JP2011159650A - Light-emitting element - Google Patents

Abstract

A light-emitting element with improved light extraction efficiency is provided.
[Solution]
The light-emitting element of the present invention includes an optical semiconductor layer 2 that emits light toward one main surface 2A, and an inclined surface 4 that has an inner angle t1 that is less than 90 degrees with respect to one main surface 2A. A plurality of light-transmitting protrusions 3 arranged in a row on the surface 2A, and when the plurality of protrusions 3 are viewed in plan, each inclined surface 4 is a row in which the plurality of protrusions 3 are disposed. When the plurality of protrusions 3 are viewed in cross-section from a direction perpendicular to the column direction Ge, the cross-sectional outline is non-axisymmetric with respect to the normal Hb of the one main surface 2A.
[Selection] Figure 1

Description

  The present invention relates to a light emitting element.

  Currently, light emitting elements that emit ultraviolet light, blue light, green light, and the like are being developed. For example, Patent Document 1 is disclosed as such a light emitting element.

JP 2005-277374 A

  In the development of a light emitting element, it is required to improve the light extraction efficiency for extracting light emitted internally when the light emitting element emits light. The present invention has been made in view of the above, and an object thereof is to provide a light emitting element with improved light extraction efficiency.

  The light-emitting element according to the present invention has an optical semiconductor layer that emits light toward one main surface, an inclined surface that has an inner angle of less than 90 degrees with the one main surface, and is provided on one main surface of the optical semiconductor layer. A plurality of light-transmitting protrusions arranged in rows, and when the plurality of protrusions are viewed in plan, each inclined surface faces one direction of the row where the plurality of protrusions are arranged When the plurality of protrusions are viewed in cross-section from a direction perpendicular to the column direction, the cross-sectional outline is non-axisymmetric with respect to the normal of one main surface.

  The light-emitting element according to the present invention includes a substrate, an optical semiconductor layer that is provided on one main surface of the substrate, and emits light toward the one main surface, and an internal angle between the other main surface of less than 90 degrees. A plurality of light-transmitting protrusions arranged in a row on the other main surface of the substrate, and when the plurality of protrusions are viewed in plan, each of the inclined surfaces is When the plurality of protrusions are arranged in one direction of the row in which the plurality of protrusions are arranged and the plurality of protrusions are viewed in a cross section from a direction perpendicular to the row direction, the cross-sectional outline line is relative to the normal line of the other main surface It has a non-axisymmetric shape.

  ADVANTAGE OF THE INVENTION According to this invention, the light emitting element which improved light extraction efficiency can be provided.

1 is a perspective view of a light emitting device according to a first embodiment of the present invention. It is a top view of the light emitting element concerning the 1st Embodiment of this invention, and is equivalent to the plane when planarly viewing FIG. FIG. 3 is a cross-sectional view of the light-emitting element shown in FIG. 1 or 2, and corresponds to a cross section taken along line AA ′ of FIG. 1. It is sectional drawing to which some light emitting elements concerning the 1st Embodiment of this invention were expanded. It is sectional drawing to which some light emitting elements concerning the 1st Embodiment of this invention were expanded. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is sectional drawing of the light emitting element which shows the manufacturing process of the light emitting element concerning the 1st Embodiment of this invention. It is a top view of the light emitting element concerning the 2nd Embodiment of this invention. It is sectional drawing of the light emitting element shown in FIG. 14, and is equivalent to a cross section when cut | disconnected by the BB 'line | wire of FIG. It is sectional drawing of the light emitting element which shows the modification of the light emitting element concerning embodiment of this invention. It is sectional drawing of the light emitting element which shows the modification of the light emitting element concerning embodiment of this invention.

  Embodiments of a light-emitting element according to the present invention will be described below in detail with reference to the drawings.

  The present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention.

(First embodiment)
<Structure of light emitting element>
FIG. 1 is a perspective view of a light emitting element 20 according to the present embodiment, and FIG. 2 is a plan view of the light emitting element 20 shown in FIG. FIG. 3 is a cross-sectional view, and corresponds to a cross section taken along the line AA ′ of FIGS.

  1 to 3, the light emitting element 20 includes a substrate 1, an optical semiconductor layer 2 formed on the substrate 1, a protrusion 3 formed on one main surface 2A of the optical semiconductor layer 2, an optical A pair of electrodes 5 for applying a voltage to the semiconductor layer 2.

  For the substrate 1, a material capable of growing the optical semiconductor layer 2 can be used. As a material capable of growing the optical semiconductor layer 2, for example, a crystalline material such as sapphire, gallium nitride, aluminum nitride, or zinc oxide can be used. The substrate 1 is prepared by single-crystallizing such a crystalline material and then cutting the single crystal into a desired shape. Further, such a substrate 1 is set to have a planar shape such as a rectangular flat plate or a substantially circular wafer.

  When the light emitted from the light emitting layer 2b is extracted from the first semiconductor layer 2a side of the light emitting layer 2b, the substrate 1 can be made of a material capable of removing the substrate 1 or a light transmissive material. Specifically, when a material capable of removing the substrate 1 is used as the substrate 1, a step of removing the substrate 1 by etching or the like after forming the optical semiconductor layer 2 on the substrate 1 may be added. Further, when a light-transmitting material is used for the substrate 1, the light-transmitting material can be selected from the above materials in consideration of the emission wavelength with respect to the light emitted from the light-emitting layer 2b. In addition, the board | substrate 1 is set to the thickness of 10 micrometers or more and 1000 micrometers or less, for example.

  An optical semiconductor layer 2 is provided on the substrate 1. The optical semiconductor layer 2 includes a first semiconductor layer 2a formed on the main surface 1A of the substrate 1, a light emitting layer 2b formed on the first semiconductor layer 2a, and a second semiconductor layer formed on the light emitting layer 2b. 2c. Note that the entire thickness of the optical semiconductor layer 2 is, for example, not less than 100 nm and not more than 5000 nm.

The optical semiconductor layer 2 can use a group III-V semiconductor. Examples of group III-V semiconductors include group III nitride semiconductors, gallium phosphide, gallium arsenide, and the like. Examples of the group III nitride semiconductor include gallium nitride, aluminum nitride, indium nitride, and the like. When exemplified by a chemical formula, Al _x1 Ga _(1-x1-y1) In _y1 N (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, x1 + y1 ≦ 1). In addition to the group III-V semiconductor, for example, zinc oxide can be used.

  The first semiconductor layer 2a and the second semiconductor layer 2c are formed so as to have opposite conductivity types. As a method for imparting such a conductivity type, for example, a method of mixing magnesium or silicon as an impurity can be used.

The light emitting layer 2b is provided between the first semiconductor layer 2a and the second semiconductor layer 2c. The light-emitting layer 2b is a multilayer quantum well in which a quantum well structure composed of a barrier layer having a wide forbidden band and a well layer having a narrow forbidden band is repeatedly stacked a plurality of times (for example, 2 to 10 times). It is good also as a structure (MQW). As the above-described barrier layer, an In _0.01 Ga _0.99 N layer or the like can be used as exemplified by the above chemical formula. Examples of the well layer described above include an In _0.11 Ga _0.89 N layer. In this case, the thickness of the barrier layer can be set to, for example, 5 nm to 15 nm, the thickness of the well layer can be set to, for example, 2 nm to 10 nm, and the total thickness of the light emitting layer 2b is, for example, 25 nm to 150 nm. In addition, the light emitting layer 2b configured as described above emits light having a wavelength of, for example, 350 nm or more and 600 nm or less. In addition, the refractive index of each layer of the optical semiconductor layer 2 is set to, for example, 1.70 or more and 2.70 or less.

  A pair of electrodes 5 for applying a voltage for light emission is further formed on the optical semiconductor layer 2 on which the protrusions 3 are formed. Such a pair of electrodes 5 is paired with a first electrode 5a electrically connected to the first semiconductor layer 2a and a second electrode 5b electrically connected to the second semiconductor layer 2c. Yes. The first electrode 5a is formed on the first semiconductor layer 2a, and the second electrode 5b is formed on the second semiconductor layer 2c. By applying a voltage to the first electrode 5a and the second electrode 5b of the pair of electrodes 5 thus formed, the light emitting layer 2b can emit light.

  A plurality of protrusions 3 are arranged in a row on the main surface 2A of the second semiconductor layer 2c. These protrusions 3 have inclined surfaces 4 having an inner angle t1 formed with the main surface 2A of less than 90 degrees. FIG. 4 is an enlarged cross-sectional view showing a part of the protrusion 3 and the second semiconductor layer 2c shown in FIG. The protrusion 3 is configured such that, when viewed in a cross-section from a direction perpendicular to the column direction Ge of the plurality of protrusions 3, its cross-sectional outline is axisymmetric with respect to the normal Hb of the one main surface. Here, the inclined side 4a indicates a side when the inclined surface 4 is viewed in a cross section from a direction perpendicular to the column direction Ge of the plurality of protrusions 3. The non-axisymmetric shape is the normal line Hb of the main surface 2A. A shape that is not line-symmetric. Further, the cross-sectional outline is a line on the outer periphery of the protrusion 3 when viewed in cross section, and indicates an envelope when the surface of the protrusion 3 is rough at a wavelength or less.

  Such a protrusion 3 is formed in a circular or polygonal shape in plan view, and the diameter of the bottom surface can be set to 450 nm or more and 1000 nm or less, for example. Further, the height of the protrusion 3 can be set to 400 nm or more and 1000 nm or less, for example. When the protrusion 3 and the second semiconductor layer 2c are made of different materials, the height of the protrusion 3 indicates the height from the bottom surface to the apex, and the protrusion 3 is formed integrally with the second semiconductor layer 2c. In this case, a line segment where the main surface 2A and the protrusion 3 overlap each other in a cross-sectional view can be used as the base.

  The protrusion 3 is made of a light-transmitting material that transmits light emitted from the light emitting layer 2b. Examples of such protrusions 3 include at least one of oxides, fluorides or nitrides of titanium, tantalum, aluminum, magnesium, silicon, zirconium, hafnium, yttrium, sodium, thorium, scandium, neodymium, niobium. A translucent material can be used.

  Of such translucent materials, a material having a higher refractive index than the second semiconductor layer 2 c is preferably used for the protrusions 3. Specifically, zirconium oxide, titanium oxide, magnesium oxide, hafnium oxide, niobium oxide, or the like can be used. By forming the protrusion 3 with a material having a higher refractive index than that of the second semiconductor layer 2c, the protrusion 3 can be totally reflected at the interface between the second semiconductor layer 2c and the protrusion 3 and hardly returned to the second semiconductor layer 2c. The protrusion 3 may be formed of the same material as the second semiconductor layer 2c. In that case, the protrusion 3 may be formed integrally with the second semiconductor layer 2c.

  Furthermore, the protrusion 3 has the inclined surface 4 so that the cross-sectional outline is non-axisymmetric. Since the cross-sectional outline of the protrusion 3 has a non-axisymmetric shape, the number of total reflections in the protrusion 3 can be reduced compared with the case of the line-symmetric shape, and the optical semiconductor layer 2 is returned to. Can be difficult. As a result, the light extraction efficiency of the light emitting element 20 can be improved.

  Specifically, since the protrusion 3 has a shape that is not line symmetric with respect to the normal Hb of the main surface 2A, the critical angle at each side of the protrusion 3 is different, and light incident from the bottom surface of the protrusion 3 Even if it is a case where it totally reflects on the end surface of the protrusion 3, it becomes difficult to repeat total reflection. As a result, the light once incident on the protrusion 3 is less likely to return to the optical semiconductor layer 2, and the light extraction efficiency of the light emitting element 20 can be improved.

  On the other hand, when the protrusion is formed from a line-symmetric shape that is line-symmetric with respect to the normal line of the main surface of the optical semiconductor layer, light incident on the protrusion is likely to return to the optical semiconductor layer by repeating total reflection. Become. Specifically, once the light incident on the protrusion is totally reflected at the end face of the protrusion, it is likely to be larger than the critical angle and easily reflected at the other end face, so that it easily returns to the optical semiconductor layer. The light extraction efficiency of the light emitting element is likely to be reduced. Further, since the amount of light returning to the optical semiconductor layer increases, the light returning to the optical semiconductor layer is non-radiatively recombined and converted into heat, so that the light emission efficiency of the light emitting element is likely to be reduced.

  In the present embodiment, as shown in FIGS. 2 and 3, the plurality of protrusions 3 are formed so that each inclined surface 4 of the plurality of protrusions 3 is in one direction of the column direction Ge when the plurality of protrusions 3 are viewed in plan view. Therefore, the light extraction efficiency can be further improved. This will be described below with reference to FIG.

  The light beam Li shown in FIG. 4 illustrates the path of light emitted from the light emitting layer 2 b of the optical semiconductor layer 2. Specifically, as shown by the light beam Li in FIG. 4, a part of the light entering the protrusion 3, that is, light whose incident angle to the inclined side 4a is larger than the critical angle is totally reflected by the inclined side 4a. Then, it proceeds toward the adjacent protrusion 3. Thereafter, the light reflected by the inclined side 4 a is more likely to be further totally reflected upward by the inclined side 4 a of the adjacent protrusion 3. As a result, the light extraction efficiency above the light emitting element 20 can be improved. Further, the amount of light totally reflected upward may be adjusted by adjusting the internal angle t1 formed by the inclined surfaces 4 of the plurality of protrusions 3 and the main surface 2A. Thus, the light extraction efficiency can be adjusted by adjusting the inner angle t1. The interior angle t1 may be set to 0 degree or more and less than 90 degrees. Among these, it is preferable that the angle is set to about 40 degrees or more and less than 70 degrees from the viewpoint of the number of the protrusions 3 and total reflection at the end face of the protrusion 3.

  Further, as shown in FIG. 5, a reflective layer 6 may be provided on the inclined surface 4. By providing the reflective layer 6 on the inclined surface 4 in this way, the light reflected by the inclined side 4a of the adjacent projection 3 can be more easily reflected upward. As a result, the light extraction efficiency above the light emitting element 20 can be further improved. For example, a metallic material can be used as the reflective layer 6.

<Method for manufacturing light-emitting element>
Next, a method for manufacturing the light emitting element 20 will be described. 6 to 16 are cross-sectional views for explaining a method for manufacturing the light-emitting element 20, and show a portion corresponding to a cross section taken along the line AA 'of the light-emitting element 20 shown in FIGS.

(Optical semiconductor layer preparation process)
As shown in FIG. 6, a substrate 1 is prepared. As the substrate 1, as described above, a planar substrate such as a rectangular flat plate or a substantially circular wafer can be used.

  Next, as shown in FIG. 7, the optical semiconductor layer 2 is formed on the main surface 1 </ b> A of the substrate 1. As a method for growing the optical semiconductor layer 2, that is, the first semiconductor layer 2a, the light emitting layer 2b, and the second semiconductor layer 2c, molecular beam epitaxy (MBE) method, metal organic epitaxy (MOVPE) For example, a hydride vapor phase epitaxy (HVPE) method or a pulsed laser deposition (PLD) method can be used. As a material of such an optical semiconductor layer 2, for example, a group III-V semiconductor can be used. In addition, the optical semiconductor layer 2 laminated | stacked on the board | substrate 1 can set the whole thickness to 100 nm or more and 2000 nm or less, for example.

(Projection formation process)
Next, the protrusion 3 having the inclined surface 4 is formed on the main surface 2A of the second semiconductor layer 2c of the optical semiconductor layer 2 formed in this way. The formation direction of the protrusion 3 will be described below with reference to FIGS.

  First, as shown in FIG. 8, the laminated film 10 is formed on the main surface 2A of the second semiconductor layer 2c. As the material of the laminated film 10, a material that becomes the protrusion 3 is used. As the material of the protrusion 3, for example, a material containing at least one kind of oxide, fluoride, or nitride made of Ti, Ta, Al, Mg, Si, Zr, Hf, Y, Th, Sc, Nd, Nb, and Na. Of these, a translucent material can be used. Further, the thickness of the laminated film 10 may be formed to the same thickness as that of the protrusion 3, and can be set to 400 nm or more and 1000 nm or less, for example.

  Such a laminated film 10 can be formed by a physical lamination method such as a spin coating method, a sputtering method, or a vapor deposition method. When the spin coating method is used among the laminating methods exemplified as described above, a uniform film can be formed in a short time, so that the formation time of the laminated film 10 can be shortened, and the productivity is improved. Can be improved.

  After forming the laminated film 10 on the main surface 2A of the second semiconductor layer 2c, as shown in FIG. 9, the exposed area 13 where a part of the laminated film 10 is exposed is formed on the main surface 10A of the laminated film 10. Thus, the first mask pattern 11 having a plurality of through holes is formed. The planar view shape of the exposed region 13 of the first mask pattern 11 can be set according to the shape of the protrusion 3 to be formed, and for example, a polygonal shape or a circular shape can be used.

  As a method of forming the first mask pattern 11, for example, a conventional photolithography method can be used. By forming such a first mask pattern 11, it is possible to form a line-symmetric preliminary projection 14 at a position where the first mask pattern 11 and the laminated film 10 overlap with each other in a plan view.

  After forming the first mask pattern 11 on the main surface 2A of the optical semiconductor layer 2 in this way, the exposed region 13 of the stacked film 10 is etched from the main surface 10A by an etching method such as wet etching or dry etching. By removing a part of the laminated film 10 in the depth direction, the preliminary protrusion 14 is formed. Specifically, for example, when the trapezoidal preliminary protrusion 14 is formed using wet etching, side etching or the like can be used. The preliminary projections 14 formed in this way have a line-symmetric shape on the main surface 2A of the second semiconductor layer 2 with respect to the normal line of the main surface 2A. Further, the preliminary projection 14 can be set to have a polygonal shape such as a trapezoidal shape or a quadrangular shape as a cross-sectional outline when viewed in cross-section.

  Thereafter, as shown in FIG. 11, a second mask pattern 12 covering a part of the preliminary projection 14 is formed. The second mask pattern 12 is prepared by using a physical layering method such as a sputtering method or a vapor deposition method for the material of the second mask pattern 12 from an upward direction inclined with respect to the main surface 2A of the second semiconductor layer 2c. A second mask pattern 12 covering a part of the protrusion 14 can be formed. Among such lamination methods, it is preferable to use a vapor deposition method in which the material of the second mask pattern 12 is less wraparound. Specifically, for example, the second mask pattern 12 can be formed by a vapor deposition method from a position inclined about 45 degrees from the X axis to the Z axis. Here, the X axis and the Y axis are taken so that the XY plane is parallel to the main surface 2A of the second semiconductor layer 2c, and the Z axis is a direction perpendicular to the XY plane.

  The mask material of the first mask pattern 11 and the second mask pattern 12 can be selected depending on the selection ratio of the laminated film 10 to be etched and the mask material that is difficult to etch. For example, inorganic materials such as silicon oxide and silicon nitride, chromium, etc. A metal such as nickel can be used.

  Further, after the second mask pattern 12 is formed in this way, a part of the preliminary projection 14 is removed from the upper direction perpendicular to the Z-axis direction by using an etching method or the like. Thereby, as shown in FIG. 12, the protrusion 3 having a non-symmetrical shape with respect to the normal line of the main surface 2A of the second semiconductor layer 2c can be formed.

(Electrode formation process)
Next, a pair of electrodes 5 for emitting light from the light emitting layer 2b is formed by applying a voltage to the optical semiconductor layer 2 formed in this way. Such a pair of electrodes 5 includes a first electrode 5a connected to the first semiconductor layer 2a and a second electrode 5b connected to the second semiconductor layer 2c.

  An electrode groove 15 is formed in the optical semiconductor layer 2 in order to provide the first electrode 5a. Specifically, as shown in FIG. 13, the second semiconductor layer 2c, the light emitting layer 2b, and a part of the first semiconductor layer 2a are sequentially etched from the upper surface of the second semiconductor layer 2c using an etching method or the like. Form.

  Thereafter, the first electrode 5a electrically connected to the first semiconductor layer 2a is formed on the bottom surface of the electrode groove 15, that is, the exposed portion of the first semiconductor layer 2a. Further, a second electrode 5b electrically connected to the second semiconductor layer 2c is formed on the main surface 2A of the second semiconductor layer 2c. As described above, a pair of electrodes 5 is formed.

  Examples of the material for the pair of electrodes 5 include metals such as aluminum, titanium, nickel, chromium, indium, tin, molybdenum, silver, gold, niobium, tantalum, vanadium, platinum, lead, and beryllium, tin oxide, indium oxide, and oxide. An oxide such as indium tin or an alloy film such as a gold-silicon alloy, a gold-germanium alloy, a gold-zinc alloy, or a gold-beryllium alloy can be preferably used. Further, the pair of electrodes 5 may be formed by laminating a plurality of layers selected from the above materials.

(Second Embodiment)
Next, the light emitting element 21 according to the second embodiment will be described. Portions overlapping with the light emitting element 20 according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  14 and 15 are diagrams showing a light emitting device 21 according to the second embodiment. 14 corresponds to a plan view of the light-emitting element 21, and FIG. 15 corresponds to a cross section taken along line BB ′ of FIG. The light emitting device 21 according to the second embodiment is different from the light emitting device 20 according to the first embodiment in that the protrusion 8 is provided on the main surface 1B of the substrate 1.

  Specifically, the light-emitting element 21 according to the present embodiment includes a substrate 1, an optical semiconductor layer 2 that is provided on the main surface 1A of the substrate 1, and emits light toward the main surface 1A, and an internal angle t2 formed with the main surface 1B. A plurality of light-transmitting protrusions 8 are formed which have an inclined surface 9 of less than 90 degrees and are arranged in a row on the main surface 1B of the substrate 1. Further, when the plurality of protrusions 8 are viewed in plan, each of the protrusions 8 is arranged so that each inclined surface 9 faces in one direction of the row in which the plurality of protrusions 8 are arranged. When viewed in a cross-section from the vertical direction, the cross-sectional outline is non-axisymmetric with respect to the normal line of the main surface 1B.

  Since the protrusions 8 are thus formed on the main surface 1B of the substrate 1, the light extraction efficiency can be improved when the light emitted from the light emitting layer 2b is extracted from the substrate 1 side.

(Modification 1)
FIG. 16 is an enlarged cross-sectional view showing a modification of the protrusion 3 of the light emitting element 20 according to the above-described embodiment. Portions overlapping with the light emitting element 20 according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The enlarged sectional view of FIG. 16 corresponds to the enlarged sectional view of FIG. In FIG. 16A, the inclined side 4b is provided to form a pentagonal cross-sectional outline, and a non-axisymmetric shape with respect to the normal Hb of the main surface 2A of the second semiconductor layer 2c. In this case, the internal angle t3 formed by the inclined side 4b and the main surface 2A indicates an internal angle formed by the virtual line extending the inclined side 4b and the main surface 2A. The projection 3 having such a pentagonal cross-sectional outline becomes a pentagonal cross-sectional outline by, for example, forming a mask on a part of the upper surface of the preliminary projection 14 and then etching the main surface 2A from the inclined direction. The protrusion 3 can be formed. Therefore, the non-axisymmetric protrusion 3 can be formed with a small number of etchings, and can be formed relatively easily.

  Next, FIG. 16B shows that the inclined side 4c is provided at the tip of the protrusion 3, thereby forming a quadrangular cross-sectional outline and non-linear with respect to the normal Hb of the main surface 2A of the second semiconductor layer 2c. It has a symmetrical shape. In this case, the internal angle t4 formed with the main surface 2A indicates the internal angle formed between the virtual surface extending the inclined side 4c and the main surface 2A. Thus, when forming the protrusion 3, a non-axisymmetric shape can be formed by etching from the inclined direction with respect to the main surface 2A. Therefore, the non-axisymmetric protrusion 3 can be formed with a small number of etchings, and can be formed relatively easily. Further, since the upper surface of the protrusion 3 is inclined, it is difficult to totally reflect on the upper surface, and a large amount of light can be extracted above the protrusion 3.

  Further, FIG. 16 (c) forms a pentagonal cross-sectional outline by having the inclined sides 4d and 4e having different angles, and is not relative to the normal Hb of the main surface 2A of the second semiconductor layer 2c. It has a line-symmetric shape. In this case, the internal angle t5 formed with the main surface 2A indicates the internal angle formed between the virtual line extending the inclined side 4d and the main surface 2A, and the internal angle t6 formed with the main surface 2A is the virtual straight line extended through the inclined side 4e and the main surface 2A. Indicates the inner angle formed by As described above, the protrusion 3 having the cross-sectional outline having two inclined sides can be provided by etching twice with changing the angle from the inclined direction with respect to the main surface 2A. For this reason, the side of the projection 3 that is inclined with respect to the main surface 2A of the optical semiconductor layer 2 is increased, and total reflection can be made difficult to repeat in the projection 3.

  In the first modification, the case of the protrusion 3 formed on the second semiconductor layer 2c has been described. However, such a first modification can be easily applied to the protrusion 8 formed on the substrate 1. Even when applied to the protrusion 8, the same effect can be obtained.

(Modification 2)
FIG. 17 is an enlarged cross-sectional view showing a modification of the protrusion 3 of the light emitting element 20 according to the above-described embodiment. Portions overlapping with the light emitting element 20 according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 17A is a perspective view of the light emitting element 20 according to this modification, and FIG. 17B is a plan view of the light emitting element 20 shown in FIG. In the light emitting element 20 according to this modification, the outline of the protrusion 16 is a quadrangle when viewed in plan. Further, two adjacent sides of the quadrangle are arranged on one side of the column direction Ge-Y parallel to the Y axis, and the inclined side 17 arranged in one direction of the column direction Ge-X parallel to the X axis. The inclined sides 17 arranged in the direction are continuously formed. Here, the X-axis and the Y-axis indicate axes that constitute a plane parallel to the main surface 2A of the second semiconductor layer 2c. Note that the outline is not limited to a quadrangle, and a polygon such as a pentagon or a hexagon can be used.

  Since the protrusions 16 are formed in this way, the cross-sectional outline line has a non-symmetrical shape with respect to the two column directions in which the protrusions 16 are arranged, and as a result, the light extraction efficiency is further improved. be able to.

(Modification 3)
In the above description, the case where a flat plate is used as the substrate 1 has been described, but the substrate 1 may be formed by forming irregularities on the main surface 1A. Such a substrate 1 can be prepared by forming irregularities on the main surface 1A of the substrate 1 by etching a part of the substrate 1, for example. By growing the first semiconductor layer 2a in the lateral direction on such a substrate 1, the optical semiconductor layer 2 with few dislocations can be formed.

  As a method for laterally growing the first semiconductor layer 2a, for example, the growth conditions such as the composition ratio, growth temperature, and growth pressure of the first semiconductor layer 2a may be adjusted. Thereby, the growth rate of the first semiconductor layer 2a can be controlled in the vertical direction and the horizontal direction with respect to the main surface 1A of the substrate 1, and the first semiconductor layer 2a can be grown in the lateral direction.

  By growing the first semiconductor layer 2a laterally on the substrate 1 in this way, the growth rate can be increased while controlling the number and position of dislocations extending to the light emitting layer 2b. Productivity can be improved. When unevenness is formed on the substrate 1 in this way and grown in the lateral direction, dislocations extending to the light emitting layer 2b tend to exist on the convex portion. In addition, such a convex part can set height to 50 micrometers or more and 300 micrometers or less, for example.

  Furthermore, when the first semiconductor layer is grown in the lateral direction on the substrate 1 having irregularities in this way, the position of dislocations extending to the light emitting layer 2b can be controlled. Therefore, it is preferable to form the first mask pattern 11 at a position overlapping the concave portion of the substrate 1 as seen through the plane. When the first mask pattern 11 corresponding to the position of the concave portion of the substrate 1 is formed, the projection 3 can be formed at a position overlapping with the substrate 1 as seen through the plane, so that the light emitted from the light emitting layer 2b can be emitted. It can be taken out efficiently.

(Modification 4)
In the above description, the method of forming the protrusion 3 using the mask pattern has been described as one of the methods for forming the protrusion 3, but the nanoimprint method may be used as one of the methods for forming the protrusion 3.

  In the case of forming the protrusion 3 using the nanoimprint method, after forming the laminated film 10 on the second semiconductor layer 2c, a mask having the same shape as the protrusion 3 is formed on the laminated film 10. Thereafter, by etching the mask formed in this way, the same shape as the mask, that is, the shape of the protrusion 3 can be transferred to the laminated film 10. Here, such a mask can be formed in a desired shape by forming a resist film on the laminated film 10 and then pressing a nanoimprint mold against the resist film.

  Here, the nanoimprint mold has a concave portion having the same shape as the protrusion 3 on the surface pressed against the resist film, and can be formed into a desired shape by pressing it against the resist film. Such a nanoimprint mold can use, for example, a crystalline material such as silicon or silicon carbide. If silicon is used, a recess can be formed by anisotropic etching or the like.

  Examples of the light emitting device of the present invention will be described below.

  In order to confirm the effect of the light emitting element of the present invention, the light extraction efficiency was simulated by the ray tracing method. The simulation model is a light emitting element in which a protrusion 8 is formed on the substrate 1 as shown in FIG.

  In the light-emitting element in this example, the substrate is made of sapphire with a thickness of 250 μm (refractive index 1.79), and the optical semiconductor layer is made of gallium nitride with a thickness of 3 μm (refractive index 2.5).

  Although the refractive index of each layer of the optical semiconductor layer varies depending on its composition, the difference is only a few percent, so in this simulation it was set to a constant refractive index. The outside was air (refractive index 1), and the emission wavelength of light emitted from the light emitting layer was 400 nm. Further, the protrusion had a bottom diameter of 1 μm and a height of 1 μm.

  As a result of this simulation, the projection having the non-axisymmetric shape by providing the inclined surface 9 is more in comparison with the projection having the quadrangular shape of the cross-sectional outline of the projection with respect to the normal line of the main surface 1B. It was found that the light extraction efficiency was improved 1.3 times.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical semiconductor layer 2a 1st semiconductor layer 2b Light emitting layer 2c 2nd semiconductor layer 3 Protrusion 4 Inclined surface 4a Inclined side 5 A pair of electrodes 5a 1st electrode 5b 2nd electrode 6 Reflective layer 10 Multilayer film 11 1st mask pattern 12 Second mask pattern 13 Exposed region 14 Preliminary protrusion 15 Electrode groove 20 Light emitting element

Claims (6)

On the other hand, an optical semiconductor layer that emits light toward the main surface;
A plurality of light-transmitting protrusions arranged in a row on the one main surface of the optical semiconductor layer, and having an inclined surface whose inner angle with the one main surface is less than 90 degrees,
When the plurality of protrusions are viewed in plan, each of the inclined surfaces is disposed toward one direction of the row in which the plurality of protrusions are disposed,
When the plurality of protrusions are viewed in cross section from a direction perpendicular to the column direction, the light emitting element has a cross-sectional outline that is non-axisymmetric with respect to a normal line of one main surface.   The light emitting element according to claim 1, wherein the plurality of protrusions are made of a material different from that of the optical semiconductor layer.   3. The light emitting device according to claim 1, wherein when the plurality of protrusions are viewed in plan, the outline thereof is a polygon, and the inclined surface is continuously formed on two adjacent sides of the polygon. element.   4. The light emitting device according to claim 1, further comprising a reflective layer that reflects light emitted from the optical semiconductor layer on a surface of the inclined surface. A substrate,
An optical semiconductor layer provided on one main surface of the substrate and emitting light toward the one main surface;
A plurality of light-transmitting protrusions having an inclined surface with an inner angle of less than 90 degrees formed with the other main surface and arranged in a row on the other main surface of the substrate,
When the plurality of protrusions are viewed in plan, each of the inclined surfaces is disposed toward one direction of the row in which the plurality of protrusions are disposed,
The light emitting element, wherein when the plurality of protrusions are viewed in cross-section from a direction perpendicular to the column direction, a cross-sectional outline thereof is axisymmetric with respect to a normal of the other main surface.   The light emitting device according to claim 5, wherein the plurality of protrusions are made of the same material as the substrate.

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