Semiconductor devices, power semiconductor devices, and methods for forming a semiconductor device

A semiconductor device, comprising:

• a drift region of a device structure arranged in a semiconductor layer located adjacently to a semiconductor substrate,
• wherein a doping concentration at a transition from the drift region to the semiconductor substrate varies between a first doping concentration value and a second doping concentration value over a distance of less than 500 nm,
• wherein the first doping concentration value is an average net doping concentration of a mid-portion of the drift region plus 20% of the average net doping concentration of the mid-portion of the drift region,
• wherein the mid-portion of the drift region lies within a middle 50% of a vertical dimension of the drift region,
• wherein the second doping concentration value is an average net doping concentration of the mid-portion of the drift region plus one decade.

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

• epitaxially growing a first epitaxial semiconductor sub layer of a semiconductor layer on a semiconductor substrate, wherein a majority of dopants within the first epitaxial semiconductor sub layer are a first species of dopants having a diffusivity less than a diffusivity of phosphor within the semiconductor layer;
• epitaxially growing a second epitaxial semiconductor sub layer of a semiconductor layer after forming the first epitaxial semiconductor sub layer, wherein a majority of dopants within the second epitaxial semiconductor sub layer are a second species of dopants;
• and
• forming a trench extending from a surface of the semiconductor layer into the semiconductor layer, wherein a vertical distance of a border between the first epitaxial semiconductor sub layer and the second epitaxial semiconductor sub layer to the surface of the semiconductor layer is larger than 0.5 times a maximal depth of the trench and less than 1.5 times the maximal depth of the trench.