Method of forming source/drain regions of transistors

A method for fabricating a semiconductor device, the method comprising:

• patterning a first semiconductor material layer and a second semiconductor material layer to create a first structure having the first semiconductor material layer and a second structure having the first semiconductor material layer, an interposing layer, and the second semiconductor material layer;
• forming a first type of transistor in the first semiconductor material layer of the first structure including forming a source/drain region for the first type of transistor that has a superlattice structure that alternates between two different semiconductor materials wherein the alternating is in a direction that is substantially parallel to a top surface of the first semiconductor material layer, the two different semiconductor materials having a same type of dopant;
• and
• forming a second type of transistor in the second semiconductor material layer of the second structure.

A method for fabricating a semiconductor device, the method comprising:

• providing a first stack and a second stack over a substrate, each of the first stack and second stack including a first semiconductor material layer, a bonding layer, and a second semiconductor material layer, wherein the first stack is a spaced a distance from the second stack;
• removing the second semiconductor material layer and the bonding layer from the first stack exposing the first semiconductor material layer;
• forming a first gate structure on the first semiconductor material layer of the first stack and etching a first set of recesses in the first semiconductor material layer, wherein the etching the first set of recesses includes forming a recess edges meeting in a vertex;
• forming a second gate structure on the second semiconductor material layer of the second stack and etching a second set of recesses in the second semiconductor material layer;
• and
• filling the first set of recesses with source/drain material;
• wherein the filling the first set of recesses includes filling each of the first set of recesses having a first boron concentration at a center of each of the first set of recesses and a second boron concentration the vertex of each of the first set of recesses, wherein the second boron concentration is greater than the first boron concentration, the first and second boron concentrations greater than zero and wherein the first boron concentration and the second boron concentration are of boron.