P-type field effect transistor and method for fabricating the same

A method for fabricating a p-type field effect transistor (pFET), comprising:

• providing a substrate;
• forming a pad layer on the substrate;
• performing an ion implantation process to implant germanium (Ge) into the substrate through the pad layer to form a channel region, wherein a concentration of Ge closer to a boundary between the pad layer and the channel region is greater than a concentration of Ge closer to a boundary between the channel region and the substrate;
• performing an anneal process while the pad layer is disposed on a top surface of the channel region to separate the channel region into a top portion and a bottom portion, wherein a depth of the top portion is equal to a depth of the bottom portion and the concentration of germanium in the bottom portion is lower than the concentration of germanium in the top portion, and after the anneal process, the top portion and the bottom portion of the channel region is made of SiGe;
• and
• forming a gate structure on the substrate.