Semiconductor device and method for manufacturing the same

1. A nitride-based semiconductor device, comprising:

a substrate;

a buffer disposed over the substrate;

a first nitride-based semiconductor layer disposed over the buffer and forming a first interface with the buffer;

a shield layer comprising a first isolation compound and interposed between the buffer and the first nitride-based semiconductor layer, wherein the first isolation compound has a bandgap greater than a bandgap of the buffer and greater than a bandgap of the first nitride-based semiconductor layer, forming at least one electrical isolation region between the buffer and the first nitride-based semiconductor layer;

a second nitride-based semiconductor layer disposed on the first nitride-based semiconductor layer and having a bandgap less than the bandgap of the first isolation compound and greater than the bandgap of the first nitride-based semiconductor layer; and

a pair of source/drain (S/D) electrodes and a gate electrode disposed over the second nitride-based semiconductor layer, wherein the gate electrode is present between the S/D electrodes.

2. The semiconductor device of claim 1 , wherein the first interface is in a position lower than a top-most surface of the shield layer.

3. The semiconductor device of claim 2 , wherein the shield layer forms a second interface with a top-most portion of the buffer.

4. The semiconductor device of claim 3 , wherein the top-most surface of the shield layer forms a third interface with a bottom-most portion of the first nitride-based semiconductor layer, and the shield layer has a sidewall forming a fourth interface with the bottom-most portion of the first nitride-based semiconductor layer.

5. The semiconductor device of claim 1 , wherein the first nitride-based semiconductor layer extends downward to a top-most surface of the buffer to form the first interface.

6. The semiconductor device of claim 1 , wherein the shield layer has a plurality of isolation islands enclosed by the buffer and the first nitride-based semiconductor layer.

7. The semiconductor device of claim 6 , wherein the first nitride-based semiconductor layer extends downward to fully fill intervals between the isolation islands.

8. The semiconductor device of claim 6 , wherein each of the isolation islands has a first interface area with the first nitride-based semiconductor layer and a second interface area with the buffer, and the first interface area is greater than the second interface area.

9. The semiconductor device of claim 1 , wherein the first nitride-based semiconductor layer extends downward to penetrate the shield layer, so as to form the first interface with the buffer.

10. The semiconductor device of claim 1 , wherein the shield layer viewed along a direction normal to the substrate has at least one inner boundary surrounding the buffer.

11. The semiconductor device of claim 1 , wherein the buffer comprises at least one layer of a doped nitride-based semiconductor compound at a top-most portion of the buffer, wherein at least one dopant of the doped nitride-based semiconductor compound is selected from one or more of carbon, silicon, germanium, or tin, and wherein the shield layer is in contact with the doped nitride-based semiconductor compound.

12. The semiconductor device of claim 11 , wherein the doped nitride-based semiconductor compound of the buffer is carbon-doped gallium nitride.

13. The semiconductor device of claim 1 , wherein the shield layer has a thickness in a range from 1 nm to 100 nm.

14. The semiconductor device of claim 1 , further comprising:

a passivation layer disposed over the gate electrode and comprising a second isolation compound that is devoid of metal elements, wherein the first isolation compound comprises at least one metal element.

15. The semiconductor device of claim 1 , further comprising:

a passivation layer disposed over the gate electrode and comprising a second isolation compound having the same composition as that of the first isolation compound.

16. A method for manufacturing a semiconductor device, comprising:

forming a buffer over a substrate;

forming a shield layer in contact with the buffer;

patterning the shield layer to expose portions of the buffer;

growing a first nitride-based semiconductor layer from the exposed portion of the buffer, such that the first nitride-based semiconductor layer is formed to cover the shield layer, wherein the first nitride-based semiconductor layer has a bandgap less than a bandgap of the shield layer;

forming a second nitride-based semiconductor layer on the first nitride-based semiconductor layer, wherein the second nitride-based semiconductor layer has a bandgap less than the bandgap of the shield layer and greater than the bandgap of the first nitride-based semiconductor layer;

forming two or more source/drain (S/D) electrodes over the second nitride-based semiconductor layer; and

forming a gate electrode over the second nitride-based semiconductor layer and between the S/D electrodes.

17. The method of claim 16 , wherein the first nitride-based semiconductor layer is formed to cover a top-most surface and a side surface of the shield layer.

18. The method of claim 16 , wherein patterning the shield layer is performed such that a plurality of isolation islands are formed.

19. The method of claim 16 , wherein pattering the shield layer is performed such that the shield layer has a plurality of apertures to expose the buffer.

20. The method of claim 16 , wherein the first nitride-based semiconductor layer grows laterally in a position higher than a top-most surface of the shield layer.