The present invention relates to a method for producing a group III compound substrate, including: a base substrate forming step for forming a group III nitride base substrate by a vapor phase synthesis method; a seed substrate forming step for forming a seed substrate on the base substrate; and a group III compound crystal forming step for forming a group III compound crystal on the seed substrate by a hydride vapor phase epitaxy method. The group III compound substrate of the present invention is produced by the method for producing a group III compound substrate of the present invention. According to the present invention, a large-sized and high-quality group III compound substrate can be obtained at a low cost while taking advantage of the high film formation rate characteristic of the hydride vapor phase epitaxy method.

A cover glass for an electronic display comprises a plurality of layers of sapphire material, each of the layers having a substantially single crystal plane orientation, with adjacent layers having different substantially single crystal plane orientations. One or more interface layers are defined between adjacent layers of the sapphire material, with the adjacent layers of sapphire material bonded together at the one or more interface layers. A display window is defined in the cover glass, and configured for viewing a viewable area of the electronic display through the plurality of layers of the sapphire material bonded together at the one or more interface layers.

A cover glass for an electronic display comprises a plurality of layers of sapphire material, each of the layers having a substantially single crystal plane orientation, with adjacent layers having different substantially single crystal plane orientations. One or more interface layers are defined between adjacent layers of the sapphire material, with the adjacent layers of sapphire material bonded together at the one or more interface layers. A display window is defined in the cover glass, and configured for viewing a viewable area of the electronic display through the plurality of layers of the sapphire material bonded together at the one or more interface layers.

A method for producing a Group III nitride crystal, includes: preparing an RAMO.sub.4 substrate containing a single crystal represented by the general formula RAMO.sub.4 (wherein R represents one or a plurality of trivalent elements selected from a group consisting of Sc, In, Y, and a lanthanoid element, A represents one or a plurality of trivalent elements selected from a group consisting of Fe(III), Ga, and Al, and M represents one or a plurality of divalent elements selected from a group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd) and having a notch on a side portion thereof; growing a Group III nitride crystal on the RAMO.sub.4 substrate; and cleaving the RAMO.sub.4 substrate from the notch.

An engineered substrate comprising: a seed layer made of a first semiconductor material for growth of a solar cell; a first bonding layer on the seed layer; a support substrate made of a second semiconductor material; a second bonding layer on a first side of the support substrate; a bonding interface between the first and second bonding layers; the first and second bonding layers each made of metallic material; wherein doping concentration and thickness of the engineered substrate, in particular, of the seed layer, the support substrate, and both the first and second bonding layers, are selected such that the absorption of the seed layer is less than 20%, preferably less than 10%, as well as total area-normalized series resistance of the engineered substrate is less than 10 mOhm.Math.cm.sup.2, preferably less than 5 mOhm.Math.cm.sup.2.

In an X-ray diffraction diagram of a cordierite sintered body of the present invention, the ratio of the total of the maximum peak intensities of components other than cordierite components to the peak top intensity of the (110) plane of cordierite is 0.0025 or less. Since having a significantly small amount of different phases other than the cordierite components, this cordierite sintered body has a high surface flatness when the surface thereof is mirror-polished.

In an X-ray diffraction diagram of a cordierite sintered body of the present invention, the ratio of the total of the maximum peak intensities of components other than cordierite components to the peak top intensity of the (110) plane of cordierite is 0.0025 or less. Since having a significantly small amount of different phases other than the cordierite components, this cordierite sintered body has a high surface flatness when the surface thereof is mirror-polished.

A composite substrate includes a sapphire substrate and a layer of a nitride of a group 13 element provided on the sapphire substrate. The layer of the nitride of the group 13 element is composed of gallium nitride, aluminum nitride or gallium aluminum nitride. The composite substrate satisfies the following formulas (1), (2) and (3). A laser light is irradiated to the composite substrate from the side of the sapphire substrate to decompose crystal lattice structure at an interface between the sapphire substrate and the layer of the nitride of the group 13 element. 5.0≦(an average thickness (μm) of the layer of the nitride of the group 13 element/a diameter (mm) of the sapphire substrate)≦10.0 . . . (1); 0.1≦ a warpage (mm) of said composite substrate×(50/a diameter (mm) of said composite substrate).sup.20.6 . . . (2); 1.10≦a maximum value (μm) of a thickness of said layer of said nitride of said group 13 element/a minimum value (μm) of said thickness of said layer of said nitride of said group 13 element . . . (3)

A substrate for an electronic device, including a nitride semiconductor film formed on a joined substrate including a silicon single crystal, where the joined substrate has a plurality of silicon single crystal substrates that are joined and has a thickness of more than 2000 μm, and the plurality of silicon single crystal substrates are produced by a CZ method and have a resistivity of 0.1 Ωcm or lower. This provides: a substrate for an electronic device having a nitride semiconductor film formed on a silicon substrate, where the substrate for an electronic device can suppress a warp and can also be used for a product with a high breakdown voltage; and a method for producing the same.

A composite that includes a base including an oxide layer MOx of an element M on a surface thereof and a diamond crystal base bonded to the surface of the base. The M is one or more selected from among metal elements capable of forming an oxide (excluding alkali metals and alkaline earth metals), Si, Ge, As, Se, Sb, Te, and Bi, and the diamond crystal base is bonded to the surface of the base by M-O-C bonding of at least some C atoms of the (111) surface of the diamond crystal base.