Nitride semiconductor crystal, manufacturing method of the nitride semiconductor freestanding substrate and nitride semiconductor device

1. A nitride semiconductor crystal, comprising:

laminated homogeneous nitride semiconductor layers, with a thickness of 2 mm or more,

wherein the laminated homogeneous nitride semiconductor layers are constituted so that a nitride semiconductor layer with low dopant concentration and a nitride semiconductor layer with high dopant concentration are alternately laminated by two cycles or more.

2. The nitride semiconductor crystal according to claim 1 , wherein a thickness of the nitride semiconductor layer with low dopant concentration is 1/20 or more of a thickness of the nitride semiconductor layer with high dopant concentration.

3. The nitride semiconductor crystal according to claim 1 , wherein the nitride semiconductor layer with low dopant concentration has a dopant concentration of less than 5×10 17 cm −3 , and the nitride semiconductor layer with high dopant concentration has a dopant concentration of 5×10 17 cm −3 or more.

4. The nitride semiconductor crystal according to claim 1 , wherein the dopant contained in the laminated homogeneous nitride semiconductor layers is any one of a n-type dopant, a p-type dopant, and a semi-insulating dopant.

5. The nitride semiconductor crystal according to claim 1 , wherein the nitride semiconductor layer with low dopant concentration is an updoped nitride semiconductor layer.

6. The nitride semiconductor crystal according to claim 1 , wherein the nitride semiconductor layer with high dopant concentration is a n-type or p-type conductive nitride semiconductor layer, with a carrier concentration being 1×10 18 cm −3 or more.

7. The nitride semiconductor crystal according to claim 1 , wherein the nitride semiconductor layer with high dopant concentration is a semi-insulating nitride semiconductor layer, with resistivity being 1×10 5 Ωcm or more.

8. The nitride semiconductor crystal according to claim 1 , wherein the laminated homogeneous nitride semiconductor layers are GaN layers.

9. A manufacturing method of a nitride semiconductor freestanding substrate, comprising the steps of:

forming a nitride semiconductor crystal with a thickness of 2 mm or more on a base substrate, composed of homogeneous nitride semiconductor layers, in which a nitride semiconductor layer with low dopant concentration and a nitride semiconductor layer with high dopant concentration, are laminated by 2 cycles or more; and

slicing the nitride semiconductor crystal formed by lamination on the base substrate, with the nitride semiconductor layer with low dopant concentration as a cutting position.

10. The manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 , wherein the nitride semiconductor freestanding substrate is manufactured, with the nitride semiconductor layer with high dopant concentration set as at least a surface of the nitride semiconductor freestanding substrate.

11. The manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 , wherein a thickness of the nitride semiconductor layer with low dopant concentration is 1/20 or more of a thickness of the nitride semiconductor layer with high dopant concentration.

12. The manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 , wherein the nitride semiconductor layer with low dopant concentration has a dopant concentration of less than 5×10 17 cm −3 , and the nitride semiconductor layer with high dopant concentration has a dopant concentration of 5×10 17 cm −3 or more.

13. The manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 , wherein the dopant contained in the homogeneous nitride semiconductor layers is any one of a n-type dopant, a p-type dopant, and a dopant that gives semi-insulating property.

14. The manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 , wherein the nitride semiconductor layer with low dopant concentration is an undoped nitride semiconductor layer formed without supplying dopant raw materials thereto.

15. The manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 , wherein the homogeneous nitride semiconductor layers are GaN layers.

16. The manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 , wherein HVPE is used in the step of forming the nitride semiconductor crystal.

17. A nitride semiconductor device, manufactured by forming the nitride semiconductor layers having a device structure by lamination, on the nitride semiconductor freestanding substrate manufactured by the manufacturing method of the nitride semiconductor freestanding substrate according to claim 9 .