Abstract:
A patterned substrate is provided, including: a substrate having a (0001) crystal plane and a plurality of alternatively arranged recess structures therein, thereby forming a plurality of alternatively arranged top surfaces; and a dielectric barrier layer covering the bottom surface and/or the sidewalls of the recess structures. Each of the alternatively arranged recess structures includes a bottom surface and a plurality of sidewalls surrounding the bottom surface.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority of Taiwan Patent Application No. 101102782, filed on Jan. 30, 2012, the entirety of which is incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a semiconductor structure and a method for fabricating the same, and in particularly to a method for fabricating a patterned substrate with epitaxial layers having improved crystal quality and stacked semiconductor structures with epitaxial layers having improved crystal quality. 
         [0004]    2. Description of the Related Art 
         [0005]    Light emitting diode (LED) is one of the most applied semiconductor devices in recent years, for having characteristics such as low power consumption, low pollution, and long lifetime. As such, the LED can be used in such as traffic lights, outdoor displays, and back light modules for displays. 
         [0006]    Most of the modern advanced semiconductor electronic devices and electric optical device are fabricated by growth and stacking of epitaxy as a crystal, and a substrate is a key issue for the epitaxial growth of semiconductor structure in the devices. When the respective crystal constants of the substrate and the formed epitaxial layers are lattice mismatched with each other, the defect density in the epitaxial layer will be affected by the stress difference between the substrate and the subsequently formed epitaxial layers. The greater the defect density is, the more likely the excited electrons and holes recombine in traps of the crystal and release energy in non-radiation way. In this regard, the defect density is reduced by the improved crystal quality, and the internal quantum efficiency of LED can be increased as well. 
         [0007]    To improve the crystal quality of the epitaxial layers, U.S. Pat. No. 7,445,673 discloses a method for laterally growing a semiconductor device, comprising a semiconductor layer and a partially mask layer disposed over the semiconductor substrate, wherein a plurality of growth openings are formed over the surface of the semiconductor layer using the mask layer, and the semiconductor layer exposed from the growth openings can adjust its epitaxial parameters through lateral homo-epitaxial growth method, to speed up a lateral growth thereof faster than its vertical growth, so as to bend the epitaxial defects and reduce penetrations of the defects from extending through the active lighting layer to its surface. However, the masks are all formed in the semiconductor layer and a current transmitting path will be thus affected. 
         [0008]    To improve a patterned substrate, attempts also be tried by providing partial mask layer material, so as to improve the quality of the subsequent epitaxial layers. For instance, in Taiwan Patent No. M361771, a sapphire substrate and an epitaxial layer formed over the sapphire substrate are provided. A plurality of protrusions are disposed over the surface of the sapphire substrate, and each of the protrusions has a flat top surface and a mask layer is formed over the top surface. In the epitaxial growth, the epitaxial layer can be formed with an arrangement of low defect density using the sapphire substrate to perform epitaxial growth, and to improve the yield of subsequently formed elements. 
         [0009]    Therefore, an improved method is needed to reduce above defects due to lattice mismatch between the substrate and the epitaxial layer, thereby forming improved epitaxial layers with better crystal quality and an optical electric device using the epitaxial layers with improved crystal quality. 
       SUMMARY 
       [0010]    In view of this, the invention provides a patterned substrate for forming an epitaxial layer with a better crystal quality and a stacked light emitting diode (LED) structure having the epitaxial layer with the better crystal quality to solve the above problems of undesired defect. 
         [0011]    According an embodiment, the invention provides a patterned substrate, including: a substrate having a (0001) crystal plane and a plurality of alternatively arranged recess structures therein, such that a plurality of alternatively arranged top surfaces are formed, wherein each of the recess structures includes a bottom surface and a plurality of sidewalls surrounding the bottom surface; and a dielectric barrier layer covering the bottom surface and/or the sidewalls of the recess structures. 
         [0012]    In other embodiments, the dielectric barrier layer further covers all or a part of each of the top surfaces of the substrate. The bottom surface is the (0001) crystal plane. The aforementioned material of the barrier layer is made of a low-conductive material such as silicon dioxide, silicon nitride or titanium dioxide. The substrate material may be one of sapphire, silicon, silicon carbide and the like. A yellow light lithographic process can be used for manufacturing the patterned substrate. 
         [0013]    According to another embodiment, the invention provides a stacked LED structure, including: the patterned substrate, and an un-doped semiconductor epitaxial layer disposed on the dielectric barrier layer and the substrate. 
         [0014]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0016]      FIGS. 1-5  show fabrications of a stacked light emitting diode structure according to an embodiment of the invention; 
           [0017]      FIGS. 6-10  show fabrications of a stacked light emitting diode structure according to another embodiment of the invention; 
           [0018]      FIGS. 11-15  show fabrications of a stacked light emitting diode structure according to yet another embodiment of the invention; 
           [0019]      FIG. 16  shows a stacked light emitting diode structure according to an embodiment of the invention; 
           [0020]      FIGS. 17-21  show fabrications of a stacked light emitting diode structure according to an embodiment of the invention; 
           [0021]      FIG. 22  shows a stacked light emitting diode structure according to an embodiment of the invention; and 
           [0022]      FIGS. 23-27  show fabrications of a stacked light emitting diode structure according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0024]      FIGS. 1-27  illustrate fabrications of a stacked light emitting device structure according to various embodiments of the invention. 
         [0025]    Referring to  FIGS. 1-5 , a manufacturing process of a stacked LED structure is shown according to an embodiment of the invention. Referring to  FIG. 1 , a substrate  100  with a flat surface is provided first, such as the sapphire substrate, having a top surface  102  which is substantially a flat surface. The material of the substrate  100  may include sapphire, silicon, silicon carbide and so on. Then, by applying a suitable patterned mask (not shown), the photolithography is used to define an etching area, and then by implementing an etching process (not shown), several portions of the substrate  100  are partially removed from the top surface  102 , so as to form several separated islands  100   a  on the substrate  100 . These separated islands  100   a  define several alternatively arranged recess structures  100   b  therebetween. These recess structures  100   b  may be a trench or an opening, which is formed as defining by a sidewall  100   c  of the adjacent island  100   a  and a bottom surface  100   d  surrounded by several sidewalls  100   c  of the adjacent island  100   a . Herein, crystalline planes of the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure  100   b  are (0001) crystal planes. 
         [0026]    Referring to  FIG. 2 , a layer of low-conducive dielectric material is deposited on the substrate  100 , such as silicon dioxide. The top surface  102  and the sidewall  100   c  of each island  100   a  and the bottom surface  100   d  of each recess structure are covered accordingly by this layer of dielectric material. Then by applying the suitable patterned mask (not shown) and implementing the etching process (not shown), the dielectric material located on the top surface  102  of each island  100   a  is partially removed, so as to partially expose the top surface  102  of each island  100   a  and form a dielectric barrier layer  106  in each recess structure  100   b . Herein, the top surface  102  of each island  100   a  is partially covered by the dielectric barrier layer  106 , and the sidewall  100   c  of each island  100   a  and the bottom surface  100   d  in each recess structure  100   b  are completely covered by the dielectric barrier layer  106 . The material of the dielectric barrier layer  106  may include silicon dioxide, silicon nitride or titanium dioxide and other dielectric materials, which may be formed through a metal organic chemical vapor deposition (MOCVD), a hydride vapor phase epitaxy (HVPE) and other deposition processes. 
         [0027]    Referring to  FIG. 3 , an epitaxial growth process  108  is implemented, such as an epitaxial growth process of the MOCVD, HVPE, so as to grow up an un-doped semiconductor epitaxial layer  110   a  on the substrate  100 . The material is for example aluminum indium gallium nitride, and the indium content and aluminum content in this un-doped semiconductor epitaxial layer  110   a  can be adjusted through the epitaxial parameter. Herein, since the top surface  102  of each island  100   a  is partially exposed, the un-doped semiconductor epitaxial layer  110   a  performs the epitaxial growth at the (0001) crystal plane of the partially-exposed top surface  102  of the islands  100   a , thereby growing up to form an un-doped semiconductor epitaxial layer  110   a . Herein, a main growth direction of the un-doped semiconductor epitaxial layer  110   a  is a direction perpendicular to the top surface  102  of each island  110   a.    
         [0028]    Referring to  FIG. 4 , the epitaxial growth process  108  continues to be implemented, and with the extension of the time of the epitaxial growth process  108  and the adjustment of the epitaxial parameters (such as temperature and pressure), in addition to continuing to grow up towards the direction perpendicular to the top surface  102  of each island  110   a , the un-doped semiconductor epitaxial layer  110   a  (referring to  FIG. 3 ) higher than the dielectric barrier layer  106  also grows up towards the direction horizontal to the top surface  102  of each island  110   a , thereby causing a side merging with the un-doped semiconductor epitaxial layer  110   a  formed on the top surface  102  of the adjacent island  110   a  and finally forming an un-doped semiconductor epitaxial layer  110  having a flat surface as shown in  FIG. 4 . 
         [0029]    As shown in  FIG. 4 , the recess structure  100   b  located between adjacent islands  1000   a  is not filled up of this un-doped semiconductor epitaxial layer  110  at this time, and a gap  112  exists among each recess structure  100   b , which locates between the un-doped semiconductor epitaxial layer  110  and the adjacent island  100   a , and the adjacent dielectric barrier layer  106  as well as the un-doped semiconductor epitaxial layer  110 . As an embodiment, the gap  112  between the recess structure  100   b  and the un-doped semiconductor epitaxial layer  110  has a height ranging from 0.1-2 μm. 
         [0030]    As shown in  FIG. 4 , since the formed un-doped semiconductor epitaxial layer  110  performs the epitaxial growth at the (0001) crystal plane of the partially-exposed top surface  102  of each island  100   a  in a patterned substrate as shown in  FIG. 2 , the epitaxial direction in the formed un-doped semiconductor epitaxial layer  110  can be controlled, thereby reducing the problem of threading dislocations caused by mismatch of the lattice between the material of the un-doped semiconductor epitaxial layer  110  and the material of the substrate  100 . In addition, since the material of the un-doped semiconductor epitaxial layer  110  performs the epitaxial growth only at part of the (0001) crystal plane, generation of the defect density in the un-doped semiconductor epitaxial layer  110  can be reduced. Therefore, the un-doped semiconductor epitaxial layer  110  formed on a patterned substrate shown in  FIG. 4  has a better epitaxial quality, so it is beneficial for improving light emitting efficiency and reliability of the electronic element and the photoelectric element such as the LED formed thereon. 
         [0031]    Referring to  FIG. 5 , then a conventional process (not shown) may be employed to form a light emitting element structure  170  on the un-doped semiconductor epitaxial layer  110 . Herein, the light emitting element structure  170  mainly includes a n-type semiconductor epitaxial layer  150 , an active layer  152 , a p-type semiconductor epitaxial layer  154 , a transparent conductive layer  156 , electrodes  158  and  160  that are used for forming the epitaxial layer sequentially. As shown in  FIG. 5 , the active layer  152  is located on a part of areas of the n-type semiconductor epitaxial layer  150 , while a part of areas of the n-type semiconductor epitaxial layer  150  are exposed. The p-type semiconductor epitaxial layer  154  is located on the active layer  152 , while the transparent conductive layer  156  is formed on the p-type semiconductor epitaxial layer  154 , and the electrode  158  may be formed on the transparent conductive layer  156 . Another electrode  160  may be formed on a part of areas of the n-type semiconductor epitaxial layer  150  that are exposed. In another embodiment, the transparent conductive layer  156  is a selective film layer, and so it may be omitted, such that the electrode  158  may be directly formed on the p-type semiconductor epitaxial layer  154 . The above n-type semiconductor epitaxial layer  150  is, for example, a Si-doped n-type semiconductor epitaxial layer, while the above p-type semiconductor epitaxial layer  154  is, for example, an Mg-doped p-type semiconductor epitaxial layer. The n-type semiconductor epitaxial layer  150  and the p-type semiconductor epitaxial layer  154  may include aluminum indium gallium nitride (Al x In y Ga 1-x-y N, 0≦x≦1, 0≦y≦1) and other epitaxial materials, and the indium content and the aluminum content may be adjusted by the epitaxial parameter. The active layer  152  may be, for example, indium gallium nitride/gallium nitride multiple quantum wells of indium gallium nitride and gallium nitride, and the transparent conductive layer  156  may include indium tin oxide (ITO), nickel (Ni)/gold (Au) structure and other materials. 
         [0032]    Since the un-doped semiconductor epitaxial layer  110  exists below the light emitting element  170 , the dielectric barrier layer  106  is used and the epitaxial parameter is adjusted to make the un-doped semiconductor epitaxial layer  110  perform lateral epitaxial growth, such that the epitaxial layer has less defect problems, and the efficiency and reliability of the light emitting element  170  formed on the epitaxial layer  110  may be improved. Additionally, since several gaps  112  and the dielectric barrier layer  106  are formed below the un-doped semiconductor epitaxial layer  110 , and since different refraction coefficients exist among the dielectric barrier layer  106  and the substrate  100  and the un-doped semiconductor epitaxial layer  110  and the gaps  112  may act as a scattering center of photons, the light emitted from the active layer  152  may pass through these gaps  112  and the dielectric barrier layer  106  and then a refraction angle and a reflection angle of the light are changed, so as to enhance a light extraction efficiency of the light emitting element  170 . 
         [0033]    Referring to  FIGS. 6-10 , they show the manufacturing of a stacked LED structure according to another embodiment of the invention. Herein, the embodiment as shown in  FIGS. 6-10  is a variation of the embodiment shown in  FIGS. 1-4 , and so a same reference number refers to a same element herein. 
         [0034]    Referring to  FIG. 6 , the substrate  100  with the flat surface is firstly provided, which has the top surface  102 . The substrate  100  may include sapphire, silicon, silicon carbide and other materials. Then, by applying the suitable patterned mask (not shown), the photolithography is used to define the etching area, and then by implementing the etching process (not shown), several portions of the substrate  100  are partially removed from the top surface  102 , so as to form several separated islands  100   a  on the substrate  100 . These separated islands  100   a  define several alternatively arranged recess structures  100   b  therein. These recess structures  100   b  may be the trench or the opening, which is defined and formed by the sidewall  100   c  of the adjacent island  100   a  and the bottom surface  1000   d  surrounded by several sidewalls  100   c  of the adjacent island  100   a . Herein, the crystalline planes of the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure  100   b  are the kind of (0001) crystal plane. 
         [0035]    Referring to  FIG. 7 , then, a layer of dielectric material is deposited on the substrate  100 , for example: silicon dioxide. The top surface  102  and the sidewall  100   c  of each island  100   a  and the bottom surface  100   d  of each recess structure are covered correspondingly by this layer of dielectric material. Then, by applying the suitable patterned mask (not shown) and implementing the etching process (not shown), the dielectric material located on the top surface  102  of each island  100   a  is completely removed, so as to completely expose the top surface  102  of each of the semiconductor islands  100   a  and form the dielectric barrier layer  106  in each recess structure  100   b . Herein, the dielectric barrier layer  106  completely covers the sidewall  100   c  of each island  100   a  and the bottom surface  100   d  in each recess structure  100   b , but not covers all the top surface  102  of each island  100   a . The dielectric barrier layer  106  may include silicon dioxide, silicon nitride or titanium dioxide and other dielectric materials, and may be formed by the MOCVD, the HVPE and other deposition processes. 
         [0036]    Referring to  FIG. 8 , the epitaxial growth process  108  is implemented, for example, the epitaxial growth process of the MOCVD, so as to grow up the un-doped semiconductor epitaxial layer  110   a  such as the gallium nitride material on the substrate  100 . Herein, since the top surface  102  of each island  100   a  is completely exposed, the un-doped semiconductor epitaxial layer  110   a  performs the epitaxial growth from the (0001) crystal plane of the top surface  102  of each island  100   a , thereby growing up to form the un-doped semiconductor epitaxial layer  110   a . Herein, the main growth direction of the un-doped semiconductor epitaxial layer  110   a  is the direction perpendicular to the top surface  102  of each island  110   a.    
         [0037]    Referring to  FIG. 9 , then, the epitaxial growth process  108  continues to be implemented, and with the extension of the time of the epitaxial growth process  108 , in addition to continue to grow up towards the direction perpendicular to the top surface  102  of each island  110   a , the un-doped semiconductor epitaxial layer  110   a  (see  FIG. 8 ) higher than the dielectric barrier layer  106  also grows up towards the direction horizontal to the top surface  102  of each island  110   a , thereby generating a side merging with the un-doped semiconductor epitaxial layer  110   a  located on the top surface  102  of the adjacent island  110   a  and finally forming the un-doped semiconductor epitaxial layer  110  having the flat surface as shown in  FIG. 9 . 
         [0038]    As shown in  FIG. 9 , the recess structure  100   b  between adjacent islands  100   a  is not filled with this un-doped semiconductor epitaxial layer  110  at this time, while the gap  112  may exist among each recess structure  100   b  between the un-doped semiconductor epitaxial layer  110  and the adjacent island  100   a  and the adjacent dielectric barrier layer  106  as well as the un-doped semiconductor epitaxial layer  110 . As an embodiment, the gap  112  between the recess structure  100   b  and the un-doped semiconductor epitaxial layer  110  has a height ranging from 0.1-2 μm. The formed un-doped semiconductor epitaxial layer  110  performs the epitaxial growth from the (0001) crystal plane of the completely-exposed top surface  102  of each island  100   a  in the patterned substrate as shown in  FIG. 7 , therefore, the epitaxial direction in the formed un-doped semiconductor epitaxial layer  110  may be controlled, thereby reducing the threading dislocations due to the mismatch of the lattice between the material of the un-doped semiconductor epitaxial layer  110  and the material of the substrate  100 . In addition, since the material of the un-doped semiconductor epitaxial layer  110  performs the epitaxial growth only from the (0001) crystal plane, generation of the defect density in the un-doped semiconductor epitaxial layer  110  may be reduced. Therefore, since the un-doped semiconductor epitaxial layer  110  formed on the patterned substrate shown in  FIG. 9  has the better epitaxial quality, it is beneficial to improve the light emitting efficiency and reliability of the electronic element and the photoelectric element such as the LED formed thereon. 
         [0039]    Referring to  FIG. 10 , then, the conventional process (not shown) may be employed to form the light emitting element  170  in the above embodiment on the un-doped semiconductor epitaxial layer  110 . Since the un-doped semiconductor epitaxial layer  110  exists below the light emitting element  170 , the defect problems are less and the epitaxial quality is better, such that the light emitting efficiency and reliability of the light emitting element  170  formed on the un-doped semiconductor epitaxial layer  110  may be improved. Additionally, since several gaps  112  and the dielectric barrier layer  106  are formed below the un-doped semiconductor epitaxial layer  110 , and since different refraction coefficients exist among the dielectric barrier layer  106  and the substrate  100  and the un-doped semiconductor epitaxial layer  110  and the gaps  112  may act as the scattering center of the photons, the light emitted from the active layer  152  may pass through these gaps  112  and the dielectric barrier layer  106  and then the refraction coefficient of the light is different, so as to enhance the light extraction efficiency of the light emitting element  170 . As an embodiment, the gap  112  between the recess structure  100   b  and the un-doped semiconductor epitaxial layer  110  has a height ranging from 0.1-2 μm. 
         [0040]    Referring to  FIGS. 11-15 , they show the manufacturing of a stacked LED structure according to yet another embodiment of the invention. Herein, the embodiment as shown in  FIGS. 11-15  is the variation of the embodiment shown in  FIGS. 1-4 , and so the same reference number refers to the same element herein. 
         [0041]    Referring to  FIG. 11 , the substrate  100  with the flat surface is firstly provided, which has the top surface  102 . The substrate  100  may include sapphire, silicon, silicon carbide and other materials. Then, by applying the suitable patterned mask (not shown) and implementing the etching process (not shown), several portions of the substrate  100  are partially removed from the top surface  102 , so as to form several separated islands  100   a  on the substrate  100 . These separated islands  100   a  define several alternatively arranged recess structures  100   b  therein. These recess structures  100   b  may be the trench or the opening, which is defined and formed by the sidewall  100   c  of the adjacent island  100   a  and the bottom surface  100   d  surrounded by several sidewalls  100   c  of the adjacent island  100   a . Herein, the crystalline planes of the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure  100   b  are the kind of (0001) crystal plane. 
         [0042]    Referring to  FIG. 12 , then, a layer of dielectric material is deposited on the substrate  100 , for example: silicon dioxide. The top surface  102  and the sidewall  100   c  of each island  100   a  and the bottom surface  100   d  of each recess structure are covered correspondingly by this layer of dielectric material. Then, by applying the suitable patterned mask (not shown) and implementing the etching process (not shown), the dielectric material located on the bottom surface  100   d  in each recess structure  100   b  is only partially removed, so as to partially expose the bottom surface  100   d  in each recess structure  100  and form the dielectric barrier layer  106  in each island  100   a . Herein, the sidewall  100   c  and the top surface  102  of each island  100   a  are completely covered by the dielectric barrier layer  106 , but by which the bottom surface  100   d  in each recess structure  100   b  is partially exposed. The dielectric barrier layer  106  may include silicon dioxide, silicon nitride or titanium dioxide and other dielectric materials, and which may be formed by the MOCVD, the HVPE and other deposition processes. 
         [0043]    Referring to  FIG. 13 , then, the epitaxial growth process  108  is implemented, for example, the epitaxial growth process of the MOCVD and the HVPE, so as to grow up the un-doped semiconductor epitaxial layer  110   a  such as the gallium nitride material on the substrate  100 . Herein, since the bottom surface  100   d  in each recess structure  100   b  is partially exposed, the un-doped semiconductor epitaxial layer  110   a  performs the epitaxial growth from the (0001) crystal plane of the bottom surface  100   d  in each recess structure  100   b , thereby growing up to form the un-doped semiconductor epitaxial layer  110   a . Herein, the main growth direction of the un-doped semiconductor epitaxial layer  110   a  is the direction perpendicular to the bottom surface  100   d  in each recess structure  1100   b.    
         [0044]    Referring to  FIG. 14 , then, the epitaxial growth process  108  continues to be implemented, and with the extension of the time of the epitaxial growth process  108 , in addition to continue to grow up towards the direction perpendicular to the bottom surface  100   d  in each recess structure  100   b , the un-doped semiconductor epitaxial layer  110   a  (see  FIG. 13 ) higher than the dielectric barrier layer  106  and the islands  100   a  also grows up towards the direction horizontal to the bottom surface  100   d  in each recess structure  100   b , thereby generating the side merging with the un-doped semiconductor epitaxial layer  110   a  higher than the top surface  102  of the adjacent island  110   a  and finally forming the un-doped semiconductor epitaxial layer  110  having the flat surface as shown in  FIG. 14 . 
         [0045]    As shown in  FIG. 14 , the recess structure  100   b  between adjacent islands  100   a  is not filled with this un-doped semiconductor epitaxial layer  110  at this time, while no gap may exist among each recess structure  100   b  between the un-doped semiconductor epitaxial layer  110  and the adjacent island  100   a  and the adjacent dielectric barrier layer  106  as well as the un-doped semiconductor epitaxial layer  110 . 
         [0046]    As shown in  FIG. 14 , the formed un-doped semiconductor epitaxial layer  110  performs the epitaxial growth from the (0001) crystal plane of the bottom surface  100   d  of each recess structure  100   b  in the patterned substrate as shown in  FIG. 12 , therefore, the epitaxial direction in the formed un-doped semiconductor epitaxial layer  110  may be controlled, thereby reducing the threading dislocations due to the mismatch of the lattice between the material of the un-doped semiconductor epitaxial layer  110  and the material of the substrate  100 . In addition, since the material of the un-doped semiconductor epitaxial layer  110  performs the epitaxial growth only from the (0001) crystal plane, generation of the defect density in the un-doped semiconductor epitaxial layer  110  may be reduced. Therefore, since the un-doped semiconductor epitaxial layer  110  formed on the patterned substrate shown in  FIG. 12  has less defect problems, it may have the better epitaxial quality, and so it is beneficial to improve the efficiency and reliability of the electronic element and the photoelectric element such as the LED formed thereon. 
         [0047]    Referring to  FIG. 15 , then, the conventional process (not shown) may be employed to form the light emitting element  170  in the above embodiment on the un-doped semiconductor epitaxial layer  110 . Since the un-doped semiconductor epitaxial layer  110  exists below the light emitting element  170 , the defect problems are less and the epitaxial quality is better, such that the light emitting efficiency and reliability of the light emitting element  170  formed on the un-doped semiconductor epitaxial layer  110  may be improved. Additionally, since several dielectric barrier layers  106  are formed below the un-doped semiconductor epitaxial layer  110 , and since different refraction coefficients exist among the dielectric barrier layer  106  and the substrate  100  and the un-doped semiconductor epitaxial layer  110 , the light emitted from the active layer  152  may be scattered by these dielectric barrier layers  106 , so as to enhance the light extraction efficiency of the light emitting element  170 . 
         [0048]    Referring to  FIG. 16 , it shows a stacked LED structure according to an embodiment of the invention, which is the variation of the embodiment shown in  FIG. 14 . In this embodiment, a profile of the island  110   a  in the stacked LED structure is not limited to a tapered profile shown in  FIG. 14 , for example, the top surface of the island  110   a  is an arc shape. As shown in  FIG. 16 , the island  110   a  has a approximate semicircle profile, while the dielectric barrier layer  106  may formed on the surface of this approximate semicircle island  100   a , and the un-doped semiconductor epitaxial layer  110  grows up from the bottom surface  100   d  of the recess structure between adjacent semiconductor islands  100   a  and fills with the recess structure. 
         [0049]    In the stacked LED structure as shown in  FIG. 16 , the above light emitting element  170  (not shown herein) may also be formed on the un-doped semiconductor epitaxial layer  110 , while the light emitting element formed on the un-doped semiconductor epitaxial layer  110  may also have the same advantages as described in the above embodiments. 
         [0050]    Referring to  FIGS. 17-21 , they show the manufacturing of a stacked LED structure according to yet another embodiment of the invention. Herein, the embodiment as shown in  FIGS. 17-21  is the variation of the embodiment shown in  FIGS. 1-4 , and so the same reference number refers to the same element herein. 
         [0051]    Referring to  FIG. 17 , the substrate  100  with the flat surface is firstly provided, which has the top surface  102 . The substrate  100  may include sapphire, silicon, silicon carbide and other materials. Then, by applying the suitable patterned mask (not shown) and implementing the etching process (not shown), several portions of the substrate  100  are partially removed from the top surface  102 , so as to form several separated islands  1000   a  on the substrate  100 . These separated islands  1000   a  define several alternatively arranged recess structures  100   b  therein. These recess structures  100   b  may be the trench or the opening, which is defined and formed by the sidewalls  100   c  of adjacent several islands  100   a  and the bottom surface  100   d  surrounded by several sidewalls  100   c  of the adjacent island  100   a . Herein, the crystalline planes of the top surface  102  of each island  100   a  and the bottom surface  1000   d  of each recess structure  100   b  are the kind of (0001) crystal plane. 
         [0052]    Referring to  FIG. 18 , a layer of dielectric material is deposited on the substrate  100 . The sidewall  100   c  of each island  100   a  and the bottom surface  100   d  of each recess structure are covered correspondingly by this layer of dielectric material. Then, the suitable patterned mask (not shown) is applied and the etching process (not shown) is implemented to completely remove the dielectric material located on the top surface  102  of each island  100   a  and remove the dielectric material located on the bottom surface  100   d  in each recess structure  100   b , so as to completely expose the top surface of each island  100   a  and expose the bottom surface  100   d  in each recess structure  100   b , and form the dielectric barrier layer  106  on the sidewall  100   c  of each island  100   a . Herein, the dielectric barrier layer  106  covers only the sidewall  100   c  of each island  100   a , but not all the top surface  102  of each island  100   a  and the bottom surface  100   d . The dielectric barrier layer  106  includes silicon dioxide, silicon nitride or titanium dioxide and other dielectric materials, and may be formed by the MOCVD, the HVPE and other deposition processes. 
         [0053]    Referring to  FIG. 19 , the epitaxial growth process  108  is implemented, for example, the deposition process of the MOCVD, HVPE, so as to grow up the epitaxial layer  110   a  such as the gallium nitride material on the substrate  100 . Herein, since the top surface  102  of each island  100   a  and the bottom surface  100   d  in each recess structure  100   b  are completely exposed, the epitaxial layer  110   a  performs the epitaxial growth from the (0001) crystal plane of the top surface  102  of each island  100   a  and the bottom surface  100   d  in each recess structure  100   b , thereby growing up to form the un-doped semiconductor epitaxial layer  110   a . Herein, the main growth direction of the un-doped semiconductor epitaxial layer  110   a  is the direction perpendicular to the top surface  102  of each island  100   a  and the bottom surface  100   d  in each recess structure  100   b.    
         [0054]    Referring to  FIG. 20 , the epitaxial growth process  108  continues to be implemented, and with the extension of the time of the epitaxial growth process  108 , in addition to continue to face towards the direction perpendicular to the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure  100   b , the un-doped semiconductor epitaxial layer  110   a  (see  FIG. 19 ) higher than the dielectric barrier layer  106  and the islands  100   a  also faces towards the direction horizontal to the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure  100   b , thereby generating the side merging with the un-doped semiconductor epitaxial layer  110   a  higher than the top surface  102  of the adjacent island  110   a  and finally forming the un-doped semiconductor epitaxial layer  110  having the flat surface as shown in  FIG. 20 . 
         [0055]    As shown in  FIG. 20 , the recess structure  100   b  between adjacent islands  100   a  is not filled with this un-doped semiconductor epitaxial layer  110  at this time, while no gap may exist among each recess structure  100   b  between the un-doped semiconductor epitaxial layer  110  and the adjacent island  100   a  and the adjacent dielectric barrier layer  106  as well as the un-doped semiconductor epitaxial layer  110 . 
         [0056]    As shown in  FIG. 20 , the formed un-doped semiconductor epitaxial layer  110  performs the epitaxial growth from the (0001) crystal plane of the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure  100   b  in the patterned substrate as shown in  FIG. 18 , therefore, the epitaxial direction in the formed un-doped semiconductor epitaxial layer  110  may be controlled. 
         [0057]    Referring to  FIG. 21 , then, the conventional process (not shown) may be employed to form the light emitting element  170  in the above embodiment on the un-doped semiconductor epitaxial layer  110 . Since the un-doped semiconductor epitaxial layer  110  exists below the light emitting element  170 , the defect problems are less and the epitaxial quality is better, such that the efficiency and reliability of the light emitting element  170  formed on the un-doped semiconductor epitaxial layer  110  may be improved. Additionally, since several dielectric barrier layers  106  are formed below the un-doped semiconductor epitaxial layer  110 , and since different refraction coefficients exist among the dielectric barrier layer  106  and the substrate  100  and the un-doped semiconductor epitaxial layer  110 , the light emitted from the active layer  152  may be scattered by these dielectric barrier layers  106  to enhance the light extraction efficiency of the light emitting element  170 . 
         [0058]    Referring to  FIG. 22 , it shows a stacked LED structure according to an embodiment of the invention, which is the variation of the embodiment shown in  FIG. 16 . In this embodiment, the profile of the recess structure  100   b  in the stacked LED structure is not limited to the tapered profile shown in  FIG. 16 , which may have the approximate semicircle profile, while the dielectric barrier layer  106  may formed on the sidewall surface of this approximate semicircle recess structure  100   b , and the un-doped semiconductor epitaxial layer  110  grows up from the top surface  102  of the island  100   a  adjacent to each recess structure  100   b  and the gap  112  exists between the un-doped semiconductor epitaxial layer  110  and the recess structure  100   b . As an embodiment, the gap  112  between the recess structure  100   b  and the un-doped semiconductor epitaxial layer  110  has a height ranging from 0.1-2 μm. In the stacked LED structure as shown in  FIG. 22 , the above light emitting element  170  (not shown herein) may also be formed on the un-doped semiconductor epitaxial layer  110 , while the light emitting element formed on the un-doped semiconductor epitaxial layer  110  may also have the same advantages as described in the above embodiments. 
         [0059]    Referring to  FIGS. 23-27 , they show the manufacturing of a stacked LED structure according to yet another embodiment of the invention. Herein, the embodiment as shown in  FIGS. 23-27  is the variation of the embodiment shown in  FIGS. 1-4 , and so the same reference number refers to the same element herein. 
         [0060]    Referring to  FIG. 23 , the substrate  100  with the flat surface is firstly provided, which has the top surface  102 . The substrate  100  may include sapphire, silicon, silicon carbide and other materials. Then, by applying the suitable patterned mask (not shown) and implementing the etching process (not shown), several portions of the substrate  100  are partially removed from the top surface  102 , so as to form several separated islands  100   a  on the substrate  100 . These separated islands  100   a  define several alternatively arranged recess structures  100   b  therein. These recess structures  100   b  may be the trench or the opening, which is defined and formed by the sidewalls  100   c  of the adjacent several islands  100   a  and the bottom surface  100   d  surrounded by several sidewalls  100   c  of the adjacent island  100   a . Herein, the crystalline planes of the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure  100   b  is the kind of (0001) crystal plane. 
         [0061]    Referring to  FIG. 24 , then, a layer of dielectric material is deposited on the substrate  100 , for example: silicon dioxide. The top surface  102  of each island and the bottom surface  100   d  are covered correspondingly by this layer of dielectric material. Then, by applying the suitable patterned mask (not shown) and implementing the etching process (not shown), only the top surface  102  of each island and the bottom surface  100   d  are covered by the dielectric material layer, so as to only partially expose the sidewall  100   c  of each island  100   a  and respectively form the dielectric barrier layer  106  on the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure. Herein, only the top surface  102  of each island  100   a  and the bottom surface  100   d  of each recess structure are covered by the dielectric barrier layer  106 , but by which the sidewall  100   c  of each island  100   a  is not completely covered. The dielectric barrier layer  106  may include silicon dioxide, silicon nitride or titanium dioxide and other dielectric materials, and which may be formed by the MOCVD, the HVPE and other deposition processes. 
         [0062]    Referring to  FIG. 25 , then, the epitaxial growth process  108  is implemented, for example, formed by the deposition process of the MOCVD and the HVPE, so as to grow up an un-doped semiconductor epitaxial layer  110   b  such as the aluminum nitride material on the substrate  100 . Herein, since only the sidewall  100   c  of each island  100   a  is partially exposed, the un-doped semiconductor epitaxial layer  110   a  performs the epitaxial growth from an inclined surface of the sidewall  100   c  of each island  100   a , thereby growing up to form the un-doped semiconductor epitaxial layer  110   b . Herein, the main growth direction of the un-doped semiconductor epitaxial layer  110   b  is the direction perpendicular to the inclined surface of each island  100   a.    
         [0063]    Referring to  FIG. 26 , then, the epitaxial growth process  108  continues to be implemented, and with the extension of the time of implementing the epitaxial growth process  108 , in addition to continue to face towards the direction perpendicular to the inclined surface of each island  100   a , the un-doped semiconductor epitaxial layer  110   b  (see  FIG. 25 ) higher than the dielectric barrier layer  106  and the islands  100   a  also faces towards the un-doped semiconductor epitaxial layer  110   b  horizontal to the adjacent island  100   a  to side merge into the un-doped semiconductor epitaxial layer  110  having the flat surface. 
         [0064]    As shown in  FIG. 26 , the recess structure  100   b  between adjacent islands  100   a  is not filled with this un-doped semiconductor epitaxial layer  110  at this time, while no gap may exist among each recess structure  100   b  between the un-doped semiconductor epitaxial layer  110  and the adjacent island  100   a  and the adjacent dielectric barrier layer  106  as well as the un-doped semiconductor epitaxial layer  110 . 
         [0065]    As shown in  FIG. 26 , the formed un-doped semiconductor epitaxial layer  110  performs the epitaxial growth from the inclined surface of the sidewall  100   c  of each island  100   a  in the patterned substrate as shown in  FIG. 24 , therefore, the epitaxial direction in the formed un-doped semiconductor epitaxial layer  110  may be controlled, thereby reducing the defect density between the material of the un-doped semiconductor epitaxial layer  110  and the material of the substrate  100 . Therefore, since the un-doped semiconductor epitaxial layer  110  formed on the patterned substrate shown in  FIG. 26  has less defect problems, it may have the better epitaxial quality, so it is beneficial to improve photoelectric efficiency and reliability of the electronic element and the photoelectric element such as the LED formed thereon. 
         [0066]    Referring to  FIG. 27 , then, the conventional process (not shown) may be employed to form the light emitting element  170  in the above embodiment on the un-doped semiconductor epitaxial layer  110 . Since the un-doped semiconductor epitaxial layer  110  exists below the light emitting element  170 , the defect problems are less and the epitaxial quality is better, such that the efficiency and reliability of the light emitting element  170  formed on the un-doped semiconductor epitaxial layer  110  may be improved. Additionally, since several dielectric barrier layers  106  are formed below the un-doped semiconductor epitaxial layer  110 , and since different refraction coefficients exist among the dielectric barrier layer  106  and the substrate  100  and the un-doped semiconductor epitaxial layer  110 , the light emitted from the active layer  152  may be refracted and reflected by these dielectric barrier layers  106  to enhance the light extraction efficiency of the light emitting element  170 . 
         [0067]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.