An epitaxial nitride semiconductor is formed over a buffer layer and over a silicon single crystal substrate. A misfit dislocation layer in the silicon single crystal substrate mitigates distortion due to lattice mismatch generated during epitaxial growth of the nitride semiconductor and thermal distortion due to difference in the thermal expansion coefficient occurring during the cooling process after epitaxial growth of the nitride semiconductor. The resulting nitride semiconductor substrate has excellent crystallinity without the occurrence of cracks or large warpage.

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.

A method of manufacturing a graphene-baseddevice, comprising (i) providing a graphene assembly comprising one or more layers of graphene, a first photoresist layer disposed on the one or more layers of graphene, and an ultra-violet (UV) barrier layer disposed on the photoresist layer on an opposite side to the one or more layers of graphene; (ii) transferring the graphene assembly onto a substrate comprising at least one cavity so that the one or more layers of graphene traverse the at least one cavity; (iii) using photolithography to expose portions of the one or morelayers of graphene on opposite sides of the at least one cavity;(iv) forming conductive contacts over the exposed portions of graphene; (v) removing the UV barrier layer; and (vi) removing the first photoresist layer.

A method forms one or more diamonds. The method provides a growth chamber having a gas environment. A single crystal diamond substrate is positioned within the growth chamber. Diamond material is deposited on the single crystal diamond substrate for epitaxial growth. The single crystal diamond substrate has a given crystal orientation. Growth is continued at a prescribed temperature, prescribed pressure, and with a prescribed gas content for the gas environment. The prescribed gas environment has a nitrogen concentration of greater than about 0.5 ppm and less than about 5.0 ppm. The prescribed temperature is greater than about 650 degrees C. and less than about 950 degrees C. The prescribed pressure is greater than about 130 Torr and less than about 175 Torr.

A method forms one or more diamonds. The method provides a growth chamber having a gas environment. A single crystal diamond substrate is positioned within the growth chamber. Diamond material is deposited on the single crystal diamond substrate for epitaxial growth. The single crystal diamond substrate has a given crystal orientation. Growth is continued at a prescribed temperature, prescribed pressure, and with a prescribed gas content for the gas environment. The prescribed gas environment has a nitrogen concentration of greater than about 0.5 ppm and less than about 5.0 ppm. The prescribed temperature is greater than about 650 degrees C. and less than about 950 degrees C. The prescribed pressure is greater than about 130 Torr and less than about 175 Torr.

A method of forming a plurality of diamonds provides a base, epitaxially forms a first sacrificial layer on the base, and then epitaxially forms a first diamond layer on the first sacrificial layer. The first sacrificial layer has a first material composition, and the first diamond layer is a material that is different from the first material composition. The method then epitaxially forms a second sacrificial layer on the first diamond layer, and epitaxially forms a second diamond layer on the second sacrificial layer. The second sacrificial layer has the first material composition. The base, first and second sacrificial layers, and first and second diamond layers form a heteroepitaxial super-lattice.

A method of forming a plurality of diamonds provides a base, epitaxially forms a first sacrificial layer on the base, and then epitaxially forms a first diamond layer on the first sacrificial layer. The first sacrificial layer has a first material composition, and the first diamond layer is a material that is different from the first material composition. The method then epitaxially forms a second sacrificial layer on the first diamond layer, and epitaxially forms a second diamond layer on the second sacrificial layer. The second sacrificial layer has the first material composition. The base, first and second sacrificial layers, and first and second diamond layers form a heteroepitaxial super-lattice.

A method of forming a plurality of diamonds provides a base, epitaxially forms a first sacrificial layer on the base, and then epitaxially forms a first diamond layer on the first sacrificial layer. The first sacrificial layer has a first material composition, and the first diamond layer is a material that is different from the first material composition. The method then epitaxially forms a second sacrificial layer on the first diamond layer, and epitaxially forms a second diamond layer on the second sacrificial layer. The second sacrificial layer has the first material composition. The base, first and second sacrificial layers, and first and second diamond layers form a heteroepitaxial super-lattice.

A method of forming a plurality of diamonds provides a base, epitaxially forms a first sacrificial layer on the base, and then epitaxially forms a first diamond layer on the first sacrificial layer. The first sacrificial layer has a first material composition, and the first diamond layer is a material that is different from the first material composition. The method then epitaxially forms a second sacrificial layer on the first diamond layer, and epitaxially forms a second diamond layer on the second sacrificial layer. The second sacrificial layer has the first material composition. The base, first and second sacrificial layers, and first and second diamond layers form a heteroepitaxial super-lattice.