Semiconductor device with doped semiconductor and dielectric trench sidewall layers

A semiconductor device having an ohmic contact to a buried layer comprising:

• a device wafer of monocrystalline semiconductor material having a first and a second surface;
• a first dielectric layer disposed on said device wafer first surface;
• a heavily doped buried layer contiguous to said dielectric layer and comprising a dopant having a first polarity;
• a doped epitaxial layer disposed on said wafer second surface and comprising a dopant having said first polarity;
• a plurality of trenches, each said trench comprising spaced apart sidewalls and extending from an upper surface of the epitaxial layer through said epitaxial layer to a trench floor, wherein at least a portion of said trenches include a layer of doped semiconductor material disposed on the sidewalls, said layer comprising a dopant having said first polarity and providing electrical contact between the doped buried layer and a surface collector region in said monocrystalline semiconductor material having said first polarity, and a layer of dielectric material disposed on each said layer of doped semiconductor material disposed on the sidewalls and acting as a diffusion barrier to prevent dopants in said sidewall semiconductor material from diffusing into said trench and for enabling an effective concentration of said dopant in the device layer adjacent said trench.