Mobility Enhancement in Strained Ge Heterostructures by Planarization of SiGe Buffer Layers Grown on Si Substrates

Compressively strained Ge channel p-type modulation-doped structures were fabricated on SiGe buffer layers planarized by chemical mechanical polishing (CMP). While the hole mobility of the sample without CMP was drastically reduced with decreasing channel thickness, a much higher mobility was maintained for the sample with CMP, suggesting that atomic-scale interface roughness as well as long-ranged roughness was significantly eliminated by CMP. As a result, mobility enhancement factors of 8 and 1.8 at 10 and 300 K, respectively, were obtained by CMP for a channel thickness of 7.5 nm, indicating that the planarization is very essential for realization of high-mobility strained Si/Ge heterostructures.