Integrated devices on a common compound semiconductor III-V wafer

1. A III-V compound semiconductor structure comprising epitaxial structures that include an integrated pair of different types of active devices, the semiconductor structure comprising:

a semi-insulating substrate of a compound semiconductor III-V material; and

a first compound semiconductor III-V epitaxial structure disposed on the substrate, the first epitaxial structure forming at least a portion of one of the active devices;

wherein a doping concentration profile in the semiconductor structure decreases substantially smoothly across an interface between the substrate and first epitaxial structure in a direction from the first epitaxial structure toward the substrate, and continues to decrease substantially smoothly from the interface with increasing depth into the substrate despite the presence of silicon or oxygen contaminant at the interface.

2. The III-V compound semiconductor structure of claim 1 wherein the concentration of the contaminant at the interface is less than 10 16 cm −3 .

3. The III-V compound semiconductor structure of claim 1 wherein the epitaxial structures include an integrated pair of HBT and FET transistors.

4. The III-V compound semiconductor structure of claim 3 wherein the HBT and FET transistors share a common compound semiconductor III-V epitaxial layer in one of the epitaxial structures.

5. The III-V compound semiconductor structure of claim 1 further including:

a second compound semiconductor III-V epitaxial structure over of the first epitaxial structure, and

a third compound semiconductor III-V epitaxial structure disposed over the second epitaxial structure, the second epitaxial structure forming at least a portion of a second one of the active devices of a different type than the first active device;

wherein the first and second active devices share a common compound semiconductor epitaxial layer in one of the epitaxial structures.

6. The III-V compound semiconductor structure of claim 5 wherein the concentration of the contaminant at the interface between the substrate and the first epitaxial structure is less than 10 16 cm −3 .

7. A III-V compound semiconductor structure comprising epitaxial structures that include an integrated pair of different types of active devices, the semiconductor structure comprising:

a semi-insulating substrate of a compound semiconductor III-V material; and

a first compound semiconductor 111 -V epitaxial structure disposed on the substrate, the first epitaxial structure forming at least a portion of one of the active devices;

wherein a doping concentration profile in the semiconductor structure across an interface between the substrate and the first epitaxial structure decreases substantially smoothly across the interface in a direction from the first epitaxial structure toward the substrate and wherein the doping concentration profile continuously decreases from the interface with increasing depth into the substrate despite the presence of a contaminant at the interface, wherein the contaminant is a chemical element of the periodic table whose presence at or near the interface contributes electrical charge.

8. The III-V compound semiconductor structure of claim 7 wherein the contaminant is silicon.

9. The III-V compound semiconductor structure of claim 7 wherein the concentration of the contaminant at the interface is less than 10 16 cm −3 .

10. The III-V compound semiconductor structure of claim 7 wherein the epitaxial structures include an integrated pair of HBT and FET transistors.

11. The III-V compound semiconductor structure of claim 10 wherein the HBT and PET transistors share a common compound semiconductor III-V epitaxial layer in one of the epitaxial structures.

12. The III-V compound semiconductor structure of claim 7 further including:

a second compound semiconductor III-V epitaxial structure over of the first epitaxial structure, and

a third compound semiconductor III-V epitaxial structure disposed over the second epitaxial structure, the second epitaxial structure forming at least a portion of a second one of the active devices of a different type than the first active device;

wherein the first and second active devices share a common compound semiconductor III-V epitaxial layer in one of the epitaxial structures.

13. The III-V compound semiconductor structure of claim 12 wherein the concentration of the contaminant at the interface between the substrate and the first epitaxial structure is less than 10 16 cm − .