Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• two isolation insulating layers disposed at least partially in a semiconductor substrate;
• a buffer layer disposed over the semiconductor substrate;
• and
• an alloy semiconductor material layer comprising Sn and disposed over the buffer layer and at least partially in a recess between the two isolation insulating layers, and comprising:
• a surface region in an end portion of the alloy semiconductor material layer at both ends thereof,
• an internal region in the end portion and surrounded by the surface region, wherein the surface region covers a top surface of the internal region and a side surface of the internal region, and
• a channel region in a middle portion of the alloy semiconductor material layer and between the both ends,
• wherein a concentration of Sn in the channel region is higher than a concentration of Sn in the internal region and less than a concentration of Sn in the surface region.

A semiconductor device, comprising:

• a first layer comprising Ge disposed in a recess between two isolation insulating layers that are at least partially in a semiconductor substrate;
• and
• a second layer of a second semiconductor material disposed over the first layer, and comprising:
• a surface region in an end portion of the second layer at both ends thereof,
• an internal region in the end portion and surrounded by the surface region, wherein the surface region covers a top surface of the internal region and a side surface of the internal region, and
• a channel region in a middle portion of the second layer and between the both ends,
• wherein the second semiconductor material is an alloy comprising Ge and Sn, and wherein a concentration of Sn in the channel region is higher than a concentration of Sn in the internal region and less than a concentration of Sn in the surface region.