Patent Publication Number: US-2012032192-A1

Title: Light emitting diode

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure relates generally to light emitting diodes, and more particularly to a light emitting diode with multiple wavelengths. 
     2. Description of the Related Art 
     Many illumination products use light emitting diode or laser diodes as a light source, such as environmental lighting or display backlighting, thanks to optimum lifetime, low energy consumption and heat generation, and compact profile. White light is often generated by blue chips packaged with yellow phosphor, or multiple chip packages, such as those combining red, green, and blue chips. U.S. Pat. No. 7,635,870 discloses a multiple chip package like that described. 
     Although the blue chip with yellow phosphor package can generate white light, the color rendering index (CRI) is insufficient, especially in the red spectrum range, being less than other ranges, such as yellow and green. Additionally, while the multi-chip package has a higher CRI, the different color chips exhibit different decay times, to result in the yield of the package decreasing. Another issue in the multi-chip package is the distance between the chips for wire bonding, resulting in excessive total volume of the package. Therefore, it is desired to provide an LED package which can overcome the described limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section of a light emitting diode in accordance with a first embodiment of the disclosure. 
         FIG. 2A  to  FIG. 2E  shows different circuit structures of the light emitting diode in accordance with a first embodiment of the disclosure. 
         FIG. 3  is a cross section of a light emitting diode in accordance with a second embodiment of the disclosure. 
         FIG. 4  is a cross section of a light emitting diode in accordance with a third embodiment of the disclosure. 
         FIG. 5  is a cross section of a light emitting diode in accordance with a fourth embodiment of the disclosure. 
         FIG. 6  is a cross section of a light emitting diode in accordance with a fifth embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a light emitting diode  1  in accordance with a first embodiment of the disclosure includes a substrate  10 , an illumination structure  20 , a first fluorescent conversion layer  14 , and a second fluorescent conversion layer  15 . In the first embodiment, the substrate  10  is a semiconductor substrate of aluminum oxide, silicon carbide, lithium aluminate, lithium gallate, silicon, gallium nitride, zinc oxide, aluminum zinc oxide, gallium arsenide, gallium phosphide, gallium antimonide, indium phosphide, indium arsenide, zinc selenide or metal. 
     The illumination structure  20  is disposed on the substrate  10  and includes a first illumination region  11 , a second illumination region  12 , and a third illumination region  13 . In the first embodiment, a space between the first illumination region  11  and the second illumination region  12  or between the second illumination region  12  and the third illumination region  13  is less than 50 μm. The first illumination region  11 , the second illumination region  12 , and the third illumination region  13  have p-type semiconductor layers  111 ,  121 ,  131 , n-type semiconductor layers  113 , 123 , 133 , and illumination layers  112 ,  122 ,  132 , wherein the illumination layers  112 ,  122 ,  132  are between the p-type semiconductor layers  111 ,  121 ,  131  and the n-type semiconductor layers  113 , 123 , 133  respectively. The illumination structure  20  can be Group III-V or Group II-VI compound semiconductor, such as gallium nitride, indium gallium nitride, aluminum gallium nitride, aluminum indium gallium nitride, zinc oxide, or zinc sulfide, formed by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). The p-type semiconductor layers  111 ,  121 ,  131  are doped by Group II, such as magnesium (Mg). The n-type semiconductor layers  113 ,  123 ,  133  are doped by Group IV, such as silicon (Si). The illumination layers  112 ,  122 ,  132  can be single quantum well or multiple quantum well, and emit the same wavelength, such as ultraviolet, blue light, or green light. Furthermore, the n-type semiconductor layers  113 ,  123 ,  133  of the illumination structure  20  are physically separated from each other. In the different electrical connections as shown in  FIG. 2A  to  FIG. 2E , the first illumination region  11 , the second illumination region  12 , and the third illumination region  13  can be electrically connected together in series ( FIG. 2A ) to a DC (direct current) power source, in parallel to a DC power source ( FIG. 2B ), in hybrid (i.e., series-parallel) to a DC power source ( FIG. 2C ), or to an AC (alternating current) power source ( FIG. 2D ). Alternatively, the first, second and third illumination regions  11 ,  12 ,  13  are independently connected to different DC power sources ( FIG. 2E ). 
     In the first embodiment, the n-type semiconductor layers  113 ,  123 ,  133  and the substrate  10  can have an undoped semiconductor layer (not shown in  FIG. 1 ) therebetween to minimize the differences of the lattice constant and the thermal expansion coefficient between the illumination structure  20  and the substrate  10 , thereby avoiding dislocation. 
     Referring to  FIG. 1  again, the first fluorescent conversion layer  14  covers the surface of the first illumination region  11  and can convert light from the first illumination region  11  to another light having a different wavelength. For example, the first illumination region  11  can generate blue light, and the first fluorescent conversion layer  14  can convert the blue light to red light, resulting in that light from the first fluorescent conversion layer  14  on the first illumination region  11  appears to be red. Similarly, the second fluorescent conversion layer  15  covers the surface of the second illumination region  12  and can convert light from the second illumination region  12  to another light having a different wavelength. For example, the second illumination region  12  can generate blue light, and the second fluorescent conversion layer  15  can convert the blue light to green light. Therefore, the second fluorescent conversion layer  15  on the second illumination region  12  can radiate green light. The light emitting diode  1  thereby is capable of mixing different colored lights to obtain a light with a desired color. 
     Referring to  FIG. 3 , a light emitting diode  2  in accordance with a second embodiment of the disclosure has the similar structure as the first embodiment. The difference therebetween is in that the light emitting diode  2  further comprises a photo detector  100  on the substrate  10 . The photo detector  100  detects the light intensity from the light emitting diode  2 , and provides a feedback system to control the input current to the light emitting diode  2 , so that the light emitting diode  2  can obtain the desired color rendering index (CRI) from the mixed different colored lights. For example, when the photo detector detects that the intensity of light from the second illumination region  12  is insufficient, the feedback system would increase the input current to the second illumination region  12  so as to obtain the desired color rendering index (CRI) of the mixed light. Therefore, the photo detector  100  allows adjustment of the input currents to obtain a desired color rendering index (CRI) of the light mixed. 
     Referring to  FIG. 4 , a light emitting diode  3  in accordance with a third embodiment of the disclosure differs from the first embodiment in that the first illumination region  11 , the second illumination region  12 , and the third illumination region  13  are integrally formed as a single piece of an n-type semiconductor layer. The first illumination region  11  has a part of the n-type semiconductor layer  210 , an illumination layer  112 , and a p-type semiconductor layer  111 , wherein the illumination layer  112  is on the part of the n-type semiconductor layer  210  and the p-type semiconductor layer  111  is on the illumination layer  112 . The second illumination region  12  has a part of the n-type semiconductor layer  210 , an illumination layer  122 , and a p-type semiconductor layer  121 , wherein the illumination layer  122  is on the part of the n-type semiconductor layer  210  and the p-type semiconductor layer  121  is on the illumination layer  122 . The third illumination region  13  has a part of the n-type semiconductor layer  210 , an illumination layer  132 , and a p-type semiconductor layer  131 , wherein the illumination layer  132  is on the part of the n-type semiconductor layer  210  and the p-type semiconductor layer  131  is on the illumination layer  132 . The three illumination regions  11 ,  12 ,  13  sharing the n-type semiconductor layer  210  results in formation of a co-electrode. Therefore, the first illumination region  11 , the second illumination region  12 , and the third illumination region  13  can be used in a parallel circuit or a part of a parallel circuit. 
     Referring to  FIG. 5 , a light emitting diode  4  of a fourth embodiment of the disclosure includes a substrate  30 , an illumination structure  40 , a first fluorescent conversion layer  34 , a second fluorescent conversion layer  35 , and a third fluorescent conversion layer  36 , wherein the illumination structure  40  has a first illumination region  31 , a second illumination region  32 , and a third illumination region  33 . In the fourth embodiment, a space between the first illumination region  31  and the second illumination region  32 , or between the second illumination region  32  and the third illumination region  33  is less than 50 μm, wherein the first illumination region  31  has a p-type semiconductor layer  311 , an n-type semiconductor layer  313 , and an illumination layer  312  between the p-type semiconductor layer  311  and the n-type semiconductor layer  313 , the second illumination region  32  has a p-type semiconductor layer  321 , an n-type semiconductor layer  323  and an illumination layer  322  between the p-type semiconductor layer  321  and the n-type semiconductor layer  323 , the third illumination region  33  has a p-type semiconductor layer  331 , an n-type semiconductor layer  333  and an illumination layer  332  between the p-type semiconductor layer  331  and the n-type semiconductor layer  333 . Furthermore, the fourth embodiment differs from the first embodiment in that the surface of the third illumination region  33  is covered a third fluorescent conversion layer  36  thereon. The illumination layers  112 ,  122 ,  132  emit light with the same wavelength, such as ultraviolet. Since the three illumination regions  31 ,  32 ,  33  are physically separated from each other and each have its own electrical circuit, the three illumination regions  31 ,  32 ,  33  can be used in series circuit, parallel circuit, series-parallel circuit, or independent circuit. Additionally, the areas between the n-type semiconductor layers  313 ,  323 ,  333  and the substrate  30  can further comprise undoped semiconductor layers (not shown). 
     The first fluorescent conversion layer  34  covers the surface of first illumination region  31 , wherein the first fluorescent conversion layer  34  can convert light from the first illumination region  31  to another light having a different wavelength. For example, the first fluorescent conversion layer  34  converts ultraviolet emitted from the first illumination region  31  to red light. Similarly, the second fluorescent conversion layer  35  covers the surface of the second illumination region  32  and converts the ultraviolet light emitted from the second illumination region  32  to green light. Similarly, the third fluorescent conversion layer  36  converts the ultraviolet light emitted from the third illumination region  33  to blue light. As a result, the light emitting diode  4  can mix the red light, green light, and blue light to obtain a desired color rendering index (CRI). Furthermore, a photo-detector can be disposed on the substrate  30  (not shown in  FIG. 5 ) to adjust the input current in the light emitting diode  4  to obtain a desired color rendering index (CRI) of the light mixed. 
     Referring to  FIG. 6 , a light emitting diode  5  of a fifth embodiment of the disclosure differs from the fourth embodiment in that the first illumination region  31 , the second illumination region  32 , and the third illumination region  33  share an n-type semiconductor layer  410 . The illumination structure  50  has an n-type semiconductor layer  410 , p-type semiconductor layers  311 ,  321 ,  331 , and illumination layers  312 ,  322 ,  332 , wherein the illumination layers  312 ,  322 ,  332  are between the n-type semiconductor layer  410  and the p-type semiconductor layers  311 ,  321 ,  331 . In other words, the first illumination region  31  has the p-type semiconductor layer  311 , a part of the n-type semiconductor layer  410 , and the illumination layer  312  therebetween. The second illumination region  32  has the p-type semiconductor layer  321 , a part of the n-type semiconductor layer  410 , and the illumination layer  322  therebetween, and the third illumination region  33  has the p-type semiconductor layer  331 , a part of the n-type semiconductor layer  410 , and the illumination layer  332  therebetween. Sharing among the three illumination regions  31 ,  32 ,  33  of the n-type semiconductor layer  410  results in formation of a co-electrode, whereby the first illumination region  31 , the second illumination region  32 , and the third illumination region  33  can be used in a parallel circuit or a part of a parallel circuit. 
     As disclosed, the fluorescent conversion layer covering the surface of the light emitting diode to obtain light mixed as white light can minimize the capacity of the package, and the disclosure of the light emitting diode has multiple wavelength regions, avoiding the different lifetimes between chips and enhancing efficiency of package. As well, the different wavelengths on the light emitting diode can be mixed better than R, G, B chips, because of distances between the chips.