Distributed current blocking structures for light emitting diodes

#The present disclosure relates generally to semiconductor light emitting devices and particularly to the efficient generation of light in semiconductor light emitting devices.

#A Light Emitting Diode (LED) is a solid state device that converts electrical energy to light. Light is emitted from an active layer of semiconductor materials sandwiched between oppositely doped layers when a voltage is applied across the doped layers. The efficiency of an LED structure at converting energy to light determines whether the LED is suitable for certain applications. For example, use of LEDs in lighting applications requires high efficiency, reliability, and low cost. Advances in semiconductor materials and improvement in LED architectures have led to improvement in efficiency.

#U.S. Pat. No. 6,121,635 to Watanabe discloses a current blocking layer positioned below a top electrode for increasing the luminous efficiency of the LED. Because the current blocking layer is below the top electrode, is light transparent, and extends beyond the perimeter of the top electrode, the current blocking layer prevents high current density in a region of the LED where any light emitted would be blocked by the nontransparent top electrode. The disclosure of Watanabe indicates that increased efficiency is achieved by preventing emission of light under the nontransparent electrode. The current is directed elsewhere so that the resulting generated light can escape the device. U.S. Pat. No. 7,247,985 to Koneko similarly suggests improved electrical energy conversion by providing two current blocking structures in an LED. A first current blocking structure is disposed directly under the top electrode in a central region. A second current blocking structure is disposed in an outer region surrounding the central region. The second region functions to define the shape of the light emitting region and Koneko says improved light-emission performance is achieved. The use of one current blocking structure or a pair of current blocking structures as disclosed in these patents may create some gains in efficiency but these prior art structures also have limitations.

#The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.

#FIG. 1 (Prior Art) is a cross-sectional diagram of light generation in a lateral Light Emitting Diode (LED) device.

#FIG. 2 (Prior Art) is a cross-sectional diagram of light generation in a vertical LED device.

#Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the description and claims below, when a first layer is referred to as being disposed “over” a second layer, it is to be understood that the first layer can be directly on the second layer, or an intervening layer or layers may be present between the first and second layers. The terms such as “over”, “under”, “underneath”, “upper”, “lower”, “top”, “bottom”, “upward”, “downward”, “vertically”, and “laterally” are used herein to describe relative orientations between different parts of the LED being described, and it is to be understood that the overall LED structure being described can actually be oriented in any way in three-dimensional space.

#FIG. 3 is a top-down diagram of an LED device 40. LED device 40 includes a strip-shaped electrode 41, a strip-shaped current blocking structure 42, and a plurality of current blocking structures 43. The plurality of current blocking structures 43 includes multiple rows of disc-shaped current blocking structures, “discs”, disposed on each side of electrode 41 in the lateral dimension. The strip-shaped current blocking structure 42 and the plurality of current blocking structures 43 are disposed in a layer of the LED device 40 that is below the layer of the metal of electrode 41. Sectional line A-A is shown in FIG. 3 extending perpendicularly outward from a strip-shaped portion of electrode 41. Sectional line B-B is also shown in FIG. 3 and line B-B perpendicularly dissects another strip-shaped portion of electrode 41.

#FIG. 4 is a simplified conceptual cross-sectional diagram of a generic LED device. This LED device may either be a vertical LED device or a lateral LED device. In the case of the LED of FIG. 4 being a vertical LED device, current 44 flows from a p-electrode (not shown) below the structure shown, up through the current blocking layer 45, then through an p-GaN layer (not shown), a light generating active layer (not shown), an n-GaN layer (not shown), and to the strip-shaped electrode 41. In the case of the LED of FIG. 4 being a lateral LED device, current 44 flows from strip-shaped electrode 41, laterally through a transparent conductor layer (not shown), then vertically down through the current blocking layer 45, then through a p-GaN layer (not shown), an active layer (not shown), an n-GaN layer (not shown), and to an n-electrode (not shown). In both cases, the current blocking layer 45 includes the strip-shaped current blocking structure 42 and the plurality of current blocking structures 43. Four of the plurality of current blocking structures (46, 50, 54, 58) are illustrated in cross-section in FIG. 4. Strip-shaped current blocking structure 42 is disposed directly underneath metal strip-shaped electrode 41, but is slightly wider than strip-shaped electrode 41. Strip-shaped current blocking structure 42 blocks current from flowing through the portion of the active layer (not shown) directly underneath the strip-shaped electrode 41. Consequently substantially no light is emitted in the portion of the active layer directly underneath strip-shaped electrode 41.