Thermal stability of a novel graded buffer layer for relaxed SIGE/SI heteroepitaxy

Biaxial strained Si is commonly prepared by growing Si epitaxially on a larger-lattice constant-Silicon Germanium (SiGe) layer, itself grown epitaxially onto a Si bulk substrate. To accommodate lattice mismatch and minimize relaxation-induced defects, a forward graded SiGe buffer layer (increasing Ge content) is usually inserted between SiGe and Si substrate. However, thick graded layers are unfavorable as SiGe has poor thermal conductivity and may aggravate heat management problems. Recently, we developed a novel reverse-graded (RG) buffer system, in which Ge content decreases with distance from the Si interface. On top of this thin (90 nm) RG layer, a relaxed SiGe layer with Ge concentration ranging from 14% to 32% has been grown. The relaxation of these SiGe layers is ± 85% and the defect density is comparable to, if not better than, the best reported values. In this paper, the thermal stability of the novel structure has been investigated. A combination of High-Resolution X-Ray Diffraction (HR-XRD), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Nomarsky microscopy were used to study the epitaxial quality and relaxation mechanism. We have established that the heterostructure is stable up to 1000°C with no further strain relaxation and a minimal increment of defect density.