Electron microscopy of voids in Si formed by permeable pulse laser irradiation.

Voids formed in Si by a laser were observed by electron microscopy. Two types of void were identified: One is associated with high-pressure phase of Si, the other is free from high-pressure phase.Voids formed in Si by permeable laser irradiation were investigated by comprehensive electron microscopy. Two types of voids were identified: Type (1): This type was formed mostly closer to the entrance surface of a laser, and a considerable volume of a non-diamond Si (DS) phase was formed in the surrounding matrix. Type (2): This type was formed at the focus of an incident laser, and none of dislocations, cracks and non-DS phase was observed in the surrounding matrix. Type (1) voids are considered to be formed to accommodate volume change resulting from transformation from DS to the non-DS. However, it is difficult to explain formation of Type (2) voids by this mechanism.