Diffused extrinsic base and method for fabrication

A transistor, comprising:

• an epitaxial layer on a semiconductor substrate;
• a dopant source layer on a first portion of the epitaxial layer;
• an emitter material on a second portion of the epitaxial layer, said second portion of the epitaxial layer being adjacent to said first portion of the epitaxial layer;
• dopant from the dopant source layer within the epitaxial layer to form at least a portion of an extrinsic base for the transistor within the epitaxial layer, said portion of the extrinsic base being in direct mechanical contact with the dopant source layer, a first surface of said portion of the extrinsic base being disposed between the dopant source layer and an intrinsic base for the transistor, said intrinsic base being totally within the epitaxial layer, a second surface of said portion of the extrinsic base being in direct mechanical contact with the intrinsic base, said second surface being opposite said first surface and not contacting said first surface;
• and
• emitter dopant from the emitter material within said second portion of the epitaxial layer, said emitter dopant forming an emitter for the transistor, said emitter being totally within the epitaxial layer, said emitter being surrounded by said portion of the extrinsic base.

A transistor, comprising:

• semiconductor substrate;
• epitaxial layer on the substrate;
• a dopant source layer on the epitaxial layer;
• dopant from the dopant source layer distributed within the epitaxial layer to form a first portion of an extrinsic base for the transistor within the epitaxial layer, said first portion of the extrinsic base being in direct mechanical contact with the dopant source layer, said first portion of the extrinsic base being disposed between the dopant source layer and an intrinsic base for the transistor, said intrinsic base being totally within the epitaxial layer;
• and
• a pedestal on the epitaxial layer, wherein the dopant source layer is formed around the pedestal such that the pedestal defines a portion of the epitaxial layer in which the dopant source layer is not formed on the epitaxial layer, wherein the pedestal comprises a high pressure oxide layer, a nitride layer above the high pressure oxide layer, and an oxide layer above the nitride layer, and patterning the high pressure oxide layer, nitride layer and oxide layer, and wherein the dopant source layer does not exist above the high pressure oxide layer.