Electron mobility characteristics of n-channel metal-oxide-semiconductor field-effect transistors fabricated on Ge-rich single- and dual-channel SiGe heterostructures (original) (raw)

Strained Si ͑-Si͒ grown on Si-rich relaxed Si 1Ϫx Ge x buffers ͑single-channel heterostructures͒ can be used to fabricate n-channel metal-oxide-semiconductor field-effect transistors ͑n-MOSFETs͒ with enhanced performance over bulk Si. However, single-channel heterostructures grown on Ge-rich Si 1Ϫx Ge x buffers ͑i.e., xу0.5) exhibit much larger hole mobility enhancements than those on Si-rich buffers, and the highest hole mobilities have been attained in heterostructures where a compressively strained Ge ͑-Ge͒ layer is grown beneath the-Si cap ͑-Si/-Ge dual-channel heterostructures͒. In this article, we report on n-MOSFET mobility characteristics in single-and dual-channel heterostructures grown on Ge-rich Si 1Ϫx Ge x buffers. Single-channel n-MOSFETs were fabricated on virtual substrates with Ge contents as high as 70%, and electron mobility enhancements of 1.4-1.6 were observed. For dual-channel heterostructures, electron mobility enhancements of 1.7-1.9 were attained when the-Si cap was thick enough to confine electrons. Despite the high intrinsic electron mobility of bulk Ge, dual-channel n-MOSFETs with extremely thin Si caps ͑ϳ3 nm͒ exhibited mobility significantly below that of bulk Si. We speculate that the low extracted mobility in such heterostructures results from the difference in conduction band minima between Ge and Si.