A GaN substrate doped with manganese, in which an activation energy of a carrier is 0.7 eV or more when a carrier concentration is represented by the formula (I): carrier concentration (atoms/cm.sup.3)=AEXP(Ea/kT). In the formula (I), A represents a proportional constant, EXP represents an exponential function, Ea represents a carrier activation energy (eV), k represents a Boltzmann constant (8.61710.sup.5 eV/K), and T represents a temperature (K) in Kelvin units.

A SiC epitaxial wafer includes a SiC substrate and an epitaxial layer laminated on the SiC substrate, wherein the epitaxial layer contains an impurity element which determines the conductivity type of the epitaxial layer and boron which has a conductivity type different from the conductivity type of the impurity element, and the concentration of boron is less than 1.010.sup.14 cm.sup.3 at any position in the plane of the epitaxial layer.

A CVD single crystal diamond material suitable for use in, or as, an optical device or element. It is suitable for use in a wide range of optical applications such as, for example, optical windows, laser windows, optical reflectors, optical refractors and gratings, and etalons. The CVD diamond material is produced by a CVD method in the presence of a controlled low level of nitrogen to control the development of crystal defects and thus achieve a diamond material having key characteristics for optical applications.

A method of forming a diamond composite body and the diamond composite body. A first single crystal diamond body is provided, which contains nitrogen and has a uniform strain such that over an area of at least 11 mm, at least 90 percent of points display a modulus of strain-induced shift of NV resonance of less than 200 kHz, wherein each point in the area is a resolved region of 50 m.sup.2. The first single crystal diamond body is treated to convert at least some of the nitrogen to form at least 0.3 ppm nitrogen-vacancy, NV.sup., centres. A CVD process is used to grow a second single crystal diamond body on a surface of the first single crystal diamond body. The second single crystal diamond body has an NV concentration less than or equal to 10 times lower than the NV.sup. concentration in the first single crystal diamond body.

A method of growing single crystal diamond assisted by polycrystalline diamond growth to enhance dimensions and quality of the single crystal diamond includes thermally mating a diamond seed on a top surface of a substrate holder providing a growth surface for a combination of single crystal diamond and polycrystalline diamond. A predetermined temperature difference between the diamond seed and the substrate holder during processing along with the plasma process conditions causes a single crystal diamond growth rate to be different from a polycrystalline growth rate by a predetermined amount. Process gasses are introduced, and a plasma is formed to grow both single crystal diamond and polycrystalline diamond on the growth surface so that the polycrystalline diamond grown adjacent to the single crystal diamond shields side surfaces of the growing single crystal diamond, thereby improving growth quality across the growing single crystal diamond.

A SiC epitaxial wafer includes a SiC substrate and an epitaxial layer laminated on the SiC substrate, wherein the epitaxial layer contains an impurity element which determines the conductivity type of the epitaxial layer and boron which has a conductivity type different from the conductivity type of the impurity element, and the concentration of boron is less than 1.010.sup.14 cm.sup.3 at any position in the plane of the epitaxial layer.

A method for producing a substrate for the epitaxial growth of a gallium-based III-N alloy layer comprises the following successive steps: providing a donor substrate of single-crystal silicon carbide; implanting ions in the donor substrate to form an embrittlement zone defining a thin film layer of single-crystal SiC; bonding the donor substrate onto a first receiving substrate via a bonding layer; detaching the donor substrate along the embrittlement zone to transfer the thin film of SiC onto the first receiving substrate; epitaxially growing a layer of semi-insulating SiC having a thickness greater than 1 m on the thin film of SiC; bonding the layer of semi-insulating SiC onto a second receiving substrate having a high electrical resistivity; removing at least a portion of the bonding layer to detach the first receiving substrate; and removing the transferred thin film of single-crystal SiC, to expose the semi-insulating SiC layer.

A microwave plasma reactor for manufacturing synthetic diamond material via chemical vapour deposition, the microwave plasma reactor comprising: a plasma chamber defining a resonant cavity for supporting a primary microwave resonance mode having a primary microwave resonance mode frequency f; a plurality of microwave sources coupled to the plasma chamber for generating and feeding microwaves having a total microwave power P into the plasma chamber; a gas flow system for feeding process gases into the plasma chamber and removing them therefrom; and a substrate holder disposed in the plasma chamber and comprising a supporting surface for supporting a substrate on which the synthetic diamond material is to be deposited in use, wherein the plurality of microwave sources are configured to couple at least 30% of the total microwave power P into the plasma chamber in the primary microwave resonance mode frequency f, and wherein at least some of the plurality of microwave sources are solid state microwave sources.

A CVD single crystal diamond material suitable for use in, or as, an optical device or element. It is suitable for use in a wide range of optical applications such as, for example, optical windows, laser windows, optical reflectors, optical refractors and gratings, and etalons. The CVD diamond material is produced by a CVD method in the presence of a controlled low level of nitrogen to control the development of crystal defects and thus achieve a diamond material having key characteristics for optical applications.

A laser activated luminescence system is provided. Another aspect pertains to a system employing a plasma assisted vapor deposition reactor which creates diamond layers on a substrate, in combination with a laser system to at least photoactivate and anneal the diamond layers. Yet another aspect of the present system uses a laser to assist with placement of color centers, such as nitrogen vacancy centers, in diamond. The present method uses lasers to manufacture more than two activated nitrogen vacancy center nodes in a diamond substrate, with nanometer spatial resolution and at a predetermined depth.