There is provided a self-supporting polycrystalline gallium nitride substrate having excellent characteristics such as high luminous efficiency and high conversion efficiency when used for devices, such as light emitting devices and solar cells. The self-supporting polycrystalline gallium nitride substrate is composed of gallium nitride-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate, and has a top surface and a bottom surface. The crystal orientations of individual gallium nitride-based single crystal grains as determined from inverse pole figure mapping by electron backscatter diffraction (EBSD) analysis on the top surface are distributed at various tilt angles from the specific crystal orientation, in which the average tilt angle thereof is 0.1 or more and less than 1 and the cross-sectional average diameter D.sub.T of the gallium nitride-based single crystal grains at the outermost surface exposed on the top surface is 10 m or more.

A free-standing substrate of a polycrystalline nitride of a group 13 element contains a plurality of monocrystalline particles having a particular crystal orientation in approximately a normal direction. The polycrystalline nitride of the group 13 element is composed of gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof. The free-standing substrate has a top surface and bottom surface. The free-standing substrate contains at least one of zinc and calcium. A root mean square roughness Rms at the top surface is 3.0 nm or less.

A free-standing substrate of a polycrystalline nitride of a group 13 element is composed of a plurality of monocrystalline particles having a particular crystal orientations in approximately a normal direction. The free-standing substrate has a top surface and a bottom surface. The polycrystalline nitride of the group 13 element is gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof and contains zinc at a concentration of 110.sup.17 atoms/cm.sup.3 or more and 110.sup.20 atoms/cm.sup.3 or less.

Methods for large-scale manufacturing of semipolar gallium nitride boules are disclosed. The disclosed methods comprise suspending large-area single crystal seed plates in a rack, placing the rack in a large diameter autoclave or internally-heated high pressure apparatus along with ammonia and a mineralizer, and growing crystals ammonothermally. A bi-faceted growth morphology may be maintained to facilitate fabrication of large area semipolar wafers without growing thick boules.

Disclosed is a nonlinear optical material (NLO) for use in deep-UV applications, and methods of fabrication thereof. The NLO is fabricated from a plurality of components according to the formula A.sub.qB.sub.yC.sub.z and a crystallographic non-centrosymmetric (NCS) structure. The NLO material may be fabricated as a polycrystalline or a single crystal material. In an embodiment, the material may be according to a formula Ba.sub.3ZnB.sub.5PO.sub.14.

A device substrate in which no streaked morphological abnormality occurs is achieved. A GaN template substrate includes: a base substrate; and a first GaN layer epitaxially formed on the base substrate, wherein the first GaN layer has a compressive stress greater than or equal to 260 MPa that is intrinsic in an inplane direction, or a full width at half maximum of a peak representing E2 phonons of GaN near a wavenumber of 568 cm.sup.1 in a Raman spectrum is lower than or equal to 1.8 cm.sup.1. With all of these requirements, a device substrate includes: a second GaN layer epitaxially formed on the first GaN layer; and a device layer epitaxially formed on the second GaN layer and made of a group 13 nitride.

A device substrate in which no streaked morphological abnormality occurs is achieved. A GaN template substrate includes: a base substrate; and a first GaN layer epitaxially formed on the base substrate, wherein the first GaN layer has a compressive stress greater than or equal to 260 MPa that is intrinsic in an inplane direction, or a full width at half maximum of a peak representing E2 phonons of GaN near a wavenumber of 568 cm.sup.1 in a Raman spectrum is lower than or equal to 1.8 cm.sup.1. With all of these requirements, a device substrate includes: a second GaN layer epitaxially formed on the first GaN layer; and a device layer epitaxially formed on the second GaN layer and made of a group 13 nitride.

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 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 crystal substrate 1 includes an underlying layer 2 and a thick film 3. The underlying layer 2 is composed of a crystal of a nitride of a group 13 element and includes a first main face 2a and a second main face 2b. The thick film 3 is composed of a crystal of a nitride of a group 13 element and provided over the first main face of the underlying layer. The underlying layer 2 includes a low carrier concentration region 5 and a high carrier concentration region 4 both extending between the first main face 2a and the second main face 2b. The low carrier concentration region 5 has a carrier concentration of 10.sup.17/cm.sup.3 or lower and a defect density of 10.sup.7/cm.sup.2 or lower. The high carrier concentration region 4 has a carrier concentration of 10.sup.19/cm.sup.3 or higher and a defect density of 10.sup.8/cm.sup.2 or higher. The thick film 3 has a carrier concentration of 10.sup.18/cm.sup.3 or higher and 10.sup.19/cm.sup.3 or lower and a defect density of 10.sup.7/cm.sup.2 or lower.