JP2008108973A - Semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element which can take out light with high polarization ratio. <P>SOLUTION: The semiconductor light emitting element 1 comprises a substrate 2, a nitride semiconductor laminate structure 3 on the substrate 2, an anode 4, a cathode 6, and an absorption layer 7. The substrate 2 is composed of GaN single crystal and the major surface of the substrate 2 consists of a nonpolar m-surface. The nitride semiconductor laminate structure 3 includes an active layer 12 capable of emitting light, and consists of a GaN layer, an InGaN layer and an AlGaN layer. The absorption layer 7 absorbs light traveling reversely to the light take-out direction A or traveling in the horizontal direction out of light emitted from the active layer 12 and it is composed of SiN. The absorption layer 7 is formed to cover the bottom face 2a and the side face 2b of the substrate 2, a portion of the side face 3a of the nitride semiconductor laminate structure 3, and a portion of the side face 4b of the anode electrode 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device having a nitride semiconductor multilayer structure.

  2. Description of the Related Art Conventionally, semiconductor light emitting devices having various nitride semiconductor multilayer structures having active layers capable of emitting blue light or the like are known.

  For example, Patent Document 1 discloses a semiconductor light emitting device having a nitride semiconductor multilayer structure in which a plurality of nitride semiconductor layers such as n-type and p-type GaN layers and AlGaN layers are laminated on a sapphire substrate. Yes. In addition, an insulating film is provided on the side surface of the semiconductor light emitting element in order to prevent a short circuit between the electrode provided on the side surface and the nitride semiconductor laminated structure except for a desired region.

In the semiconductor light emitting device of Patent Document 1, since an insulating film and an electrode are provided on the side surface, there is nothing to block the upper surface of the nitride semiconductor multilayer structure, so that light can be extracted from the entire upper surface (light extraction surface). Thereby, the amount of light extracted from the light extraction surface could be improved.
Japanese Patent No. 3303154

  However, in the semiconductor light emitting device of Patent Document 1 described above, the amount of light that can be extracted from the light extraction surface can be improved by providing an insulating film and an electrode on the side surface, but the light emitted from the active layer is not polarized. Therefore, there is a problem that the polarization ratio of the extracted light is low.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a semiconductor light emitting device capable of extracting light having a high polarization ratio.

  In order to achieve the above object, the invention according to claim 1 is a semiconductor light emitting device having a nitride semiconductor multilayer structure including an active layer capable of emitting light, wherein the main surface of the nitride semiconductor multilayer structure is: It is a substantially nonpolar surface or a substantially semipolar surface, and is provided with an absorption layer for absorbing light on a surface opposite to a light extraction surface from which light emitted by the active layer is extracted. This is a semiconductor light emitting device.

  Here, the substantially nonpolar plane is a concept including a nonpolar plane and a plane whose off angle from the plane orientation of the nonpolar plane is within ± 1 °. Further, the substantially semipolar plane is a concept including a semipolar plane and a plane whose off angle from the plane orientation of the semipolar plane is within ± 1 °.

  According to a second aspect of the present invention, the semiconductor light emitting device according to the first aspect is provided with a substrate, and the absorption layer is formed on a side surface of the substrate and a side surface of the nitride semiconductor multilayer structure. It is prime.

  The invention according to claim 3 is the semiconductor light emitting element according to claim 1, wherein the absorption layer is made of an insulating film.

  The invention according to claim 4 is the semiconductor light emitting element according to claim 1, wherein the absorption layer is made of an organic substance.

  According to a fifth aspect of the present invention, there is provided the semiconductor according to the first aspect, further comprising a substrate, wherein the absorption layer is made of a metal film that is ohmically connected to the substrate or the nitride semiconductor multilayer structure. It is a light emitting element.

  According to the present invention, by providing a nitride semiconductor multilayer structure having a substantially nonpolar surface or a substantially semipolar surface as a main surface, it is possible to emit polarized light in the active layer. Can be increased. Of the emitted light, the light traveling to the opposite side of the light extraction surface is generally scattered by an external housing or the like and the polarization ratio is lowered, but in the present invention, the light emitted from the active layer is absorbed. By providing an absorption layer for absorbing light, it is possible to absorb light traveling in a direction opposite to the light extraction surface, and thus it is possible to suppress light from being emitted and scattered from the surface opposite to the light extraction surface. . Thereby, since it can suppress that the light which was scattered outside and the polarization ratio fell is mixed with the light with a high polarization ratio taken out from the light extraction surface, light with a high polarization ratio can be taken out.

  In addition, by forming the absorption layer on the side surface of the substrate and the side surface of the nitride semiconductor multilayer structure, more light emitted from regions other than the light extraction surface can be absorbed. Can be further enhanced.

  Moreover, an absorption layer can be easily formed by comprising an absorption layer with an insulating film.

  Moreover, it can form more easily and cheaply by comprising an absorption layer with organic substances, such as a colored paint.

  In addition, by configuring the absorption layer with a metal film that is ohmically connected to the substrate or the nitride semiconductor multilayer structure, the absorption layer and the electrode can be used together, so that the structure can be simplified.

  Hereinafter, a first embodiment in which the present invention is applied to a light emitting diode (LED) will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the semiconductor light emitting device (light emitting diode) according to the first embodiment.

  As shown in FIG. 1, the semiconductor light emitting device 1 includes a substrate 2, a nitride semiconductor multilayer structure 3 laminated on the substrate 2, an anode electrode 4, a cathode electrode 6, and an absorption layer 7. .

  The substrate 2 is made of a single crystal of GaN (gallium nitride). The method for producing a single crystal of GaN is not particularly limited. A nitride semiconductor multilayer structure 3 is laminated on the main surface of the substrate 2. The main surface of the substrate 2 is an m-plane that is a nonpolar surface. The m-plane is a plane (for example, (10-10) plane) corresponding to the side of the hexagonal column when the crystal structure of GaN is approximated to a hexagonal hexagonal crystal.

  In the nitride semiconductor multilayer structure 3, an n-type contact layer 11, an active layer 12, a final barrier layer 13, a p-type electron blocking layer 14, and a p-type contact layer 15 are laminated in order from the substrate 2 side. Yes. Here, as described above, since the main surface of the substrate 2 is configured by the m-plane, the main surface of the nitride semiconductor multilayer structure 3 laminated on the main surface of the substrate 2 is also polarized in the active layer 12. The m-plane is a nonpolar plane capable of emitting light.

The n-type contact layer 11 is composed of an n-type GaN layer having a thickness of about 3 μm or more doped with silicon having a concentration of about 1 × 10 ¹⁸ cm ⁻³ as an n-type dopant.

  The active layer 12 has a quantum well structure in which an InGaN layer with a thickness of about 3 nm doped with silicon and a GaN layer with a thickness of about 9 nm are alternately stacked for five periods. This active layer 12 emits light of about 430 nm.

  The final barrier layer 13 is composed of a GaN layer having a thickness of about 40 nm. The doping may be any of p-type, n-type and non-doped, but non-doped is preferred.

The p-type electron blocking layer 14 is an AlGaN layer having a thickness of about 28 nm doped with magnesium having a concentration of about 3 × 10 ¹⁹ cm ⁻³ as a p-type dopant.

The p-type contact layer 15 is made of a GaN layer having a thickness of about 70 nm doped with magnesium having a concentration of about 1 × 10 ²⁰ cm ⁻³ as a p-type dopant. The light extraction side surface 15 a on the light extraction direction A side of the p-type contact layer 15 is for extracting light emitted from the active layer 12 from the nitride semiconductor multilayer structure 3. The surface of the light extraction side surface 15a is mirror-finished so that the unevenness is about 100 nm or less in order to suppress light scattering and suppress a decrease in the polarization ratio. For example, a flat mirror surface as described above can be obtained by crystal growth.

  The anode electrode 4 is made of a metal layer in which a Ni layer and an Au layer are stacked in order from the p-type contact layer 15 side. The anode electrode 4 is ohmically connected to the p-type contact layer 15 and the p-type contact layer 15 in order to allow a current to flow uniformly in the entire region of the nitride semiconductor multilayer structure 3 in the horizontal direction (direction perpendicular to the stacking direction). It is formed so as to cover substantially the entire upper surface. The anode electrode 4 has a thickness of about 200 mm or less capable of transmitting the light emitted from the active layer 12. The light extraction surface 4a of the anode electrode 4 is a surface from which the light emitted by the active layer 12 is extracted, and the surface unevenness is about 100 nm or less, like the light extraction side surface 15a of the p-type contact layer 15. Mirror finish. For example, if the electron beam evaporation method is used, the mirror surface as described above can be obtained. In this way, the light emitted from the active layer 12 is suppressed by the mirror-extracted light extraction side surface 15a and the light extraction surface 4a, so that the light is extracted while maintaining a high polarization ratio. A connection portion 5 in which a Ti layer and an Au layer are stacked is provided in a partial region on the anode electrode 4.

  The cathode electrode 6 is formed by laminating a Ti layer and an Al layer. The cathode electrode 6 is formed in an ohmic connection with the exposed region of the upper surface of the n-type contact layer 11.

The absorption layer 7 is for absorbing light that travels in the direction opposite to the light extraction direction A or in the horizontal direction among the light emitted from the active layer 12, and is made of a SiN film that is an insulating film. The absorption layer 7 includes a bottom surface 2a of the substrate 2, which is a surface opposite to the light extraction surface 4a, a side surface 2b of the substrate 2, a part of the side surface 3a of the nitride semiconductor multilayer structure 3, and a side surface of the anode electrode 4. It is formed so as to cover part of 4b. Note that the SiN film includes a Si _X N _Y film (X and Y are positive integers).

  Next, the operation of the semiconductor light emitting device 1 described above will be described. In the semiconductor light emitting device 1, when electrons are supplied from the anode electrode 4 and holes are supplied from the cathode electrode 6, electrons are injected into the active layer 12 through the n-type contact layer 11, and the semiconductor layers 13 to 13 are formed. Holes are injected into the active layer 12 via 15. The electrons and holes injected into the active layer 12 are combined to emit light of about 430 nm. Here, since the main surface of the nitride semiconductor multilayer structure 3 is a non-polar m-plane, the light emitted from the active layer 12 is polarized.

  Of the polarized light, the light traveling in the light extraction direction A passes through the semiconductor layers 13 to 15 and the anode electrode 4 and is extracted from the light extraction surface 4a to the outside. On the other hand, the light traveling in the direction opposite to the light extraction direction A is absorbed by the absorption layer 7 and the emission to the outside is suppressed. Therefore, since it is possible to suppress the light extracted from the light extraction surface 4a from being mixed with light that has been emitted to the outside and then scattered and the polarization ratio has been reduced, a decrease in the polarization ratio can be suppressed.

  Next, a method for manufacturing the semiconductor light emitting element described above will be described.

  First, a substrate 2 made of a single crystal of GaN having a non-polar m-plane main surface is prepared. Here, the substrate 2 having the m-plane which is a nonpolar plane as the main surface is first cut out of a GaN single crystal substrate having the C-plane as the main surface, and then both the (0001) direction and the (11-20) direction. The surface is polished by a CMP method (chemical mechanical polishing method) so that the azimuth error is within ± 1 ° (preferably within ± 0.3 °), and is mirror-finished. As a result, it is possible to obtain the substrate 2 having the m-plane as a main surface, few crystal defects such as dislocations and stacking faults, and the surface step is suppressed to the atomic level.

  Next, the nitride semiconductor multilayer structure 3 is grown on the above-described substrate 2 by MOCVD. Specifically, first, the substrate 2 is introduced into a processing chamber of an MOCVD apparatus (not shown) and placed on a susceptor that can be heated and rotated. Note that the inside of the processing chamber is set to 1/10 atm to normal pressure, and the atmosphere in the processing chamber is always exhausted.

Next, in order to grow a GaN layer while suppressing surface roughness, the temperature of the substrate 2 is set to about 1000 ° C. while ammonia gas is supplied by a carrier gas (H ₂ gas) into the processing chamber in which the substrate 2 is held. Raise the temperature to about 1100 ° C.

  Next, after the temperature of the substrate 2 rises to about 1000 ° C. to about 1100 ° C., ammonia, trimethyl gallium, and silane are supplied to the processing chamber by a carrier gas, and an n-type GaN layer made of silicon-doped n-type GaN layer is formed. The contact layer 11 is grown.

  Next, after the temperature of the substrate 2 is set to about 700 ° C. to about 800 ° C., ammonia and trimethyl gallium are supplied to the processing chamber by a carrier gas to grow a non-doped GaN layer. An InGaN layer doped with silicon is grown by supplying trimethylindium.

  Then, the active layer 12 having a quantum well structure is formed by alternately repeating the process of growing the non-doped GaN layer and the silicon-doped InGaN layer a desired number of times. Thereafter, ammonia and trimethylgallium are supplied to the processing chamber by the carrier gas, and the final barrier layer 13 made of the GaN layer is grown.

  Next, after raising the temperature of the substrate 2 to about 1000 ° C. to about 1100 ° C., ammonia gas, trimethylgallium, trimethylaluminum and ethylcyclopentadienylmagnesium are supplied to the processing chamber by a carrier gas, A p-type electron blocking layer 14 made of a doped p-type AlGaN layer is grown.

  Next, while maintaining the temperature of the substrate 2 at about 1000 ° C. to about 1100 ° C., ammonia gas, trimethyl gallium and ethylcyclopentadienyl magnesium are supplied to the processing chamber by a carrier gas, and the GaN layer doped with magnesium is supplied. A p-type contact layer 15 made of is grown. Thereby, the nitride semiconductor multilayer structure 3 is completed.

  Next, the anode electrode 4 is formed by a resistance heating method or a metal vapor deposition apparatus using an electron beam. Thereafter, the substrate 2 on which the nitride semiconductor multilayer structure 3 is formed is moved to the etching chamber, and a part of the nitride semiconductor multilayer structure 3 is plasma etched so that a part of the n-type contact layer 11 is exposed.

  Next, the connection portion 5 and the cathode electrode 6 are formed by a metal vapor deposition apparatus using a resistance heating method or an electron beam vapor deposition method, and then divided for each element by cleavage.

Next, by sputtering a SiN target using a magnetron sputtering apparatus, a part of the side surface 3a of the nitride semiconductor multilayer structure 3 and a part of the side surface 4b of the anode electrode 4 are formed. Then, an absorption layer 7 made of SiN capable of absorbing light emitted from the active layer 12 is formed. Here, SiN that can absorb light can be obtained by, for example, suppressing the flow rate ratio of N _{2 to} Ar flowing in the chamber and forming it to a desired film thickness. Specifically, by reducing the flow rate of N ₂ from 10 sccm to 5 sccm with respect to Ar having a flow rate of 50 sccm, the absorption coefficient of light having a wavelength of 400 nm to 500 nm can be increased four times or more.

  As a result, the semiconductor light emitting device 1 shown in FIG. 1 is completed.

  As described above, the semiconductor light emitting device 1 according to the first embodiment includes the nitride semiconductor multilayer structure 3 whose main surface is the nonpolar m-plane, so that polarized light is emitted from the active layer 12. . Of the light emitted here, the light traveling in the direction opposite to the light extraction direction A is generally emitted from the bottom surface of the substrate and then scattered by an external housing or the like to lower the polarization ratio. In the semiconductor light emitting device 1 according to the embodiment, the light extraction direction A is obtained by providing the absorption layer 7 on the bottom surface 2 a and the side surface 2 b of the substrate 2, the side surface 3 a of the nitride semiconductor multilayer structure 3, and the side surface 4 b of the anode electrode 4. Can absorb the light traveling in the opposite direction or the horizontal direction, so that it is possible to suppress the light from being emitted outside the light extraction surface 4a. As a result, it is possible to prevent light having a low polarization ratio scattered by an external housing or the like from being mixed with light having a high polarization ratio extracted from the light extraction surface 4a. Can be taken out.

  Thus, since the semiconductor light emitting device 1 can extract light having a high polarization ratio, when the semiconductor light emitting device 1 is applied as a light source of a liquid crystal display, one polarizing filter for polarizing the light can be omitted. Or the ratio of the light which permeate | transmits a polarizing filter can be enlarged.

  Further, the absorption layer 7 can be easily formed by sputtering by forming it with SiN which is an insulating film.

  Next, a second embodiment in which a part of the first embodiment is changed will be described. FIG. 2 is a cross-sectional view of the semiconductor light emitting device according to the second embodiment. In addition, the same code | symbol is attached | subjected to the structure similar to 1st Embodiment, and description is abbreviate | omitted.

  As shown in FIG. 2, in the semiconductor light emitting device 1 </ b> A, the absorption layer 7 </ b> A is formed only on the bottom surface 2 a of the substrate 2. The absorption layer 7A is made of a metal film such as Al that is ohmically connected to the bottom surface 2a of the substrate 2. Such an absorption layer 7A can be formed by annealing after forming a metal thin film on the bottom surface 2a of the substrate 2 by a resistance heating method or an electron beam.

  As described above, since the semiconductor light emitting device 1A can absorb light by the absorption layer 7A by providing the absorption layer 7A that is ohmic-connected to the bottom surface 2a of the substrate 2, the light emission from the bottom surface 2a of the substrate 2 to the outside. The emitted light can be suppressed. As a result, it is possible to suppress mixing of light having a low polarization ratio due to scattering of light from the outside with light having a high polarization ratio extracted from the light extraction surface 4a, so that the light is extracted while maintaining a high polarization ratio. be able to.

  When the absorption layer 7A is formed of a metal film formed on the bottom surface 2a of the substrate 2 as in the second embodiment, the cathode electrode 6 may be omitted and the absorption layer 7A may be used as the cathode electrode. Good. When the absorption layer 7A is also used as a cathode electrode in this way, the absorption layer 7A may be formed by laminating Ti and Al. By comprising in this way, the structure and manufacturing process of a semiconductor light-emitting device can be simplified more.

  As mentioned above, although this invention was demonstrated in detail using embodiment, this invention is not limited to embodiment described in this specification. The scope of the present invention is determined by the description of the claims and the scope equivalent to the description of the claims. Hereinafter, modified embodiments in which the above-described embodiment is partially modified will be described.

  For example, the material and thickness constituting each layer, the concentration of the dopant, and the like can be changed as appropriate.

  Moreover, although the example which applied this invention to the light emitting diode was shown in the above-mentioned embodiment, you may apply this invention to other apparatuses, such as a laser.

  Moreover, you may comprise the absorption layers 7 and 7A with organic substance. As the organic substance, for example, a colored paint such as black that can absorb the light emitted from the active layer 12 is conceivable. Thus, the absorption layers 7 and 7A can be formed more easily and cheaply by comprising the absorption layers 7 and 7A with an organic substance.

  Further, light may be extracted from the bottom surface of the substrate. In such a configuration, an absorption layer is not formed on the bottom surface of the substrate, but an ohmic connection is formed on the top surface of the p-type contact layer. An anode electrode may be applied as the absorption layer. In such a configuration, the anode electrode is formed to a thickness that does not transmit light. An absorption layer made of an insulating film or an organic material may be formed on the anode electrode that can transmit light.

  In the above-described embodiment, the main surface of the substrate 2 is the m-plane, but the main surface of the substrate is not limited to the m-plane, and it is an abbreviation that can polarize light emitted from the active layer. You may comprise by a nonpolar surface or a substantially semipolar surface. In addition, a non-polar surface or a substantially non-polar surface is not only a non-polar surface and a semi-polar surface, but also a surface having an off angle within ± 1 ° from the non-polar surface and an off within ± 1 ° from the semi-polar surface. It is a concept including a surface having a corner. Here, the crystal structure and crystal plane of GaN constituting the substrate will be briefly described. The crystal structure of GaN can be approximated by a hexagonal hexagonal system. A surface having the C axis along the axial direction of the hexagonal column as a normal is a C surface (0001). As is known, in the GaN crystal structure, since the polarization direction is along the C-axis direction, the C-plane shows different properties between the + C-axis side surface and the −C-axis side surface. (Polar Plane). On the other hand, the side surfaces of the hexagonal columns are m-planes (10-10), respectively, and the plane passing through a pair of ridge lines that are not adjacent to each other is the a-plane (11-20). These are crystal planes perpendicular to the C-plane and orthogonal to the polarization direction, and thus are nonpolar planes having no polarity. Further, the crystal plane that is neither parallel nor perpendicular to the C plane is inclined with respect to the polarization direction, and is therefore a semipolar plane having a slight polarity. Specific examples of the semipolar plane include (10-1-1) plane, (10-1-3) plane, (11-22) plane, (11-24) plane, and (10-12) plane. .

The material constituting the substrate is not limited to a GaN single crystal, but a sapphire substrate whose principal surface is an m-plane or a-plane, a spinel substrate whose principal surface is a (100) plane or (110) plane, An m-plane SiC substrate, LiAlO ₂ substrate, or the like can also be applied.

It is sectional drawing of the semiconductor light-emitting device by 1st Embodiment. It is sectional drawing of the semiconductor light-emitting device by 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A Semiconductor light-emitting device 2 Substrate 2a Bottom surface 2b Side surface 3 Nitride semiconductor laminated structure 3a Side surface 4 Anode electrode 4a Light extraction surface 4b Side surface 5 Connection portion 6 Cathode electrode 7, 7A Absorbing layer 11 N-type contact layer 12 Active layer 13 Final Barrier layer 14 p-type electron blocking layer 15 p-type contact layer 15a Light extraction side

Claims (5)

In a semiconductor light emitting device having a nitride semiconductor multilayer structure including an active layer capable of emitting light,
The main surface of the nitride semiconductor multilayer structure is a substantially nonpolar surface or a substantially semipolar surface,
A semiconductor light emitting device comprising an absorption layer for absorbing light on a surface opposite to a light extraction surface from which light emitted by the active layer is extracted. Equipped with a substrate,
The semiconductor light emitting element according to claim 1, wherein the absorption layer is formed on a side surface of the substrate and a side surface of the nitride semiconductor multilayer structure.   The semiconductor light emitting element according to claim 1, wherein the absorption layer is made of an insulating film.   The semiconductor light-emitting element according to claim 1, wherein the absorption layer is made of an organic material. Equipped with a substrate,
The semiconductor light emitting device according to claim 1, wherein the absorption layer is made of a metal film that is ohmically connected to the substrate or the nitride semiconductor multilayer structure.

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