A method for fabricating a semiconductor device includes forming a channel region in a semiconductor substrate. The channel region is made of a first material. The method also includes forming source and drain regions in the semiconductor substrate. The method further includes forming a recess between the channel region and the drain region. The method further includes forming a tunnel barrier layer in the recess. The tunnel barrier layer is made of a second material, and a bandgap of the second material is greater than a bandgap of the first material. The method further includes forming a gate stack on the channel region.