A semiconductor structure and a method of forming the same are provided. In an embodiment, an exemplary semiconductor method includes forming a fin-shaped structure extending from a substrate, the fin-shaped structure includes a number of channel layers interleaved by a number of sacrificial layers, recessing a source/drain region to form a source/drain opening, performing a PAI process to amorphize a portion of the substrate exposed by the source/drain opening, forming a tensile stress film over the substrate, performing an annealing process to recrystallize the portion of the substrate, the recrystallized portion of the substrate includes dislocations, forming an epitaxial source/drain feature over the source/drain opening, and forming a gate structure wrapping around each of the plurality of channel layers. By performing the above operations, dislocations are controllably and intentionally formed and carrier mobility in the number of channel layers may be advantageously enhanced, leading to improved device performance.

A semiconductor device includes: a drift region of a first conductivity type between first and second surfaces of a semiconductor body; a first region of a second conductivity type at the second surface; and a field stop region of the first conductivity type between the drift region and first region. The field stop region includes first and second sub-regions with hydrogen related donors. A p-n junction separates the first region and first sub-region. A concentration of hydrogen related donors, along a first vertical extent of the first sub-region, steadily increases from the pn-junction to a maximum value, and steadily decreases from the maximum value to a value at a first transition between the sub-regions. A second vertical extent of the second sub-region ends at a second transition to the drift region where the concentration of hydrogen related donors equals 10% of the value at the first transition.

Provided is a semiconductor device provided with an IGBT, comprising: a semiconductor substrate having upper and lower surfaces, throughout which bulk donors are distributed; a hydrogen peak including a local maximum arranged 25 m or more away from the lower surface of the semiconductor substrate in a depth direction, at which a hydrogen chemical concentration shows a local maximum value; an upper tail where the hydrogen chemical concentration decreases in a direction from the local maximum toward the upper surface; and a lower tail where the hydrogen chemical concentration decreases in a direction from the local maximum toward the lower surface more gradually than the upper tail; and a first high concentration region having a donor concentration higher than a bulk donor concentration and including a region extending for 4 m or more in a direction from the local maximum of the hydrogen peak toward the upper surface.