A nonlinear optical crystal of cesium fluorooxoborate, and a method of preparation and use thereof. The crystal has a chemical formula of CsB.sub.4O.sub.6F and a molecular weight of 291.15. It belongs to an orthorhombic crystal system, with a space group of Pna2.sub.1, crystal cell parameters of a=7.9241 , b=11.3996 , c=6.6638 , and ===90, and a unit cell volume of 601.95 .sup.3. A melt method, high temperature solution method, vacuum encapsulation method, hydrothermal method or room temperature solution method is used to grow the crystal of CsB.sub.4O.sub.6F.

It is an object of the present invention to provide a silicon carbide substrate having a low defect density that does not contaminate a process device and a silicon carbide semiconductor device including the silicon carbide substrate. A silicon carbide substrate according to the present invention is a silicon carbide substrate including: a substrate inner portion; and a substrate outer portion surrounding the substrate inner portion, wherein non-dopant metal impurity concentration of the substrate inner portion is 110.sup.16 cm.sup.3 or more, and a region of the substrate outer portion at least on a surface side thereof is a substrate surface region in which the non-dopant metal impurity concentration is less than 110.sup.16 cm.sup.3.

A low-resistance p-type SiC single crystal containing no inclusions is provided. A method for producing a SiC single crystal in which a SiC seed crystal substrate is contacted with a SiC solution having a temperature gradient such that a temperature of the SiC solution decreases from an interior of the SiC solution toward a surface of the SiC solution, to grow the SiC single crystal, wherein the SiC solution comprises Si, Cr, Al and B, and wherein the Al is comprised in the SiC solution in an amount of 10 at % or greater, based on the total of the Si, Cr, Al and B, and the B is comprised in the SiC solution in an amount of greater than 0.00 at % and no greater than 1.00 at %, based on the total of the Si, Cr, Al and B.

In a first step, protrusions (42) are formed on a surface of an SiC substrate (40), and the SiC substrate (40) is etched. In a second step, the protrusions (42) of the SiC substrate (40) are epitaxially grown through MSE process, and an epitaxial layer (43a) containing threading screw dislocation, which has been largely grown in the vertical (c-axis) direction as a result of MSE process, is at least partially removed. In a third step, MSE process is performed again on the SiC substrate (40) after the second step, to cause epitaxial layers (43) containing no threading screw dislocation to be grown in the horizontal (a-axis) direction to be connected at the molecular level, so that one monocrystalline 4HSiC semiconductor wafer (45) having a large area is generated throughout an Si-face or a C-face of the SiC substrate (40).

In a first step, protrusions (42) are formed on a surface of an SiC substrate (40), and the SiC substrate (40) is etched. In a second step, the protrusions (42) of the SiC substrate (40) are epitaxially grown through MSE process, and an epitaxial layer (43a) containing threading screw dislocation, which has been largely grown in the vertical (c-axis) direction as a result of MSE process, is at least partially removed. In a third step, MSE process is performed again on the SiC substrate (40) after the second step, to cause epitaxial layers (43) containing no threading screw dislocation to be grown in the horizontal (a-axis) direction to be connected at the molecular level, so that one monocrystalline 4HSiC semiconductor wafer (45) having a large area is generated throughout an Si-face or a C-face of the SiC substrate (40).

A method of producing a crystal includes a step of preparing a solution containing carbon and a silicon solvent, and a seed crystal of silicon carbide; a step of contacting a lower face of the seed crystal with the solution; a step of raising a temperature of the solution to a first temperature zone; a step of relatively elevating the seed crystal with respect to the solution in a state where a temperature of the solution is being lowered from the first temperature zone to a second temperature zone; a step of raising a temperature of the solution from the second temperature zone to the first temperature zone; and a step of relatively elevating the seed crystal with respect to the solution in a state where a temperature of the solution is being lowered from the first temperature zone to the second temperature zone.

A method of producing a crystal includes a step of preparing a solution containing carbon and a silicon solvent, and a seed crystal of silicon carbide; a step of contacting a lower face of the seed crystal with the solution; a step of raising a temperature of the solution to a first temperature zone; a step of relatively elevating the seed crystal with respect to the solution in a state where a temperature of the solution is being lowered from the first temperature zone to a second temperature zone; a step of raising a temperature of the solution from the second temperature zone to the first temperature zone; and a step of relatively elevating the seed crystal with respect to the solution in a state where a temperature of the solution is being lowered from the first temperature zone to the second temperature zone.

Provided are a Faraday rotator having a high light transmittance and a high Verdet constant and an optical isolator using the same. The Faraday rotator of the present invention contains a garnet type crystal represented by (Tb.sub.3-x-yR.sub.xBi.sub.y)Al.sub.5O.sub.12 (R represents one or more elements selected from Y, Er, Yb, or Lu, 0<x, and 0y). It is preferable that the Faraday rotator contains a garnet type crystal represented by (Tb.sub.3-x-yR.sub.xBi.sub.y)Al.sub.5O.sub.12 (R is one or more elements selected from Y or a lanthanoid (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu), 0x, and 0<y)).

Provided are a practical method for manufacturing TAG single crystal. The method of manufacturing a garnet type crystal brings a raw material solution into contact with a substrate formed of a Y.sub.3Al.sub.5O.sub.12 crystal or a Dy.sub.3Al.sub.5O.sub.12 crystal and performs liquid phase epitaxial growth. The garnet type crystal is represented by (Tb.sub.3-x-yR.sub.xBi.sub.y) Al.sub.5O.sub.12 (R is one or more elements selected from Y or a lanthanoid (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu), 0x, and 0y)).

A high-quality SiC single crystal and a method for producing such a SiC single crystal is provided. In the SiC single crystal, the threading dislocation density including screw dislocation, edge dislocation and micropipe defect is reduced. The method for producing the SiC single crystal according to a solution technique involves bringing an SiC seed crystal into contact with an SiC solution having a temperature gradient in which a temperature of the SiC solution is lower towards the surface of the SiC seed crystal. Growing an SiC single crystal includes setting the temperature gradient of the surface region of the SiC solution to 10 C/cm or below, bringing the (1-100) face of the SiC seed crystal into contact with the SiC solution, and growing an SiC single crystal on the (1-100) face of the seed crystal at a ratio (single crystal growth rate/temperature gradient) of less than 2010.sup.4 cm.sup.2/h.Math. C.