Relaxation Mechanism of Low Temperature SiGe/Si(001) Buffer Layers

摘要

To realize SiGe/Si devices with strained Si layers strain-relaxed SiGe buffer layers are necessary. These relaxed substrates must be thin, have a smooth surface morphology and a low density of threading dislocations. One concept of relaxed buffers was proposed by Kasper et al. It consists of the controlled introduction of a high density of point defects at the beginning of the epitaxial growth of the buffer, necessary to induce the relaxation of the SiGe buffer from the bottom instead from the top surface. We have applied this concepts to realize a relaxed buffer with x = 0.20. We used reduced temperature to grow first a strained Low Temperature (LT)- buffer with a high density of nucleation centers, then at higher temperature (HT), the Si_(0.80)Ge_(0.20) layer, strain relaxed and free of threading dislocations (TD). The relaxation was induced by point defects from the bottom LT-birffer.