A Gunn diode comprising a. a GaN substrate i. having n-type conduction and ii. having a first major side, a second major side on an opposite side of the substrate, a first termination edge at an end of the substrate, a second termination edge at an opposite end of the substrate, a first lateral boundary at a side of the substrate, and a second lateral boundary at an opposite side of the substrate, and iii. having a refractive index n at the emission wave-length, λ, b. an anode contact on the first major side of the GaN substrate, c. a n-GaN active layer residing on the second major side of the substrate, and d. a cathode so that the Gunn diode is configured to emit the terahertz wave formed on the second major side of the GaN substrate, wherein: a length, a width, a thick-ness, and the refractive index of the GaN substrate define a slab waveguide for the terahertz wave such that the Gunn diode emits the terahertz wave from a first termination edge of the slab waveguide during opera-tion, the first termination edge of the slab waveguide corresponding to a plane of the first termination edge of the substrate and a second termination edge of the slab waveguide corresponding to a plane of the second termination edge of the substrate.

A Gunn diode according to paragraph 1, wherein the n-GaN active layer has an electron saturation velocity of Vsat, and the thickness t of the active layer is provided by the equation t=λVsat/c, wherein c is the speed of light.

A Gunn diode according to paragraph 1 or paragraph 2, wherein the Gunn diode further comprises a contact layer of n+-GaN on a top of the n-GaN active layer, a passiva-tion layer with a contact hole in the contact layer, and a portion of the metal cathode contact in electrical contact with the n-GaN active layer through the contact hole, wherein the cross-sectional area of the contact hole is less than 0.01 mm2.

A Gunn diode according to paragraph 3, wherein the n-GaN active layer and the contact layer are electrically insulating due to ions implanted within the active layer and the contact layer.

A Gunn diode according to paragraph 4, wherein the ions comprise at least one member selected from the set comprised of nitrogen, magnesium, carbon, iron, and manganese ions.

A Gunn diode according to any one of paragraphs 3-5, wherein the n-GaN active layer and the n+-GaN contact layer additionally form a mesa extending through the passivation layer from the GaN substrate to a portion of the metal cathode contact that is in electrical contact with the n+-GaN contact layer of the mesa through the contact hole in the passivation layer.

A Gunn diode according to any one of paragraphs 1-6, wherein a longitudinal dimension L of the Gunn diode is 60 a multiple of λ/2n.

A Gunn diode according to any one of paragraphs 1-7, wherein the slab waveguide has a width W that provides a single mode transmission of the terahertz wave during operation.

A Gunn diode according to any one of paragraphs 1-8, wherein the contact hole is located at L/2 where L is the B₂ distance between the first and second termination edges of the waveguide and W/2, where W is the distance between first and second lateral boundaries of the waveguide.

A Gunn diode according to any one of paragraphs 1-9, wherein the anode contact has a periodic pattern perpen-dicular to the longitudinal dimension with a periodicity of λ/2n.

A Gunn diode according to any one of paragraphs 1-10, wherein the GaN substrate has dislocation density less than 1×106 cm⁻².

A Gunn diode according to any one of paragraphs 1-11, wherein the GaN substrate is free of grain structure.

A Gunn diode according to any one of paragraphs 1-12, wherein the GaN substrate is made by an ammonothermal growth.

A Gunn diode according to any one of paragraphs 1-13, wherein the lateral direction of the waveguide is along an m-direction of the GaN substrate.

A Gunn diode according to any one of paragraphs 1-14, and further comprising a wave reflector adjacent to the second termination edge of the slab waveguide.

A Gunn diode according to paragraph 15, wherein the reflector is a Bragg reflector comprised of a set of plates adjacent to the second termination edge of the substrate, wherein the plates have an identical material composition to the materials of the Gunn diode at the second termi-nation edge of the substrate and immediately adjacent to the set of plates, and the set of plates have air gaps between adjacent plates of the set of width λ/4.

A Gunn diode according to any paragraph above, wherein the cathode has an exposed surface that is planar across the entire surface.

A terahertz oscillator comprising a Gunn diode of any paragraph above and a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator comprising a Gunn diode of any one of paragraphs 1-14 and a wave reflector comprised of one or more metal walls, with an air gap between a first of the metal walls and the second termination edge of the substrate of width λ/4.

A terahertz oscillator according to paragraph 19, wherein the one or more metal walls of the wave reflector are secured to a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator according to any one of paragraphs 18-20, wherein a metal bond layer resides between the cathode and the conductive base and the GaN substrate has a sufficient thickness that a volume of the GaN substrate through which current flows acts as a vertical antenna in operation.

A terahertz oscillator according to paragraph 21, wherein the GaN substrate has a thickness T of 5/λ4n or 9λ/4n. A Gunn diode may, of course, emit at a frequency that is not within the range of terahertz waves whereas a terahertz oscillator is configured to emit at a frequency within the range of terahertz waves. Possible Modifications Although the preferred embodiment uses Ti/Al/Ti/Au as cathode contact and Ti/In/Ti/Au as anode contact, other stack of metals such as Ti/Al/Ni/Au, Ti/Al/Pd/Au, Ti/Al/Pt/Au, Ti/Al/Mo/Au, Ti/Al/Re/Au, and Ti/Al/Ir/Au. Although the preferred embodiment uses MOCVD as a growth method of GaN layers, other methods such molecu-lar beam epitaxy (MBE) can be used. Although the preferred embodiment grew GaN layers on the entire surface of the GaN substrate, these layers can be grown on a limited area of the GaN substrate. Although the preferred embodiment uses ion-implanta-tion to create a current-confinement structure, mesa-struc-ture using etching of the n-GaN active layer, and n+-GaN contact layer can be used to create a current-confinement structure. The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illus-tration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. All references discussed herein are incorporated by ref-erence in their entirety as if put forth in full below and for all purposes (e.g. to satisfy any statutory requirements such as written description for any features and combination of features described in the references; to further explain points herein; to provide background information for additional understanding of the invention in context; and so forth). Although the Example 1 showed a device with a contact hole of 10 micron in diameter, the size of the contact hole can be larger or smaller depending on the required power output and heat management design of the devices. What is claimed is:

A Gunn diode comprising a. a GaN substrate i. having n-type conduction and ii. having a first major side, a second major side on an opposite side of the substrate, a first termination edge at an end of the substrate, a second termination edge at an opposite end of the substrate, a first lateral boundary at a side of the substrate, and a second lateral boundary at an opposite side of the substrate, and iii. having a refractive index n at the emission wave-length, λ, b. an anode contact on the first major side of the GaN substrate, c. a n-GaN active layer residing on the second major side of the substrate, and d. a cathode so that the Gunn diode is configured to emit the terahertz wave formed on the second major side of the GaN substrate, wherein: a length, a width, a thick-ness, and the refractive index of the GaN substrate define a slab waveguide for the terahertz wave such that the Gunn diode emits the terahertz wave from a first termination edge of the slab waveguide during opera-tion, the first termination edge of the slab waveguide corresponding to a plane of the first termination edge of the substrate and a second termination edge of the slab waveguide corresponding to a plane of the second termination edge of the substrate.

A Gunn diode according to paragraph 1, wherein the n-GaN active layer has an electron saturation velocity of Vsat, and the thickness t of the active layer is provided by the equation t=λVsat/c, wherein c is the speed of light.

A Gunn diode according to paragraph 1 or paragraph 2, wherein the Gunn diode further comprises a contact layer of n+-GaN on a top of the n-GaN active layer, a passiva-tion layer with a contact hole in the contact layer, and a portion of the metal cathode contact in electrical contact with the n-GaN active layer through the contact hole, wherein the cross-sectional area of the contact hole is less than 0.01 mm2.

A Gunn diode according to paragraph 3, wherein the n-GaN active layer and the contact layer are electrically insulating due to ions implanted within the active layer and the contact layer.

A Gunn diode according to paragraph 4, wherein the ions comprise at least one member selected from the set comprised of nitrogen, magnesium, carbon, iron, and manganese ions.

A Gunn diode according to any one of paragraphs 3-5, wherein the n-GaN active layer and the n+-GaN contact layer additionally form a mesa extending through the passivation layer from the GaN substrate to a portion of the metal cathode contact that is in electrical contact with the n+-GaN contact layer of the mesa through the contact hole in the passivation layer.

A Gunn diode according to any one of paragraphs 1-6, wherein a longitudinal dimension L of the Gunn diode is 60 a multiple of λ/2n.

A Gunn diode according to any one of paragraphs 1-7, wherein the slab waveguide has a width W that provides a single mode transmission of the terahertz wave during operation.

A Gunn diode according to any one of paragraphs 1-8, wherein the contact hole is located at L/2 where L is the B₂ distance between the first and second termination edges of the waveguide and W/2, where W is the distance between first and second lateral boundaries of the waveguide.

A Gunn diode according to any one of paragraphs 1-9, wherein the anode contact has a periodic pattern perpen-dicular to the longitudinal dimension with a periodicity of λ/2n.

A Gunn diode according to any one of paragraphs 1-10, wherein the GaN substrate has dislocation density less than 1×106 cm⁻².

A Gunn diode according to any one of paragraphs 1-11, wherein the GaN substrate is free of grain structure.

A Gunn diode according to any one of paragraphs 1-12, wherein the GaN substrate is made by an ammonothermal growth.

A Gunn diode according to any one of paragraphs 1-13, wherein the lateral direction of the waveguide is along an m-direction of the GaN substrate.

A Gunn diode according to any one of paragraphs 1-14, and further comprising a wave reflector adjacent to the second termination edge of the slab waveguide.

A Gunn diode according to paragraph 15, wherein the reflector is a Bragg reflector comprised of a set of plates adjacent to the second termination edge of the substrate, wherein the plates have an identical material composition to the materials of the Gunn diode at the second termi-nation edge of the substrate and immediately adjacent to the set of plates, and the set of plates have air gaps between adjacent plates of the set of width λ/4.

A Gunn diode according to any paragraph above, wherein the cathode has an exposed surface that is planar across the entire surface.

A terahertz oscillator comprising a Gunn diode of any paragraph above and a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator comprising a Gunn diode of any one of paragraphs 1-14 and a wave reflector comprised of one or more metal walls, with an air gap between a first of the metal walls and the second termination edge of the substrate of width λ/4.

A terahertz oscillator according to paragraph 19, wherein the one or more metal walls of the wave reflector are secured to a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator according to any one of paragraphs 18-20, wherein a metal bond layer resides between the cathode and the conductive base and the GaN substrate has a sufficient thickness that a volume of the GaN substrate through which current flows acts as a vertical antenna in operation.

A terahertz oscillator according to paragraph 21, wherein the GaN substrate has a thickness T of 5/λ4n or 9λ/4n. A Gunn diode may, of course, emit at a frequency that is not within the range of terahertz waves whereas a terahertz oscillator is configured to emit at a frequency within the range of terahertz waves. Possible Modifications Although the preferred embodiment uses Ti/Al/Ti/Au as cathode contact and Ti/In/Ti/Au as anode contact, other stack of metals such as Ti/Al/Ni/Au, Ti/Al/Pd/Au, Ti/Al/Pt/Au, Ti/Al/Mo/Au, Ti/Al/Re/Au, and Ti/Al/Ir/Au. Although the preferred embodiment uses MOCVD as a growth method of GaN layers, other methods such molecu-lar beam epitaxy (MBE) can be used. Although the preferred embodiment grew GaN layers on the entire surface of the GaN substrate, these layers can be grown on a limited area of the GaN substrate. Although the preferred embodiment uses ion-implanta-tion to create a current-confinement structure, mesa-struc-ture using etching of the n-GaN active layer, and n+-GaN contact layer can be used to create a current-confinement structure. The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illus-tration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. All references discussed herein are incorporated by ref-erence in their entirety as if put forth in full below and for all purposes (e.g. to satisfy any statutory requirements such as written description for any features and combination of features described in the references; to further explain points herein; to provide background information for additional understanding of the invention in context; and so forth). Although the Example 1 showed a device with a contact hole of 10 micron in diameter, the size of the contact hole can be larger or smaller depending on the required power output and heat management design of the devices. What is claimed is:

A Gunn diode comprising a. a GaN substrate i. having n-type conduction and ii. having a first major side, a second major side on an opposite side of the substrate, a first termination edge at an end of the substrate, a second termination edge at an opposite end of the substrate, a first lateral boundary at a side of the substrate, and a second lateral boundary at an opposite side of the substrate, and iii. having a refractive index n at the emission wave-length, λ, b. an anode contact on the first major side of the GaN substrate, c. a n-GaN active layer residing on the second major side of the substrate, and d. a cathode so that the Gunn diode is configured to emit the terahertz wave formed on the second major side of the GaN substrate, wherein: a length, a width, a thick-ness, and the refractive index of the GaN substrate define a slab waveguide for the terahertz wave such that the Gunn diode emits the terahertz wave from a first termination edge of the slab waveguide during opera-tion, the first termination edge of the slab waveguide corresponding to a plane of the first termination edge of the substrate and a second termination edge of the slab waveguide corresponding to a plane of the second termination edge of the substrate.

A Gunn diode according to paragraph 1, wherein the n-GaN active layer has an electron saturation velocity of Vsat, and the thickness t of the active layer is provided by the equation t=λVsat/c, wherein c is the speed of light.

A Gunn diode according to paragraph 1 or paragraph 2, wherein the Gunn diode further comprises a contact layer of n+-GaN on a top of the n-GaN active layer, a passiva-tion layer with a contact hole in the contact layer, and a portion of the metal cathode contact in electrical contact with the n-GaN active layer through the contact hole, wherein the cross-sectional area of the contact hole is less than 0.01 mm2.

A Gunn diode according to paragraph 3, wherein the n-GaN active layer and the contact layer are electrically insulating due to ions implanted within the active layer and the contact layer.

A Gunn diode according to paragraph 4, wherein the ions comprise at least one member selected from the set comprised of nitrogen, magnesium, carbon, iron, and manganese ions.

A Gunn diode according to any one of paragraphs 3-5, wherein the n-GaN active layer and the n+-GaN contact layer additionally form a mesa extending through the passivation layer from the GaN substrate to a portion of the metal cathode contact that is in electrical contact with the n+-GaN contact layer of the mesa through the contact hole in the passivation layer.

A Gunn diode according to any one of paragraphs 1-6, wherein a longitudinal dimension L of the Gunn diode is 60 a multiple of λ/2n.

A Gunn diode according to any one of paragraphs 1-7, wherein the slab waveguide has a width W that provides a single mode transmission of the terahertz wave during operation.

A Gunn diode according to any one of paragraphs 1-8, wherein the contact hole is located at L/2 where L is the B₂ distance between the first and second termination edges of the waveguide and W/2, where W is the distance between first and second lateral boundaries of the waveguide.

A Gunn diode according to any one of paragraphs 1-9, wherein the anode contact has a periodic pattern perpen-dicular to the longitudinal dimension with a periodicity of λ/2n.

A Gunn diode according to any one of paragraphs 1-10, wherein the GaN substrate has dislocation density less than 1×106 cm⁻².

A Gunn diode according to any one of paragraphs 1-11, wherein the GaN substrate is free of grain structure.

A Gunn diode according to any one of paragraphs 1-12, wherein the GaN substrate is made by an ammonothermal growth.

A Gunn diode according to any one of paragraphs 1-13, wherein the lateral direction of the waveguide is along an m-direction of the GaN substrate.

A Gunn diode according to any one of paragraphs 1-14, and further comprising a wave reflector adjacent to the second termination edge of the slab waveguide.

A Gunn diode according to paragraph 15, wherein the reflector is a Bragg reflector comprised of a set of plates adjacent to the second termination edge of the substrate, wherein the plates have an identical material composition to the materials of the Gunn diode at the second termi-nation edge of the substrate and immediately adjacent to the set of plates, and the set of plates have air gaps between adjacent plates of the set of width λ/4.

A Gunn diode according to any paragraph above, wherein the cathode has an exposed surface that is planar across the entire surface.

A terahertz oscillator comprising a Gunn diode of any paragraph above and a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator comprising a Gunn diode of any one of paragraphs 1-14 and a wave reflector comprised of one or more metal walls, with an air gap between a first of the metal walls and the second termination edge of the substrate of width λ/4.

A terahertz oscillator according to paragraph 19, wherein the one or more metal walls of the wave reflector are secured to a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator according to any one of paragraphs 18-20, wherein a metal bond layer resides between the cathode and the conductive base and the GaN substrate has a sufficient thickness that a volume of the GaN substrate through which current flows acts as a vertical antenna in operation.

A terahertz oscillator according to paragraph 21, wherein the GaN substrate has a thickness T of 5/λ4n or 9λ/4n. A Gunn diode may, of course, emit at a frequency that is not within the range of terahertz waves whereas a terahertz oscillator is configured to emit at a frequency within the range of terahertz waves. Possible Modifications Although the preferred embodiment uses Ti/Al/Ti/Au as cathode contact and Ti/In/Ti/Au as anode contact, other stack of metals such as Ti/Al/Ni/Au, Ti/Al/Pd/Au, Ti/Al/Pt/Au, Ti/Al/Mo/Au, Ti/Al/Re/Au, and Ti/Al/Ir/Au. Although the preferred embodiment uses MOCVD as a growth method of GaN layers, other methods such molecu-lar beam epitaxy (MBE) can be used. Although the preferred embodiment grew GaN layers on the entire surface of the GaN substrate, these layers can be grown on a limited area of the GaN substrate. Although the preferred embodiment uses ion-implanta-tion to create a current-confinement structure, mesa-struc-ture using etching of the n-GaN active layer, and n+-GaN contact layer can be used to create a current-confinement structure. The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illus-tration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. All references discussed herein are incorporated by ref-erence in their entirety as if put forth in full below and for all purposes (e.g. to satisfy any statutory requirements such as written description for any features and combination of features described in the references; to further explain points herein; to provide background information for additional understanding of the invention in context; and so forth). Although the Example 1 showed a device with a contact hole of 10 micron in diameter, the size of the contact hole can be larger or smaller depending on the required power output and heat management design of the devices. What is claimed is:

A Gunn diode comprising a. a GaN substrate i. having n-type conduction and ii. having a first major side, a second major side on an opposite side of the substrate, a first termination edge at an end of the substrate, a second termination edge at an opposite end of the substrate, a first lateral boundary at a side of the substrate, and a second lateral boundary at an opposite side of the substrate, and iii. having a refractive index n at the emission wave-length, λ, b. an anode contact on the first major side of the GaN substrate, c. a n-GaN active layer residing on the second major side of the substrate, and d. a cathode so that the Gunn diode is configured to emit the terahertz wave formed on the second major side of the GaN substrate, wherein: a length, a width, a thick-ness, and the refractive index of the GaN substrate define a slab waveguide for the terahertz wave such that the Gunn diode emits the terahertz wave from a first termination edge of the slab waveguide during opera-tion, the first termination edge of the slab waveguide corresponding to a plane of the first termination edge of the substrate and a second termination edge of the slab waveguide corresponding to a plane of the second termination edge of the substrate.

A Gunn diode according to paragraph 1, wherein the n-GaN active layer has an electron saturation velocity of Vsat, and the thickness t of the active layer is provided by the equation t=λVsat/c, wherein c is the speed of light.

A Gunn diode according to paragraph 1 or paragraph 2, wherein the Gunn diode further comprises a contact layer of n+-GaN on a top of the n-GaN active layer, a passiva-tion layer with a contact hole in the contact layer, and a portion of the metal cathode contact in electrical contact with the n-GaN active layer through the contact hole, wherein the cross-sectional area of the contact hole is less than 0.01 mm2.

A Gunn diode according to paragraph 3, wherein the n-GaN active layer and the contact layer are electrically insulating due to ions implanted within the active layer and the contact layer.

A Gunn diode according to paragraph 4, wherein the ions comprise at least one member selected from the set comprised of nitrogen, magnesium, carbon, iron, and manganese ions.

A Gunn diode according to any one of paragraphs 3-5, wherein the n-GaN active layer and the n+-GaN contact layer additionally form a mesa extending through the passivation layer from the GaN substrate to a portion of the metal cathode contact that is in electrical contact with the n+-GaN contact layer of the mesa through the contact hole in the passivation layer.

A Gunn diode according to any one of paragraphs 1-6, wherein a longitudinal dimension L of the Gunn diode is 60 a multiple of λ/2n.

A Gunn diode according to any one of paragraphs 1-7, wherein the slab waveguide has a width W that provides a single mode transmission of the terahertz wave during operation.

A Gunn diode according to any one of paragraphs 1-8, wherein the contact hole is located at L/2 where L is the B₂ distance between the first and second termination edges of the waveguide and W/2, where W is the distance between first and second lateral boundaries of the waveguide.

A Gunn diode according to any one of paragraphs 1-9, wherein the anode contact has a periodic pattern perpen-dicular to the longitudinal dimension with a periodicity of λ/2n.

A Gunn diode according to any one of paragraphs 1-10, wherein the GaN substrate has dislocation density less than 1×106 cm⁻².

A Gunn diode according to any one of paragraphs 1-11, wherein the GaN substrate is free of grain structure.

A Gunn diode according to any one of paragraphs 1-12, wherein the GaN substrate is made by an ammonothermal growth.

A Gunn diode according to any one of paragraphs 1-13, wherein the lateral direction of the waveguide is along an m-direction of the GaN substrate.

A Gunn diode according to any one of paragraphs 1-14, and further comprising a wave reflector adjacent to the second termination edge of the slab waveguide.

A Gunn diode according to paragraph 15, wherein the reflector is a Bragg reflector comprised of a set of plates adjacent to the second termination edge of the substrate, wherein the plates have an identical material composition to the materials of the Gunn diode at the second termi-nation edge of the substrate and immediately adjacent to the set of plates, and the set of plates have air gaps between adjacent plates of the set of width λ/4.

A Gunn diode according to any paragraph above, wherein the cathode has an exposed surface that is planar across the entire surface.

A terahertz oscillator comprising a Gunn diode of any paragraph above and a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator comprising a Gunn diode of any one of paragraphs 1-14 and a wave reflector comprised of one or more metal walls, with an air gap between a first of the metal walls and the second termination edge of the substrate of width λ/4.

A terahertz oscillator according to paragraph 19, wherein the one or more metal walls of the wave reflector are secured to a conductive base in electrical and heat-conductive contact with the cathode.

A terahertz oscillator according to any one of paragraphs 18-20, wherein a metal bond layer resides between the cathode and the conductive base and the GaN substrate has a sufficient thickness that a volume of the GaN substrate through which current flows acts as a vertical antenna in operation.

A terahertz oscillator according to paragraph 21, wherein the GaN substrate has a thickness T of 5/λ4n or 9λ/4n. A Gunn diode may, of course, emit at a frequency that is not within the range of terahertz waves whereas a terahertz oscillator is configured to emit at a frequency within the range of terahertz waves. Possible Modifications Although the preferred embodiment uses Ti/Al/Ti/Au as cathode contact and Ti/In/Ti/Au as anode contact, other stack of metals such as Ti/Al/Ni/Au, Ti/Al/Pd/Au, Ti/Al/Pt/Au, Ti/Al/Mo/Au, Ti/Al/Re/Au, and Ti/Al/Ir/Au. Although the preferred embodiment uses MOCVD as a growth method of GaN layers, other methods such molecu-lar beam epitaxy (MBE) can be used. Although the preferred embodiment grew GaN layers on the entire surface of the GaN substrate, these layers can be grown on a limited area of the GaN substrate. Although the preferred embodiment uses ion-implanta-tion to create a current-confinement structure, mesa-struc-ture using etching of the n-GaN active layer, and n+-GaN contact layer can be used to create a current-confinement structure. The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illus-tration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. All references discussed herein are incorporated by ref-erence in their entirety as if put forth in full below and for all purposes (e.g. to satisfy any statutory requirements such as written description for any features and combination of features described in the references; to further explain points herein; to provide background information for additional understanding of the invention in context; and so forth). Although the Example 1 showed a device with a contact hole of 10 micron in diameter, the size of the contact hole can be larger or smaller depending on the required power output and heat management design of the devices. What is claimed is: