Electrical field enhances crystallization of amorphous silicon

Electrical field enhances crystallization of amorphous silicon

Physicists at Kyung Hee University and Han Yang University (Seoul, Korea) increased the crystallization speed of amorphous silicon (a-Si) while simultaneously limiting defects. To reduce the temperature at which a-Si crystallizes, manufacturers often add certain metals, such as nickel. The group showed that by applying a modest electrical field as well, the speed of the process can be significantly increased--a crystallization time of 25 hours at 500C was reduced to 10 min by adding an electrical field of 80 V cm-1. The researchers started with 400-nm-thick films of hydrogenated a-Si to which they added a thin layer of nickel by sputtering. The samples were placed between two electrodes in a vacuum and crystallized at 500C.

Longer crystallization times allow crystalline regions to meet, and the interfaces form clear grain boundary regions with defect states that can trap carriers--in the Korean method there are no grain-boundary states. The researchers suggest that the electric-field-enhanced technique could be applied widely to crystallize amorphous materials, which could be significant because thin films of polycrystalline silicon are important to large-area electronic applications, such as in the switching electronics of flat-panel displays.