Patent ID: 8702865

Claim:
An Al x Ga 1-x N crystal (0<x≦1) substrate, the substrate defining a major growth plane, with the major growth plane having been processed into a planar major face, the Al x Ga 1-x N crystal substrate grown by sublimation onto an undersubstrate under a controlled ambient in a reaction vessel, by setting up in the reaction vessel a crystal-growth ambient containing suitable Al x Ga 1-x N crystal-growth precursors and a flowing carrier gas; heating the undersubstrate to a temperature of from 1600° C. to less than 2000° C.; introducing into the ambient at least one Group-IVb element in gaseous form, together with the carrier gas, at a flow rate of 0.005 sccm to 250 sccm or in solid form together with the Al x Ga 1-x N precursors, so as to incorporate into the ambient at a concentration of from 1 ppm to 15 mass %, for a predetermined period of time extending at least from the start of the growing of the crystal until half the period required for the crystal growth has passed, impurities constituted by the at least one Group-IVb element and thereby form, in the growing of crystal onto the undersubstrate, plural-faceted pits with hexagonal openings in the major face, the pits defining bottoms from which linear dislocation-concentrating areas extend into the Al x Ga 1-x N substrate substantially perpendicularly to the major growth plane; and controlling the crystal-growth temperature, the concentration of the ambient impurities, and the predetermined time period during which the impurities are introduced into the ambient so as to grow the Al x Ga 1-x N crystal such that the ratio of the total area of the plane of the pit openings to the total area of the major face is at least 30%; the Al x Ga 1-x N crystal substrate characterized by: having high- and low-dislocation-density regions, with the low-dislocation-density regions defining first and second portions and the dislocation density of the low-dislocation-density regions being less than 2×10 6 cm −2 , and with the high-dislocation-density regions being centered on the linear dislocation-concentrating areas and sandwiched between the first and second portions of the low-dislocation-density regions; and maximum angular discrepancy between the crystallographic orientation of the first portion of the low-dislocation-density regions, and the crystallographic orientation of the second portion of the low-dislocation-density regions being not greater than 50 arcsec.