Abstract: Structures and methods for fabricating high speed digital, analog, and combined digital/analog systems using planarized relaxed SiGe as the materials platform. The relaxed SiGe allows for a plethora of strained Si layers that possess enhanced electronic properties. By allowing the MOSFET channel to be either at the surface or buried, one can create high-speed digital and/or analog circuits. The planarization before the device epitaxial layers are deposited ensures a flat surface for state-of-the-art lithography.

Abstract: Semiconductor-based devices, and methods for making the devices, involve a first device that includes a buried channel layer, a dielectric layer, and a compositionally graded spacer layer. The spacer layer includes a first material and a second material, and is located between the buried channel layer and the dielectric layer. A second device includes a buried channel layer, a relaxed surface layer, and a spacer layer located between the buried channel layer and the relaxed surface layer. The spacer layer has a composition that is different from a composition of the relaxed layer. The spacer layer and the relaxed surface layer each have bandgap offsets relative to the buried channel layer to reduce a parasitic channel conduction. A substrate for fabrication of devices, and methods for making the substrate, involves a substrate that includes a first layer, such as a silicon wafer, a substantially uniform second layer, and a graded-composition third layer.