JP2011517100A - LED with reduced electrode area - Google Patents

Abstract

A light source (40) and a method for manufacturing the same are disclosed. The light source includes semiconductor first and second layers (22, 24) surrounding a substrate (21) and an active layer (23). The first layer includes a first conductivity type material adjacent to the substrate. The active layer covers the first layer where it generates light when holes and electrons recombine. The second layer covers the active layer and includes a second conductivity type material, and the second layer has a first surface covering the active layer and a second surface facing the first surface. A trench (48) extends through the second layer and the active layer to the first layer. The trench has an electrically insulating wall (45). The first electrode (47) is disposed in the trench such that the first electrode is in electrical contact with the first layer, and the second electrode (26) is in electrical contact with the second layer.
[Selection] Figure 3

Description

  Light emitting elements (LEDs) are one important class of semiconductor elements that convert electrical energy. Improvements to these elements result in use in the field of luminaires intended to replace incandescent and fluorescent light sources. LEDs have a significantly longer lifetime and in some cases a significantly higher efficiency of converting electrical energy to light.

  The cost per lumen of light produced is an important factor in determining the speed with which this new technology can replace conventional light sources. For a given material system, the light generated per unit area of the LED surface has a maximum value determined by the temperature at which the LED operates and thermal factors such as heat dissipation. As the LED temperature increases, the light conversion efficiency decreases. The cost of an LED is proportional to the area of the die on which the LED is manufactured. Since there is a maximum light output per unit area of the LED surface, the area of the die that does not generate light increases the cost per lumen of the LED.

  An LED is considered a three-layer structure formed on a substrate, and an active layer that generates light is sandwiched between a p-layer and an n-layer. Power is applied through the p-layer and n-layer contacts that spread the current throughout the layer in question. Typically, the n layer is adjacent to the substrate and the p layer is the top layer. The current diffused throughout the p layer is easily obtained by the electrode structure covering the surface of the p layer. When the LED emits light through the p layer, the electrode structure includes a transparent layer such as ITO.

  A contact to the n layer is formed in a trench etched through the p layer and the active layer. In order to provide a sufficient current spreading area, the surface area used for this trench is a significant percentage of the LED's surface area. The size of this trench is further increased to accommodate alignment dimensional tolerances in the manufacturing process. The area of the trench does not generate light. This trench is therefore an important factor in the cost per lumen of the LED.

  The present invention includes a light source and a method of manufacturing the same. The light source includes a substrate and a first layer and a second layer of semiconductor surrounding the active layer. The first layer includes a first conductivity type material adjacent to the substrate. The active layer covers the first layer where it generates light when holes and electrons recombine. The second layer covers the active layer and includes a material of the second conductivity type, and the second layer has a first surface that covers the active layer and a second surface that faces the first surface. A trench extends through the second layer and the active layer to the first layer. The trench has an electrically insulating wall. The first electrode is disposed in the trench so as to be in electrical contact with the first layer, and the second electrode is in electrical contact with the second layer. In one aspect of the invention, the electrically insulating wall comprises a layer of SiN. In another aspect of the present invention, the first electrode includes a metal layer filling the trench and is in contact with the insulating wall. In yet another aspect of the invention, a layer of transparent conductive material is disposed between the second electrode and the second surface. In a further aspect of the invention, an electrical insulator is laid under the second electrical electrode and disposed between the second layer of transparent conductive material and the second surface. The insulating material is the same as the insulating layer on the trench walls.

FIG. 1 is a top view of a prior art LED 20. FIG. 2 is a cross-sectional view of the LED 20 along the line 2-2 shown in FIG. FIG. 3 is a cross-sectional view of an LED according to an aspect of the present invention. FIG. 4 is a cross-sectional view of manufacturing an LED 50 according to one aspect of the present invention. FIG. 5 is a cross-sectional view of manufacturing an LED 50 according to one aspect of the present invention. FIG. 6 is a cross-sectional view of manufacturing an LED 50 according to one aspect of the present invention.

  The manner in which the present invention provides its advantages can be easily understood with reference to FIGS. 1 and 2, which show prior art LEDs. FIG. 1 is a top view of the LED 20, and FIG. 2 is a cross-sectional view of the LED 20 along the line 2-2 shown in FIG. The LED 20 is made on the substrate 21 by stacking several layers on the substrate 21. The LED 20 is considered to have three layers consisting of an n-type layer 22, an active layer 23 and a p-type layer 24. Each of these layers includes several sublayers, but the sublayers are not relevant to the present invention, so the sublayers are omitted from the drawings for the sake of simplicity.

  The active layer 23 generates light when it reacts with a potential difference generated between the layer 22 and the layer 24 and holes and electrons are combined there. The potential difference is generated by connecting the contacts 26 and 27 to a power source. The resistivity of the p-layer is usually too large to provide sufficient current diffused throughout the p-layer, so a transparent electrode 25 is placed between the contact 26 and the layer 24 to spread the current. make it easier.

  To provide access to layer 22, trench 28 is etched through layer 23, 24 into layer 22. A contact 27 is then placed in the trench 28. In order to provide sufficient current spreading, the trench extends across the LED 20. In large LEDs, there are multiple trenches. Therefore, the area of the trench is a significant proportion of the light emitting area of the LED. Since the trenched portion of the LED does not generate light, the area of the trench is useless from a light generation standpoint, thus increasing the cost per lumen of the LED.

  In the prior art design, the area of the trench is much larger than the area covered by the contact 27. It is very important that the contact 27 is not in electrical contact with either the layer 23 or the layer 24 because a short circuit as a result of the contact will cause the LED to move. In prior art LED manufacturing systems, the contacts 27 are placed directly in the trenches 28. To ensure that no contact is made when placing the metal layer in the trench, the trench is made much wider than the contact 27 to allow for alignment errors during the manufacturing process. In a subsequent manufacturing process, as part of the process of encapsulating the LEDs to prevent moisture and other environmental contaminants from damaging those layers, the area between the contacts 27 and the trench walls is filled with an insulating material. It is. Since contact 27 is not in contact with the walls of trench 28, the quality of the insulating material is not critical. For example, a pinhole of insulating material does not lead to a short circuit.

  The present invention overcomes the short circuit problem by lining the trench with insulating material without pinholes and then placing the contact material in the lined trench. The thickness of the trench lining is much smaller than the air gap used in the above manufacturing method, and therefore the area lost due to the trench is considerably reduced. The masking operation required to provide the trench lining is combined with another masking operation used to further improve the current conversion efficiency of the LED, and therefore the cost of the additional overlap process is negligible.

  Reference is now made to FIG. 3, which is a cross-sectional view of an LED according to one embodiment of the present invention. The LED 40 is also shown as having three layers consisting of an n-type layer 22, an active layer 23 and a p-type layer 24. Prior to overlaying transparent electrode 44, trench 48 is etched through layer 23 and layer 24 into layer 22. Next, a patterned layer of SiN is overlaid to create an insulating island 43 underneath the contact 26 and insulate the walls of the trench 48 as shown as 45. The insulating layer 45 prevents the contact 47 from being short-circuited with the layer 23 and the layer 24. The width of the trench 48 is typically 10 μm and the thickness of the layer 45 is typically 100 nm. In prior art devices, the trench is typically 30 μm. Therefore, the present invention provides a significant reduction in the area required for the trench.

  The insulating island 43 basically blocks the current passing through the active layer directly below the contact 26. In general, the contact 26 is opaque and partially absorbs, so a significant percentage of the light generated in the region directly below the contact 26 is lost. Thus, in the absence of islands 43, a significant percentage of the current through the area underneath contact 26 is wasted, resulting in a reduction in efficiency as measured by the light output per watt of power consumed. Furthermore, the wasted current generates heat that must be removed. The island 26 prevents this waste and therefore increases the power conversion efficiency of the LED 40 and reduces the heat generated by the LED per lumen of light exiting the LED 40. In prior art designs using islands such as island 43, the islands were fabricated with PECVD SiOx thin films. However, SiOx is not a suitable dielectric material to insulate the walls of the trench 48 because of the normal pinholes in the SiOx dielectric layer film.

  The method of manufacturing the LED 40 can be readily understood with reference to FIGS. 4-6, which are cross-sectional views of the manufacture of the LED 50 according to one aspect of the present invention. Referring to FIG. 4, layers 22-24 are overlaid on substrate 21 as described above. The trench 58 is then etched through the layer 23 and the layer 24 into the layer 22. Referring to FIG. 5, a patterned SiN layer is then stacked to form an insulating layer 55 on the island 53 and trench 58 walls. The bottom 52 of layer 55 is etched to provide electrical access to layer 22. Next, while protecting the trench 58, the current diffusion layer 44 is overlaid and patterned on the island 53. Finally, the patterned metal layer is overlaid to form contacts 56 and contacts 57 as shown in FIG.

  The LED according to the present invention utilizes a current block island such as island 53 as described above. However, LEDs according to the invention that do not have this feature can also be produced. This feature is obtained at a fraction of the cost by the same layer used to insulate the trench walls and is therefore particularly attractive in the LED of the present invention.

  The above-described LED according to the present invention utilizes SiN as the insulating material of the trench wall. This material is particularly attractive because it is superimposed on the thin film layer without pinholes that can cause a short circuit between contact 27 and layer 23 or layer 24. However, other insulating materials can be used. For example, AlNx, TiOx, AlOx, or SiOxNy can be used.

  The above-described LEDs according to the invention emit light from the top surface of the LEDs and therefore use a transparent current spreading layer. However, embodiments can be made that emit light through the bottom surface of the substrate. In this case, the current diffusion layer on the upper surface may be a reflective surface that changes the direction of light from the upper surface of the LED toward the substrate. Such an embodiment would lack the insulation islands as it would not benefit from the insulation islands under the electrical contacts.

  The LED described above utilizes a configuration in which an n-type layer is stacked on a substrate and a p-type layer is stacked last. However, it is also possible to make an LED according to the invention with the p-type layer first superimposed.

  Various modifications of the present invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, the invention is limited only by the following claims.

Claims (10)

A substrate;
A first layer comprising a first conductivity type material adjacent to the substrate;
An active layer covering the first layer, wherein the active layer generates light when holes and electrons recombine;
A second layer covering the active layer and comprising a second conductivity type material, the second layer having a first surface covering the active layer and a second surface facing the first surface;
A trench extending through the first layer and the active layer to the first layer, the trench having an electrically insulating wall;
A first electrode disposed in the trench, wherein the first electrode is in electrical contact with the first layer;
A second electrode in electrical contact with the second layer;
light source. The electrically insulating wall comprises a layer of SiN;
The light source of claim 1. The first electrode comprises a metal layer filling the trench and in contact with the insulating wall;
The light source of claim 1. Further comprising a layer of transparent conductive material between the second electrode and the second surface;
The light source of claim 1. Further comprising an electrical insulator disposed under the second electrical contact and disposed between the second layer of the transparent conductive material and the second surface;
The light source of claim 4. The electrically insulating wall comprises a layer of insulating material and the electrical insulator comprises the same insulating material;
The light source according to claim 5. The insulating material is selected from the group consisting of SiN, AlNx, TiOx, AlOx and SiOxNy;
The light source of claim 6. A method of manufacturing a light emitting device,
Overlaying a first layer comprising a first conductivity type material adjacent to the substrate;
Overlaying the first layer over the first layer, wherein the active layer generates light when holes and electrons recombine there;
A step of covering the active layer with a second layer comprising a second conductivity type material, the second layer having a first surface covering the active layer and a second surface facing the first surface; And process;
Etching a trench extending through the second layer and the active layer to the first layer;
Overlaying the trench with an insulating material;
Etching the holes in the insulating layer into a portion of the insulating layer and exposing a portion of the first layer to the trench;
Forming a first contact electrically overlapping the first layer by overlaying a layer of conductive material on the trench;
Method. At the same time as overlaying the insulating layer in the trench, the method further comprises overlaying the insulating material on the second surface and patterning the insulating material to form an island of insulating material adjacent to the second surface. ;
The method of claim 8. Overlaying a transparent layer of conductive material on the island and the second surface, and then overlaying a patterned layer of conductive material on the conductive material to provide a second contact for electrical connection to the transparent layer; Further comprising forming;
The method of claim 9.

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