A device includes a semiconductor substrate containing gallium nitride and having a crystal face inclined from 0.05 to 15 inclusive with respect to the c-plane. The semiconductor substrate includes an irregular portion on the crystal face, and the contact angle of pure water having a specific resistance of 18 M.Math.cm or more on the surface of the irregular portion is 10 or less.

A piezoelectric monocrystalline substrate is composed of a material represented by LiAO.sub.3 (A represents at least one element selected from the group consisting of niobium and tantalum), a bonding layer is compose of a material of an oxide of at least one element selected from the group consisting of niobium and tantalum, and an interface layer is provided along an interface between the piezoelectric monocrystalline substrate 6 and bonding layer, and the interface layer has a composition of E.sub.xO.sub.(1-x) (E represents at least one element selected from the group consisting of niobium and tantalum and 0.29x0.89).

It is provided first electrode piece part-arrays each comprising a plurality of electrode piece parts on a first main face of a ferroelectric crystal substrate. A voltage is applied on the first electrode piece part-arrays to form first periodic polarization inversion structures. It is provided second electrode piece part-arrays each comprising a plurality of electrode piece parts between the adjacent plural first periodic polarization inversion structures. A voltage is applied on the second electrode piece part-arrays to form second polarization inversion structures.

It is provided first electrode piece part-arrays each comprising a plurality of electrode piece parts on a first main face of a ferroelectric crystal substrate. A voltage is applied on the first electrode piece part-arrays to form first periodic polarization inversion structures. It is provided second electrode piece part-arrays each comprising a plurality of electrode piece parts between the adjacent plural first periodic polarization inversion structures. A voltage is applied on the second electrode piece part-arrays to form second polarization inversion structures.

A wafer is produced from an ingot by confirming whether or not an inclined c-axis of the ingot and a second orientation flat of the ingot are perpendicular to each other, and detecting a processing feed direction perpendicular to the direction in which the c-axis is inclined. The method includes performing sampling irradiation of the ingot with a laser beam, along a direction parallel to the second orientation flat and a plurality of directions inclined clockwise and counterclockwise by respective predetermined angles from the second orientation flat, thereby forming a plurality of sampled reduced strength areas in the ingot; measuring the number of nodes which exist per unit length on each of the sampled reduced strength areas, and determining a direction in which the sampled reduced strength area where the measured number of nodes is zero extends as a processing feed direction.

A wafer is produced from an ingot by confirming whether or not an inclined c-axis of the ingot and a second orientation flat of the ingot are perpendicular to each other, and detecting a processing feed direction perpendicular to the direction in which the c-axis is inclined. The method includes performing sampling irradiation of the ingot with a laser beam, along a direction parallel to the second orientation flat and a plurality of directions inclined clockwise and counterclockwise by respective predetermined angles from the second orientation flat, thereby forming a plurality of sampled reduced strength areas in the ingot; measuring the number of nodes which exist per unit length on each of the sampled reduced strength areas, and determining a direction in which the sampled reduced strength area where the measured number of nodes is zero extends as a processing feed direction.

A method for forming a silicon carbide material with a plurality of negatively charged silicon mono-vacancy defects includes irradiating a silicon carbide sample, annealing the irradiated silicon carbide sample in an annealing operation, and quenching the annealed silicon carbide sample. Quenching may include heating the annealed silicon carbide sample to a maximum temperature and quenching the annealed silicon carbide sample to form the silicon carbide sample with the plurality of negatively charged silicon mono-vacancy defects.

A method for forming a silicon carbide material with a plurality of negatively charged silicon mono-vacancy defects includes irradiating a silicon carbide sample, annealing the irradiated silicon carbide sample in an annealing operation, and quenching the annealed silicon carbide sample. Quenching may include heating the annealed silicon carbide sample to a maximum temperature and quenching the annealed silicon carbide sample to form the silicon carbide sample with the plurality of negatively charged silicon mono-vacancy defects.

A diamond smoothing method of irradiating a laser light onto a raised and recessed surface of a diamond, so as to smooth the raised and recessed surface, by ablation that is caused to occur in the diamond by irradiation of the laser light onto the raised and recessed surface. The method includes: a threshold-energy-density detecting step of irradiating the laser light onto the raised and recessed surface, and changing an irradiation energy density of the laser light, so as to detect a threshold energy density as a lower threshold value of the irradiation energy density that causes the ablation to occur; and a smoothing processing step of executing a smoothing processing by irradiating the laser light onto the raised and recessed surface with a smoothing irradiation energy density that is set to be within a range from 1 to 15 times as large as the threshold energy density.

A diamond smoothing method of irradiating a laser light onto a raised and recessed surface of a diamond, so as to smooth the raised and recessed surface, by ablation that is caused to occur in the diamond by irradiation of the laser light onto the raised and recessed surface. The method includes: a threshold-energy-density detecting step of irradiating the laser light onto the raised and recessed surface, and changing an irradiation energy density of the laser light, so as to detect a threshold energy density as a lower threshold value of the irradiation energy density that causes the ablation to occur; and a smoothing processing step of executing a smoothing processing by irradiating the laser light onto the raised and recessed surface with a smoothing irradiation energy density that is set to be within a range from 1 to 15 times as large as the threshold energy density.