Structural characterization of polycrystalline Ge thin films on insulators formed by diffusion-enhanced Al-induced layer exchange

The low-temperature formation of the polycrystalline Ge thin film on an insulating substrate is investigated to develop advanced Ge-based devices onto plastic substrates. We propose a growth promotion technique in Al-induced crystallization (AIC) of amorphous Ge: the modulation of the interlayer between the Ge and Al layers for enhancing the diffusion rate of Ge atoms during annealing. By substituting a conventional AlOx interlayer with a GeOx interlayer, the growth temperature is significantly reduced from 325 to 200 C, probably due to the difference of the diffusion coefficient of Ge in the interlayers. The electron backscatter diffraction measurement reveals that the grain size and the crystal orientation strongly depend on the annealing temperature. The 200 degrees C annealed sample yields a preferentially (111)-oriented Ge layer with large grains (average diameter: 57 mu m). Therefore, a large-grained, orientation-controlled Ge layer is simultaneously achieved on an insulating substrate at a low temperature of 200 degrees C using the diffusion-enhanced AIC technique. (C) 2014 The Japan Society of Applied Physics