III-V compound semiconductor layer stacks with electrical isolation provided by a trap-rich layer

1. A structure comprising:

a semiconductor substrate comprising a single-crystal semiconductor material, the semiconductor substrate having a top surface;

a layer stack positioned on the top surface of the semiconductor substrate, the layer stack including a first layer comprising a first III-V compound semiconductor material; and

a polycrystalline layer in the semiconductor substrate, the polycrystalline layer extending laterally beneath the layer stack, the polycrystalline layer including a first section having a first thickness and a second section having a second thickness that is greater than the first thickness, and the second section of the polycrystalline layer has a boundary that substantially coincides with the top surface of the semiconductor substrate.

2. The structure of claim 1 wherein the single-crystal semiconductor material of the semiconductor substrate is oriented with a <111> surface normal.

3. The structure of claim 2 wherein the polycrystalline layer has an electrical resistivity that is within a range of 10,000 ohm-cm to 1,000,000 ohm-cm.

4. The structure of claim 1 wherein the polycrystalline layer includes an upper boundary and a lower boundary, and the semiconductor substrate includes a layer of the single-crystal semiconductor material between the top surface and the upper boundary of the polycrystalline layer.

5. The structure of claim 1 wherein the first III-V compound semiconductor material of the first layer has a crystal structure that is substantially single crystal.

6. The structure of claim 1 further comprising:

an active device including a gate electrode on the layer stack.

7. The structure of claim 6 wherein the active device is a high-electron-mobility transistor.

8. The structure of claim 1 further comprising:

an interconnect structure over the layer stack and the polycrystalline layer; and

a passive device in the interconnect structure.

9. The structure of claim 1 wherein the layer stack includes a second layer comprising a second III-V compound semiconductor material, and the second III-V compound semiconductor material has a different composition than the first III-V compound semiconductor material.

10. The structure of claim 9 wherein the first III-V compound semiconductor material is gallium nitride.

11. The structure of claim 1 wherein the first III-V compound semiconductor material of the first layer over the first section of the polycrystalline layer is substantially single crystal, and the first III-V compound semiconductor material of the first layer over the second section of the polycrystalline layer is disordered.

12. A structure comprising:

a semiconductor substrate comprising a single-crystal semiconductor material;

a layer stack on the semiconductor substrate, the layer stack including a first layer comprised of a first III-V compound semiconductor material; and

a polycrystalline layer in the semiconductor substrate, the polycrystalline layer extending laterally beneath the layer stack, the polycrystalline layer including a first section having a first thickness and a second section having a second thickness that is greater than the first thickness,

wherein the first III-V compound semiconductor material of the first layer over the first section of the polycrystalline layer is substantially single crystal, and the first III-V compound semiconductor material of the first layer over the second section of the polycrystalline layer is disordered.

13. The structure of claim 12 wherein the layer stack includes a second layer comprising a second III-V compound semiconductor material, and the second III-V compound semiconductor material has a different composition than the first III-V compound semiconductor material.

14. The structure of claim 12 further comprising:

an active device including a gate electrode on the layer stack over the first section of the polycrystalline layer.

15. A method comprising:

forming a polycrystalline layer in a semiconductor substrate, of wherein the semiconductor substrate comprises a single-crystal semiconductor material; and

forming a layer stack positioned on a top surface of the semiconductor substrate,

wherein the layer stack includes a layer comprising a III-V compound semiconductor material, the polycrystalline layer extends laterally beneath the layer stack, the polycrystalline layer includes a first section having a first thickness and a second section having a second thickness that is greater than the first thickness, and the second section of the polycrystalline layer has a boundary that substantially coincides with the top surface of the semiconductor substrate.

16. The method of claim 15 wherein forming the polycrystalline layer in the semiconductor substrate comprised of the single-crystal semiconductor material comprises:

implanting ions into the semiconductor substrate to produce crystalline damage to the single-crystal semiconductor material of the semiconductor substrate in an implanted layer beneath the top surface of the semiconductor substrate; and

recrystallizing the implanted layer of the semiconductor substrate with an annealing process to produce the polycrystalline layer.

17. The method of claim 16 further comprising:

applying a patterned dielectric layer over the top surface of the semiconductor substrate that exposes a first region of the semiconductor substrate and that covers a second region of the semiconductor substrate.

18. The method of claim 17 wherein the patterned dielectric layer is applied before the implanted layer of the semiconductor substrate is recrystallized.

19. The method of claim 15 further comprising:

forming a gate electrode of an active device on the layer stack.

20. The method of claim 15 wherein the single-crystal semiconductor material of the semiconductor substrate is oriented with a <111> surface normal.