Different architectures of relaxed Si1−xGex/Si pseudo-substrates grown by low-pressure chemical vapor deposition: Structural and morphological characteristics

A detailed characterization of SiGe thin layers grown by low-pressure chemical vapor deposition (LP-CVD) on different types of Si buffer layers (BLs) is presented. Using the same conditions of SiGe growth, Si BLs were elaborated in ultra-high vacuum conditions at low (575 °C) and medium (700 °C) temperatures to improve the crystalline quality of the Si buffer layer. Using both types of Si BLs, the SiGe layer exhibits a very high density of dislocations (>105 cm−2). Here, we proposed to create a ductile area in the Si BL, before the SiGe deposition. It consists of nanocavities located at about 100 nm under the Si BL surface and obtained by He+ implantation at 10 keV and at room temperature with fluencies of 5×1015 ions cm−2 or 5×1016 ions cm−2. The creation of the nanocavity layer is enabled by an annealing step at 700 °C for one hour. These kinds of Si BLs were studied by cross section transmission electron microscopy, X-ray diffraction, Rutherford backscattering, photoluminescence, atomic force and optical microscopy before and after revealing the dislocations by the chemical etching of SiGe layers. From these analyses, we evidenced the blocking of threading dislocations by the formation of loops located between the region of nanocavities formed in the substrate and the SiGe/Si interface. This method allows to strongly enhance the relaxation rate (97%) of SiGe layers, and to improve their crystalline and morphological quality for their use for high-speed microelectronic and optoelectronic devices for which the surface roughness and the threading dislocation density are key issues.

► We grew SiGe thin layers on Si buffer layers by low-pressure chemical vapor deposition technique. ► We evidence the role of nanocavity layer, created by He+ implantation, in SiGe/Si relaxation. ► We examine the impact of annealing temperature on the relaxation rate of SiGe pseudo-substrates. ► We obtain reduced threading dislocation density below 103 cm−2 in thin SiGe pseudo-substrates.