Abstract: Bulk single crystals of AlN having a diameter greater than about 25 mm and dislocation densities of about 10,000 cm?2 or less and high-quality AlN substrates having surfaces of any desired crystallographic orientation fabricated from these bulk crystals.

Abstract: A crucible for growing III-nitride (e.g., aluminum nitride) single crystals is provided. The crucible includes an elongated wall structure defining an interior crystal growth cavity. Embodiments include a plurality of grains and a wall thickness of at least about 1.5 times the average grain size. In particular embodiments, the crucible includes first and second layers of grains the first layer including grains forming an inside surface thereof and the second layer being superposed with the first layer. The crucible may be fabricated from tungsten-rhenium (W—Re) alloys; rhenium (Re); tantalum monocarbide (TaC); tantalum nitride (Ta2N); hafnium nitride (HfN); a mixture of tungsten and tantalum (W—Ta); tungsten (W); and combinations thereof.

Abstract: Fabrication of AlN substrates suitable for epitaxial deposition of high-quality nitride-based compounds thereon having at least one single-crystal and substantially planarized useful area exceeding about 1 cm2 with a peak-to-valley surface topography in the useful area being less than about 50 nm is accomplished by, for example, employing an active solution that reacts non-selectively with the substrate material.

Abstract: An apparatus and method for fabricating a mount for an aluminum nitride (AlN) seed for single crystal aluminum nitride growth is provided. A holder having a proximal base and wall portions extending therefrom is fabricated from crystal growth crucible material, and defines an internal cavity. An AlN seed is placed within the holder, and placed within a nitrogen atmosphere at a temperature at or exceeding the melting point of a suitable material capable of forming a nitride ceramic by nitridation, such as aluminum. Pellets fabricated from this material are dropped into the holder and onto the seed, so that they melt and react with the nitrogen atmosphere to form a nitride ceramic. The seed is effectively molded in-situ with the ceramic, so that the ceramic and holder forms a closely conforming holder for the seed, suitable for single crystal AlN growth.

Abstract: According to one aspect of the invention, an improved process for preparing a surface of substrate is provided wherein the surface of the substrate is prepared for a chemical mechanical polishing (CMP) process, the CMP process is performed on the surface of the substrate, and the surface of the substrate is finished to clear the substrate surface of any active ingredients from the CMP process. Also, an improved substrate produced by the method is provided. According to one aspect of the invention, particular polishing materials and procedures may be used that allow for increased quality of AlN substrate surfaces.

Abstract: A method and apparatus for producing bulk single crystals of AlN having low dislocation densities of about 10,000 cm?2 or less includes a crystal growth enclosure with Al and N2 source material therein, capable of forming bulk crystals. The apparatus maintains the N2 partial pressure at greater than stoichiometric pressure relative to the Al within the crystal growth enclosure, while maintaining the total vapor pressure in the crystal growth enclosure at super-atmospheric pressure. At least one nucleation site is provided in the crystal growth enclosure, and provision is made for cooling the nucleation site relative to other locations in the crystal growth enclosure. The Al and N2 vapor is then deposited to grow single crystalline low dislocation density AlN at the nucleation site. High efficiency ultraviolet light emitting diodes and ultraviolet laser diodes are fabricated on low defect density AlN substrates, which are cut from the low dislocation density AlN crystals.

Abstract: A process for creating a broadly tunable Distributed Bragg Reflector (DBR) with a reduced recombination rate. According to the current invention, this may be achieved by creating electron confinement regions and hole confinement regions in the waveguide of the DBR. Preferably, this is achieved by engineering the band gaps of the DBR waveguide and cladding materials. Preferably, the materials selected for use in the DBR may be lattice matched. Alternately, two or more thin electron confinement regions and two or more thin hole confinement regions may be created to take advantage of strain compensation in thinner layers thereby broadening the choices of materials appropriate for use in creating a broadly tunable DBR. Alternately, graded materials and/or graded interfaces may be created according to alternate processes according to the current invention to provide effective electron and/or hole confinement regions in various DBR designs.

Abstract: A method and apparatus for producing bulk single crystals of AlN includes a crystal growth enclosure with Al and N2 source material therein, capable of forming bulk crystals. The apparatus maintains the N2 partial pressure at greater than stoichiometric pressure relative to the Al within the crystal growth enclosure, while maintaining the total vapor pressure in the crystal growth enclosure at super-atmospheric pressure. At least one nucleation site is provided in the crystal growth enclosure, and provision is made for cooling the nucleation site relative to other locations in crystal growth enclosure. The Al and N2 vapor is then deposited to grow single crystalline AlN at the nucleation site.

Abstract: A crucible for growing III-nitride (e.g., aluminum nitride) single crystals is provided. The crucible includes an elongated wall structure defining an interior crystal growth cavity. The crucible includes a plurality of tungsten grains and a wall thickness of at least about 1.5 times the average tungsten grain size. In particular embodiments, the crucible includes first and second layers of tungsten grains the first layer including grains forming an inside surface thereof and the second layer being superposed with the first layer. The crucible may be machined from a bar, plate, or billet of powder metallurgy tungsten.

Abstract: An emitter for use with a generator has a tube closed at one end, heated from its outside with a water-cooled photovoltaic converter array mounted inside for glass-melting application. Several TPV tubes may be inserted through holes in the insulation into the port sections between the glass-melting furnace and the regenerators. Any one of these tubes may be removed for maintenance at any time and replaced with a closure to close off the hole, without affecting the industrial process. The emitter tube may be a SiC or KANTHAL tube. The tube may be lines on its inside with AR coated tungsten foil or the tungsten may be deposited on the inner tube surface as a film followed by the AR coating. The photovoltaic converter array may comprise a polygonal array of shingle circuits where the circuits are fabricated using low bandgap GaSb cells.

Abstract: Our cylindrical TPV generator uses low bandgap PV cells mounted on circuits in a polygonal array around an IR emitter. The combustion gases are completely contained within the radiant tube burner. The PV array is mounted inside a leak-tight envelope cooled on its outer surface by either water or air flow. Flanges on either end of this PV array container allow for hermetic seals. A folded back coaxial emitter support tube provides a long path length limiting thermal conduction along its cylindrical wall from the very hot emitter section to the cooled seal flange. In our improved cylindrical TPV generator, we provide for a low temperature catalytic after-burn by providing a perforated turnaround plate coupling between the inner disk stack and the outer disk stack. This perforated turnaround plate provides a small amount of combustion air for the after-burn. A catalyst coating can be provided on the hotter surface of the outer finned disks. The after-burn occurs in the outer finned disk stack.

Abstract: A hydrocarbon thermophotovoltaic (TPV)electric generator insert has applications as a replacement burner to retrofit existing appliances. The retrofitted appliance is thus upgraded to either a cogeneration or self-powered unit. The design of the TPV burner insert is independent of the appliance to be retrofitted except for external adapters and can be easily retrofitted to any appliance design requiring a hydrocarbon burner. The burner uses fully premixed air and fuel near stoichiometry to attain a short duration, high intensity burn through optically dense porous ceramic emitters. The emitters attain temperatures between 1300° and 1500° C. The infrared radiation is collected by low bandgap photovoltaic cells with optical response at least out to a wavelength of 1.7 micrometers such as GaSb cells to produce DC power. The circuit cooling system uses fans or circulating water for cooling.

Abstract: A wavelength-tunable distributed feedback (DFB) laser is disclosed where the lasing wavelength can be adjusted by adjusting the bias current of the laser diode. Since the output power of the laser diode also changes with the bias current, a one-to-one correspondence between the lasing wavelength and the output power of the laser can be established. Consequently, the lasing wavelength can be measured directly from the photocurrent of a power monitoring detector facing the back-end of the laser diode. This provides an extremely simple method for wavelength monitoring.

Abstract: An integrated surface emitting laser and modulator device is disclosed that includes a detector for monitoring the optical power output of the laser and another detector for monitoring an extinction ratio of the modulator. A cleave physically and electrically separates the laser from the modulator device. The device has a collimating lens disposed on a top surface.

Abstract: A wavelength-tunable distributed feedback (DFB) laser is disclosed where the lasing wavelength can be adjusted by adjusting the bias current of the laser diode. Since the output power of the laser diode also changes with the bias current, a one-to-one correspondence between the lasing wavelength and the output power of the laser can be established. Consequently, the lasing wavelength can be measured directly from the photocurrent of a power monitoring detector facing the back-end of the laser diode. This provides an extremely simple method for wavelength monitoring.

Abstract: A method is disclosed for separating a semiconductor epitaxial structure from an insulating growth substrate. The method utilizes electrochemical anodic reactions to remove a thin etch layer disposed near the growth interface. The thin etch layer can be an intentional layer made of a material different from the epitaxial structure and/or can include a material with a high defect density. The method can be applied in the fabrication of optoelectronic and electronic devices from III-V materials, in particular gallium-nitride based materials.

Abstract: This invention describes a method for fabricating light-emitting diodes with an improved external quantum efficiency on a transparent substrate. The LED device structure is mounted face-down on and bonded to a handling wafer. The LED dies on the transparent substrate are separated by applying mutually aligned separation cuts from both sides of the transparent substrate and by then cutting through the handling wafer and the substrate wafer. This method allow the use of substrates that are difficult to thin and cleave. Contacts can be applied from one side of the devices only. The method is suitable for low cost high volume manufacturing.

Abstract: An avalanche photodetector (APD) is made from composite semiconductor materials. The absorption region of the APD is formed in a n-type InGaAs layer. The multiplication region of the APD is formed in a p-type silicon layer. The two layers are bonded together. The p-type silicon layer may be supported on an n+ type silicon substrate. A p-n junction formed at the interface between the silicon layer and the substrate. Alternatively, the n-type InGaAs layer may be supported on an InP substrate. In this case, a p-n junction is formed by making n-doped surface regions in the p-type silicon superlayer. In either case, the p-n junction is reverse biased for avalanche multiplication of charge carriers. The maximum of the electric field distribution in the APD under reverse bias operating conditions is located at p-n junction. This maximum is at a distance equal to about the thickness of the p-type silicon layer away from the absorption region.

Abstract: A planar avalanche photodetector (APD) is fabricated by forming a, for example, InGaAs absorption layer on a p+-type semiconductor substrate, such as InP, and wafer-bonding to the absorption layer a second p-type semiconductor, such as Si, to form a multiplication layer. The layer thickness of the multiplication layer is substantially identical to that of the absorption layer. A region in a top surface of the p-type Si multiplication layer is doped n+-type to form a carrier separation region and a high electric field in the multiplication region. The APD can further include a guard-ring to reduce leakage currents as well as a resonant mirror structure to provide wavelength selectivity. The planar geometry furthermore favors the integration of high-speed electronic circuits on the same substrate to fabricate monolithic optoelectronic transceivers.

Abstract: A method for producing a stress-engineered substrate includes selecting first and second materials for forming the substrate. An epitaxial material for forming a heteroepitaxial layer is then selected. If the lattice constant of the heteroepitaxial layer (aepi) is greater than that (asub) of the immediate substrate layer the epitaxial layer is deposited on, then the epitaxial layer is kept under “compressive stress” (negative stress) at all temperatures of concern. On the other hand, if the lattice constant of the heteroepitaxial layer (aepi) is less than that (asub) of the immediate substrate layer the epitaxial layer is deposited on, then the epitaxial layer is kept under “tensile stress” (positive stress). The temperatures of concern range from the annealing temperature to the lowest temperature where dislocations are still mobile.