Heterojunction bipolar transistor architecture
A transistor includes a sub-collector, a base, a collector between the sub-collector and the base, and an emitter on the base opposite the collector. The collector includes a first region adjacent to the base and a second region between the first region and the sub-collector. The first region has a graduated doping profile such that a doping concentration of the first region decreases in proportion to a distance from the base. The second region has a substantially constant doping profile. By providing the collector with a doping profile as described, the linearity of the transistor is significantly improved while maintaining the radio frequency (RF) gain thereof.
1. A transistor comprising:
a sub-collector;
a base;
a collector between the sub-collector and the base and comprising:
a first region comprising a first end adjacent to the base and a second end opposite the first end, wherein a doping profile of the first region is graduated such that a doping concentration of the first region decreases from a first doping concentration at the first end to a second doping concentration at the second end; and
a second region between the first region and the sub-collector and comprising a substantially constant doping profile at the second doping concentration; and
an emitter on the base opposite the collector.
2. The transistor of claim 1 wherein the doping concentration of the first region decreases by more than an order of magnitude between the first end of the first region and the second end of the first region.
3. The transistor of claim 2 wherein the doping concentration of the first region is between about 3×10 16 cm −3 and 9×10 16 cm −3 at the first end of the first region and between about 1×10 15 cm −3 and 1×10 16 cm −3 at the second end of the first region.
4. The transistor of claim 3 wherein a doping concentration of the second region is between about 1×10 15 cm −3 and 1×10 16 cm −3 .
5. The transistor of claim 3 wherein the doping concentration of the first region is graduated one of linearly and in a step-wise approximation of linearly.
6. The transistor of claim 3 wherein the doping concentration of the first region is graduated one of parabolically and exponentially.
7. The transistor of claim 3 wherein the first region has a thickness between about 1000 Å and 3000 Å.
8. The transistor of claim 7 wherein the second region has a thickness between about 0 Å and 8000 Å.
9. The transistor of claim 8 wherein a doping concentration of the second region is between about 1×10 15 cm −3 and 1×10 16 cm −3 .
10. The transistor of claim 1 wherein the second region has a thickness between about 0 Å and 8000 Å.
11. The transistor of claim 10 wherein the first region has a thickness between about 1000 Å and 3000 Å.
12. The transistor of claim 1 wherein the transistor is a heterojunction bipolar transistor (HBT).
13. The transistor of claim 1 further comprising a third region comprising a first end adjacent to the second region and a second end opposite the first end, wherein a doping profile of the third region is graduated such that a doping concentration of the third region increases from the second doping concentration at the first end to a third doping concentration at the second end.
14. The transistor of claim 13 wherein:
the doping concentration of the first region decreases by more than an order of magnitude between the first end of the first region and the second end of the first region; and
the doping concentration of the third region increases by more than an order of magnitude between the first end of the third region and the second end of the third region.
15. The transistor of claim 14 wherein:
the doping concentration of the first region is between about 3×10 16 cm −3 and 9×10 16 cm −3 at the first end of the first region and between about 1×10 15 cm −3 and 1×10 16 cm −3 at the second end of the first region;
a doping concentration of the second region is between about 1×10 15 cm −3 and 1×10 16 cm −3 ; and
the doping concentration of the third region is between about 1×10 16 cm −3 and 5×10 16 cm −3 at the first end of the third region and between about 5×10 16 cm −3 and 5×10 18 cm −3 at the second end of the third region.
16. The transistor of claim 15 wherein the doping concentration of the first region is graduated one of linearly and in a step-wise approximation of linearly.
17. The transistor of claim 16 wherein the doping concentration of the third region is graduated one of linearly, parabolically, and exponentially.
18. The transistor of claim 15 wherein the doping concentration of the first region is graduated one of parabolically and exponentially.
19. The transistor of claim 18 wherein the doping concentration of the third region is graduated one of linearly, parabolically, and exponentially.
20. The transistor of claim 15 wherein:
the first region has a thickness between about 1000 Å and 3000 Å;
the second region has a thickness between about 0 Å and 8000 Å; and
the third region has a thickness between about 2000 Å and 5000 Å.