JP3936368B2 - Gallium nitride compound semiconductor light emitting device - Google Patents

Description

  The present invention relates to a gallium nitride-based compound semiconductor light-emitting device that extracts light from the surface of a semiconductor substrate, and more particularly to a configuration that emits light emitted from the device to a phosphor to obtain light emission with a desired wavelength.

  In recent years, gallium nitride compounds using Alx, Gay, In1-xyN (0 ≦ x, y ≦ 1, x + y ≦ l) as materials for light emitting diodes (LEDs) ranging from the ultraviolet region to the blue and green regions Semiconductors are attracting attention. With compound semiconductors of such materials, it has become possible to emit ultraviolet light, blue light, green light, and the like with high light emission intensity, which has been difficult until now. Such a gallium nitride compound semiconductor is generally grown on a sapphire substrate, which is an insulating substrate.

  For this reason, an electrode cannot be provided on the substrate side like a GaAs-based light emitting element, and it is necessary to form both an anode and a cathode electrode on the crystal growth substrate side. Thus, the cathode electrode is formed by etching away the p-type layer to expose the n-type layer. The anodic electrode needs to be formed on the surface of the p-type layer, but the p-type layer emits light only directly under the electrode because of its low conductivity. For this reason, the external quantum efficiency decreases unless an electrode transparent to the emission wavelength is formed on the entire surface of the light emitting region.

  FIG. 11 shows a structural example of a conventional gallium nitride-based compound semiconductor light-emitting device (hereinafter sometimes simply referred to as a semiconductor light-emitting device). A GaN buffer layer (not shown), an n-type GaN layer 2 and a p-type GaN layer 3 are grown on the sapphire substrate 1, and a part of the p-type GaN layer 3 is etched away to expose the n-type GaN layer 2. Has been. A p-side transparent electrode 6 and a p-side bonding electrode 5 are formed on the p-type Ga layer 3, and an n-side electrode 4 is formed on the n-type GaN layer 2.

  As shown in FIG. 12, the semiconductor light emitting device 10 having the above structure is generally mounted on a lead frame 12 with a conductive adhesive material 11 such as silver paste, and a resin mold 8 is applied. Further, in order to cause the phosphor to emit light, the phosphor 9 is generally mixed in the resin mold 8. The current flowing from the p-side bonding electrode 5 is spread by the transparent electrode 6 having good conductivity, and the current is injected from the p-type GaN layer 3 to the n-type GaN layer 2. Light is emitted from a pn junction formed between the type GaN layers 2, and the light is extracted out of the chip through the transparent electrode 6. Further, light is emitted to the outside through the resin mold 8 as shown in FIG. At this time, if the phosphor 9 is present in the resin mold 8, the phosphor also emits light by the light emitted from the pn junction, and light emission of a desired color can be obtained by selecting the type of color of the phosphor. .

  In the conventional gallium nitride compound semiconductor light emitting device as described above, the light emitted from the pn junction is absorbed by the p-type GaN layer 3, does not reach the transparent electrode 6 on the surface, and cannot be taken out to the outside. There was a problem.

  In addition, when the p-type GaN layer 3 is thinned, light that is not absorbed by the layer 3 is extracted through the transparent electrode 6, but is highly conductive, ohmic to the semiconductor layer, and has a light emission wavelength. There is a problem that an electrode material having a small amount of absorption cannot be easily realized. In addition, as the emission wavelength becomes shorter, there is a problem that a material having a small absorption power at the emission wavelength is more difficult to realize. In particular, in order to cause the phosphor 9 to emit light (especially red) with the light emitted from the pn junction, it is necessary to extract light having a short wavelength of about 300 nm, which has high emission conversion efficiency of the phosphor 9, from the pn junction. There is a problem that it is very difficult to realize a material that absorbs little in this wavelength region.

  In addition, when the phosphor 9 is included in the resin mold 8, most of the light emitted from the pn junction is not immediately converted by the phosphor 9, but as the light passes through the resin mold 8 portion. Since the light is converted by the phosphor 9, there is a problem that light cannot be efficiently converted by the phosphor 9 due to attenuation when propagating through the resin mold 8, and deterioration of the resin mold 8 due to short wavelength light (ultraviolet light). There were also problems such as being caused. Further, since the optical power converted by the phosphor 9 cannot be measured unless the semiconductor element is resin-molded, there is a problem that chip selection in the wafer state is difficult and mass productivity is lacking.

  The present invention has been made to solve the above-described conventional problems, and its purpose is to efficiently use the generated short-wavelength light (ultraviolet light) without using a transparent electrode that is difficult to realize. It is an object to provide a gallium nitride-based compound semiconductor light-emitting element that can be converted into visible light or the like by a phosphor and can be efficiently extracted outside and can emit three primary colors of red, green, and blue.

In order to achieve the above object, the present invention is characterized in that, in a gallium nitride-based compound semiconductor having a pn junction, a cross section formed from the semiconductor surface toward the inside so that a part of the pn junction is removed. recessed pn junction removal unit is provided with, the phosphor layer on the inside or periphery of the pn junction removal unit is filled or formed, on the pn junction of each side of the recess-like pn junction removal section, the concave shape Current is injected from the p-type semiconductor layer of the pn junction through the electrodes provided on the pn junction on both sides of the pn junction removal portion .

  As described in detail above, according to the first, second, third, and seventh inventions, the pn junction removing portion that removes a part of the pn junction is provided to expose the end face of the pn junction. By extracting ultraviolet light from the end face of the pn junction, the generated ultraviolet light can be efficiently extracted to the outside without using a transparent electrode made of a material that is difficult to realize.

  According to the fourth and fifth inventions, by arranging the phosphor in the vicinity of the end surface of the pn junction, the ultraviolet light extracted from the pn junction is immediately converted into visible light by the phosphor. A sufficient level of visible light such as red can be obtained efficiently.

  According to the eighth invention, since the concentric pn junction removing portion is provided in the vicinity of the exposed hole of the n-type GaN layer where the semiconductor surface current is concentrated, the semiconductor surface current flows over the entire surface, and the semiconductor surface More uniform light emission can be obtained.

  According to the sixth aspect, by arranging a plurality of colored phosphors in the vicinity of the end face of the pn junction, it is possible to simultaneously obtain a plurality of colors of visible light irradiation.

  According to the ninth and tenth aspects of the invention, the phosphor layers having different colors are filled in the pn junction removal portions of the respective divided regions, so that visible light having different colors can be obtained for the respective divided regions. In particular, if the divided region is divided into three and the phosphor layers of different colors are made three primary colors of red, blue, and green, a color LED can be easily realized with only a gallium nitride compound semiconductor light emitting element. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a configuration example of a first embodiment of a gallium nitride-based compound semiconductor light emitting device of the present invention. A GaN buffer layer (not shown), an n-type GaN layer 2 and a p-type GaN layer 3 are sequentially grown on the sapphire substrate 1. Next, the p-type GaN layer 3 is patterned by the PEP method and etched by the RIE method or the like to expose the n-type GaN layer 2.

Thereafter, patterning is performed using the PEP method, and Ti / Au or the like is deposited on the n-type GaN layer 2 as the n-side electrode 4 and formed by lift-off. As the transparent electrode 6, after patterning by the PEP method, a Ni layer having a thickness of 10 nm is formed on the p-type GaN layer 3 by a vacuum deposition method.

  Further, after patterning by the PEP method for forming a stripe, Ni is wet-etched with HCl or the like using a 10 μm-wide resist as a mask, and then the p-type GaN layer 3 is etched and removed in a stripe shape by the RIE method or the like. By exposing the GaN layer 2, the pn junction removing portion 100 from which a part of the pn junction is removed is formed. Further, after the SiO2 film is formed by the thermal CVD method, the p-side bonding electrode 5 connected to the Ni thin film is formed by the PEP method. Note that the GaN layer located between the pn junction removal portions 100 has a mesa shape.

  Although this SiO2 film is not clearly shown in FIG. 1, it is formed over the mesa end surface of the pn junction removing portion 100, the exposed surface of the pn junction, and the surface of the transparent electrode 6, and the n-side electrode 4 portion. The transparent electrode 6 and the p-side bonding electrode 5 are also formed under the p-side electrode except for the overlapping portion. If the surface of the semiconductor layer is free of oxide or the like and is sufficiently clean, it may be an unnecessary process. However, in order to improve adhesion and ohmic properties between the transparent electrode 6 and the n-side electrode 4 and the semiconductor layer, 450 may be used. An electrode is formed by performing flash annealing at 20 ° C. for 20 seconds.

  Next, the operation of this embodiment will be described. When a voltage is applied between the cathode p-side bonding electrode 5 and the anode n-side electrode 4, the current flowing from the p-side bonding electrode 5 is spread by the transparent electrode 6 having good conductivity, and p-type GaN. It is injected from the layer 3 into the n-type GaN layer 2 and emits light at the pn junction between the p and n-type GaN layers 3 and 2, and the emitted ultraviolet light is a side wall of the pn junction removal unit 100 formed in a stripe shape. Irradiated to the outside through the end face of the pn junction exposed to p, the p-type GaN layer 3 and the transparent electrode 6.

  Here, if the phosphor is applied or filled on the wall surface or bottom surface of the pn junction removing unit 100 formed in a stripe shape, the ultraviolet light emitted from the pn junction end surface of the pn junction removing unit 100 is visible by this phosphor. It is converted into light and irradiated outside. At this time, if the color of the phosphor is red, red is emitted, blue if the color of the phosphor is blue, and green if the color of the phosphor is green.

  FIG. 2 shows the current-voltage characteristics (IV characteristics) and the current-light output (Po) characteristics of the present example thus obtained. In FIG. 2, it can be seen that when the current value is 20 mA, a voltage of 4.3 V, an optical output of 58 μW, and an emission wavelength of 360 nm are obtained.

  According to the present embodiment, by forming a plurality of pn junction removal portions 100 on the semiconductor surface, a part of the pn junction formed by the p-type GaN layer 3 and the n-type GaN layer 2 is removed, Even if the ultraviolet light is attenuated by the p-type GaN layer 3 or the transparent electrode 6 by taking out the ultraviolet light emitted from the pn junction to the outside from the pn junction end face exposed on the side wall of the pn junction removing portion 100, the pn junction end face A sufficient level of ultraviolet light can be extracted outside. Therefore, a normal material can be used for the transparent electrode 6, and the above effects can be easily obtained. In addition, the emitted ultraviolet light has a short wavelength of about 360 nm, which is high in the light emission conversion efficiency of the phosphor, and is immediately converted into visible light by the phosphor coated or filled close to the pn junction end face. Conversion efficiency is extremely high, a sufficient level of visible light can be obtained efficiently, and the light emission source can be easily miniaturized because of the structure in which light is led out from the PN junction end face. Furthermore, since the short wavelength ultraviolet rays can be efficiently extracted from the pn junction as described above, the ultraviolet rays can be converted into red by a red phosphor, and red light of a practical level can be obtained. . In addition, the phosphor is not present in the resin mold as in the prior art, and since the phosphor is applied in the wafer state, the intensity of the light converted by the phosphor can be measured even in the wafer state. Further, it is possible to easily perform chip selection in the wafer state, and it is possible to improve the mass productivity and the yield of the semiconductor light emitting device.

  Note that if the ratio of the area of the pn junction removing portion 100 to the semiconductor surface is large, the area of the pn junction is reduced, and the amount of ultraviolet light emission is reduced. Conversely, the area of the pn junction removing portion 100 is small. Since the amount of ultraviolet rays extracted from the pn junction portion to the outside decreases, the ratio of the pn junction removal portion 100 to the semiconductor surface has an appropriate range.

  FIG. 3 is a perspective view showing a configuration example of the second embodiment of the gallium nitride compound semiconductor light emitting device of the present invention. This example is different from the first embodiment shown in FIG. 1 except that the transparent electrode 6 formed on the p-type GaN layer 3 and the phosphor layer 7 are formed on the pn junction removing portion 100. It has the same structure as the form. Thus, when a voltage is applied between the cathode p-side bonding electrode 5 and the anode n-side electrode 4, light is emitted at the pn junction between the p-type GaN layer 3 and the n-type GaN layer 2, The emitted ultraviolet light is irradiated to the outside through the pn junction end face exposed on the side surface of the pn junction removal portion 100 formed in a stripe shape, the p-type GaN layer 3, and the transparent electrode 6. At this time, the ultraviolet rays are converted into visible rays when passing through the phosphor layer 7, and the visible rays are irradiated to the outside.

  Also in this case, since the phosphor layer 7 is disposed in the vicinity of the pn junction removing portion 100 and the transparent electrode 6 formed in a stripe shape, the emitted ultraviolet rays are not attenuated, and the phosphor layer 7 is more efficient. It is converted into visible light and has the same effect as in the first embodiment. In particular, in this example, the ultraviolet rays can be converted to visible light by the phosphor layer 7 by being irradiated to the outside through the p-type GaN layer 3 and the transparent electrode 6, and the efficiency is improved accordingly.

  FIG. 4 is a perspective view showing a configuration example of the third embodiment of the present invention of a gallium nitride-based compound semiconductor light emitting device. This example has a configuration in which the entire semiconductor light emitting device is surrounded by a phosphor layer 7 formed by applying a phosphor-containing organosilane solution to the entire semiconductor light emitting device, except that the second embodiment shown in FIG. This is similar to the embodiment and has the same effect.

  FIG. 5 is a perspective view showing a configuration example of the fourth embodiment of the gallium nitride compound semiconductor light emitting device of the present invention. In this example, the pn junction removing portion 100 for removing a part of the pn junction between the p-type GaN layer 3 and the n-type GaN layer 2 is formed in a stripe shape. In this example, the pn junction formed in the stripe shape is used. The difference between the p-type GaN layer 3 and the n-type GaN layer 2 between the junction removal portions 100 is an inverted mesa type, and the other configuration is the same as that of the first embodiment shown in FIG. It is the same and has the same effect.

  In particular, since the portion of the p-type GaN layer 3 and the n-type GaN layer 2 between the pn junction removal portions 100 formed in a stripe shape is an inverted mesa type, the contact area between the transparent electrode 6 and the semiconductor layer is increased. The organic silane solution containing the phosphor or the phosphor itself is packed in the bottom portion 21 of the mesa-etched hole, so that the ultraviolet light emitted to the outside from the end face of the pn junction can be efficiently reddish with the phosphor. Can be converted into visible light.

  FIG. 6 is a plan view showing a configuration example of the fifth embodiment of the gallium nitride-based compound semiconductor light emitting device of the present invention. In this example, the shape of the pn junction removal portion 100 between the p-type GaN layer 3 and the n-type GaN layer 2 is an elongated groove shape, and the pn junction removal portion 100 having such a shape extends from the center of the chip surface to the peripheral portion. A plurality of straight lines are extended toward. Since the other configuration is the same as that of the first embodiment shown in FIG. 1, the ultraviolet light is irradiated to the outside from the end face of the pn junction exposed on the wall surface of the pn junction removing unit 100, and the first embodiment. Has the same effect. In addition, if the phosphor layer is provided in the pn junction removing part 100 and its peripheral part, the ultraviolet rays can be efficiently converted into visible light.

  FIG. 7 is a plan view showing a configuration example of the sixth embodiment of the gallium nitride-based compound semiconductor light emitting device of the present invention. In this example, the central portion of the p-type GaN layer 3 is etched in a circular shape to expose the n-type GaN layer 2 in a circular shape, and a circular n-side electrode 4 is formed at the center of the surface of the n-type GaN layer 2. Has been. Further, the shape of the pn junction removing portion 100 for removing a part of the pn junction between the p-type GaN layer 3 and the n-type GaN layer 2 is an elongated groove type, but the circular n-type GaN layer 2 is exposed. A plurality of pn junction removal portions 100 are arranged radially from the edge of the p-type GaN layer 3 forming the outer periphery of the hole toward the outside. In addition, one end of the pn junction removing portion 100 communicates with the exposed hole. Since the other configuration is the same as that of the first embodiment shown in FIG. 1, the ultraviolet light is irradiated to the outside from the end face of the pn junction exposed on the wall surface of the pn junction removing unit 100, and the first embodiment. Has the same effect. If the phosphor layer is filled in the pn junction removing unit 100 or the like, the phosphor layer can efficiently convert the ultraviolet light into visible light.

  FIG. 8 is a plan view showing a configuration example of the eighth embodiment of the gallium nitride-based compound semiconductor light emitting device of the present invention. In this example, the central portion of the p-type GaN layer 3 is etched in a circular shape to expose the n-type GaN layer 2 in a circular shape, and a circular n-side electrode 4 is formed at the center of the surface of the n-type GaN layer 2. A P-side bonding electrode 5 is formed at the corner of the p-type GaN layer 3. Except for the P-side bonding electrode 5 portion, a plurality of circular pn junction removal portions 100 are formed substantially concentrically around the n-side electrode 4. Except for the pn junction removing portion 100 and the P-side bonding electrode 5, the transparent electrode 6 covers almost the entire surface of the p-type GaN layer 3, and the transparent electrode 6 and the P-side bonding electrode 5 are connected to each other. .

  In this embodiment, the pn junction portion in the region of the transparent electrode 6 near the n-side electrode 4 where current tends to flow due to concentration is partially concentrically formed by the pn junction removal portion 100 by adopting the structure as described above. Since the current is removed, the current flows also to the peripheral portion of the P-type GaN layer 3, and uniform light emission can be obtained from the entire surface. Since the other configuration is the same as that of the first embodiment shown in FIG. 1, the ultraviolet light is irradiated to the outside from the end face of the pn junction exposed on the wall surface of the pn junction removing unit 100, and the first embodiment. Has the same effect. If the phosphor layer is filled in the pn junction removing unit 100 or the like, the phosphor layer can efficiently convert the ultraviolet light into visible light.

  FIG. 9 is a perspective view showing a configuration example of the eighth embodiment of the gallium nitride-based compound semiconductor light emitting device of the present invention. In this example, a pn junction removing portion 100 that removes a part of the pn junction between the p-type GaN layer 3 and the n-type GaN layer 2 by etching using the RIE method has a cylindrical shape. A plurality of layer removal portions 100 are arranged at an appropriate interval.

  The other configuration is the same as that of the first embodiment shown in FIG. 1, and ultraviolet rays are taken out from the end surface of the pn junction part exposed on the wall surface of the columnar pn junction removal unit 100, and the same effect is obtained. In particular, by making the size and number of columnar pn junction removal portions 100 appropriate, the contact area between the p-type GaN layer 3 and the transparent electrode 6 can be increased, so that the IV characteristics of the device are improved. And more stable light emission can be performed.

  FIG. 10 is a perspective view showing a configuration example of the ninth embodiment of the gallium nitride-based compound semiconductor light emitting device of the present invention. In this example, the phosphor layer 7 is provided so as to close the opening of the columnar pn junction removing unit 100. However, this embodiment is different from the eighth embodiment shown in FIG. This is the same as the eighth embodiment.

  Thereby, the ultraviolet rays extracted from the columnar pn junction removing unit 100 are immediately and efficiently converted into visible light by the phosphor layer 7, and the visible light is irradiated to the outside. Therefore, by changing the type of the phosphor layer 7, the type of visible light can be changed to, for example, red, blue, and green. Other effects are the same as in the eighth embodiment, and there are similar effects.

  FIG. 11 is a perspective view showing a configuration example of a tenth embodiment of a gallium nitride-based compound semiconductor light-emitting element according to the present invention. In this example, three semiconductor light emitting elements shown in FIG. 10 are formed adjacent to each other. The upper part of the three semiconductor light emitting elements from the p-type GaN layer 3 is divided from the others, but the n-type GaN layer 2 and the sapphire substrate 1 are common, and the n-side electrode 4 is also common. The openings of the cylindrical pn junction removal portions of these three semiconductor light emitting elements are filled with phosphor layers 13, 14, and 15 of three primary colors so as to close the openings. For this reason, red light is emitted from the phosphor layer 13, blue light is emitted from the phosphor layer 14, and green light is emitted from the phosphor layer 15.

  According to the present embodiment, it is possible not only to realize a full color with only a gallium nitride-based compound semiconductor light-emitting element, but also to reduce the production cost and improve the yield, and to miniaturize the light-emitting source. Can do.

1 is a perspective view showing a configuration example of a first embodiment of a gallium nitride-based compound semiconductor light-emitting element according to the present invention. FIG. 2 is a characteristic diagram showing current-voltage characteristics and current-light output characteristics of the optical semiconductor element shown in FIG. 1. It is the perspective view which showed the structural example of 2nd Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the perspective view which showed the example of a structure of 3rd Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the perspective view which showed the structural example of 4th Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the top view which showed the example of a structure of 5th Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the top view which showed the structural example of 6th Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the top view which showed the example of a structure of 7th Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the perspective view which showed the example of a structure of 8th Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the perspective view which showed the structural example of 9th Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the perspective view which showed the structural example of 10th Embodiment of the gallium nitride type compound semiconductor light-emitting device of this invention. It is the perspective view which showed the structural example of the conventional gallium nitride type compound semiconductor light-emitting device. It is the perspective view which showed the other structural example of the conventional gallium nitride type compound semiconductor light emitting element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 n-type GaN layer 3 p-type GaN layer 4 n-side electrode 5 p-side bonding electrode 6 transparent electrode 7, 13, 14, 15, 16 phosphor layer 100 pn junction removal part

Claims (8)

In a gallium nitride compound semiconductor having a pn junction,
A pn junction removing portion having a concave section formed from the semiconductor surface toward the inside so as to remove a part of the pn junction is provided, and a phosphor layer is provided in or around the pn junction removing portion. Is filled or formed, and the pn junction is formed on the pn junction on both sides of the recess-shaped pn junction removal portion via electrodes provided on the pn junction on both sides of the recess-shaped pn junction removal portion. A gallium nitride-based compound semiconductor light emitting device, wherein current is injected from a p-type semiconductor layer . The light emitted from the pn junction is irradiated to the outside through any one of an end surface of the pn junction in the pn junction removal portion and a p-type semiconductor layer and an n-type semiconductor layer of the pn junction. The gallium nitride-based compound semiconductor light-emitting device according to claim 1. The gallium nitride-based compound semiconductor light-emitting element according to claim 2, wherein the light emitted from the pn junction is ultraviolet light. 4. The gallium nitride compound semiconductor light emitting device according to claim 1, wherein the phosphor converts short wavelength light emitted from the pn junction into visible light. 5. 5. The gallium nitride-based compound according to claim 1, wherein the pn junction removal portion has an elongated groove shape, and a plurality of the pn junction removal portions are provided on the semiconductor surface at an appropriate interval. Semiconductor light emitting device. 5. The pn junction removal portion according to claim 1, wherein a plurality of openings are circular or polygonal holes, and a plurality of the pn junction removal portions are provided at an appropriate interval on the semiconductor surface. Gallium nitride compound semiconductor light emitting device. The phosphor layer is formed on the semiconductor surface so as to cover at least a part of the inside of the pn junction removing portion and a peripheral portion of the pn junction removing portion. The gallium nitride compound semiconductor light-emitting element according to any one of the above. The gallium nitride-based compound semiconductor light-emitting element according to any one of claims 1 to 7, wherein a region containing phosphors that emit different colors exists in a part of the phosphor layer.