New Method to Produce High-Quality Epitaxial Ge on Si Using SiO2-Lined Etch Pits and Epitaxial Lateral Overgrowth for III-V Integration

Abstract

We have developed a unique method of reducing the threading dislocation density in Ge epitaxially grown on Si. A heteroepitaxial layer of Ge is initially grown on Si substrate in which the threading dislocation density is 2.6 x 108 cm-2. The Ge film is etched to produce pits on the surface that correspond to the location of threading dislocations. The Ge surface with etch pits is processed further to produce a 15 nm thick layer of SiO2 within the etch pits, but not on the top planar Ge film surface. Further lateral and selective epitaxial Ge growth results in a Ge film that forms and coalesces over the SiO2 lined etch pits. The SiO2 blocks the threading dislocations from propagating into the subsequent Ge epilayer. Etching the subsequent Ge epilayer reveals a density of 1.7 x 106 cm-2 threading dislocations. This corresponds to a decrease in the overall defect density by a factor of 31 compared to the initial Ge on Si layer. The threading dislocations likely result from shallow etch pits in which SiO2 is inadvertently removed from the pit during one of the processing steps. The dislocations in pits without SiO2 continue to propagate into the subsequent Ge epilayer. Reducing the dislocation density in the initial Ge layer should result in fewer defects in the subsequent Ge layer, making the layer suitable for electronic device fabrication.