A -Ga.sub.2O.sub.3-based single-crystal substrate includes a -Ga.sub.2O.sub.3-based single crystal, and a principal surface being a plane parallel to a b-axis of the -Ga.sub.2O.sub.3-based single crystal. A maximum value of on an arbitrary straight line on the principal surface that passes through a center of the principal surface is not more than 0.7264. The is a difference between a maximum value and a minimum value of values obtained by subtracting .sub.a from .sub.s at each of measurement positions, where .sub.s represents an angle defined by an X-ray incident direction and the principal surface at a peak position of an X-ray rocking curve on the straight line and .sub.a represents an angle on an approximated straight line obtained by using least-squares method to linearly approximate a curve representing a relationship between the .sub.s and the measurement positions thereof.

A -Ga.sub.2O.sub.3-based single-crystal substrate includes a -Ga.sub.2O.sub.3-based single crystal, and a principal surface being a plane parallel to a b-axis of the -Ga.sub.2O.sub.3-based single crystal. A maximum value of on an arbitrary straight line on the principal surface that passes through a center of the principal surface is not more than 0.7264. The is a difference between a maximum value and a minimum value of values obtained by subtracting .sub.a from .sub.s at each of measurement positions, where .sub.s represents an angle defined by an X-ray incident direction and the principal surface at a peak position of an X-ray rocking curve on the straight line and .sub.a represents an angle on an approximated straight line obtained by using least-squares method to linearly approximate a curve representing a relationship between the .sub.s and the measurement positions thereof.

A high withstand voltage Schottky barrier diode includes a first layer that includes a first Ga.sub.2O.sub.3-based single crystal including a first Group IV element and Cl at a concentration of not more than 510.sup.16 cm.sup.3 and that has an effective donor concentration of not less than 110.sup.13 and not more than 6.010.sup.17 cm.sup.3, a second layer that includes a second Ga.sub.2O.sub.3-based single crystal including a second Group IV element and that has a higher effective donor concentration than the first layer and is laminated on the first layer, an anode electrode formed on the first layer, and a cathode electrode formed on the second layer.

A high withstand voltage Schottky barrier diode includes a first layer that includes a first Ga.sub.2O.sub.3-based single crystal including a first Group IV element and Cl at a concentration of not more than 510.sup.16 cm.sup.3 and that has an effective donor concentration of not less than 110.sup.13 and not more than 6.010.sup.17 cm.sup.3, a second layer that includes a second Ga.sub.2O.sub.3-based single crystal including a second Group IV element and that has a higher effective donor concentration than the first layer and is laminated on the first layer, an anode electrode formed on the first layer, and a cathode electrode formed on the second layer.

In an embodiment, a method includes treating an edge region of a wafer including a substrate having an upper surface and one or more epitaxial Group III nitride layers arranged on the upper surface of the substrate, so as to remove material including at least one Group III element from the edge region.

In an embodiment, a method includes treating an edge region of a wafer including a substrate having an upper surface and one or more epitaxial Group III nitride layers arranged on the upper surface of the substrate, so as to remove material including at least one Group III element from the edge region.

A high withstand voltage Schottky barrier diode includes a first layer that includes a first Ga.sub.2O.sub.3-based single crystal including a first Group IV element and Cl at a concentration of not more than 510.sup.16 cm.sup.3 and that has an effective donor concentration of not less than 110.sup.13 and not more than 6.010.sup.17 cm.sup.3, a second layer that includes a second Ga.sub.2O.sub.3-based single crystal including a second Group IV element and that has a higher effective donor concentration than the first layer and is laminated on the first layer, an anode electrode formed on the first layer, and a cathode electrode formed on the second layer.

A high withstand voltage Schottky barrier diode includes a first layer that includes a first Ga.sub.2O.sub.3-based single crystal including a first Group IV element and Cl at a concentration of not more than 510.sup.16 cm.sup.3 and that has an effective donor concentration of not less than 110.sup.13 and not more than 6.010.sup.17 cm.sup.3, a second layer that includes a second Ga.sub.2O.sub.3-based single crystal including a second Group IV element and that has a higher effective donor concentration than the first layer and is laminated on the first layer, an anode electrode formed on the first layer, and a cathode electrode formed on the second layer.

Various single crystals are disclosed including sapphire. The single crystals have desirable geometric properties, including a width not less than about 15 cm and the thickness is not less than about 0.5 cm. The single crystal may also have other features, such as a maximum thickness variation, and as-formed crystals may have a generally symmetrical neck portion, particularly related to the transition from the neck to the main body of the crystal. Methods and for forming such crystals and an apparatus for carrying out the methods are disclosed as well.

Various single crystals are disclosed including sapphire. The single crystals have desirable geometric properties, including a width not less than about 15 cm and the thickness is not less than about 0.5 cm. The single crystal may also have other features, such as a maximum thickness variation, and as-formed crystals may have a generally symmetrical neck portion, particularly related to the transition from the neck to the main body of the crystal. Methods and for forming such crystals and an apparatus for carrying out the methods are disclosed as well.