Laser-crystallized microcrystalline SiGe alloys for thin film solar cells

Abstract Thin films of crystalline silicon–germanium (SiGe) alloys could be an interesting material for next generation solar cells. SiGe alloys with a Ge content of approximately 80 at.% have an indirect band gap only slightly smaller than that of Si. However, the first direct optical transition occurs at approximately 1.5 eV, leading to a strongly enhanced optical absorption compared to Si. Thin μc-SiGe films were prepared by crystallization of evaporated amorphous or nanocrystalline alloys with a pulsed Nd:YAG laser, using homogeneous as well as laser interference methods to achieve lateral grain growth. Structural properties were characterized by atomic force microscopy and transmission electron microscopy. Raman measurements were performed to study possible phase separation and to analyze residual strain in the recrystallized films.