A method for producing a wafer from a hexagonal single crystal ingot includes: planarizing an upper surface of the hexagonal single crystal ingot; applying a laser beam of such a wavelength as to be transmitted through the ingot, with a focal point positioned in an inside of a region not to be formed with devices of a wafer to be produced from the upper surface of the ingot which has been planarized, to form a production history; and applying a laser beam of such a wavelength as to be transmitted through the hexagonal single crystal ingot with a focal point of the laser beam positioned at a depth corresponding to a thickness of the wafer to be produced from the upper surface of the hexagonal single crystal ingot which has been planarized, to form an exfoliation layer.

A method for producing a wafer from a hexagonal single crystal ingot includes: planarizing an upper surface of the hexagonal single crystal ingot; applying a laser beam of such a wavelength as to be transmitted through the ingot, with a focal point positioned in an inside of a region not to be formed with devices of a wafer to be produced from the upper surface of the ingot which has been planarized, to form a production history; and applying a laser beam of such a wavelength as to be transmitted through the hexagonal single crystal ingot with a focal point of the laser beam positioned at a depth corresponding to a thickness of the wafer to be produced from the upper surface of the hexagonal single crystal ingot which has been planarized, to form an exfoliation layer.

A semiconductor stack includes a substrate made of silicon carbide, and an epi layer disposed on the substrate and made of silicon carbide. An epi principal surface, which is a principal surface opposite to the substrate, of the epi layer is a carbon surface having an off angle of 4 or smaller relative to a c-plane. In the epi principal surface, a plurality of first recessed portions having a rectangular circumferential shape in a planar view is formed. Density of a second recessed portion that is formed in the first recessed portions and is a recessed portion deeper than the first recessed portions is lower than or equal to 10 cm.sup.2 in the epi principal surface.

A semiconductor stack includes a substrate made of silicon carbide, and an epi layer disposed on the substrate and made of silicon carbide. An epi principal surface, which is a principal surface opposite to the substrate, of the epi layer is a carbon surface having an off angle of 4 or smaller relative to a c-plane. In the epi principal surface, a plurality of first recessed portions having a rectangular circumferential shape in a planar view is formed. Density of a second recessed portion that is formed in the first recessed portions and is a recessed portion deeper than the first recessed portions is lower than or equal to 10 cm.sup.2 in the epi principal surface.

A silicon carbide single crystal substrate includes a first main surface and an orientation flat. The orientation flat extends in a <11-20> direction. The first main surface includes an end region extending by at most 5 mm from an outer periphery of the first main surface. In a direction perpendicular to the first main surface, an amount of warpage of the end region continuous to the orientation flat is not greater than 3 m.

A silicon carbide single crystal substrate includes a first main surface and an orientation flat. The orientation flat extends in a <11-20> direction. The first main surface includes an end region extending by at most 5 mm from an outer periphery of the first main surface. In a direction perpendicular to the first main surface, an amount of warpage of the end region continuous to the orientation flat is not greater than 3 m.

The present invention comprises directionally solidified multicrystalline silicon ingots, a silicon masteralloy for increasing the efficiency of solar cells made from wafers cut from the silicon ingots, method for increasing the yield when producing multicrystalline silicon ingots from a silicon melt by directional solidification. Further the present invention comprises a method for preparing said silicon masteralloy.

A semiconductor stack includes a substrate made of silicon carbide, and an epi layer disposed on the substrate and made of silicon carbide. An epi principal surface, which is a principal surface opposite to the substrate, of the epi layer is a carbon surface having an off angle of 4 or smaller relative to a c-plane. In the epi principal surface, a plurality of first recessed portions having a rectangular circumferential shape in a planar view is formed. Density of a second recessed potion that is formed in the first recessed portions and is a recessed portion deeper than the first recessed portions is lower than or equal to 10 cm.sup.2 in the epi principal surface.

A semiconductor stack includes a substrate made of silicon carbide, and an epi layer disposed on the substrate and made of silicon carbide. An epi principal surface, which is a principal surface opposite to the substrate, of the epi layer is a carbon surface having an off angle of 4 or smaller relative to a c-plane. In the epi principal surface, a plurality of first recessed portions having a rectangular circumferential shape in a planar view is formed. Density of a second recessed potion that is formed in the first recessed portions and is a recessed portion deeper than the first recessed portions is lower than or equal to 10 cm.sup.2 in the epi principal surface.

The present invention relates to a composition comprising one or more perovskite precursors dissolved in a mixture of solvents comprising: i. one or more polar aprotic solvents, each selected in such a way that it can, when used in absence of other components, dissolve said one or more perovskite precursors, ii. one or more linear alcohols of general formula C.sub.nH.sub.2n+1OH, wherein n is from 1 to 12, and iii. optionally, one or more acids
wherein the polar aprotic solvent or mixture of polar aprotic solvents represent between 50 and 95 vol % of the mixture of solvents, wherein the vol % of the mixture of solvents not occupied by polar aprotic solvents is occupied for at least 90 vol %, preferably for 100 vol %, by the one or more linear alcohols, and the one or more acids if present.