Abstract:
A semiconductor light emitting device including a substrate including a plurality of discrete and separated protruding reflective patterns protruding from the substrate and including a valley; a first semiconductor layer on the substrate and covering the reflective patterns; a gap formed in the valley of a corresponding reflective pattern between the substrate and the first semiconductor layer; an active layer on the first semiconductor layer; and a second semiconductor layer on the active layer.

Description:
The present application is a continuation of application Ser. No. 12/103,553, filed on Apr. 15, 2008 now U.S. Pat. No. 7,732,802, and claims priority under 35 U.S.C. 119 and 35 U.S.C. 365 to Korean Patent Application No. 10-2007-0036856 filed on Apr. 16, 2007, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Light emitting diodes (LEDs) can emit light having various colors by using GaAs, AlGaAs, GaN, InGaN, and InGaAlP-based compound semiconductor materials. Such LEDs are packaged to be used as a light source in various fields such as a lightening indicator, a character indicator, and an image indicator. 
     Such a LED has a structure in which an N-type semiconductor layer, an active layer, and a P-type semiconductor layer are stacked on each other, and light is generated from the active layer and emitted to an exterior if power is applied to the LED. 
     SUMMARY 
     The embodiment provides a semiconductor light emitting device comprising an air gap on a substrate or on a pattern of the substrate. 
     The embodiment provides a semiconductor light emitting device comprising an air gap on a reflective pattern of a substrate. 
     The embodiment provides a semiconductor light emitting device, in which an air gap is formed between a substrate and a semiconductor layer, thereby improving external quantum efficiency. 
     The embodiment provides a semiconductor light emitting device comprising; a substrate comprising a reflective pattern with a valley, a first nitride semiconductor layer on the substrate, an air gap formed between the reflective pattern and the first nitride semiconductor layer, an active layer on the first nitride semiconductor layer, and a second nitride semiconductor layer on the active layer. 
     The embodiment provides a semiconductor light emitting device comprising; a substrate comprising a valley, a first nitride semiconductor layer on the substrate, an air gap formed in the valley between the substrate and the first nitride semiconductor layer, an active layer on the first nitride semiconductor layer, and a second nitride semiconductor layer on the active layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view showing a semiconductor light emitting device according to a first embodiment; 
         FIGS. 2 to 10  are views showing a method for manufacturing a semiconductor light emitting device according to the first embodiment; and 
         FIG. 11  is a side sectional view showing a semiconductor light emitting device according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a semiconductor light emitting device according to the embodiments will be described with respect to accompanying drawings. 
       FIG. 1  is a side sectional view showing a semiconductor light emitting device  100  according to the first embodiment. 
     Referring to  FIG. 1 , the semiconductor light emitting device  100  comprises a substrate  110  comprising a reflective pattern  115 , a first nitride semiconductor layer  120 , an active layer  130 , a second nitride semiconductor layer  140 , a first electrode  151 , and a second electrode  153 . 
     The substrate  110  comprises one of Al 2 O 3 , SiC, ZnO, Si, GaAs, GaN, and a substrate with metal ingredient. The substrate  110  may comprise conductivity. Such a substrate  110  maybe formed on a surface  113  thereof with a plurality of reflective patterns  115 . The reflective pattern  115  comprises a ring-shape profile, and is formed therein with a valley  117  comprising a predetermined depth. The ring-shape profile may correspond to one of a cylindrical shape, a ring shape, a doughnut shape, and a polygonal prism shape. 
     The reflective patterns  115  may be formed on the substrate  110  at a constant interval or a random interval, but the embodiment is not limited thereto. 
     The first nitride semiconductor layer  120  is formed on the substrate  110 . An air gap  119  is formed between the substrate  110  and the first nitride semiconductor layer  120 . 
     The air gap  119  is formed in a portion of or an entire area of the valley  117  provided in the reflective pattern  115 , and filled with air. Such an air gap may comprise a reverse pyramid shape such as a reverse conical shape or a reverse polygonal pyramid shape. 
     The refractive index of the air gap  119  is 1, and comprises a value different from the refractive index of the substrate  110 , the reflective pattern  115 , and the first nitride semiconductor layer  120 . Accordingly, light generated from the active layer  130  is refracted or reflected from the reflective pattern  115  and the air gap  119  positioned at the border of the substrate  110  and the first nitride semiconductor layer  120 , so that the light may be emitted to an exterior. 
     The first nitride semiconductor layer  120  comprises at least one of a buffer layer, an undoped semiconductor layer, and an N-type semiconductor layer. For example, the N-type semiconductor layer may be formed on the substrate  110 , or the buffer layer and the N-type semiconductor layer may be sequentially stacked on the substrate  110 . In addition, the buffer layer, the undoped semiconductor layer, and the N-type semiconductor layer may be sequentially stacked on the substrate  110 . The buffer layer comprises GaN, InN, AlN, AlInN, InGaN, AlGaN, or InAlGaN. The undoped semiconductor layer comprises GaN. The N-type semiconductor layer comprises GaN, InN, AlN, InGaN, AlGaN, or InAlGaN. The N-type semiconductor layer may be doped with an N-type dopant such as Si, Ge, Sn, Se, or Te. 
     The active layer  130  is formed on the first nitride semiconductor layer  120 , and may comprise a single quantum well or a multiple quantum well. 
     The second nitride semiconductor layer  140  is formed on the active layer  130 . The second nitride semiconductor layer  140  may be a P-type semiconductor layer comprising one selected from the group consisting of GaN, AlGaN, InGaN, and InAlGaN, and is doped with a P-type dopant such as Mg, Be, or Zn. 
     In this case, another semiconductor layer may be additionally formed over and/or under each of the semiconductor layers  120 ,  130 , and  140 , and such a stacked structure of the semiconductor layers may be modified. In addition, the second nitride semiconductor layer  140  may comprise a semiconductor layer comprising a P-type semiconductor layer and an N-type semiconductor layer stacked on the P-type semiconductor layer. 
     The first electrode  151  may be formed on the first nitride semiconductor layer, and the second electrode  153  may be formed on the second nitride semiconductor layer  140 . The second electrode  153  selectively comprises ITO, ZnO, RuOx, TiOx, or IrOx, or may comprise a one layer or multiple layers comprising a material such as Ti, Au, Pd, or Ni. However, the embodiment is not limited thereto. 
     The first nitride semiconductor layer  120  may comprise a P-type semiconductor layer, and the second nitride semiconductor layer  140  may comprise an N-type semiconductor layer. In addition, the first electrode may be formed under the substrate  110 , and the substrate  110  may be the conductive support substrate. 
       FIGS. 2 to 10  are views showing the manufacturing process of the semiconductor light emitting device according to the first embodiment. 
     Referring to  FIGS. 2 and 3 , after coating a photoresist layer  111  on the substrate  110 , a light is exposed on the photoresist layer  111 , thereby forming mask patterns  111 A. According to the embodiment, such a mask pattern forming process or the interval of the mask patterns  111 A may vary. The substrate  110  comprises one of Al 2 0 3 , SiC, ZnO, Si, GaAs, GaN, and a substrate with metal ingredient. The substrate  110  may employ a conductive substrate. 
       FIG. 4  is a plan view showing the mask pattern  111 A formed on the substrate  110  according to the first embodiment. 
     Referring to  FIG. 4 , the mask pattern  111 A comprises a ring-shape of ring profile. The ring-shape profile corresponds to one of a cylindrical shape, a ring shape, and a doughnut shape. The mask pattern  111 A may comprise an oval prism shape or a polygonal prism shape. In addition, the mask pattern  111 A may comprise a structure in which a plurality shapes, oval shapes, and polygonal shapes are coupled to each other. 
     Referring to  FIG. 5 , an etching process may be formed over the substrate  110 . The etching process is performed except for the mask pattern  111 A. At this time, the reflective pattern  115  is formed on the surface  113  of the substrate  110 . The above etching scheme comprises a dry etching scheme such as a reactive ion etching (RIE) scheme or an inductive coupled plasma scheme. 
     The reflective pattern  115  comprising a ring shape is formed on the surface  113  of the substrate  110 . If such a reflective pattern  115  is formed, the mask pattern  111 A is removed or cleaned. 
     The valley  117  is formed in the reflective pattern  115  by a predetermined depth. The depth of the valley  117  corresponds to a surface depth of the substrate  110 , and the embodiment is not limited thereto. 
       FIG. 6  is a perspective view showing the substrate comprising the reflective pattern according to the first embodiment. 
     Referring to  FIG. 6 , a plurality of reflective patterns  115  are formed on the surface  113  of the substrate  110 , and the adjacent reflective patterns  115  are arranged in a zigzag way. The valley  117  comprising a reverse conical shape is formed in the reflective pattern  115  by a predetermined depth. 
       FIGS. 7(A) and 7(B)  are a plan view and a side sectional view showing the reflective pattern  115  according to the first embodiment. 
     Referring to  FIG. 7 , the ring-shape profile of the reflective pattern  115  is formed corresponding to a triangle shape or a pyramid shape, and the valley  117  comprising a reverse conical shape or a reverse polygonal pyramid shape is formed in the reflective pattern  115 . 
       FIG. 8  is a side sectional view showing the substrate formed with a light emitting structure according to the first embodiment, and  FIG. 9  is an enlarged view partially showing the reflective pattern  115  of  FIG. 8 . 
     Referring to  FIGS. 8 and 9 , the first nitride semiconductor layer  120  is formed on the substrate  110 . The first nitride semiconductor layer  120  comprises at least one of the buffer layer, the undoped semiconductor layer, and the N-type semiconductor layer. If the first nitride semiconductor layer  120  is an N-type GaN layer, the N-type GaN layer is formed by supplying an atmospheric gas (selected from H 2 , N 2 , and NH 3 ), a source gas (TMGa or TEGa), and Si. 
     The air gap  119  is formed between the reflective pattern  115  comprising a ring-shape profile and the first nitride semiconductor layer  120 . The air gap  119  corresponds to a predetermined area of the inner valley  117  of the reflective pattern  115 . The air gap  119  comprises air instead of the first nitride semiconductor layer  120 . In this case, when the valley  117  of the reflective pattern  115  comprises a diameter smaller than or equal to a predetermined diameter (e.g., 0.5 μm to 1 μm), the air gap  119  may be formed. Therefore, the shape of the reflective pattern  115  can be changed within the range that the valley  117  of the reflective pattern  115  satisfies the above diameter. 
     The air gap  119  comprises a refractive index of 1 which is an air refractive index. In detail, the refractive index of the air gap  119  is different from those of the substrate  110 , the reflective pattern  115 , and the first nitride semiconductor layer  120 . 
     Referring to  FIG. 9 , the ring thickness D 2  of the reflective pattern  115  is in the range of about 1.5 um to about 2 um. The least diameter D 1  of the valley  117  maybe 0.5 um or less, and the interval D 5  between rings may be in the range of about 1.5 um to about 2 um. In addition, the diameter D 4  of the reflective pattern  115  is in the range of about 3.5 um to about 5 um. The height H 1  of the ring or depth of the valley  117  of the reflective pattern  115  maybe the range of about 1.5 um to about 2 um, and the distance D 3  between adjacent reflective patterns may be in the range of about 2 um or about 3 um. The embodiment is not limited to the size of the reflective pattern and the air gap, and the size of the reflective pattern and the air gap may be changed. 
     Referring to  FIG. 10 , a portion of the first nitride semiconductor layer  120  is exposed by etching a portion of the second nitride semiconductor layer  140 . The first electrode  151  is formed on the exposed portion of the first nitride semiconductor layer  120 , and the second electrode  153  is formed on the second nitride semiconductor layer  140 . 
     The embodiment can employ one of a P-N junction structure, an N-P junction structure, a P-N-P junction structure, and an N-P-N junction structure based on compound semiconductor materials comprising GaAs, AlGaAs, GaN, InGaN, and AlGaInP. 
     If current is applied through the first and second electrodes  151  and  153 , the semiconductor light emitting device  100  generates a light from the active layer  130  and emits the light in all directions. At this time, a light toward the substrate  110  is scattered by the reflective pattern  115  positioned at the border of the substrate  110  and the first nitride semiconductor layer  120 . In addition, the light toward the substrate  110  is refracted by the air gap  119  of the reflective pattern  115  or reflected by the substrate surface  113 . Therefore, a light progressing to the substrate  110  is reflected or the incident angle of the light is changed by the reflective pattern  115  and the air gap  119 , so that the light maybe sufficiently delivered to the outside of the semiconductor light emitting device. Accordingly, it is possible to improve external quantum efficiency. 
       FIG. 11  is a side sectional view showing a semiconductor light emitting device according to a second embodiment. The same reference numerals will be assigned to elements identical to those of the first embodiment, and details of thereof will be omitted. 
     Referring to  FIG. 11 , a semiconductor light emitting device  100 A comprises an air gap  119 A formed on a surface  113  of a substrate  110 . The air gap  119 A may comprise a reverse conical shape or a reverse polygonal pyramid shape, and a predetermined length within a predetermined diameter (e.g., 2 um). 
     The air gap  119 A exists as air in a valley  117 A or a portion of the valley  117 A formed on the surface  113  of the substrate  110 , and refracts or reflects an incident light. 
     The first nitride semiconductor layer  120  is formed on the substrate  110 , comprises at least one of a buffer layer, an undoped semiconductor layer, and an N-type semiconductor layer. Here, the first nitride semiconductor layer  120  may comprises P-type semiconductor. 
     The embodiment can employ a vertical semiconductor light emitting device. In the vertical semiconductor light emitting device, a first nitride semiconductor layer, an active layer, a second nitride semiconductor, a adhesive layer, a conductive support substrate are formed on a substrate (not shown). The conductive support substrate is formed on the second nitride semiconductor, and the second electrode is formed on the conductive support substrate. In here, the conductive support substrate may be coupled to the second nitride semiconductor layer  120  by the adhesive layer. Also The substrate (not shown) is removed by a physical or chemical removal method, for instance a laser lift off (LLO) method. Next, the conductive support substrate is positioned on a base, and a first electrode is formed on the first nitride semiconductor. In this case, the reflective pattern  115  comprising the valley may be formed at the conductive support substrate 
     Also, the conductive support substrate is formed under the first nitride semiconductor, and the first electrode is formed under the conductive support substrate. 
     When it is described according to the embodiment that a layer (films), a region, a pattern, or structures are formed “on” or “under” another layer, another region, another pad, other patterns, it means that they are “directly” or “indirectly” formed “on” or “under” another layer, another region, another pad, other patterns. The substrate and the thickness of each semiconductor layer have been described for illustrative purposes, and the embodiment is not limited to a thickness ratio shown in drawings. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.