Abstract:
A semiconductor light emitting device and a method for manufacturing the same are disclosed. The semiconductor comprises a light scattering-deflecting layer located on a semiconductor layer having a scraggly surface. Light is deflected due to the difference of refractive index when the light enters the semiconductor layer from the light scattering-deflecting layer, and the light scatters when the light enters the scraggly surface of the semiconductor layer, thereby enabling the semiconductor light emitting device to emit more light so as to increase the light emitting efficiency of the semiconductor light emitting device.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor light emitting device and a method for manufacturing the same, and more particularly, to a semiconductor light emitting device having a light scattering-deflecting layer and a method for manufacturing the same. 
     BACKGROUND OF THE INVENTION 
     Semiconductor light emitting devices, such as light emitting diodes (LED), are formed by using semiconductor materials. The semiconductor light emitting devices are one kind of minute solid-state light sources that can transform electrical energy into light energy. The semiconductor light emitting devices not only have the features of small volume, long life, low driving voltage, rapid response speed, and shockproof, but also can meet the needs of various application apparatuses of lightness, thinness, and miniaturization, thus having become very popular electric products in daily life. 
     Referring to FIG. 1, FIG. 1 illustrates a cross-sectional view of a conventional semiconductor light emitting device. In the formation of the semiconductor light emitting device, a semiconductor layer  102  is first formed on a substrate  100  that is transparent by using a deposition method, and a n-type semiconductor layer  104  is formed on the semiconductor layer  102  by using an epitaxy method. Then, a luminescent structure  106  is formed on the n-type semiconductor layer  104  by using an epitaxy method similarly. A p-type semiconductor layer  108  is formed on the luminescent structure  106  similarly by using an epitaxy method, wherein the n-type semiconductor layer  104 , the luminescent structure  106 , and the p-type semiconductor layer  108  constitute a semiconductor light emitting structure. 
     Next, a definition step is performed by using a photolithograph technique and an etching technique to remove a portion of the luminescent structure  106  and a portion of the p-type semiconductor layer  108 , so as to expose a portion of the n-type semiconductor layer  104 . Thereafter, an electrode  110  and an electrode  112  are formed respectively on the p-type semiconductor layer  108  and on the n-type semiconductor layer  104  by using a thermal evaporation method, an e-beam evaporation method, or an ion sputtering method, so as to complete the semiconductor light emitting device. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a semiconductor light emitting device, such as a light emitting diode, the semiconductor light emitting device comprising a semiconductor layer having a scraggly surface and a light scattering-deflecting layer of which a refractive index is different from that of the semiconductor layer. Therefore, light is deflected while the light enters the semiconductor layer from the light scattering-deflecting layer, and the light is scattered while the light enters the scraggly surface of the semiconductor layer, so that the semiconductor light emitting device emits more light. 
     Another objective of the present invention is to provide a method for manufacturing a semiconductor light emitting device, by forming a semiconductor layer having a scraggly surface, and then forming a light scattering-deflecting layer of which a refractive index is different from that of the semiconductor layer. Thus, after light is deflected by the light scattering-deflecting layer and scattered by the semiconductor layer, the light emitting efficiency of the semiconductor light emitting device can be enhanced. 
     According to the aforementioned objectives of the present invention, the present invention provides a semiconductor light emitting device comprising: a transparent substrate, wherein the transparent substrate comprises a semiconductor layer formed thereon, and the semiconductor layer comprises a scraggly surface; a light scattering-deflecting layer located on the scraggly surface of the semiconductor layer; and a semiconductor luminescent epitaxial structure located on the light scattering-deflecting layer. A refractive index of the light scattering-deflecting layer is different from that of the semiconductor layer. 
     According to a preferred embodiment of the present invention, the light scattering-deflecting layer can fill up and level the scraggly surface of the semiconductor layer, or can be conformal with the scraggly surface of the semiconductor layer. 
     According to the aforementioned objectives of the present invention, the present invention provides a method for manufacturing a semiconductor light emitting device comprising the following steps: providing a transparent substrate, wherein the transparent substrate comprises a semiconductor layer formed thereon, and the semiconductor layer comprises a scraggly surface; forming a light scattering-deflecting layer located on the scraggly surface of the semiconductor layer; and forming a semiconductor luminescent epitaxial structure located on the light scattering-deflecting layer. 
     According to a preferred embodiment of the present invention, the step of forming the light scattering-deflecting layer is performed by using a metal organic chemical vapor deposition (MOCVD) method to fill up and level the scraggly surface of the semiconductor layer. 
     The refractive index of the light scattering-deflecting layer is different from that of the semiconductor layer, and the semiconductor layer has a scraggly surface, so that light is deflected and scattered while the light enters the semiconductor layer from the light scattering-deflecting layer. Therefore, the semiconductor light emitting device can emit more light, thus achieving the objective of enhancing the light emitting efficiency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 illustrates a cross-sectional view of a conventional semiconductor light emitting device. 
     FIG. 2 illustrates a cross-sectional view of a semiconductor light emitting device in accordance with a preferred embodiment of the present invention. 
     FIG. 3 illustrates a cross-sectional view of a semiconductor light emitting device in accordance with another preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention discloses a semiconductor light emitting device and a method for manufacturing the same, wherein the semiconductor light emitting device comprises a semiconductor layer having a scraggly surface and a light scattering-deflecting layer located on the semiconductor layer. Therefore, while light enters the semiconductor layer from the light scattering-deflecting layer, the light is deflected and scattered, whereby the semiconductor light emitting device can emit more light, and the light emitting efficiency can be increased. In order to make the illustration of the present invention more explicitly and completely, the following description is stated with reference to the accompanying drawings of FIG.  2  and FIG.  3 . 
     Referring to FIG. 2, FIG. 2 illustrates a cross-sectional view of a semiconductor light emitting device in accordance with a preferred embodiment of the present invention. While forming the semiconductor light emitting device, a semiconductor buffer layer  202  is formed to cover a substrate  200  that is transparent by using such as a metal organic chemical vapor deposition method, wherein the material of the semiconductor buffer layer  202  can be, for example, a III-V semiconductor. Next, a semiconductor film (only a semiconductor layer  204  is shown) is formed to cover the semiconductor buffer layer  202  by using such as a metal organic chemical vapor deposition method. After the semiconductor film is formed, the semiconductor film is defined by using such as a photolithograph method and an etching method to remove a portion of the semiconductor film, so as to form the semiconductor layer  204  having a scraggly surface  206 . While forming the scraggly surface  206  of the semiconductor layer  204 , a wet etching method, a dry etching, or other appropriate methods can be used. In addition, the scraggly surface  206  of the semiconductor layer  204  can have a pattern such as bar convex, circle convex, octagon convex, hexagon convex, tetragon convex, triangle convex, bar concave, circle concave, octagon concave, hexagon concave, tetragon concave, or triangle concave, etc. 
     Then, a light scattering-deflecting layer  208  is formed to cover the scraggly surface  206  of the semiconductor layer  204  by using such as an evaporation method, a plating method, a metal organic chemical vapor deposition method, a molecular beam epitaxy method, or a hydride vapor phase epitaxy method, wherein, a refractive index of the light scattering-deflecting layer  208  is different from that of the semiconductor layer  204 , and the material of the light scattering-deflecting layer  208  is a transparent material. The material of the light scattering-deflecting layer  208  can be Si, Ge, or III-V semiconductor, such as GaAs, InP, AlGaInP, GaN, AlN, InN, and AlInGaN, etc. The material of the light scattering-deflecting layer  208  can be a insulating material, such as SiO 2 , Si 3 N 4 , TiN, Al 2 O 3 , MgO, GaF 2 , ZnS, and SiC, etc. Furthermore, the material of the light scattering-deflecting layer  208  can further be a metal material, such as Cu, Ag, Au, Zn, Cd, Mg, Al, Ga, and In, etc. 
     It is worthy to be noted that, in the preferred embodiment, the light scattering-deflecting layer  208  fills up and levels the scraggly surface  206  of the semiconductor layer  204 , such as shown in FIG.  2 . However, referring to FIG. 3, FIG. 3 illustrates a cross-sectional view of a semiconductor light emitting device in accordance with another preferred embodiment of the present invention. The light scattering-deflecting layer  220  is conformal with the scraggly surface  206  of the semiconductor layer  204 . 
     After the light scattering-deflecting layer  208  or the light scattering-deflecting layer  220  is formed, a semiconductor luminescent epitaxial structure can be grown. First, a n-type semiconductor layer  210  is grown to cover the light scattering-deflecting layer  208  or the light scattering-deflecting layer  220  by using an epitaxy method. Then, a luminescent structure  212  is formed to cover the n-type semiconductor layer  210 , wherein the luminescent structure  212  can be such as a multiple quantum well (MQW) structure. Subsequently, a p-type semiconductor layer  214  is grown to cover the luminescent structure  212  to complete the semiconductor luminescent epitaxial structure. 
     After the p-type semiconductor layer  214  is formed, the p-type semiconductor layer  214  and the luminescent structure  212  are defined by using such as a photolithograph method and an etching method to remove a portion of the p-type semiconductor layer  214  and a portion of the luminescent structure  212 , so as to expose a portion of the n-type semiconductor layer  210 . Then, a p-type electrode  216  is formed on a portion of the p-type semiconductor layer  214 , and a n-type electrode  218  is formed on the exposed portion of the n-type semiconductor layer  210  by using such as a plating method to complete the forming of the semiconductor light emitting device, such as a light emitting diode. 
     In one preferred embodiment of the present invention, the semiconductor buffer layer  202  with a thickness of 25 nm is formed on the substrate  200  that is transparent by using a metal organic chemical vapor deposition method under 550° C. wherein the material of the substrate  200  is Al 2 O 3 , and the material of the semiconductor buffer layer  202  is GaN. A semiconductor layer  204  with a thickness of 2 μm is formed on the semiconductor buffer layer  202  by using a metal organic chemical vapor deposition method under 1100° C. wherein the material of the semiconductor layer  204  is GaN. Then, a photoresist layer comprising a plurality of circle patterns with a diameter of 2 μm is formed on a surface of the semiconductor layer  204  by using a photolithograph method to expose a portion of the semiconductor layer  204 , wherein the distance between two adjacent circle patterns is 2 μm. The semiconductor layer  204  is etched by using a reactive ion etching (RIE) method to form a plurality of circle concaves with a depth of about 1 μm. 
     Next, a AlN layer of about 1.5 μm in thickness of is grown by using a metal organic chemical vapor deposition method, and is used as the light scattering-deflecting layer  208 , wherein the light scattering-deflecting layer  208  fills up and levels the circle concaves on the scraggly surface  206  of the semiconductor layer  204 . A silicon-doped n-type GaN layer of 2 μm in thickness is grown by using an epitaxy method, and is used as the n-type semiconductor layer  210 . After the n-type semiconductor layer  210  is formed, a multiple quantum well structure composed of five pairs of InGaN/GaN is grown by using an epitaxy method, and is used as the luminescent structure  212 . A magnesium-doped p-type GaN layer of 0.5 μm in thickness is grown by using an epitaxy method under 1000° C. and is used as the p-type semiconductor layer  214 . 
     Subsequently, a definition step is performed by using a reactive ion etching method to remove a portion of the p-type semiconductor layer  214  and a portion of the luminescent structure  212 , so as to expose a portion of the n-type semiconductor layer  210 . A Ni/Au layer is formed on the p-type semiconductor layer  214  to be used as the p-type electrode  216 , and a Ti/Al layer is formed on the n-type semiconductor layer  210  to be used as the n-type electrode  218  by using a plating method, so as to complete the semiconductor light emitting device. 
     According to the experiment result, the light emitting brightness of a semiconductor light emitting device having a light scattering-deflecting layer formed by using the aforementioned process can be increased 5% to 15%. 
     A feature of the present invention is that: the semiconductor light emitting device of the present invention comprises the semiconductor layer  204  having the scraggly surface  206  and the light scattering-deflecting layer  208  (as shown in FIG. 2) or the light scattering-deflecting layer  220  (as shown in FIG. 3) of which a refractive index is different from that of the semiconductor layer  204 . While light enters the light scattering-deflecting layer  208  or the light scattering-deflecting layer  220  from the luminescent structure  212  and through the n-type semiconductor layer  210 , and enters the semiconductor layer  204  from the light scattering-deflecting layer  208  or the light scattering-deflecting layer  220 , the light is deflected because the refractive index of the light scattering-deflecting layer  208  or that of the light scattering-deflecting layer  220  is different from that of the semiconductor layer  204 . Besides, the light is scattered while the light enters the scraggly surface  206  because the junction surface between the semiconductor layer  204  and the light scattering-deflecting layer  208  or the light scattering-deflecting layer  220  is the scraggly surface  206 . Therefore, while the light enters the semiconductor layer  204 , the light is deflected and scattered at the same time, so as to emit more light and increase the light emitting efficiency of the semiconductor light emitting device. 
     According to the aforementioned description, one advantage of the present invention is that: because the semiconductor light emitting device of the present invention comprises a semiconductor layer having a scraggly surface and a light scattering-deflecting layer of which a refractive index differed from that of the semiconductor layer, light is deflected while the light entering the semiconductor layer from the light scattering-deflecting layer and is also scattered while the light entering the scraggly surface of the semiconductor layer, thus making the semiconductor light emitting device emit more light and increasing brightness of the semiconductor light emitting device effectively, so as to achieve the objective of enhancing the light emitting efficiency of the semiconductor light emitting device. 
     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.