Lateral bipolar transistor structure with inner and outer spacers and methods to form same

A lateral bipolar transistor structure comprising:

• an emitter/collector (E/C) layer over an insulator, the E/C layer having a first doping type;
• a first base layer on the insulator and adjacent the E/C layer, wherein the first base layer has a second doping type opposite the first doping type;
• a second base layer on the first base layer and having the second doping type, wherein a dopant concentration of the second base layer is greater than a dopant concentration of the first base layer, the second base layer including:
• a lower portion having a first horizontal width over the first base layer, and
• an upper portion having a second horizontal width over the first base layer greater than the first horizontal width;
• an inner spacer on the E/C layer and adjacent the second base layer;
• and
• an outer spacer on the E/C layer and adjacent the inner spacer.

A method of forming bipolar transistor structure, the method comprising:

• forming an emitter/collector (E/C) layer over an insulator, the E/C layer having a first doping type;
• forming a first base layer on the insulator and adjacent the E/C layer, the first base layer having a concave sidewall adjacent the E/C layer, wherein the first base layer has a second doping type opposite the first doping type;
• forming a second base layer on the first base layer and having the second doping type, wherein a dopant concentration of the second base layer is greater than a dopant concentration of the first base layer;
• forming an inner spacer on the E/C layer and adjacent the second base layer;
• and
• forming an outer spacer on the E/C layer and adjacent the inner spacer.