CMOS integrated circuit devices and substrates having unstrained silicon active layers

A semiconductor-on-insulator field effect transistor, comprising:

• an electrically insulating layer;
• an unstrained silicon active layer on said electrically insulating layer;
• an insulated gate electrode on a surface of said unstrained silicon active layer;
• a Si1−xGex layer disposed between said electrically insulating layer and said unstrained silicon active layer, said Si1−xGex layer forming a first junction with said unstrained silicon active layer and having a graded concentration of Ge therein that decreases monotonically in a first direction extending from a peak level towards the surface;
• and
• wherein said Si1−xGex layer is doped with an N-type dopant;
• and wherein a concentration of the N-type dopant in said Si1−xGex layer has a profile that decreases in the first direction.

A semiconductor-on-insulator field effect transistor, comprising:

• an electrically insulating layer;
• a composite semiconductor active region on said electrically insulating layer, said composite semiconductor active region comprising an unstrained silicon active layer having a thickness greater than about 600 Å and a single Si1−xGex layer disposed between said electrically insulating layer and said silicon active layer, said Si1−xGex layer forming a first junction with said silicon active layer and having a graded concentration of Ge therein that decreases monotonically in a first direction extending from a peak level towards a surface of said silicon active layer;
• an insulated gate electrode on the surface;
• wherein the concentration of Ge in said Si1−xGex layer varies from the peak level where 0.15<x<0.4 to a level less than about x=0.1 at the first junction;
• and
• wherein said Si1−xGex layer defines an interface with said electrically insulating layer;
• and wherein the graded concentration of Ge in said Si1−xGex layer also increases from a level less than about x=0.1 at the interface to the peak level.

A semiconductor-on-insulator field effect transistor, comprising:

• a bulk silicon region;
• an electrically insulating layer on said bulk silicon region;
• an unstrained silicon active layer having a first thickness on said electrically insulating layer;
• an insulated gate electrode on a surface of said unstrained silicon active layer;
• sidewall insulating spacers on said insulated gate electrode;
• a Si1−xGex layer of first conductivity type disposed between said electrically insulating layer and said unstrained silicon active layer, said Si1−xGex layer forming a first junction with said unstrained silicon active layer and having a graded concentration of Ge therein that decreases monotonically in a first direction extending from a peak level towards the surface;
• lightly doped source and drain regions of second conductivity type extending in said unstrained silicon active layer and having a thickness less than the first thickness;
• a source-side pocket implant region of first conductivity type in said unstrained silicon active layer, said source-side pocket implant region extending between said lightly doped source region and said Si1−xGex layer;
• and
• wherein said Si1−xGex layer has a retrograded first conductivity type doping profile therein relative to the surface.