Optimization of controlled two-step liquid phase crystallization of Ge-on-Si

This work presents a two-step liquid phase crystallization process for realizing large-grain epitaxial germanium (Ge) on silicon substrates. The process starts with amorphous Ge films on silicon (100) substrate which is subjected to a two-step annealing process. In the first step, films are heated to 950°C for 5 minutes, a temperature above the melting point of Ge. Next the films are allowed to cool down to 930°C and maintained at that temperature for 1 to 5 hours respectively in order to check its effect on the crystallization process. The 950°C for 5 mins and 930°C for 2 hours shows the optimum annealing conditions to achieve highly crystalline films. The surface morphologies of the annealed samples were characterized using scanning electron microscopy which shows grain sizes ranging from 2-5 $\mu$m. The crystallinity of the films was confirmed using Raman spectroscopy and x-ray diffraction (XRD) measurements. Theta/2-theta XRD measurements of samples show the peak for Ge(400) at 66.3°. The degree of grain orientations along Ge(400) plane is further evaluated using the rocking curve in XRD measurements which shows full-width at half maximum height value of 0.08° (or 288 arc sec) along this plane for the optimum two-step annealing process condition.