We have deposited amorphous germanium thin films on silicon using evaporation. This was followed by pulsed laser annealing using Nd: YaG laser. Above threshold intensity, it was observed that the amorphous germanium recrystallizes as crystalline germanium. However surface ripples and a pattern of lines was observed on the surface that were aligned 55 degrees to the laser scan direction.
My first idea was that you have some kind of coma aberration in your laser beam, in these cases the laser focus has that chevron shape.
Another explanation that comes to mi mind is the fact that may be you have some kind of directed crystallization. Initially your sample is amorphous, after the first line scan you get a boundary between the crystalline and the amorphous phase, so may be the crystalline part is acting as a pattern or as a border and promotes crystallization in the direction you indicates (55º respect to the scan line). It could be useful to know how the Ge cell is oriented, it could give you some clue about what is happening.
I hope it helps.
I suppose that shevron pattern in recrystallized germaium pattern results due to the used laser beam configuration for annealing when an interference of incident and reflected light can take place. It is possible to change the linearly polarized beam of Nd-YAG by circular polarized one to remove the shevron pattern or at least to deacrease that contribution.
Manuel Gómez Since you suggest the possibility the Ge cell being oriented, I suppose I can get the orientation of that by quantitatively comparing the XRD peaks for the various orientation of Ge crystal, right ?
Probably you are getting a polycrystalline Ge thin film, with each crystal domain with different orientation. Probably you can use XRD peak intensity to identify the preferent orientation.
I have found this paper, where the authors observe differences depending on the laser speed annealing:
Article Crystallization of amorphous Ge films induced by semiconduct...
The authors use XRD and Raman to identify the crystalline domains.
Fig 9, shows a oblique structures at 100mm/s, but the angle is slower than that you describe for your samples. At 200mm/s these structures dissapear.
Here there is another article where the authors use some tricks to avoid high temps and to obtain an uniform Ge thin film (with different orientations).
Article Nucleation-controlled gold-induced-crystallization for selec...
I hope it helps. Best.
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