Patent Publication Number: US-2010127635-A1

Title: Optoelectronic device

Description:
BACKGROUND 
     1. Technical Field 
     The present application relates to a structure of optoelectronic devices, and more particularly to a structure of a light emitting diode having a conductive light extraction layer. 
     2. Reference to Related Application 
     This application claims the right of priority based on TW application Ser. No. 097146119, filed Nov. 27, 2008, entitled “OPTO-ELECTRONIC DEVICE”, and the contents of which are incorporated herein by reference. 
     3. Description of Related Art 
     Optoelectronic semiconductor devices are devices emitting light from the combination of electrons and holes excited by an external voltage. Optoelectronic semiconductor device is a tiny solid-state light source. It not only has small size, long life, low driving voltage, quick response rate, and good shock-resistance, but also is able to meet the demand for light, thin and small-scale equipment, thereby becoming common products in daily life. 
       FIG. 1  shows a general structure of the optoelectronic device made of AlGaInP material, including a p-type GaP substrate  10 , a p-type AlGaInP cladding layer  11 , an active layer  12 , an n-type AlGaInP cladding layer  13 , and a metal layer  14 . Two electrodes  15 ,  16  are respectively disposed on upper side and lower side of the optoelectronic device. 
     The above-mentioned metal layer  14  helps to spread the current from the electrodes  15  to the whole device evenly to increase the luminous efficiency, but at the same time, the metal layer  14  absorbs light generated from the active layer  12 , thereby impact the efficiency of light extraction. When the area of the metal layer  14  is increased, the current can be spread further, however, the shade area is also increased. Or the shade area can be reduced, but the current is accumulated under the electrode  15 . The dilemma produced by the metal layer  14  is an issue that needs to be resolved. 
     In addition, the above-mentioned optoelectronic devices can be further combined with other devices to form a light-emitting apparatus. Such light-emitting apparatus typically includes a sub-mount containing a circuit. The photoelectric device is bonded to the sub-mount by solder to connect the substrate of the optoelectronic device with the electric circuit on the sub-mount. The above-mentioned sub-mount may be a lead-frame or a large-size mounting substrate to facilitate the layout of the circuit in the light-emitting apparatus and the heat dissipation thereof. 
     SUMMARY 
     The present application provides an optoelectronic device that distributes current uniformly without impacting light extraction efficiency. The optoelectronic device includes a substrate, and a first cladding layer, an active layer and a conductive light extraction unit formed on the substrate. The conductive light extraction unit includes a second cladding layer formed on the active layer and a metal layer formed the second cladding layer. Moreover, a plurality of openings is defined in the metal layer and extends to the second cladding layer to form a plurality of holes. The size of each of the plurality of holes is different or the distribution of the plurality of holes is irregular so that light can be evenly extracted. 
     In another embodiment of the present application, the optoelectronic device further includes a finger-like conductive body having a junction portion and an extension portion extending outwards from the junction portion. The junction portion is located between the first electrode and the metal layer. 
     In yet another embodiment of the present application, the optoelectronic device further includes a protective layer covering the metal layer. The protective layer fills the holes to keep the optoelectronic device from being contaminated by water, oxygen or dust in the air. 
     In another embodiment of the present application, the optoelectronic device further includes a transparent conductive layer disposed between the metal layer and the first electrode. The transparent conductive layer covers the metal layer and fills the holes to block water or oxygen in the air so that the uniformity of the current distribution is enhanced. 
     In the present application, as a result of the holes defined in the conductive light extraction unit, the current can be uniformly distributed not only in the horizontal direction but also in the vertical direction. In addition, light emitted by the active layer is extracted through the holes so that the light extraction efficiency of the optoelectronic device can be effectively increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide easy understanding of the application, and are incorporated herein and constitute a part of this specification. The drawings illustrate embodiments of the application and, together with the description, serve to illustrate the principles of the application. 
         FIG. 1  is a cross-sectional view of a conventional optoelectronic device; 
         FIG. 2  is a cross-sectional view of the optoelectronic device in accordance with a first embodiment of the present application; 
         FIG. 3  is a top view of the optoelectronic device in accordance with the first embodiment of the present application; 
         FIG. 4  is a top view of the optoelectronic device in accordance with a second embodiment of the present application; 
         FIG. 5  is a cross-sectional view of the optoelectronic device in accordance with the second embodiment of the present application; 
         FIG. 6  is a cross-sectional view of the optoelectronic device in accordance with a third embodiment of the present application; 
         FIG. 7  is a cross-sectional view of the optoelectronic device in accordance with a fourth embodiment of the present application; 
         FIG. 8  is a cross-sectional view of the optoelectronic device in accordance with a fifth embodiment of the present application; 
         FIG. 9  is a relation schematic view of all the layers in a conductive light extraction unit of the optoelectronic device; 
         FIG. 10  is a structural view of the optoelectronic device in accordance with a sixth embodiment of the present application; 
         FIG. 11  is a structure view of a backlight module apparatus of the present application; and 
         FIG. 12  is a structure view of an illumination apparatus of the present application. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference is made in detail to the embodiments of the present application, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 2  shows a structural view of an optoelectronic device in accordance with a first embodiment of the present application. The optoelectronic device  100  mainly includes a substrate  150  made of GaP material, a p-type cladding layer  140  formed on the substrate  150 , an active layer  130  (or light-emitting layer), and a conductive light extraction unit  102 ; and further includes a first and second electrodes  170 ,  175  respectively located on the upper and lower sides of the optoelectronic device  100 . The conductive light extraction unit  102  includes an n-type cladding layer  120  formed on the active layer  130 , and a metal layer  110  formed on the n-type cladding layer  120 . Moreover, a plurality of holes  160  is defined in the metal layer  110  and the n-type cladding layer  120 .  FIG. 3  shows a top view of the optoelectronic device  100 . As  FIG. 3  shows, the first electrode  170  is located in the center area of the optoelectronic device  100 , and the holes  160  are shown as dots around the first electrode  170 . The holes  160  shown in  FIG. 3  have different sizes and are deposed irregularly. 
     When a voltage is applied to the optoelectronic device  100 , the conductive light extraction unit  102  can make the current spread to the whole optoelectronic device  100  evenly to make the active layer  130  emit light uniformly. Thus, the current crowding effect is reduced and the light-emitting efficiency of the optoelectronic device  100  is increased. At the same time, the holes  160  are designed to enhance the light extraction efficiency of the active layer  130 . Also, the light extraction angle and light field can be adjusted by the irregular arrangement of the holes  160 . Thus, the optoelectronic device  100  with a specific light field, high light emitting efficiency and high light extraction efficiency is obtained. 
     In the embodiment, the n-type cladding layer  120  is made of n-type AlGaInP material. The active layer  130  can be a structure of double heterostructure or multi-layer quantum well structure. The p-type cladding layer  140  is made of p-type AlGaInP material. The metal layer  110  may be formed by e-beam, sputtering or other chemical deposition methods with material includes at least one of the following elements such as titanium, gold, zinc, indium, nickel, beryllium or any combination thereof, and the thickness of the metal layer  110  is so thin that light can penetrate. 
       FIGS. 4 and 5  show a structural view of an optoelectronic device in accordance with a second embodiment of the present application.  FIG. 5  is a sectional view of the device shown in  FIG. 4  along the A-A′ direction. The optoelectronic device  200  in accordance with the second embodiment is similar to the optoelectronic device  100  in accordance with the first embodiment, and the difference between the second embodiment and the first embodiment lies in the conductive light extraction unit  102  that further includes a finger-like conductive body located between the first electrode  170  and the metal layer  110 , and contains a junction portion  280  and an extension portion  285  extending outwards from the junction portion  280 .  FIG. 4  shows one example of the finger-like conductive body. As also shown in  FIG. 5 , the holes  160  below the extension portion  285  are filled up. The extension portion  285  and the junction portion  280  are made of metal, and may be the same material as the first electrode  170 , or other better conductive materials. In one of the embodiments, the material can be gold, silver, copper, aluminum and so on. Due to the better conductivity of the finger-like conductive body, the current can be conducted quickly and traversely by the extension portion  285  to avoid the localized current distribution. Consequently, the current spreads more uniformly and faster. 
       FIG. 6  shows a structural view of the optoelectronic device in accordance with a third embodiment of the present application. The difference between the third embodiment and the first embodiment lies in the conductive light extraction unit  102  that further includes a protective layer  380  covering part of the metal layer  110  where is not covered by the first electrode  170  and filling the holes  160 . The above-mentioned protective layer  380  may be made of transparent materials such as epoxy resin or polyamide (PI), insulation material, or fluorescent powder material to block water or oxygen in the air so that the components are free from being exposed to a general environment and thereby affecting the reliability of the components. 
       FIG. 7  shows a structural view of the optoelectronic device in accordance with a fourth embodiment of the present application. The difference between the fourth embodiment and the first embodiment lies in the conductive light extraction unit  102  that further includes a transparent conductive layer  480  covering the metal layer  110  and filling the holes  160 . The transparent conductive layer  480  is fabricated by electron beam, sputtering or other chemical deposition methods. The thickness of the transparent conductive layer  480  is in the range of 40 nm to 1000 nm, and the transparent conductive layer  480  has transmittance beyond 90%, and is made of indium tin oxide (ITO) or zinc oxide (ZnO). 
       FIG. 8  shows a structural view of the optoelectronic device in accordance with a fifth embodiment of the present application. The difference between the fifth embodiment and the first embodiment lies in the conductive light extraction unit  102  that further includes an ohmic contact layer  505  located between the metal layer  110  and the n-type cladding layer  120 . The ohmic contact layer  505  is made of Ni/Au to form a good ohmic contact layer between the metal layer  110  and the n-type cladding layer  120 . The holes  160  penetrate through the metal layer  110 , the ohmic contact layer  505 , and the n-type cladding layer  120 . Similarly, an ohmic contact layer can also be disposed between the metal layer  110  and the n-type cladding layer  120  in the foregoing four embodiments of the present application. 
     Because of the holes  160  defined in the conductive light extraction unit  102 , the current can be rapidly diffused not only in the horizontal direction but also in the vertical direction so that the light extraction efficiency of the components can be effectively enhanced. 
     In the above-mentioned embodiments, the holes  160  are defined in the conductive light extraction unit  102  by ion etching, dry etching, chemical etching or nano-imprinting technologies. The sizes of the holes  160  are not necessarily the same, and the diameter of the holes  160  is between 0.1 μm and 5 μm. At the same time, the arrangement of the holes  160  is in periodic or a periodic order, or other artificial design patterns. 
     Furthermore, in the fifth embodiment, after the holes  160  are defined in the conductive light extraction unit  102 , a plurality of patterned regions  161  is formed in the conductive light extraction unit  102  wherein each patterned region  161  contains the layers forming the light extraction unit  102 . For each pattern region  161 , the ratio of the bottom width of one layer and the bottom width of the adjacent layer is in the range of 0.7 to 1.3. As shown in  FIG. 9 , in a patterned region  161 , the bottom width of the metal layer  110  is W 1 , the bottom width of the ohmic contact layer  505  is W 2 , and the bottom width of the n-type cladding layer  120  is W 3 . It is obvious to tell from  FIG. 9  that W 1  is less than W 2 , and W 2  is less than W 3 . Namely, W 1 &lt;W 2 &lt;W 3 . And, the value of W 1 /W 2  or W 2 /W 3  is between 0.7 to 1.3. 
       FIG. 10  shows a structural view of the optoelectronic device in accordance with a sixth embodiment of the present application. The difference between the sixth embodiment and the first embodiment lies in the substrate  150  in the first embodiment is replaced by a binder layer  190  and a functional substrate  180 . This substrate structure is formed by the substrate transfer process. The functional substrate  180  is able to dissipate heat, conduct electricity, or transparent like ceramic substrate, copper substrate, or sapphire substrate. 
       FIG. 11  shows a structure of a backlight module in accordance with the present application. A backlight module apparatus  600  includes a light source device  610  constituted by an optoelectronic device  611  in any of the above embodiments of the present application; an optical device  620  placed on a light extraction path of the light source device  610 , and extracting the light after the appropriate treatment; and a power supply system  630  providing power for the light source device  610 . 
       FIG. 12  shows a structure view of an illumination apparatus of the present application. The above-mentioned illumination apparatus  700  may be a car lamp, a street lamp, a flashlight, a road lamp, an indication lamp and so on. The illumination apparatus  700  includes a light source device  710  which is constituted by an optoelectronic device  711  in any of the above embodiments of the present application; a power supply system  720  providing power for the light source device  710 ; and a control component  730  for controlling power input to the light source device  710 . 
     The above description is given by way of example, and not limitation. Given the above disclosure, one person having ordinary skill in the art could devise variations that are within the scope and spirit of the application disclosed herein, including configurations ways of the recessed portions and materials and/or designs of the attaching structures. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.