Bulk crystal of group III nitride having thickness greater than 1 mm with improved crystal quality, reduced lattice bowing and/or reduced crack density and methods of making. Bulk crystal has a seed crystal, a first crystalline portion grown on the first side of the seed crystal and a second crystalline portion grown on the second side of the seed crystal. Either or both crystalline portions have an electron concentration and/or an oxygen concentration similar to the seed crystal. The bulk crystal can have an additional seed crystal, with common faces (e.g. same polarity, same crystal plane) of seed crystals joined so that a first crystalline part grows on the first face of the first seed crystal and a second crystalline part grows on the first face of the second seed crystal. Each crystalline part's electron concentration and/or oxygen concentration may be similar to its corresponding seed crystal.

A self-supporting substrate includes a first nitride layer grown by hydride vapor deposition method or ammonothermal method and comprising a nitride of one or more element selected from the group consisting of gallium, aluminum and indium; and a second nitride layer grown by a sodium flux method on the first nitride layer and comprising a nitride of one or more element selected from the group consisting of gallium, aluminum and indium. The first nitride layer includes a plurality of single crystal grains arranged therein and being extended between a pair of main faces of the first nitride layer. The second nitride layer includes a plurality of single crystal grains arranged therein and being extended between a pair of main faces of the second nitride layer. The first nitride layer has a thickness larger than a thickness of the second nitride layer.

A new GaN single crystal is provided. A GaN single crystal according to the present embodiment comprises a gallium polar surface which is a main surface on one side and a nitrogen polar surface which is a main surface on the opposite side, wherein on the gallium polar surface is found at least one square area, an outer periphery of which is constituted by four sides each with a length of 2 mm or more, and, when the at least one square are is divided into a plurality of sub-areas each of which is a square of 100 μm×100 μm, pit-free areas account for 80% or more of the sub-areas.

Embodiments of the present disclosure include techniques related to techniques for processing materials for manufacture of group-III metal nitride and gallium based substrates. More specifically, embodiments of the disclosure include techniques for substrates with a controlled oxygen gradient using a combination of processing techniques. Merely by way of example, the disclosure can be applied to growing crystals of GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic and electronic devices, lasers, light emitting diodes, solar cells, photo electrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, and others.

In one instance, the invention provides a bulk crystal of group III nitride having a thickness of more than 1 mm without cracking above the sides of a seed crystal. This bulk group III nitride crystal is expressed as Ga.sub.x1Al.sub.y1In.sub.1-x1-y1N (0≦x1≦1, 0≦x1+y1≦1) and the seed crystal is expressed as Ga.sub.x2Al.sub.y2In.sub.1-x2-y2N (0≦x2≦1, 0≦x2+y2≦1). The bulk crystal of group III nitride can be grown in supercritical ammonia or a melt of group III metal using at least one seed crystal having basal planes of c-orientation and sidewalls of m-orientation. By exposing only c-planes and m-planes in this instance, cracks originating from the sides of the seed crystal are avoided.

Provided is a high-pressure reactor suitable for a high-pressure process using supercritical ammonia grow bulk crystal of group III nitride having lateral dimension larger than 2 inches or to form various transition metal nitrides. The reactor has nutrient distributed along the reactor's longitudinal axis and seed material positioned at the reactor's inner wall and along the reactor's longitudinal axis. Nutrient diffuses through supercritical ammonia from the reactor's longitudinal axis and deposits on the seed material positioned by the reactor's inner wall. Both the nutrient and seed material are heated by the same heater. Material growth can primarily be due to material diffusion through supercritical ammonia. This configuration and methodology reduce convective movement of supercritical ammonia due to temperature differential, providing a more quiescent environment in which group III nitride or transition metal nitride is formed.

A high-quality nitride crystal can be produced efficiently by charging a nitride crystal starting material that contains tertiary particles having a maximum diameter of from 1 to 120 mm and formed through aggregation of secondary particles having a maximum diameter of from 100 to 1000 μm, in the starting material charging region of a reactor, followed by crystal growth in the presence of a solvent in a supercritical state and/or a subcritical state in the reactor, wherein the nitride crystal starting material is charged in the starting material charging region in a bulk density of from 0.7 to 4.5 g/cm.sup.3 for the intended crystal growth.

A group 13 nitride crystal having a hexagonal crystal structure and containing at least a nitrogen atom and at least a metal atom selected from a group consisting of B, Al, Ga, In, and Tl. The group 13 nitride crystal includes a first region disposed on an inner side in a cross section intersecting c-axis, a third region disposed on an outermost side in the cross section and having a crystal property different from that of the first region, and a second region disposed at least partially between the first region and the third region in the cross section, the second region being a transition region of a crystal growth and having a crystal property different from that of the first region and that of the third region.

Techniques for processing materials in supercritical fluids including processing in a capsule disposed within a high-pressure apparatus enclosure are disclosed. The disclosed techniques are useful for growing crystals of GaN, AlN, InN, and their alloys, including InGaN, AlGaN, and AlInGaN for the manufacture of bulk or patterned substrates, which in turn can be used to make optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation devices, photodetectors, integrated circuits, and transistors.

A method for producing a GaN crystal is provided. In the method, front surfaces of a plurality of tiling GaN seeds closely arranged side by side on a flat surface of a plate are planarized. An aggregated seed is formed by arranging the tiling GaN seeds closely side by side on a susceptor of an HVPE apparatus in the same arrangement as when fixed on the plate, with the front planarized surfaces facing upward. A bulk GaN crystal is grown epitaxially on the aggregated seed by an HVPE method.