To reach high efficiencies, thermophotovoltaic cells must utilize the broad spectrum of a radiative thermal source. One promising approach to overcome this challenge is to have low-energy photons reflected and reabsorbed by the thermal emitter, where their energy can have another chance at contributing toward photogeneration in the cell. However, current methods for photon recuperation are limited by insufficient bandwidth or parasitic absorption, resulting in large efficiency losses relative to theoretical limits. This work demonstrates nearly perfect reflection of low-energy photons (˜99%) by embedding an air layer within the TPV cell. This result represents a four-fold reduction in parasitic absorption relative to existing TPV cells. As out-of-band reflectance approaches unity, TPV efficiency becomes nearly insensitive to cell bandgap and emitter temperature. Accessing this regime unlocks a range of possible materials and heat sources that were previously inaccessible to TPV energy conversion.

To reach high efficiencies, thermophotovoltaic cells must utilize the broad spectrum of a radiative thermal source. One promising approach to overcome this challenge is to have low-energy photons reflected and reabsorbed by the thermal emitter, where their energy can have another chance at contributing toward photogeneration in the cell. However, current methods for photon recuperation are limited by insufficient bandwidth or parasitic absorption, resulting in large efficiency losses relative to theoretical limits. This work demonstrates nearly perfect reflection of low-energy photons (˜99%) by embedding an air layer within the TPV cell. This result represents a four-fold reduction in parasitic absorption relative to existing TPV cells. As out-of-band reflectance approaches unity, TPV efficiency becomes nearly insensitive to cell bandgap and emitter temperature. Accessing this regime unlocks a range of possible materials and heat sources that were previously inaccessible to TPV energy conversion.

There is provided a nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is a (0001) plane, wherein X-ray locking curve measurement for (0002) plane diffraction, which is performed to the main surface by irradiating with (Cu) Kα1 X-rays through a two-crystal monochromator of Ge (220) plane and a slit, reveals that full width at half maximum FWHMb is 32 arcsec or less, and FWHMa−FWHMb obtained by subtracting FWHMb from FWHMa is 30% or less of FWHMa, wherein FWHMa is full width at half maximum of the (0002) plane diffraction when a slit width in ω direction is 1 mm, and FWHMb is full width at half maximum of the (0002) plane diffraction when a slit width in ω direction is 0.1 mm.

There is provided a nitride semiconductor substrate having a diameter of 2 inches or more and having a main surface whose closest low index crystal plane is a (0001) plane, wherein X-ray locking curve measurement for (0002) plane diffraction, which is performed to the main surface by irradiating with (Cu) Kα1 X-rays through a two-crystal monochromator of Ge (220) plane and a slit, reveals that full width at half maximum FWHMb is 32 arcsec or less, and FWHMa−FWHMb obtained by subtracting FWHMb from FWHMa is 30% or less of FWHMa, wherein FWHMa is full width at half maximum of the (0002) plane diffraction when a slit width in ω direction is 1 mm, and FWHMb is full width at half maximum of the (0002) plane diffraction when a slit width in ω direction is 0.1 mm.

A method making it possible to obtain, on an upper surface of a crystalline substrate, a semipolar layer of nitride material comprising any one from among gallium, aluminium or indium, the method comprises the following steps: obtaining, on the upper surface of the crystalline substrate, a plurality of parallel grooves which extend in a first direction, one of the two opposite facets exhibiting a crystal orientation; etching a plurality of parallel slices which extend in a second direction that has undergone a rotation with respect to the first direction of the grooves in such a way as to obtain individual facets exhibiting a crystal orientation; epitaxial growth of the material from the individual facets.

A method making it possible to obtain, on an upper surface of a crystalline substrate, a semipolar layer of nitride material comprising any one from among gallium, aluminium or indium, the method comprises the following steps: obtaining, on the upper surface of the crystalline substrate, a plurality of parallel grooves which extend in a first direction, one of the two opposite facets exhibiting a crystal orientation; etching a plurality of parallel slices which extend in a second direction that has undergone a rotation with respect to the first direction of the grooves in such a way as to obtain individual facets exhibiting a crystal orientation; epitaxial growth of the material from the individual facets.

The disclosure provides a film forming method that enables to obtain an epitaxial film with reduced defects such as dislocations due to a reduced facet growth industrially advantageously, even if the epitaxial film has a corundum structure. When forming an epitaxial film on a crystal-growth surface of a corundum-structured crystal substrate directly or via another layer, using the crystal substrate having an uneven portion on the crystal-growth surface of the crystal substrate, generating and floating atomized droplets by atomizing a raw material solution including a metal; carrying the floated atomized droplets onto a surface of the crystal substrate by using a carrier gas; and causing a thermal reaction of the atomized droplets in a condition of a supply rate limiting state.

A method for manufacturing a diamond substrate, including: a first step of preparing patterned diamond on a foundation surface, a second step of growing diamond from the patterned diamond prepared in the first step to form the diamond in a pattern gap of the patterned diamond prepared in the first step, a third step of removing the patterned diamond prepared in the first step to form a patterned diamond composed of the diamond formed in the second step, and a fourth step of growing diamond from the patterned diamond formed in the third step to form the diamond in a pattern gap of the patterned diamond formed in the third step. There can be provided a method for manufacturing a diamond substrate which can sufficiently suppress dislocation defects, a high-quality diamond substrate, and a freestanding diamond substrate.

A method for manufacturing a diamond substrate, including: a first step of preparing patterned diamond on a foundation surface, a second step of growing diamond from the patterned diamond prepared in the first step to form the diamond in a pattern gap of the patterned diamond prepared in the first step, a third step of removing the patterned diamond prepared in the first step to form a patterned diamond composed of the diamond formed in the second step, and a fourth step of growing diamond from the patterned diamond formed in the third step to form the diamond in a pattern gap of the patterned diamond formed in the third step. There can be provided a method for manufacturing a diamond substrate which can sufficiently suppress dislocation defects, a high-quality diamond substrate, and a freestanding diamond substrate.

A method of removing semiconducting layers from a substrate, in particular, III-nitride-based semiconductor layers from a III-nitride-based substrate, with an attached film, using a peeling technique. The method comprises forming the semiconductor layers into island-like patterns on the substrate via an epitaxial lateral overgrowth method, with a horizontal trench extending inwards from the sides of the layers. Stress is induced in the layers by raising or lowering the temperature, and applying pressure to the attached film, such that the film firmly fits a shape of the layers. Differences in thermal expansion between the substrate and the film attached to the layers initiates a crack at an interface between the layers and the substrate, so that the layers can be removed from the substrate. Once the layers are removed, the substrate can be recycled, resulting in cost savings for device fabrication.