Nitride semiconductor substrate and method of producing same

A method of producing a nitride semiconductor substrate comprising the steps of;

• forming a network mask composed of a repeating closed loop unit shape having a width of 0.05 mm to 0.3 mm and the maximum diameter of 0.1 mm to 20 mm upon a single crystal undersubstrate, preparing a covered part and exposed parts Π on the undersubstrate, growing nitride semiconductor crystals in vapor phase on the masked undersubstrate, forming convex facet hills covered with facets enclosed by the closed loop on the exposed parts Π, making closed loop concavities on the masked part which suppresses crystal growth, not burying the facets, maintaining the facets, sweeping dislocations in the crystals on the exposed parts Π down on the facets, gathering the dislocations to the closed loop concavities on the covered parts forming a defect accumulating region H for accommodating dislocations in the closed loop concavities on forming grain boundaries K and K sandwiching the defect accumulating region H, keeping the convex facet hills on Π as low defect density single crystal regions Z, keeping the regions accommodating dislocations on as defect accumulating region H composed of polycrystals or single crystals with orientation inverse to the low defect density single crystal regions Z, maintaining the convex facet hills on Π and the closed loop concavities on reducing the dislocation density in the low defect density single crystal regions Z, making a rugged nitride semiconductor crystal containing the network defect accumulating region H and the closed looped low defect density single crystal regions Z, slicing the rugged crystal into as-cut nitride semiconductor wafers, and polishing the as-cut nitride semiconductor wafers.

A method of producing a nitride semiconductor substrate comprising the steps of;

• forming a network mask composed of a repeating closed loop unit shape of an equilateral triangle, a lozenge, a parallelogram or an equiangle hexagon having a width of 0.05 mm to 3 mm and the maximum diameter of 5 mm to 100 mm upon a single crystal undersubstrate, preparing a covered part and exposed parts Π on the undersubstrate, growing nitride semiconductor crystals in vapor phase on the masked undersubstrate, forming convex facet hills covered with facets enclosed by the closed loop on the exposed parts Π, making closed loop concavities on the masked part which suppresses crystal growth, not burying the facets, maintaining the facets, sweeping dislocations in the crystals on the exposed parts Π down on the facets, gathering the dislocations to the closed loop concavities on the covered parts forming a defect accumulating region H for accommodating dislocations in the closed loop concavities on forming grain boundaries K and K sandwiching the defect accumulating region H, keeping the convex facet hills on Π as low defect density single crystal regions Z, keeping the regions accommodating dislocations on as defect accumulating region H composed of polycrystals or single crystals with orientation inverse to the low defect density single crystal regions Z, maintaining the convex facet hills on Π and the closed loop concavities on reducing the dislocation density in the low defect density single crystal regions Z, making a rugged nitride semiconductor crystal containing the network defect accumulating region H and the closed looped low defect density single crystal regions Z, supposing an ultralow defect density single crystal inner-contact cylinder column in the rugged crystal in inner contact with the closed loop mask, cutting round the rugged crystal into an ultralow defect density single crystal inner-contact cylinder column, calculating marginal heights Qc by Qc=2rcoces2Θ for all the facets within Π, where r is a radius of a facet within Π and Θ is an inclination angle of the facet to C-plane, denoting the maximum of the marginal heights by Qcmax, slicing the ultralow defect density single crystal inner-contact cylinder column in parallel planes at height h higher than the maximum marginal height Qcmax (h>Qcmax) into as-cut nitride semiconductor wafers, and polishing the as-cut nitride semiconductor wafers into ultralow defect density single crystal mirror wafers.