JP5071087B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device having a two-dimensional diffraction grating.

  An LED (Light Emitting Diode) is a light source that can be driven with low power, and is therefore widely used for illumination of a display device such as a portable information terminal including a mobile phone, or for lighting. In particular, an LED made of a GaN (gallium nitride) material emits blue light and emits white light when combined with a phosphor. For this reason, LEDs made of GaN-based materials are actively being worked on to increase brightness.

  A conventional LED made of a GaN-based material has the following structure, for example. That is, an n-type GaN layer, an InGaN active layer, a p-type GaN layer, and a p-type electrode are formed in this order on the sapphire substrate, and each of the InGaN active layer, the p-type GaN layer, and the p-type electrode is formed. An n-type electrode is formed on the surface of the n-type GaN layer exposed by removing a part.

  The light extraction efficiency of the conventional LED was low. Particularly in an LED made of a GaN-based material, since the refractive index (2.54) of GaN is very large with respect to air, the total reflection angle when blue light exits from the inside of the LED into the air is large. Due to the nature of GaN, it is difficult to efficiently extract blue light out of the device.

  Therefore, in order to improve the light extraction efficiency of the LED, a technique for covering the periphery of the LED with an epoxy resin or a silicone resin has been proposed. Since these resins have a refractive index that is approximately between the refractive index of GaN and the refractive index of air, the total reflection angle when light exits from the inside of the LED into the air gradually decreases. As a result, the light extraction efficiency of the LED can be improved.

  As another technique for improving the light extraction efficiency of the LED, a technique for forming a two-dimensional photonic crystal layer on the LED has been proposed. For example, in Japanese Patent Application Laid-Open No. 2006-49855 (Patent Document 1), a two-dimensional photonic crystal layer of an LED is manufactured by forming a plurality of columns on the surface of a p-type GaN layer exposed in the air. . In Japanese Patent Application Laid-Open No. 2006-196658 (Patent Document 2), a two-dimensional photonic crystal layer of an LED is manufactured by forming a plurality of holes on the surface of the GaN layer. Since these two-dimensional photonic crystal layers have an intermediate refractive index between air and the LED, the total reflection angle when the light exits from the inside of the LED into the air is gradually reduced. As a result, the light extraction efficiency of the LED can be improved.

Furthermore, in relation to the technology for forming a two-dimensional photonic crystal layer on a semiconductor light emitting device, for example, International Publication No. 2006/062084 (Patent Document 3) discloses a two-dimensional photonic crystal layer made of SiO ₂ and GaN. A technique for forming a semiconductor laser in a semiconductor laser is disclosed. Japanese Patent Application Laid-Open No. 2004-111766 (Patent Document 4) discloses a technique for forming a two-dimensional photonic crystal layer made of air and GaN on a semiconductor laser using a mass transport method.

Here, since SiO ₂ has a relatively high melting point, it does not deform even if it is kept at a high temperature (about 1000 ° C. to 1200 ° C.) when the GaN layer is epitaxially grown. Further, since SiO ₂ has a low refractive index (1.5 or less), it has a large refractive index difference of 1 or more with the GaN layer. Furthermore, SiO ₂ is easy to process. For these reasons, the two-dimensional photonic crystal layer made of SiO ₂ and GaN disclosed in Patent Document 3 is particularly suitable as a two-dimensional photonic crystal layer of a semiconductor light emitting device such as an LED.
JP 2006-49855 A JP 2006-196658 A International Publication No. 2006/062084 Pamphlet JP 2004-111766 A

On the other hand, the two-dimensional photonic crystal layer made of SiO ₂ and GaN has a problem that a voltage required for light emission is high. This problem is not limited to SiO ₂ but is a problem that can occur in common in a semiconductor light emitting device including a two-dimensional photonic crystal layer composed of a material containing Si and a material containing GaN.

  Accordingly, an object of the present invention is to provide a semiconductor light emitting device capable of reducing a voltage required for light emission.

The semiconductor light-emitting device of the present invention includes a light-emitting layer that emits light when carriers are injected, and a two-dimensional diffraction grating formed on one main surface side of the light-emitting layer. The two-dimensional diffraction grating has a plurality of lattice points containing Si and a mother layer. The mother layer surrounds each of the plurality of lattice points when seen in a plan view, and contains p-type GaN. An interval between one lattice point of the plurality of lattice points and the lattice point closest to one lattice point is 130 nm or more and 10 μm or less.

The inventors of the present application have found that in a two-dimensional photonic crystal layer made of SiO ₂ and GaN, the voltage required for light emission increases due to Si diffusing into the mother layer containing GaN. It was. That is, when forming the mother layer containing GaN or forming another layer after forming the two-dimensional diffraction grating, each of the plurality of lattice points containing Si is heated to a high temperature. This heating diffuses Si from the lattice points into the mother layer, adversely affects the properties of the mother layer, and increases the voltage required for light emission. In particular, when Si diffuses into the base layer made of p-type GaN, the conductivity type of the portion where Si is diffused changes from p-type to n-type. As a result, the electrical resistance of the two-dimensional diffraction grating is remarkably increased, and the voltage required for light emission is increased.

  Therefore, the inventors of the present application have found a method of reducing the voltage required for light emission by setting the distance between the lattice points to be larger than that in the prior art. Specifically, the interval between one lattice point among the plurality of lattice points and the lattice point closest to one lattice point is set to 130 nm or more. Thereby, a portion where Si is not diffused is secured in the mother layer. Moreover, a standing wave can be generated between the lattice points by setting the interval between one lattice point of the plurality of lattice points and the lattice point closest to the one lattice point to 10 μm or less. More preferably, if the thickness is 3 μm or less, higher order standing waves can be suppressed, and the diffraction effect in the direction perpendicular to the principal surface can work more effectively. As a result, the voltage required for light emission can be reduced.

  In the semiconductor light emitting device of the present invention, preferably, the interval between one lattice point of the plurality of lattice points and the lattice point closest to one lattice point is 200 nm or more. Thereby, the voltage required for light emission can be further reduced.

  In the semiconductor light emitting device of the present invention, the two-dimensional diffraction grating preferably has a triangular or square lattice shape. Since the light traveling through these gratings returns to the position of the original grating point through a plurality of diffractions, a standing wave tends to be generated between the grating points. In addition, these shapes can be easily fabricated.

  Preferably, the semiconductor light emitting device of the present invention further includes an electron block layer formed between the light emitting layer and the two-dimensional diffraction grating and having a wider band gap than the light emitting layer. Thereby, since electrons can be prevented from entering the two-dimensional diffraction grating, non-radiative recombination of carriers in the two-dimensional diffraction grating can be prevented. In addition, diffusion of Si from the lattice points to the light emitting layer can be suppressed.

In the semiconductor light emitting device of the present invention, preferably, the electron block layer is made of Al _x Ga _1-x N (0 <x <1). Since Al _x Ga _1-x N has a wide band gap, it is suitable as an electron blocking layer.

  The semiconductor light emitting device of the present invention preferably further includes an intermediate layer made of GaN formed between the light emitting layer and the two-dimensional diffraction grating. Thereby, it is possible to suppress the impurities contained in the two-dimensional diffraction grating from diffusing into the light emitting layer at the intermediate layer.

  Preferably, the semiconductor light emitting device of the present invention further includes a reflective layer that is formed on the other main surface side of the light emitting layer and reflects light propagating from the light emitting layer to the light emitting layer. Thereby, the light propagated to the other main surface side of the light emitting layer can be reflected and introduced into the two-dimensional diffraction grating. As a result, the luminous efficiency can be improved.

  In the semiconductor light emitting device of the present invention, preferably, the reflective layer has a periodic refractive index distribution along the normal line of the other main surface. Thereby, the reflective layer functions as a Bragg reflective layer, and the light reflection efficiency on the other main surface side of the light emitting layer can be increased. As a result, the light extraction efficiency can be improved.

  Preferably, the semiconductor light emitting device of the present invention further includes a substrate made of n-type GaN disposed on the other main surface side of the light emitting layer. Accordingly, carriers can be injected into the light emitting layer through the substrate by attaching the electrode to the substrate, so that a high current density current can be injected into the light emitting layer.

  According to the semiconductor light emitting device of the present invention, the voltage required for light emission can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a plan view showing the configuration of the LED according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. Referring to FIGS. 1 and 2, LED 1 in the present embodiment includes a substrate 2, an n-type GaN layer 3, an active layer 4 as a light emitting layer, a spacer layer 5 as an intermediate layer, and an electron blocking layer. 6, a p-type GaN layer 7, a photonic crystal layer 8 as a two-dimensional diffraction grating, a p-type contact layer 9, a transparent electrode 10, a p-type electrode 11, and an n-type electrode 12. .

  The substrate 2 has, for example, a rectangular planar shape. On the upper surface 2a of the substrate 2, an n-type GaN layer 3, an active layer 4, a spacer layer 5, an electron blocking layer 6, and a p-type GaN layer 7 are laminated in this order. These layers are adjacent to each other. The spacer layer 5 is formed between the active layer 4 and the photonic crystal layer 8. A photonic crystal layer 8 is formed on the p-type GaN layer 7. The photonic crystal layer 8 is formed on the upper surface 4a side of the active layer 4, and a p-type contact layer 9 and a transparent electrode 10 are laminated on the photonic crystal layer 8 in this order. ing. A p-type electrode 11 is formed on the upper surface 10 a of the transparent electrode 10, and an n-type electrode 12 is formed on the lower surface 2 b of the substrate 2. The p-type electrode 11 has, for example, a circular planar shape, and is in contact with the transparent electrode 10 at the center of the upper surface 10 a of the transparent electrode 10. N-type electrode 11 has, for example, the same planar shape as substrate 2 and is in contact with lower surface 2 b of substrate 2.

  FIG. 3 is a diagram schematically showing a configuration of the photonic crystal layer in the first embodiment of the present invention. (A) is a perspective view, (b) is a plan view. Referring to FIG. 3, photonic crystal layer 8 has a plurality of lattice points 81 and a mother layer 82. The lattice points 81 have a cylindrical shape, for example, and are uniformly distributed inside the mother layer 82. In FIG. 3, the photonic crystal layer 8 constitutes a two-dimensional diffraction grating in the form of a square lattice. Each of the lattice points 81 is formed at a position that becomes a lattice point of a square lattice, in other words, at a vertex position of a square. The mother layer 82 surrounds each of the plurality of lattice points 81 in plan view.

  When attention is paid to one lattice point 81a among the plurality of lattice points 81, the lattice point 81a is surrounded by four lattice points 81b at the vertical and horizontal positions in FIG. These lattice points 81b are present at positions closest to the lattice points 81a. When the distance from the central axis of the lattice point 81a to the central axis of the lattice point 81b is indicated by pitch p and the radius of the lattice point 81 is r, the distance c between the lattice point 81a and the lattice point 81b is “c = p− 2r ″. In the photonic crystal layer 8 of FIG. 3, the distance c between the lattice points 81a and 81b is 130 nm or more, preferably 200 nm or more, and 10 μm or less, preferably 3 μm or less.

Each of the plurality of lattice points 81 contains Si, and is made of, for example, SiO ₂ . A part of one lattice point 81 may be formed of air. The mother layer 82 contains a GaN component. For example, from GaN, In _y Ga _1-y N (0 <y <1), Al _x Ga _1-x N (0 <x <1), etc. It has become.

  Although FIG. 3 shows the case where the photonic crystal layer 8 forms a two-dimensional diffraction grating in the form of a square lattice, the photonic crystal layer is not limited to this case, for example, as shown in FIG. A two-dimensional diffraction grating in the form of a triangular grating may be configured.

  FIG. 4 is a diagram schematically showing another configuration of the photonic crystal layer in the first embodiment of the present invention. (A) is a perspective view, (b) is a plan view. Referring to FIG. 4, each of lattice points 81 is formed at a position that becomes a lattice point of a triangular lattice, in other words, at a vertex position of an equilateral triangle. When attention is paid to one lattice point 81a among the plurality of lattice points 81, the lattice point 81a is surrounded by six lattice points 81b. These lattice points 81b are present at positions closest to the lattice points 81a. The interval c between the lattice point 81a and the lattice point 81b is 130 nm or more, preferably 200 nm or more, and 10 μm or less, preferably 3 μm or less.

Referring to FIG. 2, substrate 2 is made of a conductive substrate such as n-type GaN. The n-type GaN layer 3 is formed in order to improve the crystallinity of the layer formed on the substrate 2. The active layer 4 has a multiple quantum well structure made of, for example, InGaN / GaN. Spacer layer 5 is made of, for example, p-type GaN. The electron blocking layer 6 has a wider band gap than the active layer 4 and functions as a blocking layer that blocks the entry of electrons into the photonic crystal layer 8. Thereby, non-radiative recombination of electrons and holes in the photonic crystal layer 8 can be suppressed. The electron block layer 6 is made of, for example, p-type Al _x Ga _1-x N (0 <x <1). The p-type contact layer 9 is formed to make ohmic contact with the transparent electrode 10. The p-type contact layer 9 is made of, for example, p-type GaN. The transparent electrode 10 is made of, for example, a Ni / Au laminated film, the p-type electrode 11 is made of, for example, a Ti / Au laminated film, and the n-type electrode 12 is made of, for example, a Ti / Al / Ti / Au laminated film. It consists of a film. The n-type electrode 12 may be formed of a transparent electrode or the like, but the light propagating from the active layer 4 can be reflected to the active layer 4 by using a Ti / Al / Ti / Au laminated film.

Next, the light emission principle of the semiconductor light emitting element in this embodiment will be described.
When a voltage that makes the p-type electrode 11 side positive is applied between the p-type electrode 11 and the n-type electrode 12, the transparent electrode 10, the p-type contact layer 9, the photonic crystal layer 8, the p-type GaN layer 7, Holes are injected into the active layer 4 through the electron blocking layer 6 and the spacer layer 5, and electrons are injected into the active layer 4 through the substrate 2 and the n-type GaN layer 3. Then, the injected holes and electrons are recombined in the active layer 4 to generate blue light. Of the generated light, the light traveling on the upper surface 2 a side of the substrate 2 reaches the photonic crystal layer 8. The light is diffracted at each lattice point 81 (FIG. 3), and a standing wave is generated between each lattice point 81. At the same time, the light is also diffracted in the normal direction (vertical direction in FIG. 2) of the main surface of the photonic crystal layer 8. Since this light is incident at an acute angle with respect to the boundary surface between the LED 1 (transparent electrode 10) and air, it is emitted from the upper surface 10a of the transparent electrode 10 without being reflected at this boundary surface. On the other hand, of the generated light, the light traveling toward the lower surface 4 b side of the active layer 4 is reflected by the n-type electrode 12 toward the active layer 4. As a result, the light traveling toward the lower surface 2 b side of the substrate 2 is guided into the photonic crystal layer 8.

Then, the manufacturing method of LED in this Embodiment is demonstrated.
First, the n-type GaN layer 3, the active layer 4, and the spacer layer 5 are epitaxially grown on the upper surface 2a of the substrate 2. When the spacer layer 5 is formed, undoped GaN is formed. Subsequently, the electron block layer 6 and the p-type GaN layer 7 are epitaxially grown on the spacer layer 5. Here, when the layers such as the electron block layer 6 and the p-type GaN layer 7 are formed, since the substrate 2 is maintained at a high temperature, impurities contained in the electron block layer 6 and the p-type GaN layer 7 (for example, Mg) diffuses into the spacer layer 5. As a result, the spacer layer 5 exhibits p-type conductivity.

Subsequently, a photonic crystal layer 8 is formed. Referring to FIGS. 2 and 3, in photonic crystal layer 8, first, each of lattice points 81 made of SiO ₂ is formed on p-type GaN layer 7, and then the periphery of lattice points 81 is filled. Then, a mother layer 82 made of GaN is epitaxially grown on the p-type GaN layer 7. Subsequently, the p-type contact layer 9 is epitaxially grown on the photonic crystal layer 8.

  Note that if GaN is epitaxially grown even after the periphery of the lattice point 81 is filled with GaN, GaN is epitaxially grown in a region immediately above the lattice point 81. The p-type contact layer 9 may be formed by this method. In this case, the mother layer 82 and the p-type contact layer 9 are formed of the same material, and the boundary between the mother layer 82 and the p-type contact layer 9 is eliminated. For this reason, in FIG. 2, the boundary line between the photonic crystal layer 8 and the p-type contact layer 9 is indicated by a dotted line.

  Thereafter, the transparent electrode 10 and the p-type electrode 11 are formed on the p-type contact layer 9, and the n-type electrode 12 is formed on the lower surface 2 b of the substrate 2.

  Here, referring to FIG. 2 and FIG. 5, when the p-type contact layer 9, the transparent electrode 10, the p-type electrode 11, and the n-type electrode 12 are formed, the substrate 2 is kept at a high temperature. The Si contained in the lattice points 81 of the photonic crystal layer 8 diffuses from the lattice points 81 into the mother layer 82. Si diffuses at the maximum by the distance indicated by D in FIG. As a result, a region R in which Si is diffused is formed at each lattice point 81. The region R has a circular shape with each lattice point 81 as the center. In this region R, the conductivity type of GaN constituting the mother layer 82 changes from p-type to n-type. However, since the distance c is set to be twice or more the distance D, the regions R formed around each lattice point 81 do not overlap each other. For this reason, a region having a p-type conductivity other than the region R is maintained. Through the above steps, the LED 1 in the present embodiment is obtained.

  According to the LED 1 in the present embodiment, since the interval between one lattice point 81a among the plurality of lattice points 81 and the lattice point 81b closest to the lattice point 81a is 130 nm or more, the portion where Si is not diffused Is secured in the mother layer 82. Further, by setting the interval between the lattice point 81a of the plurality of lattice points 81 and the lattice point 81b closest to the lattice point 81a to 10 μm or less, a standing wave can be generated between the lattice points. More preferably, if the thickness is 3 μm or less, higher order standing waves can be suppressed, and the diffraction effect in the direction perpendicular to the principal surface can work more effectively. As a result, the voltage required for light emission can be reduced.

  Moreover, the voltage required for light emission can be further reduced by setting the distance between the lattice point 81a and the lattice point 81b to 200 nm or more.

  Further, by making the photonic crystal layer 8 into the shape of a square lattice or a triangular lattice, the light traveling through these lattices returns to the position of the original lattice point through a plurality of diffractions, and each lattice point 81 is returned. Standing waves are more likely to stand between them. In addition, a square or triangular lattice shape can be easily produced.

Further, by forming the electron block layer 6 having a wider band gap than the active layer 4 between the active layer 4 and the photonic crystal layer 8, it is possible to prevent electrons from entering the photonic crystal layer 8. And non-radiative recombination of carriers in the photonic crystal layer 8 can be prevented. In addition, diffusion of Si from the lattice point 81 to the active layer 4 can be suppressed. In particular, Al _x Ga _1-x N has a wide band gap and is therefore suitable as the electron blocking layer 6.

  In addition, by forming the spacer layer 5 between the active layer 4 and the photonic crystal layer 8, the spacer layer 5 can prevent impurities contained in the photonic crystal layer 8 from diffusing into the active layer 4. it can.

  Further, since the n-type electrode 12 formed on the lower surface 4b side of the active layer 4 has the property of reflecting the light propagating from the active layer 4 to the active layer 4, the lower surface 4b side of the active layer 4 has The propagated light can be reflected and introduced into the photonic crystal layer 8. As a result, the light extraction efficiency can be improved.

  Furthermore, by arranging the substrate 2 made of n-type GaN on the lower surface 4b side of the active layer 4, it is possible to inject electrons into the active layer 4 through the substrate 2 by attaching electrodes to the substrate 2. A current having a high current density can be injected into the active layer 4.

(Embodiment 2)
FIG. 6A is a cross-sectional view showing the configuration of the LED according to Embodiment 2 of the present invention. Referring to FIG. 6A, LED 1a in the present embodiment is different from the LED in Embodiment 1 in that it further includes a DBR (Distributed Bragg Reflector) layer. The DBR layer 13 is formed on the lower surface 4 b side of the active layer 4 and is formed between the substrate 2 and the n-type GaN layer 3. The DBR layer 13 is formed by laminating two layers having different refractive indexes. FIG. 6B is a diagram showing the refractive index distribution of the DBR layer in the second embodiment of the present invention. Referring to FIG. 6B, the DBR layer 13 has a periodic refractive index distribution along the normal line (the middle height direction in FIG. 6A) of the lower surface 4b of the active layer 4, that is, the thickness direction. ing. Specifically, the refractive index of the DBR layer 13 changes between the refractive index n1 and the refractive index n2 along the thickness direction. The period of change in refractive index is represented by T.

  In addition, since the structure of LED1a other than this is the same as that of LED of Embodiment 1 shown in FIG. 2, the same code | symbol is attached | subjected to the same member and the description is not repeated.

  According to the LED 1a in the present embodiment, the same effect as the LED in the first embodiment can be obtained. In addition, the DBR layer 13 having a periodic refractive index distribution along the thickness direction can increase the light reflection efficiency on the lower surface 4b side of the active layer 4.

(Embodiment 3)
FIG. 7 is a cross-sectional view showing the configuration of the LED according to Embodiment 3 of the present invention. Referring to FIG. 7, LED 1 b in the present embodiment is different from the LED in Embodiment 1 in the material of substrate 2 and the position of n-type electrode 12. Specifically, the substrate 2 is made of sapphire. A portion 14 on the upper surface of the n-type GaN layer 3 is exposed, and an n-type electrode 12 is formed on this portion 14. On the lower surface 2a of the substrate 2, a reflective film 12a made of, for example, Al is formed instead of the n-electrode.

  LED 1b in the present embodiment is manufactured, for example, by the following method. First, an n-type GaN layer 3, an active layer 4, a spacer layer 5, an electron block layer 6, a p-type GaN layer 7, a photonic crystal layer 8, and a p-type contact layer are formed on the upper surface 2a of the substrate 2. 9 and the transparent electrode 10 are epitaxially grown. Next, a mask layer such as a resist is formed on the transparent electrode 10. This mask layer is formed in a region other than directly above the portion 14. Then, the transparent electrode 10, the p-type contact layer 9, the photonic crystal layer 8, the p-type GaN layer 7, the electron blocking layer 6, the spacer layer 5, and the active layer 4 are etched using this mask layer. As shown in FIG. 7, a part of the n-type GaN layer 3 may be further etched. Thereby, a portion 14 of the upper surface of the n-type GaN layer 3 is exposed. Thereafter, the n-type electrode 12 is formed on the portion 14, and the reflective film 12 a is formed on the lower surface 2 a of the substrate 2. Through the above steps, the LED 1b in the present embodiment is obtained.

  In LED1b in this Embodiment, the board | substrate 2 consists of sapphire and is insulating. However, since the n-type electrode 12 is formed in the n-type GaN layer 3, electrons can be injected from the n-type electrode 12 into the active layer 4. As a result, the same effect as the LED in Embodiment 1 can be obtained.

  Further, a DBR layer 13 similar to that of the second embodiment may be formed between the substrate 2 and the n-type GaN layer 3 as in the LED 1c shown in FIG.

(Embodiment 4)
In the first to third embodiments, the case where the semiconductor light emitting element of the present invention is an LED has been described. However, the semiconductor light emitting device of the present invention may be a semiconductor laser device as described below, for example, in addition to the LED.

  FIG. 9 is a cross-sectional view showing the configuration of the semiconductor laser element in the fourth embodiment of the present invention. Referring to FIG. 9, a semiconductor laser device 1d in the present embodiment includes a substrate 21, an n-type cladding layer 22, an active layer 23 as a light emitting layer, a p-type cladding layer 24, and a two-dimensional diffraction grating. Photonic crystal layer 8, GaN layer 25, p-type cladding layer 26, p-type contact layer 27, p-type electrode 30, and n-type electrode 31.

  The substrate 21 is made of, for example, GaN, and an n-type cladding layer 22, an active layer 23, a p-type cladding layer 24, and a photonic crystal layer 8 are formed on the upper surface 21a of the substrate 21. The photonic crystal layer 8 has the same configuration as the photonic crystal layer described in the first embodiment.

  A GaN layer 25 is formed on the photonic crystal layer 8. The photonic crystal layer 8 and the GaN layer 25 are both made of GaN and are the same layer (no boundary). A p-type cladding layer 26 and a p-type contact layer 27 are formed on the GaN layer 25. A p-type electrode 30 is formed on the upper surface 27 a of the p-type contact layer 27, and an n-type electrode 31 is formed on the lower surface 21 b of the substrate 21.

  According to the semiconductor laser element 1d in the present embodiment, the same effect as that of the LED in the first embodiment can be obtained.

  In Embodiment 1, the case where the lattice points of the photonic crystal layer are cylindrical has been described, but the shape of the lattice points in the present invention is arbitrary. Further, some of the lattice points may be made of air.

  In the first to third embodiments, the case where the photonic crystal layer is formed on the upper surface side of the active layer has been described. However, the photonic crystal layer may be formed on the lower surface side of the active layer.

  Furthermore, the present invention is not limited to application to LEDs and semiconductor laser devices, but a light emitting layer that emits light when carriers are injected, and two-dimensional diffraction formed on one main surface side of the light emitting layer. It can be applied to semiconductor light emitting devices in general. When the present invention is applied to a semiconductor laser device, in order for the photonic crystal layer to function as a resonator, the order of diffraction in the photonic crystal layer is set to about 1 or 2, and at a strict pitch according to the oscillation wavelength. It is necessary to form lattice points. On the other hand, when the present invention is applied to an LED, the order of diffraction may be high. That is, very strong diffracted light is generated even when the interval between the lattice points is 200 nm or more.

In this example, an LED having the same configuration as that of the first embodiment was manufactured and its performance was evaluated. Specifically, a conductive n-type GaN substrate was prepared, and this substrate was put into an OMVPE (Organo Metallic Vapor Phase Epitaxy) furnace. In this furnace, an n-type GaN layer having a thickness of 2000 nm, an active layer (quantum well layer) made of three periods of InGaN / GaN, a spacer layer made of GaN having a thickness of 20 nm, and a p-type having a thickness of 50 nm. An electron blocking layer made of AlGaN and a p-type GaN layer having a thickness of 10 nm were epitaxially grown in this order on the surface of the substrate. Subsequently, the substrate was put into a P-CVD (Plasma Enhanced Chemical Vapor Deposition) furnace. In this furnace, a SiH ₄ gas and a N ₂ O gas were used to form a SiO ₂ film having a thickness of 100 nm at a position to be a lattice point. Next, the substrate was taken out from the P-CVD furnace, and a resist pattern having a plurality of circular lattice points was formed on the SiO ₂ film. Specifically, an electron beam (EB) exposure resist is coated on the SiO ₂ film, and exposed using an EB exposure machine so as to leave a plurality of lattice points having a pitch of 350 nm and a diameter of 130 nm, and then developed. did. Next, the substrate was put into an RIE (Reactive Ion Etching) apparatus, and SiO ₂ was etched with CF ₄ gas using the resist as a mask. As a result, a plurality of cylinders made of SiO _{2 having} a diameter of 130 nm and a height (thickness) of 100 nm were formed at the lattice points. Next, the substrate was again put into the OMVPE furnace. In this furnace, the mother layer made of GaN and the p-type contact layer were epitaxially grown so as to embed a plurality of cylinders. Next, a transparent electrode made of Ni / Au was formed on the entire surface of the p-type contact layer, and a p-type electrode made of Ti / Au was formed on a part of the transparent electrode. A p-type electrode (reflective layer) made of Ti / Al / Ti / Au was formed on the back surface of the substrate. When voltage was applied to the LED thus obtained, blue light was emitted at a voltage of about 3V.

In this example, an LED having the same configuration as that of the second embodiment was fabricated and its performance was evaluated. Specifically, a conductive n-type GaN substrate was prepared, and this substrate was put into an OMVPE furnace. In this furnace, an n-type GaN layer having a thickness of 200 nm, a DBR layer having a thickness of 4000 nm made of 50-cycle n-type GaN / n-type AlGaN, an active layer made of 3 cycles of InGaN / GaN, and 20 nm A spacer layer made of GaN having a thickness, an electron block layer made of p-type AlGaN having a thickness of 50 nm, and a p-type GaN layer having a thickness of 10 nm were epitaxially grown in this order on the surface of the substrate. Subsequently, the substrate was put into a P-CVD furnace. In this furnace, a SiH ₄ gas and a N ₂ O gas were used to form a SiO ₂ film having a thickness of 100 nm at a position to be a lattice point. Next, the substrate was taken out from the P-CVD furnace, and a resist pattern having a plurality of circular lattice points was formed on the SiO ₂ film. Specifically, a resist for EB exposure was applied on the SiO ₂ film, and exposed using an EB exposure machine so as to leave a plurality of lattice points having a pitch of 350 nm and a diameter of 130 nm, and then developed. Next, the substrate was put into an RIE apparatus, and SiO ₂ was etched with CF ₄ gas using the resist as a mask. As a result, a plurality of cylinders made of SiO _{2 having} a diameter of 130 nm and a height (thickness) of 100 nm were formed at the lattice points. Next, the substrate was again put into the OMVPE furnace. In this furnace, the mother layer made of GaN and the p-type contact layer were epitaxially grown so as to embed a plurality of cylinders. Next, a transparent electrode made of Ni / Au was formed on the entire surface of the p-type contact layer, and a p-type electrode made of Ti / Au was formed on a part of the transparent electrode. Then, an n-type electrode (reflection layer) made of Ti / Al / Ti / Au was formed on the back surface of the substrate. When voltage was applied to the LED thus obtained, blue light was emitted at a voltage of about 3V. When voltage was applied to the LED thus obtained, blue light was emitted at a voltage of about 3V.

In this example, an LED having the same configuration as that of Embodiment 3 was manufactured and its performance was evaluated. Specifically, a sapphire substrate was prepared, and this substrate was put into an OMVPE furnace. In this furnace, an n-type GaN layer having a thickness of 2000 nm, an active layer (quantum well layer) made of two periods of InGaN / GaN, a spacer layer made of GaN having a thickness of 60 nm, and a p-type having a thickness of 20 nm. An electron blocking layer made of AlGaN and a p-type GaN layer having a thickness of 10 nm were epitaxially grown in this order on the surface of the substrate. Next, the substrate was taken out from the OMVPE furnace, and a resist pattern having a plurality of circular lattice points was formed on the p-type GaN layer. Specifically, a resist for EB exposure was applied on the p-type GaN layer, exposed to form a plurality of holes having a pitch of 450 nm and a diameter of 200 nm using an EB exposure machine, and then developed. Next, the substrate was put into a P-CVD furnace. In this furnace, a SiH ₄ gas and a N ₂ O gas were used to form a SiO ₂ film having a thickness of 100 nm at a position to be a lattice point. Thereafter, excess SiO ₂ on the resist was lifted off together with the resist. As a result, a plurality of cylinders made of SiO _{2 having} a height of 100 nm were formed at lattice points. The tip of this cylinder made of SiO ₂ was slightly narrowed. Next, the substrate was again put into the OMVPE furnace. In this furnace, the mother layer made of GaN and the p-type contact layer were epitaxially grown so as to embed a plurality of cylinders. Next, a transparent electrode made of Ni / Au was formed on the entire surface of the p-type contact layer, and a p-type electrode made of Ti / Au was formed on a part of the transparent electrode. Subsequently, a resist is formed on a part of the transparent electrode and the p-type electrode, and the transparent electrode, p-type contact layer, photonic crystal layer, p-type GaN layer, electron block layer, spacer layer, active layer are formed using this resist as a mask. The layer was etched to expose a portion of the top surface of the n-type GaN layer. This etching was performed with Cl ₂ gas using an RIE apparatus. Thereafter, an n-type electrode made of Ti / Al / Ti / Au was formed on the exposed portion of the n-type GaN layer, and a reflective film made of Ag was formed on the back surface of the substrate. When voltage was applied to the LED thus obtained, blue light was emitted at a voltage of about 3V.

In the present embodiment, the influence of the spacing between lattice points made of SiO ₂ on the voltage required for light emission was examined. Specifically, a conductive n-type GaN substrate was prepared, and this substrate was put into an OMVPE furnace. In this furnace, an n-type GaN layer having a thickness of 2000 nm, an active layer made of three periods of InGaN / GaN, a spacer layer made of GaN having a thickness of 20 nm, and an electron block made of p-type AlGaN having a thickness of 50 nm. A layer and a 10 nm thick p-type GaN layer were epitaxially grown in this order on the surface of the substrate. Subsequently, the substrate was put into a P-CVD furnace. In this furnace, a SiH ₄ gas and a N ₂ O gas were used to form a SiO ₂ film having a thickness of 100 nm at a position to be a lattice point. Next, the substrate was taken out from the P-CVD furnace, and a resist pattern having a plurality of circular lattice points was formed on the SiO ₂ film in the same manner as in Examples 1 to 3. Here, in this example, resist patterns were prepared for the samples A to L at intervals shown in Table 1, respectively.

Next, the substrate was put into an RIE apparatus, and SiO ₂ was etched with CF ₄ gas using the resist as a mask. As a result, a plurality of cylinders made of SiO ₂ were formed at lattice points. Next, the substrate was again put into the OMVPE furnace. In this furnace, the mother layer made of GaN and the p-type contact layer were epitaxially grown so as to embed a plurality of cylinders. Next, a transparent electrode made of Ni / Au was formed on the entire surface of the p-type contact layer, and a p-type electrode made of Ti / Au was formed on a part of the transparent electrode. Then, an n-type electrode (reflection layer) made of Ti / Al / Ti / Au was formed on the back surface of the substrate. With respect to the LEDs of Sample A to Sample L thus obtained, the voltage required for light emission was examined. The results are shown in Table 2 and FIG.

  Referring to Table 2 and FIG. 10, light is emitted at less than 4 V when the interval is 130 nm or more, and light is emitted at about 3 V when the interval is 200 nm or more. From this result, it can be seen that the voltage required for light emission can be lowered by setting the interval between lattice points to 130 nm or more, preferably 200 nm or more.

  The embodiments and examples disclosed above are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments and examples but by the scope of claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the scope of claims. .

  The present invention can be used for a semiconductor light emitting device having a two-dimensional diffraction grating.

It is a top view which shows the structure of LED in Embodiment 1 of this invention. It is sectional drawing along the II-II line of FIG. (A) is a perspective view which shows typically the structure of the photonic crystal layer in Embodiment 1 of this invention. (B) is a top view which shows typically the structure of the photonic crystal layer in Embodiment 1 of this invention. (A) is a perspective view which shows typically the other structure of the photonic crystal layer in Embodiment 1 of this invention. (B) is a top view which shows typically the other structure of the photonic crystal layer in Embodiment 1 of this invention. It is a figure which shows typically the spreading | diffusion of Si contained in a lattice point. (A) is sectional drawing which shows the structure of LED in Embodiment 2 of this invention. (B) is a figure which shows the refractive index distribution of the DBR layer in Embodiment 2 of this invention. It is sectional drawing which shows the structure of LED in Embodiment 3 of this invention. It is sectional drawing which shows the other structure of LED in Embodiment 3 of this invention. It is sectional drawing which shows the structure of the semiconductor laser element in Embodiment 4 of this invention. It is a graph showing a relation between the distance and the light emission voltage of a cylinder made of SiO ₂ in the fourth embodiment of the present invention.

Explanation of symbols

  1, 1a to 1c LED, 1d semiconductor laser element, 2, 21 substrate, 2a, 21a substrate upper surface, 2b, 21b substrate lower surface, 3 n-type GaN layer, 4,23 active layer, 4a active layer upper surface, 4b active layer lower surface 5, spacer layer, 6 electron block layer, 7 p-type GaN layer, 8 photonic crystal layer, 9, 27 p-type contact layer, 10 transparent electrode, 10a transparent electrode upper surface, 11, 30 p-type electrode, 12, 31 n Type electrode, 12a reflective film, 13 DBR layer, 14 parts, 22 n-type clad layer, 24, 26 p-type clad layer, 25 GaN layer, 27a p-type contact layer upper surface, 81, 81a, 81b lattice point, 82 mother layer .

Claims (9)

A light-emitting layer that emits light when carriers are injected;
A two-dimensional diffraction grating formed on one main surface side of the light emitting layer,
The two-dimensional diffraction grating includes a plurality of lattice points including silicon, and a base layer that surrounds each of the plurality of lattice points in a plan view and includes p-type gallium nitride.
A semiconductor light emitting element, wherein an interval between one lattice point of the plurality of lattice points and a lattice point closest to the one lattice point is 130 nm or more and 10 μm or less.   The semiconductor light emitting element according to claim 1, wherein the interval is 200 nm or more.   The semiconductor light-emitting element according to claim 1, wherein the two-dimensional diffraction grating has a triangular or square lattice shape.   4. The semiconductor light emitting device according to claim 1, further comprising an electron block layer formed between the light emitting layer and the two-dimensional diffraction grating and having a wider band gap than the light emitting layer. 5. . 5. The semiconductor light emitting element according to claim 4, wherein the electron block layer is made of Al _x Ga _1-x N (0 <x <1).   The semiconductor light emitting element according to claim 1, further comprising an intermediate layer made of gallium nitride formed between the light emitting layer and the two-dimensional diffraction grating.   The semiconductor light emitting element according to claim 1, further comprising a reflective layer that is formed on the other main surface side of the light emitting layer and reflects light propagating from the light emitting layer to the light emitting layer. .   The semiconductor light emitting element according to claim 7, wherein the reflective layer has a periodic refractive index distribution along a normal line of the other main surface.   The semiconductor light emitting element according to claim 1, further comprising a substrate made of n-type gallium nitride disposed on the other main surface side of the light emitting layer.

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