Abstract: A light emitting device includes a light emitting diode (LED), a concentrator element, such as a compound parabolic concentrator, and a wavelength converting material, such as a phosphor. The concentrator element receives light from the LED and emits the light from an exit surface, which is smaller than the entrance surface. The wavelength converting material is, e.g., disposed over the exit surface. The radiance of the light emitting diode is preserved or increased despite the isotropic re-emitted light by the wavelength converting material. In one embodiment, the polarized light from a polarized LED is provided to a polarized optical system, such as a microdisplay. In another embodiment, the orthogonally polarized light from two polarized LEDs is combined, e.g., via a polarizing beamsplitter, and is provided to non-polarized optical system, such as a microdisplay. If desired, a concentrator element may be disposed between the beamsplitter and the microdisplay.

Abstract: Silver electrode metallization in light emitting devices is subject to electrochemical migration in the presence of moisture and an electric field. Electrochemical migration of the silver metallization to the pn junction of the device results in an alternate shunt path across the junction, which degrades efficiency of the device. In accordance with a form of this invention, a migration barrier is provided for preventing migration of metal from at least one of the electrodes onto the surface of the semiconductor layer with which the electrode is in contact.

Abstract: A light-emitting semiconductor device includes a stack of layers including an active region. The active region includes a semiconductor selected from the group consisting of III-Phosphides, III-Arsenides, and alloys thereof. A superstrate substantially transparent to light emitted by the active region is disposed on a first side of the stack. First and second electrical contacts electrically coupled to apply a voltage across the active region are disposed on a second side of the stack opposite to the first side. In some embodiments, a larger fraction of light emitted by the active region exits the stack through the first side than through the second side. Consequently, the light-emitting semiconductor device may be advantageously mounted as a flip chip to a submount, for example.

Abstract: A light-emitting semiconductor device comprises a III-Nitride active region and a III-Nitride layer formed proximate to the active region and having a thickness that exceeds a critical thickness for relaxation of strain in the III-Nitride layer. The III-Nitride layer may be a carrier confinement layer, for example. In another aspect of the invention, a light-emitting semiconductor device comprises a III-Nitride light emitting layer, an InxAlyGa1-x-yN (0?x?1, 0?y?1, x+y?1), and a spacer layer interposing the light emitting layer and the InxAlyGa1-x-yN layer. The spacer layer may advantageously space the InxAlyGa1-x-yN layer and any contaminants therein apart from the light emitting layer. The composition of the III-Nitride layer may be advantageously selected to determine a strength of an electric field in the III-Nitride layer and thereby increase the efficiency with which the device emits light.

Abstract: A compact illumination system that is suitable for, e.g., projection systems, includes a plurality of light emitting diodes that are aligned along the same axis. The illumination system includes mirrors and a filter system for combining the light emitted by the different light emitting diodes. The light emitting diodes may be mounted within the same plane, e.g., on the same heatsink, which simplifies assembly and alignment of the system. Moreover, a collimator system with integrally formed refractive and/or reflective collimators, may be used. The use of an integrally formed collimator system advantageously reduces the number of piece parts and simplifies assembly.

Abstract: A structure includes semiconductor light emitting device and a wavelength converting layer. The wavelength converting layer converts a portion of the light emitted from the semiconductor light emitting device. The dominant wavelength of the combined light from the semiconductor light emitting device and the wavelength converting layer is essentially the same as the wavelength of light emitted from the device. The wavelength converting layer may emit light having a spectral luminous efficacy greater than the spectral luminous efficacy of the light emitted from the device. Thus, the structure has a higher luminous efficiency than a device without a wavelength converting layer.

Abstract: In an up-converter feed forward control of the output current is effected by rendering the conduction time of the switching element proportional to Vout/Vin2. This control is fast and avoids interference and loss of efficiency.

Abstract: The luminance of a system that includes a light emitting diode (LED), such as a projection system, may be increased by using an LED chip that has a light emitting surface that emits light directly into any medium with a refractive index of less than or equal to approximately 1.25. For example, the LED chip may emit light directly into the ambient environment, such as air or gas, instead of into an encapsulant. The low refractive index decreases the étendue of the LED, which increases luminance. Moreover, without an encapsulant, a collimating optical element, such as a lens, can be positioned close to the light emitting surface of the LED chip, which advantageously permits the capture of light emitted at large angles. A secondary collimating optical element may be used to assist in focusing the light on a target, such as a micro-display.

Abstract: In a circuit arrangement for driving a LED array comprising red, green and blue LEDs, a control loop is added for limiting the duty cycles of the control signals for driving the red, green and blue LEDs. In case one of the duty cycles reaches the limit value, the reference signals for the red, green and blue light are decreased with the same relative amount. The color point of the light is thereby maintained, even when the efficiency of part of the LEDs decreases.

Abstract: The amount of usefully captured light in an optical system is increased by concentrating light in a region where it can be collected by the optical system. In one embodiment, a light emitting diode is disposed on a first surface of a transparent member, which includes an exit surface. The transparent member includes a reflective element on a second surface and is shaped such that light emitted from the light emitting diode is directed toward the exit surface. A portion of the first surface of the transparent member between the first light emitting diode and the exit surface of the transparent member first surface is coated with a reflective coating. The portion of the first surface with the reflective coating may be larger than the width of the light emitting diode. In one embodiment, the transparent member is formed from two separate transparent elements.

Abstract: The invention relates to a switching arrangement for operating at least one LED, which switching arrangement is provided with input terminals (1, 2) for connecting a supply source, —output terminals (3, 4) for connecting the LED to be operated, —a first series circuit (I) between one of the input terminals (1) and one of the output terminals (3), including at least a self-inductance (L), a capacitor (C) and a diode (D), —a second series circuit (II) between the input terminals, including at least the self-inductance (L) and a switching element (S) which is alternately switched to a conducting state and a non-conducting state at a high frequency, —a third series circuit (III) between the output terminals, including the diode and an inductive winding (SW). According to the invention, the inductive winding forms a first winding (SW1) of a transformer (T) which has a second winding (SW2) that forms part of the first series circuit and which also has a connection point with the first winding.

Abstract: An electronic device comprising a population of quantum dots embedded in a host matrix and a primary light source which causes the dots to emit secondary light of a selected color, and a method of making such a device. The size distribution of the quantum dots is chosen to allow light of a particular color to be emitted therefrom. The light emitted from the device may be of either a pure (monochromatic) color, or a mixed (polychromatic) color, and may consist solely of light emitted from the dots themselves, or of a mixture of light emitted from the dots and light emitted from the primary source. The dots desirably are composed of an undoped semiconductor such as CdSe, and may optionally be overcoated to increase photoluminescence.

Abstract: P-type layers of a GaN based light-emitting device are optimized for formation of Ohmic contact with metal. In a first embodiment, a p-type GaN transition layer with a resistivity greater than or equal to about 7 ?cm is formed between a p-type conductivity layer and a metal contact. In a second embodiment, the p-type transition layer is any III-V semiconductor. In a third embodiment, the p-type transition layer is a superlattice. In a fourth embodiment, a single p-type layer of varying composition and varying concentration of dopant is formed.

Abstract: An LED package includes a datum reference feature that is external to the insulating body of the LED package and has a known, fixed relationship to the heat sink. The LED die is mounted to the heat sink such that the LED die has a fixed relationship to the heat sink. Accordingly, the reference datum feature provides a frame of reference to the position of the LED die within the LED package. The reference datum feature may be mounted to the heat sink or integrally formed from the heat sink. A pick-and-place head holds the LED package by engaging the datum reference feature, e.g., with an alignment pin. In addition, the LED package may include a lead that extends laterally into the insulating body, and extends towards the LED die to reduce the vertical distance between the lead and the LED die.

Abstract: In accordance with embodiments of the invention, a light emitting device includes a light emitting region and a reflective contact separated from the light emitting region by one or more layers. In a first embodiment, the separation between the light emitting region and the reflective contact is between about 0.5?n and about 0.9?n, where ?n is the wavelength of radiation emitted from the light emitting region in an area of the device separating the light emitting region and the reflective contact. In a second embodiment, the separation between the light emitting region and the reflective contact is between about ?n and about 1.4?n. The light emitting region may be, for example, III-nitride, III-phosphide, or any other suitable material.

Abstract: A light emitting device includes a region of first conductivity type, a region of second conductivity type, an active region, and an electrode. The active region is disposed between the region of first conductivity type and the region of second conductivity type and the region of second conductivity type is disposed between the active region and the electrode. The active region has a total thickness less than or equal to about 0.25?n and has a portion located between about 0.6?n and 0.75?n from the electrode, where ?n is the wavelength of light emitted by the active region in the region of second conductivity type. In some embodiments, the active region includes a plurality of clusters, with a portion of a first cluster located between about 0.6?n and 0.75?n from the electrode and a portion of a second cluster located between about 1.2?n and 1.35?n from the electrode.

Abstract: A method of forming a light emitting device includes providing a sapphire substrate, growing an Al1?xGaxN first layer by vapor deposition on the substrate at a temperature between about 1000° C. and about 1180° C., and growing a III-nitride second layer overlying the first layer. The first layer may have a thickness between about 500 angstroms and about 5000 angstroms. In some embodiments, reaction between the group V precursor and the substrate is reduced by starting with a low molar ratio of group V precursor to group III precursor, then increasing the ratio during growth of the first layer, or by using nitrogen as an ambient gas.

Abstract: A light emitting device is constructed on a substrate. The device includes an n-type semiconductor layer in contact with the substrate, an active layer for generating light, the active layer being in electrical contact with the n-type semiconductor layer. A p-type semiconductor layer is in electrical contact with the active layer, and a p-electrode is in electrical contact with the p-type semiconductor layer. The p-electrode includes a layer of silver in contact with the p-type semiconductor layer. A bonding layer is formed overlying the silver layer to make an electrical connection to the silver layer. The silver layer may be thin and transparent or thicker (greater than 20 nm) and reflective.

Abstract: An LED lamp includes an exterior shell that has the same form factor as a conventional incandescent light bulb, such as a PAR type bulb. The LED lamp includes an optical reflector that is disposed within the shell and that directs the light emitted from one or more LEDs. The optical reflector and shell define a space that is used to channel air to cool the device. The LED is mounted on a heat sink that is disposed within the shell. A fan moves air over the heat sink and through the spaced defined by the optical reflector and the shell. The shell includes one or more apertures that serve as air inlet or exhaust apertures. One or more apertures defined by the optical reflector and shell at the opening of the shell can also be used as air exhaust or inlet apertures.

Abstract: A dielectric layer is formed on the mesa wall of a flip-chip LED. The dielectric layer is selected to maximize reflection of light incident at angles ranging from 10 degrees towards the substrate to 30 degrees away from the substrate. In some embodiments, the LED is a III-nitride device with a p-contact containing silver, the dielectric layer adjacent to the mesa wall is a material with a low refractive index compared to GaN, such as Al2O3.