Nitride semiconductor substrate, laminated structure, and method for manufacturing nitride semiconductor substrate
A nitride semiconductor substrate that is constituted by a single crystal of a group III nitride semiconductor and includes a main surface for which the closest low index crystal plane is a (0001) plane includes an inclined interface growth region that has grown with inclined interfaces other than the (0001) plane serving as growth surfaces. A ratio of an area occupied by the inclined interface growth region in the main surface is 80% or more. When a dislocation density is determined based on a dark spot density by observing the main surface in a field of view that is 250 μm square using a multiphoton excitation microscope, the main surface does not include a region that has a dislocation density higher than 3×10 6 cm −2 , and the main surface includes dislocation-free regions that are 50 μm square and do not overlap each other, at a density of 100 regions/cm 2 or more.
1. A nitride semiconductor substrate that is constituted by a single crystal of a group III nitride semiconductor and includes a main surface for which the closest low index crystal plane is a (0001) plane, the nitride semiconductor substrate comprising
an inclined interface growth region that has grown with inclined interfaces other than the (0001) plane serving as growth surfaces,
wherein a ratio of an area occupied by the inclined interface growth region in the main surface is 80% or more,
when a dislocation density is determined based on a dark spot density by observing the main surface in a field of view that is 250 μm square using a multiphoton excitation microscope, the main surface does not include a region that has a dislocation density higher than 3×10 6 cm −2 ,
wherein regions having a dislocation density lower than 1×10 6 cm −2 constitute 80% or more of the main surface, and
the main surface includes dislocation-free regions that are 50 μm square and do not overlap each other, at a density of 100 regions/cm 2 or more.
2. The nitride semiconductor substrate according to claim 1 , wherein
when X-ray rocking curve measurement of a (0002) plane is performed at positions on a straight line that passes through the center in the main surface, and a peak angle @ formed between the main surface and X rays incident on the main surface is plotted for the positions on the straight line and approximated by a linear function of the positions,
a radius of curvature of the (0001) plane determined based on the reciprocal of a slope of the linear function is 15 m or more, and
an error of the measured peak angle ω with respect to the linear function is no greater than 0.05°.
3. The nitride semiconductor substrate according to claim 1 , wherein
the nitride semiconductor substrate does not include a c-plane growth region that has grown with the (0001) plane serving as a growth surface.
4. The nitride semiconductor substrate according to claim 1 , wherein
the nitride semiconductor substrate includes a c-plane growth region that has grown with the (0001) plane serving as a growth surface, and
the c-plane growth region in the main surface includes a dislocation-free region that is at least 50 μm square.
5. The nitride semiconductor substrate according to claim 1 , wherein
the nitride semiconductor substrate includes:
a low dislocation density region; and
a dislocation concentrated region in which dislocations are more concentrated than in the low dislocation density region, and
when a dislocation density is determined based on a dark spot density by observing the main surface in a field of view that is 50 μm square and includes the dislocation concentrated region using a multiphoton excitation microscope, the dislocation density is less than 3×10 6 cm −2 .
6. The nitride semiconductor substrate according to claim 1 , wherein
when an imaginary line segment having a length of 200 μm is arbitrarily drawn in a cathodoluminescence image of the main surface, the number of intersections between the line segment and basal plane dislocations is no greater than 10.
7. The nitride semiconductor substrate according to claim 1 , wherein
when a laminate is prepared by epitaxially growing a semiconductor layer that is constituted by a non-doped single crystal of a predetermined group III nitride semiconductor on the main surface, a reference laminate is prepared by epitaxially growing the semiconductor layer on a substrate constituted by a single crystal of a group III nitride semiconductor that is the same as the nitride semiconductor substrate in all aspects other than not including the inclined interface growth region, and photoluminescence of the semiconductor layers in the laminate and the reference laminate is measured with a temperature difference of less than 1° C.,
a difference between the maximum peak wavelength in the semiconductor layer of the laminate and the maximum peak wavelength in the semiconductor layer of the reference laminate is no greater than 1 nm.