomic-attachment-limited to surface diffusion-limited kinetics with increasing time. The transition point between these regimes depends on the Ge nucleation site density and the annealing temperature. Finally, we show that local bias-voltage stressing of the interfacial layer controls the areal density of nucleated Ge islands on the film surface.