JP4835377B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device having a roughened surface so that the thickness of a light extraction layer does not become thin.

  In recent years, light-emitting diodes (LEDs), which are semiconductor light-emitting elements, have been capable of growing GaN-based and AlGaInP-based high-quality crystals by the MOVPE method, so that blue, green, orange, yellow, red, etc. High brightness LED can be manufactured. Along with the increase in brightness of LEDs, the use is expanding to brake lamps for automobiles, backlights for liquid crystal displays, and the like, and demand is increasing year by year.

  Since high quality crystals can be grown by the MOVPE method, the luminous efficiency inside the light emitting element is approaching the limit value of the theoretical value. However, the light extraction efficiency from the light emitting element to the outside is still low, and improvement of the light extraction efficiency is desired.

  For example, a high-intensity red LED is formed of an AlGaInP-based material and sandwiched between an n-type AlGaInP layer and a p-type AlGaInP layer made of an AlGaInP-based material having a lattice-matched composition on a conductive GaAs substrate. In addition, a double hetero structure having an active layer which is a part of a light emitting portion made of AlGaInP or GaInP. Here, the AlGaInP-based material is a generic name for various materials having AlGaInP as a main component and different composition ratios or additives. A semiconductor light emitting device using an AlGaInP-based material is also used with a material such as GaInP or GaP.

  In this type of semiconductor light emitting device, since the band gap of the GaAs substrate is narrower than the band gap of the active layer, most of the light from the active layer is absorbed by the GaAs substrate, and the light extraction efficiency decreases.

  As a measure against this, light absorption at the GaAs substrate is reduced by reflecting the light toward the GaAs substrate by forming a multilayer reflective film structure layer made of semiconductors having different refractive indexes between the active layer and the GaAs substrate. There is a method for improving the light extraction efficiency. However, this method reflects only light having a limited incident angle with respect to the multilayer reflective film structure layer. That is, only a part of the light directed toward the GaAs substrate can be reflected, and it is difficult to sufficiently improve the extraction efficiency.

  Therefore, after manufacturing a semiconductor light emitting device in which a portion of a double heterostructure made of an AlGaInP-based material is formed by growth, the portion of the double heterostructure is made Si, GaAs, or the like through a metal layer having a high reflectance. A method for removing the GaAs substrate used for growth after being attached to the supporting substrate is disclosed in Patent Document 1. If this method is used, since a metal is used as the reflection layer, reflection with a high reflectance can be performed without selecting an incident angle with respect to the reflection layer. For this reason, higher brightness can be achieved than when the layer having the multilayer reflective film structure described above is formed. That is, the luminance can be increased by more effectively extracting light generated in the active layer.

  FIG. 5 shows the structure of a conventional semiconductor light emitting device. As shown in the figure, the conventional semiconductor light emitting device 101 is formed in order from the top of the figure, the first electrode 102 that partially covers the light extraction layer, and is formed just below the first electrode 102 and has the same portion as the first electrode 102. A first electrode side contact layer 103 having a band gap energy smaller than that of the active layer and opaque to light from the active layer, and a main surface on the first cladding layer side; A light extraction layer 104 that emits light traveling toward the layer side to the outside, a first cladding layer 105 that is one of two cladding layers that sandwich the active layer, and an active layer that generates light sandwiched between the first and second cladding layers 106, the second cladding layer 107 which is the other cladding layer, the intervening layer 108 interposed between the second cladding layer and the reflective metal film layer side contact layer, the reflective metal film layer side contact layer 109, the oxide layer 11 Support for attaching a reflective metal film layer 111, a metal adhesion layer 112, and a double heterostructure portion that reflects light from the active layer 106 toward the second electrode side between the second cladding layer 107 and the second electrode It consists of the board | substrate 113 and the 2nd electrode 114 which covers the surface opposite to a main surface.

  The light extraction layer 104 is also called a window layer.

  The oxide layer 110 includes an ohmic contact junction 115 that is appropriately dispersed in a plane in contact with the reflective metal film layer 111, and a portion that is not the ohmic contact junction 115 is referred to as a non-ohmic contact junction 116. To.

  The reflective metal film layer side contact layer 109 has three layers 117, 118, and 119 having different additives to the material, and the material of the intermediate layer side contact layer 117 in contact with the intermediate layer 108 among these three layers is an additive. Is Mg, and the material of the oxide layer side contact layer 119 in contact with the oxide layer 110 has an additive of Zn, and the material of the intermediate contact layer 118 between these two layers has no positive additive.

  The region from the first electrode side contact layer 103 to the reflective metal film layer side contact layer 109 is referred to as a double heterostructure portion 120. In addition, the first cladding layer 105, the active layer 106, and the second cladding layer 107 may be collectively referred to as a light emitting layer 121.

  In the semiconductor light emitting device 101 of FIG. 5, by providing the reflective metal film layer 111, light is not extracted from the main surface (opposite surface) where the support substrate 112 is present, and is formed on the light extraction layer 104. Light is extracted only from the main surface.

  The reflective metal film layer 111 disposed between the double heterostructure portion 120 and the support substrate 112 naturally has a high reflectance with respect to light from the active layer 106, and is mainly made of an AlGaInP-based material. Ohmic contact must be made with the double heterostructure 120. However, it is difficult to make an ohmic contact directly with an AlGaInP-based material using a metal such as Ag, Al, or Au having a high reflectance at the light emission wavelength of light from the active layer 106 made of an AlGaInP-based material. Therefore, it is necessary to partially arrange the ohmic contact junction 115 between the reflective metal film layer 111 and the double heterostructure portion 120. The partial arrangement means not to cover the entire surface of the reflective metal film layer 111 but to disperse it appropriately within the plane.

  The ohmic contact junction 115 is disposed between the reflective metal film layer 111 and the double heterostructure portion 120 in order to obtain an ohmic contact, and has a lower reflectance than the reflective metal film layer 111. In addition, after providing the material for the ohmic contact junction 115 in contact with the double heterostructure portion 120, it is necessary to perform heat treatment in order to obtain an ohmic contact. During the heat treatment, an alloying reaction occurs between the double heterostructure portion 120 and the material of the ohmic contact junction 115, and the light absorptance increases in the double heterostructure portion 120 in contact with the ohmic contact junction 115. For this reason, when light from the active layer 106 passes through the oxide layer 110, light absorption is increased at the ohmic contact junction 115 compared to the non-ohmic contact junction 116. As a result, the light extraction efficiency of the entire light emitting element is reduced.

JP 2004-356279 A JP 2002-217450 A

  By the way, even if the reflective metal film layer 111 has a high reflectance with respect to the light from the active layer 106, if a large amount of light cannot be extracted from the surface of the light extraction layer 104 which is the main surface, the light extraction is performed. The efficiency is reduced and the light output is not improved. Therefore, as a method for efficiently extracting light, it is known to roughen the main surface as in Patent Document 1. Roughening is forming irregularities.

  In other words, in order for light to go out from the substance, there is a restriction of a critical angle. If the angle of light is perpendicular to the surface, light can be extracted, but if there is an inclination, it cannot be extracted. The critical angle is determined by the wavelength of light and the refractive index of the material. For example, among the light emitted from the light emitting layer 121, light in a direction perpendicular to the light extraction layer 104 exits from the semiconductor light emitting element 101, but is light having a certain angle with respect to the light extraction layer 104. Can not come out of the semiconductor light emitting device 101 due to the angle with respect to the main surface. However, when the main surface is roughened, the angle with respect to the main surface of light having a certain angle with respect to the light extraction layer 104 changes, and thus the light exits from the semiconductor light emitting element 101. Therefore, the light extraction efficiency is improved by roughening the main surface.

  In order to further enhance the effect of roughening, there is a method of forming a concavo-convex pattern using photolithography, which is a well-known technique, but this method requires the formation of a fine pattern and requires an expensive apparatus. As a result, the manufacturing cost of the semiconductor light emitting device is increased. In addition, the manufacturing cost is increased due to the photolithography process. On the other hand, as a method of reducing the manufacturing cost, there is a method of roughening without forming a pattern. However, this method has the following problems.

  When the surface of the light extraction layer, which is the main surface, is roughened by etching without forming a pattern, the etching proceeds on the entire surface simultaneously with the formation of the unevenness, and the layer thickness of the light extraction layer is reduced on the entire surface. When the layer thickness is reduced over the entire surface, the current spread becomes worse, the forward voltage increases, and at the same time the light emission output decreases. As a result, the luminous efficiency decreases.

  The reason why the light emission efficiency is decreased is that the amount of heat generated in the semiconductor light emitting element is increased by increasing the forward voltage, and the light emission output is decreased due to the influence of the heat. In short, when the layer thickness of the light extraction layer is reduced, the series resistance is increased and the spread of current is deteriorated, so that the forward voltage is increased and the light emission output is decreased.

  Accordingly, an object of the present invention is to provide a semiconductor light emitting device having a roughened surface so as to solve the above-described problems and prevent the light extraction layer from becoming thin.

  In order to achieve the above object, the present invention provides a plurality of semiconductors including an active layer sandwiched between first and second cladding layers and generating light, and a light extraction layer forming a main surface on the first cladding layer side. A first electrode that partially covers the light extraction layer, a second electrode that covers the opposite surface of the main surface, and a reflective metal that reflects light between the second cladding layer and the second electrode In the semiconductor light emitting device having a film layer, an oxide layer in contact with the active layer side of the reflective metal film layer, and an ohmic contact junction partly formed in the oxide layer, the light extraction layer has a composition Consists of a plurality of layers having different ratios, and unevenness for making the main surface rough is formed over the plurality of layers.

  Of the plurality of layers constituting the light extraction layer, the outermost layer may have a concavo-convex surface having a smaller slope than the next outer layer.

  The material of the outermost layer among the plurality of layers constituting the light extraction layer may have an Al composition ratio smaller than the material of the next outer layer.

  Of the plurality of layers constituting the light extraction layer, the outermost layer may have a smaller band gap energy than the next outer layer.

Materials of the layers that constitute the light extraction layer, respectively _{(Al X Ga 1-X)} Y In 1-Y P, however, is represented by 0.3 ≦ X ≦ 1,0.4 ≦ Y ≦ 0.6 May be.

  The sum of the layer thicknesses of the light extraction layer and the first cladding layer may be 800 to 5300 nm.

  The material of the light extraction layer may have a higher refractive index than the material of the first cladding layer.

  The first electrode side that covers the same portion as the first electrode between the light extraction layer and the first electrode, has a lower band gap energy than the active layer, and is opaque to the light from the active layer You may have a contact layer.

  The first electrode-side contact layer may have a layer thickness of 5 to 200 nm.

  The material of the plurality of layers constituting the light extraction layer may have a higher Al composition ratio than the material of the active layer.

Materials of the layers that constitute the light extraction layer, respectively _{(Al X Ga 1-X)} Y In 1-Y P, however, is represented by 0.3 ≦ X ≦ 1,0.4 ≦ Y ≦ 0.6 , the material of the active layer is _{(Al X Ga 1-X)} Y in 1-Y P, however, it may be represented by 0 ≦ X ≦ 0.5,0.4 ≦ Y ≦ 0.6.

  The active layer may have a multiple quantum well structure or a strained multiple quantum well structure composed of 20 to 160 well layers.

  A second cladding layer side undoped layer may be provided between the active layer and the second cladding layer.

  The material of the second cladding layer side undoped layer may have an Al composition ratio larger than that of the material of the active layer.

  The material of the undoped layer on the second cladding layer side may have a larger band gap energy than the material of the active layer.

The material of the second cladding layer side undoped layer is _{(Al X Ga 1-X)} Y In 1-Y P, however, is represented by 0.3 ≦ X ≦ 1,0.4 ≦ Y ≦ 0.6, the material of the active layer is _{(Al X Ga 1-X)} Y in 1-Y P, but may be represented by 0 ≦ X ≦ 0.5,0.4 ≦ Y ≦ 0.6.

  The outermost layer thickness of the plurality of layers constituting the light extraction layer may be 50 to 1000 nm.

  A support substrate may be provided between the plurality of semiconductor layers and the second electrode, and the material of the support substrate may be any of Si, GaAs, Ge, Cu, Mo, W, and CuW.

  The ratio of the area of the ohmic contact junction to the total area of the oxide layer may be 20% or less.

  A reflective metal film layer side contact layer may be provided between the oxide layer and the second cladding layer, and the material of the reflective metal film layer side contact layer may be mainly GaP.

There is an intervening layer between the reflective metal film layer side contact layer and the second clad layer, and the material of the intervening layer is Ga _x In _1-X P, where 0.6 ≦ X <1 Also good.

  The reflective metal film layer side contact layer has three layers having different material additives, and the material of the layer in contact with the intervening layer among these three layers is Mg, and the layer is in contact with the oxide layer. The material of the layer is Zn as an additive, and the material of the layer between these two layers may be free of aggressive additives.

The layer thickness d at the non-ohmic contact junction of the oxide layer is:
Reference layer thickness dst = odd constant α × wavelength λp of light from the active layer
/ (4 × refractive index n of the light at the non-ohmic contact junction)
And the thickness of the oxide layer in the ohmic contact junction may be equal to the thickness of the non-ohmic contact junction. .

  An insertion layer having an Al composition ratio higher than that of the light extraction layer and a large band gap energy may be inserted between the light extraction layer and the first cladding layer.

The material of the insertion layer is _{(Al X Ga 1-X)} Y In 1-Y P, but 0.4 <may be represented by X ≦ 1,0.4 ≦ Y ≦ 0.6.

  The present invention exhibits the following excellent effects.

  (1) The layer thickness of the light extraction layer is not reduced.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the semiconductor light emitting device 1 according to the present invention includes a first electrode 2 that partially covers the light extraction layer, and is formed only immediately below the first electrode 2, and has the same portion as the first electrode 2. A first electrode side contact layer 3 having a smaller band gap energy than the active layer and opaque to the light from the active layer, and a main surface on the first clad layer side; A light extraction layer 4 that emits light traveling toward the layer side to the outside, a first cladding layer 5 that is one of two cladding layers that sandwich the active layer, and an active layer that generates light sandwiched between the first and second cladding layers 6, second clad layer 7 which is the other clad layer, intervening layer 8 interposed between second clad layer 7 and reflective metal film layer side contact layer, reflective metal film layer side contact layer 9, oxide layer 10, active layer 6 between the second cladding layer 7 and the second electrode Reflective metal film layer 11 for reflecting light toward the al second electrode side, the supporting substrate 13 for attaching the hetero structure portion to double metal contact layer 12, made of a second electrode 14 which covers the opposite surface of the main surface.

  The light extraction layer 4 is also called a window layer.

  The oxide layer 10 includes an ohmic contact junction 15 that is appropriately dispersed in a plane in contact with the reflective metal film layer 11, and a portion that is not the ohmic contact junction 15 is referred to as a non-ohmic contact junction 16. To.

  The reflective metal film layer side contact layer 9 has three layers 17, 18, 19 having different additives to the material, and the material of the intervening layer side contact layer 17 in contact with the intervening layer 8 among these three layers is an additive. Mg is the material of the oxide layer side contact layer 19 in contact with the oxide layer 10 and the additive is Zn, and the material of the intermediate contact layer 18 between these two layers has no positive additive.

  The region from the first electrode side contact layer 3 to the reflective metal film layer side contact layer 9 is referred to as a double heterostructure portion 20. In addition, the first cladding layer 5, the active layer 6, and the second cladding layer 7 may be collectively referred to as the light emitting layer 21.

  The feature of the semiconductor light emitting device 1 according to the present invention is the light extraction layer 4. That is, the light extraction layer 4 is composed of a plurality of layers having different composition ratios, and the unevenness 22 for making the main surface S rough is formed over the plurality of layers. In this embodiment, the light extraction layer 4 is composed of two layers, the outermost layer being the first light extraction layer 23, and then the outer layer being the second light extraction layer 24.

  As illustrated, the irregularities 22 are formed from the first light extraction layer 23 to the second light extraction layer 24. Further, the first light extraction layer 23 has a smaller slope of the surface of the irregularities 22 than the second light extraction layer 24.

  The first light extraction layer 23 has a smaller slope of the surface of the irregularities 22 than the second light extraction layer 24 because the etching speed of the first light extraction layer 23 is faster than that of the second light extraction layer 24.

  When the slope of the surface of the unevenness 22 is formed at various angles, light incident on the light extraction layer 4 at various angles can be extracted to the outside. Therefore, the first light extraction layer 23 and the second light extraction layer 24 are different in the inclination of the surface of the irregularities 22, so that the light extraction efficiency can be improved.

  Further, although not shown in the figure, the material of the first light extraction layer 23 has an Al composition ratio smaller than that of the material of the second light extraction layer 24, and the first light extraction layer 23 has a higher band than the second light extraction layer 24. The gap energy is small.

  In the present invention, the light extraction layer 4 is roughened by etching without forming a pattern. At this time, the structure of the light extraction layer 4 is a multi-layer structure having different composition ratios. An etching rate difference can be provided. That is, the etching rate of the second light extraction layer 24 whose material Al composition ratio is larger than that of the first light extraction layer 23 is faster than the etching rate of the first light extraction layer 23. For this reason, first, when the first light extraction layer 23 is etched and the recess formed in the first light extraction layer 23 reaches the second light extraction layer 24, the exposed portion of the second light extraction layer 24 rapidly The recess is deepened by etching. On the other hand, since the convex portion where the first light extraction layer 23 remains is still slowly etched, the first light extraction layer 23 is not lost, and the convex portion becomes relatively high. As described above, the difference in etching rate between the layers forms the irregularities 22 having desired steps in a relatively short time, and the thickness of the light extraction layer 4 as a whole is not reduced.

  In the semiconductor light emitting device 1 according to the present invention, since the light extraction layer 4 is not thinned, the forward voltage is prevented from increasing, and current concentration in the light emitting layer 21 is prevented. As a result, the light emission efficiency is reduced. The semiconductor light emitting device 1 that is suppressed and has high luminous efficiency at low cost is realized.

  In the semiconductor light emitting device 1 according to the present invention, the first light extraction layer 23 has a smaller inclination of the surface of the irregularities 22 than the second light extraction layer 24, so that the angle of the surface of the irregularities 22 is different, thereby improving the light extraction efficiency. Can be made.

  In the semiconductor light emitting device 1 according to the present invention, the first light extraction layer 23 has a smaller band gap energy than the second light extraction layer 24. In order to reduce the band gap energy in the same material, it is effective to change the Al composition. By changing the Al composition, the etching rate with the same etching solution can be changed. By changing the etching rate, the surface angle of the irregularities 22 can be varied. That is, the band gap energy of the first light extraction layer 23 is smaller than that of the second light extraction layer 24 in order to make the surface angle of the irregularities 22 different by etching with the same etching solution.

  Next, another embodiment will be described.

  The semiconductor light emitting element 1a shown in FIG. 2 is the same as the semiconductor light emitting element 1 of FIG. 1 except that the structure of the light extraction layer 4a is different. The light extraction layer 4 a includes a first light extraction layer 25, a second light extraction layer 26, and a third light extraction layer 27. These three layers 25 to 27 are different in composition ratio, inclination of the surface of the unevenness 22 and band gap energy. That is, the Al composition ratio is the same for the first light extraction layer 25 and the third light extraction layer 27, and the second light extraction layer 26 is large. The inclination of the surface of the irregularities 22 is such that the first light extraction layer 25 is small, the second light extraction layer 26 is large, and the third light extraction layer 27 is small. The band gap energy is such that the first light extraction layer 25 is small, the second light extraction layer 26 is large, and the third light extraction layer 27 is small.

  Thus, three layers of the first light extraction layer 25, the second light extraction layer 26, and the third light extraction layer 27 are provided as the light extraction layer 4a, which becomes the outermost layer when the semiconductor light emitting element is formed. The Al composition ratio of the first light extraction layer 25 and the third light extraction layer 27 which is the innermost layer are equal, and the Al composition ratio of the second light extraction layer 26 sandwiched between them is large. This is equivalent to inserting a layer having a higher Al composition ratio into the light extraction layer 104 of the conventional semiconductor light emitting device 101.

  In the semiconductor light emitting device 1 a, the etching rate of the second light extraction layer 26 having a higher Al composition ratio than the first light extraction layer 25 is faster than the etching rate of the first light extraction layer 25. Therefore, as in the case of the semiconductor light emitting device 1 of FIG. 1, each layer has an etching rate difference, so that the unevenness 22 having a desired step is formed in a relatively short time and the light extraction layer 4 as a whole. The layer thickness does not decrease.

   The semiconductor light emitting device 1b shown in FIG. 3 is obtained by adding a second cladding layer side undoped layer 28 to the semiconductor light emitting device 1 of FIG. The second cladding layer side undoped layer 28 is formed between the active layer 6 and the second cladding layer 7. The material of the second cladding layer side undoped layer 28 has a higher Al composition ratio than the material of the active layer 6. The material of the second cladding layer-side undoped layer 28 has a larger band gap energy than the material of the active layer 6.

  In the present invention, the irregularities 22 having a desired step can be formed in a relatively short time. Therefore, in the semiconductor light emitting device 1b of FIG. 3, the second light extraction layer 24b of the first light extraction layer 23b and the second light extraction layer 24b constituting the light extraction layer 4 is slightly etched although not shown. And

  A preferred numerical range regarding the above three embodiments and other embodiments will be described.

  The layer thicknesses of the first light extraction layer 23 of the semiconductor light emitting element 1 and the first light extraction layer 25 of the semiconductor light emitting element 1a are, for example, 400 nm. This is because if the first light extraction layers 23 and 25 are too thin, the first light extraction layers 23 and 25 are all lost during the etching. On the other hand, if the layer thickness is too thick, the etching time becomes longer, more material is used, and the time for epitaxial growth also becomes longer, resulting in higher costs. Moreover, when the layer thickness is too thick, there is not much effect on increasing the output. Therefore, the layer thickness of the first light extraction layers 23 and 25 is preferably 50 to 1000 nm, and more preferably 100 to 800 nm.

  When the layer thickness of the light extraction layer 4 and the light extraction layer 4a is increased, current spreading (diffusion) is improved, and thus the LED characteristics are improved. However, no matter how much the layer thickness is increased, the elongation of the effect of expanding the current is saturated. Therefore, if the layer thickness is too thick, there is no harmful effect on the characteristics, but the cost increases. When the layer thickness is too thin, the light emission output decreases and the forward voltage increases. Therefore, the layer thickness of the light extraction layers 4 and 4a is preferably 500 to 5000 nm, and more preferably 1000 to 4000 nm.

  The layer thickness of the second light extraction layer 26 of the semiconductor light emitting device 1a is preferably 50 to 1000 nm. This is because the etching rate of the second light extraction layer 26 in which the Al composition ratio of the material is larger than that of the first and third light extraction layers 25 and 27 is higher than the etching rate of the first and third light extraction layers 25 and 27. fast. Inserting the second light extraction layer 26 between the first light extraction layer 25 and the third light extraction layer 27 has an effect of suppressing etching variation. However, if the layer thickness of the second light extraction layer 26 is too thin, the second light extraction layer 26 is immediately lost by etching, so that the effect of suppressing the etching variation is diminished and the slope of the second light extraction layer 26 is reduced. Since the area of the light source becomes smaller, less light is extracted from the slope. On the other hand, if the layer thickness is too thick, there is no effect of suppressing etching variations.

  The sum of the layer thicknesses of the light extraction layers 4 and 4a and the first cladding layer 5 is preferably 800 to 5500 mm. The reason is that the first clad layer 5 is a carrier supply layer and a barrier layer for stopping holes, and also has a function of a light extraction layer (window layer). Although the characteristics of the LED are improved by increasing the sum of the layer thicknesses, the cost increases when the sum of the layer thicknesses exceeds 5500 mm. Further, the thickness of the first clad layer 5 needs to be 300 mm or more in order to have the function of a barrier layer. Since the layer thickness of the light extraction layers 4 and 4a is 500 mm or more, the sum of the layer thicknesses of the light extraction layers 4 and 4a and the first cladding layer 5 is preferably 800 to 5500 mm.

  The layer thickness of the first electrode side contact layer 3 is preferably 5 to 200 nm. This is because if this layer thickness is too thin, the function as a contact layer will be insufficient, and conversely if it is too thick, current will not flow easily, the direct current resistance will increase, and the forward voltage will increase. Therefore, a preferable layer thickness is 5 to 200 nm, and more preferably 10 to 100 nm.

The composition of the material of the intervening layer 8 is Ga _X In _1-X P, provided that 0.6 ≦ X <1. This is because when X is smaller than 0.6, the emitted light is absorbed.

  The additive added to the material of the oxide layer side contact layer 19 in contact with the oxide layer 10 in the reflective metal film layer side contact layer 9 is preferably Zn. This is because Zn can be added more easily than Mg, so that the resistance can be reduced. This is because the contact resistance can be lowered and the forward voltage can be lowered by increasing the addition amount.

  Of the reflective metal film layer side contact layer 9, the additive added to the material of the intervening layer side contact layer 17 in contact with the intervening layer 8 is preferably Mg. This is because Mg is less diffusible than Zn, so that a decrease in the initial light emission output due to diffusion can be suppressed, and reliability (relative output) is improved due to difficulty in diffusing. Reliability (relative output) is the light output after energization / initial light output.

  The intermediate contact layer 18 provided in the middle of the intervening layer side contact layer 17 and the oxide layer side contact layer 19 of the reflective metal film layer side contact layer 9 is preferably an undoped layer without any active additive in the material. . This is because mutual diffusion occurs when a layer doped with Mg and a layer doped with Zn are adjacent to each other. Interdiffusion can be prevented by sandwiching the intermediate contact layer 18.

  The active layer 6 may have a multiple quantum well structure, a strained multiple quantum well structure, or an undoped bulk layer (single layer).

  The active layer 6 preferably comprises a multiple quantum well structure of 20 to 160 layers, that is, 10 pairs to 80 pairs. This is because if the number of pairs is too small, overflow of electrons and holes will occur, the internal quantum efficiency will decrease, and if the number of pairs is too large, the emission output will decrease due to light absorption in the active layer 6. . The number of pairs is preferably 10 to 80 pairs, more preferably 20 to 60 pairs. Even when the active layer 6 is a single layer, the layer thickness is preferably 20 to 200 nm for the same reason.

When the active layer 6 has a strained multiple quantum well structure, the well layer is preferably undoped Ga _0.4 In _0.6 P (4 nm), and the barrier layer is preferably (Al _0.5 Ga _0.5 ) _0.5 InP (10 nm).

  In the semiconductor light emitting device 1b of FIG. 3, the second cladding layer-side undoped layer 28 is inserted between the active layer 6 and the p-type second cladding layer 7, but the active layer 6 and the n-type first cladding are inserted. A first cladding layer-side undoped layer (not shown) may be inserted between the layers 5. Further, these undoped layers may be low carrier concentration layers.

In the embodiment, the SiO ₂ layer (oxide layer) 10 is provided between the reflective metal film layer 11 and the double heterostructure portion 20, but the present invention is also effective in a semiconductor light emitting device without the oxide layer 10. .

  The semiconductor light emitting elements 1, 1a, 1b are, for example, red LED elements having an emission wavelength of 630 nm. In other LED elements (emission wavelength: 560 to 660 nm) using the same AlGaInP as a main component, there is no change in the material and carrier concentration of each layer, and there is no change in the light extraction layers 4, 4a and 4b. The present invention is effective.

   The surface view shape of the first electrode 2 can be a circle, a rectangle, a rhombus, a polygon, or other different shapes.

  Examples of the material of the support substrate include Si, GaAs, Ge, Cu, Mo, W, and CuW.

Example # 1)
An LED epitaxial wafer for a red LED having the structure shown in FIG. 1 and having an emission wavelength of around 630 nm was produced, and an LED element was produced. Epitaxial growth method, thickness of each epitaxial layer, structure and material of each epitaxial layer, configuration of reflective metal film layer, configuration and size of ohmic contact junction, method of attaching to support substrate, electrode formation method, etching method, etc. The details are as follows.

As shown in FIG. 4, an n-type (Se-doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P etching stop layer (layer thickness 200 nm, carrier) is formed on an n-type GaAs substrate (growth substrate) 41 by MOVPE. (Concentration 1 × 10 ¹⁸ / cm ³ ) (etching stop layer) 42, n-type (Se-doped) GaAs contact layer (layer thickness 50 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ) (first electrode side contact layer) 3, n-type (Se-doped) (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P window layer (layer thickness 400 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ) (first light extraction layer) 23, n-type (Se-doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P window layer (layer thickness 2600 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ) (second light extraction layer) 24, n-type (Se doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer (layer thickness 500 nm, carrier concentration 5 × 10 ¹⁷ / cm ³ ) (first cladding layer) 5, undoped multiple quantum well active layer (well layer undoped Ga _0.5 In _0.5 P (layer thickness 4 nm) / barrier layer ( 20 pairs of Al _0.5 Ga _0.5 ) _0.5 InP (layer thickness 10 nm)) 6, p-type (Mg doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer (layer thickness 400 nm, carrier concentration 1.2 × 10 ¹⁸ / cm ³ ) (second cladding layer) 7, p-type (Mg doped) Ga _x In _1-X P (0.6 ≦ X <1) intervening layer (layer thickness 10 nm, carrier concentration 5 × 10 ¹⁸ / cm ³ ) 8, p-type (Mg doped) GaP layer (layer thickness 200 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ) (intervening layer side contact layer) 17, undoped GaP layer (layer thickness 100 nm) (intermediate contact layer) 18, p Type (Zn-doped) GaP (Layer thickness 50 nm, carrier concentration ^{1 × 10 19 / cm 3)} ( oxide layer side contact layer) 19 sequentially stacked to obtain a LED epitaxial wafer. The active layer 3 is a pair of GaInP layer and AlGaInP layer.

The feature of this LED epitaxial wafer is that two layers of a first light extraction layer 23 and a second light extraction layer 24 are provided as the light extraction layer 4, and the outermost layer when the semiconductor light emitting element is formed. The first light extraction layer 23 as a layer has a smaller Al composition ratio than the second light extraction layer 24 as a next layer. That is, the materials of the first and second light extraction layers 23 and 24 forming the light extraction layer 4 are (Al _X Ga _{1 -X} ) _Y In ₁ -YP, respectively, where 0.3 ≦ X ≦ 1, 0.4 ≦ Y ≦ 0.6, the value of X in the material of the first light extraction layer 23 is 0.4, and the value of X in the material of the second light extraction layer 24 is 0.7.

  The layer thickness of the first light extraction layer 23 is set to 400 nm and the layer thickness of the second light extraction layer 24 is set to 2600 nm, so that the layer thickness of the light extraction layer 4 is 3000 nm. It is the same as the layer thickness.

The growth temperature in the MOVPE method was 650 ° C., the growth pressure was 6666 Pa (50 Torr), the growth rate of each layer was 0.3 to 1.0 nm / sec, and the V / III ratio was about 200. The V / III ratio is a ratio (quotient) in which the denominator is the number of moles of a group III material such as TMGa or TMAl and the molecule is the number of moles of a group V material such as AsH ₃ or PH ₃ .

As raw materials for the MOVPE method, organic metals such as trimethylgallium (TMGa), triethylgallium (TEGa), trimethylaluminum (TMAl) and trimethylindium (TMIn), and hydrides such as arsine (AsH ₃ ) and phosphine (PH ₃ ) Gas was used. Hydrogen selenide (H ₂ Se) is used as an additive material for the conductivity-type determining impurity of the n-type semiconductor layer, and biscyclopentadienyl is used as an additive material for the conductivity-type determining impurity of the p-type semiconductor layer. Magnesium (Cp ₂ Mg) and dimethyl zinc (DMZn) were used.

In addition, disilane (Si ₂ H ₆ ), monosilane (SiH ₄ ), diethyl tellurium (DETe), or dimethyl tellurium (DMTe) may be used as an additive material for the conductivity determining impurity of the n-type semiconductor layer. In addition, diethyl zinc (DEZn) can be used as an additive material for the conductivity determining impurity of the p-type semiconductor layer.

After this LED epitaxial wafer is taken out from the MOVPE apparatus, a SiO ₂ layer (oxide layer) 10 is formed to a thickness of about 100 nm on the surface of the oxide layer side contact layer 19, and a general photolithography technique is used. Further etching is performed to form oxide removal holes having a diameter of about 12 μm in the surface of the oxide layer 10 at a pitch of 30 μm, and the ohmic contact junction 15 is formed in the oxide removal holes by a vacuum vapor deposition method. It was formed so as to be almost equal to the layer 10. A gold / zinc (AuZn) alloy was used as a raw material of the ohmic contact junction 15. The ohmic contact junction 15 has a diameter of about 12 μm as viewed from the surface. This is called a dot electrode. The ohmic contact junctions 15 were formed with a thickness of 100 nm at a pitch of 30 μm when viewed from the surface. That is, the ohmic contact junction 15 was formed in the oxide removal hole by a vacuum deposition method so that the layer thickness was almost equal to that of the oxide layer 10.

  Then, the reflective metal film layer side contact layer 9 and the ohmic contact junction 15 were alloyed by an alloy process in which the epitaxial wafer for LED was heated to 350 ° C. in a nitrogen gas atmosphere and heat-treated for 5 minutes. .

  As the reflective metal film layer 11 on the oxide layer 10 (including on the ohmic contact junction 15) of the LED epitaxial wafer provided with the ohmic contact junction 15, aluminum (Al), titanium (Ti), gold (Au ) Were deposited in this order to 200 nm, 200 nm, 500 nm, and a total thickness of 900 nm.

  On the Si substrate prepared as the support substrate 13, gold / germanium (AuGe) alloy, titanium (Ti), and gold (Au) as the metal adhesion layer 12 are 100 nm, 200 nm, and 500 nm in this order, respectively, with a total thickness of 800 nm. Vapor deposition was performed.

The LED epitaxial wafer provided with the reflective metal film layer 11 and the support substrate 13 provided with the metal adhesion layer 12 were bonded together so that the reflection metal film layer 11 and the metal adhesion layer 12 were combined. The bonding was performed by holding at a temperature of 350 ° C. for 30 minutes under a pressure of 1.3 Pa (0.01 Torr) and a load of 3 MPa (30 kgf / cm ² ).

  The LED epitaxial wafer bonded to the support substrate 13 was immersed in a mixed solution of ammonia water and hydrogen peroxide solution, whereby the growth substrate 41 was removed by etching, and the etching stop layer 42 was exposed. Subsequently, the etching stop layer 42 was removed using a hydrochloric acid-based etching solution, and the first electrode side contact layer 3 was exposed.

  A pattern is formed on the surface of the first electrode side contact layer 3 by using a general photolithography technique, and a circular portion having a diameter of 100 μm in surface view and branches having a width of 10 μm radially from the circular portion are formed by vacuum deposition. A first electrode 2 having a distribution electrode distributed by extending in a shape was formed. The first electrode 2 was vapor-deposited with gold / germanium (AuGe) alloy, nickel (Ni), and gold (Au) in this order to have a layer thickness of 100 nm, 100 nm, 500 nm, and a total of 700 nm, respectively.

  Using this first electrode 2 as a mask, the first electrode side contact layer 3 other than directly under the first electrode 2 is removed by selective etching using an etching solution composed of a mixed solution of sulfuric acid, hydrogen peroxide solution and water. Then, the first light extraction layer 23 of the light extraction layer 4 was exposed.

  The surface of the light extraction layer 4 was roughened by hydrochloric acid etching. In this embodiment, the etching conditions under which a part of the second light extraction layer 24 is exposed are found, and the etching time is made longer than the etching conditions, so that the unevenness 22 becomes the first light extraction layer 23 as shown in FIG. To the second light extraction layer 24, and the first light extraction layer 23 was rougher than the second light extraction layer 24.

  Next, the second electrode 14 was formed on the entire outer surface of the support substrate 13 by vacuum deposition. Specifically, aluminum (Al), titanium (Ti), and gold (Au) are vapor-deposited in this order, and then heated to 400 ° C. in a nitrogen gas atmosphere and heat-treated for 5 minutes to form the second electrode. 14 was alloyed.

  This electrode-formed epitaxial wafer for LEDs was cut using a dicing apparatus so that the circular portion of the first electrode 2 was at the center, and an LED bare chip having a chip size of 300 μm square was produced. This LED bare chip was mounted on a TO-18 stem (die bonding), and wire bonding was performed on the mounted LED bare chip to produce an LED element.

  The initial characteristics of the LED element according to Example # 1 were evaluated. The initial characteristics were a light output of 6.64 mW and a forward voltage of 1.98 V when 20 mA was applied (evaluation).

  In Example # 1, the main surface S was roughened by the same method as the conventional example described later. However, since the light extraction layer 4 has a two-layer structure, the layer thickness of the light extraction layer 4 is entirely reduced. I was able to suppress that. This is because the etching of the second light extraction layer 24 starts when the first light extraction layer 23 is etched and a part of the second light extraction layer 24 is exposed. This is because the etching rate is higher than that of the layer 23, so that the unevenness 22 having a desired level difference is formed even if the etching time is shortened, and the thickness of the light extraction layer 4 can be suppressed from being reduced accordingly.

By preventing the light extraction layer 4 from becoming thin in this way, an increase in forward voltage can be suppressed and a forward voltage of 1.98 V can be achieved. Moreover, by suppressing the increase of the forward voltage, it was possible to suppress the heat generation of the LED, and as a result, the light emission output was improved. Furthermore, since the layer thickness of the light extraction layer 4 was not reduced, a current spread was obtained, and the current flowing through the active layer 6 could be made uniform. This also suppressed the heat generation of the LED. Furthermore, since the current dispersion characteristics are improved, it is possible to suppress a decrease in light extraction efficiency due to the shadow of the first electrode 15, and this can also increase the light emission output. In addition, it was considered that the overflow of carriers was eliminated by suppressing the current concentration, and the internal quantum efficiency was improved. A plurality of factors improved by Example # 1 overlapped to improve the light emission output.
Example # 2)
An LED epitaxial wafer for a red LED having the structure shown in FIG. 2 and having an emission wavelength of around 630 nm was produced, and an LED element was produced. Epitaxial growth method, thickness of each epitaxial layer, structure and material of each epitaxial layer, configuration of reflective metal film layer, configuration and size of ohmic contact junction, method of attaching to support substrate, electrode formation method, etching method, etc. The details are basically the same as in Example # 1. Hereinafter, only differences from Example # 1 will be described in detail.

The light extraction layer 4 a includes a first light extraction layer 25, a second light extraction layer 26, and a third light extraction layer 27. The first light extraction layer 25 is an n-type (Se doped) (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P window layer (layer thickness 400 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ), and the second light extraction layer 26 is N-type (Se-doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P window layer (layer thickness 100 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ), and the third light extraction layer 27 is n-type (Se-doped) A (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P window layer (layer thickness 2500 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ) was used.

That is, in Example # 2, three layers of the first light extraction layer 25, the second light extraction layer 26, and the third light extraction layer 27 are provided as the light extraction layer 4a, and the outermost side when the semiconductor light emitting element is formed. This is because the Al composition ratio of the first light extraction layer 25 serving as the first layer and the third light extraction layer 27 serving as the innermost layer are equal, and the Al composition ratio of the second light extraction layer 26 sandwiched between them is large. That is, the material of the first second third light extraction layer 25, 26 and 27 constituting the light extraction layer 4, respectively _{(Al X Ga 1-X)} Y In 1-Y P, however, 0.3 ≦ X ≦ 1 0.4 ≦ Y ≦ 0.6, the value of X in the material of the first third light extraction layers 25 and 27 is 0.4, and the value of X in the material of the second light extraction layer 26 is 0.00. 7.

  The distance between the second light extraction layer 26 and the surface of the light extraction layer 4a (from the first electrode side contact layer 3) is 400 nm.

  Compared to the conventional example described later, this corresponds to inserting a layer having a higher Al composition ratio of the material into the light extraction layer 104.

The initial characteristics of the LED element according to Example # 2 were evaluated. The initial characteristics were a light emission output of 6.72 mW and a forward voltage of 1.99 V when 20 mA was applied (evaluation).
Conventional example)
An LED epitaxial wafer for a red LED having the structure shown in FIG. 5 and having an emission wavelength of around 630 nm was prepared in two ways, one that was not roughened and one that was roughened, to produce an LED element. Epitaxial growth method, thickness of each epitaxial layer, structure and material of each epitaxial layer, configuration of reflective metal film layer, configuration and size of ohmic contact junction, method of attaching to support substrate, electrode formation method, etching method, etc. The details are basically the same as in Example # 1. Hereinafter, only differences from Example # 1 will be described in detail.

The light extraction layer 104 is only one layer of an n-type (Se-doped) (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P window layer (layer thickness 3000 nm, carrier concentration 1 × 10 ¹⁸ / cm ³ ).

  The initial characteristics of the LED element according to the conventional example subjected to the roughening were a light emission output of 5.0 mW and a forward voltage of 2.3 V when energized with 20 mA (during evaluation). The initial characteristics of the LED element according to the conventional example that was not roughened were a light emission output of 4.3 mW and a forward voltage of 1.96 V when 20 mA was applied (evaluation).

  As described above, when the LED elements according to Examples # 1 and # 2 and the conventional example are compared with the initial characteristics, it is confirmed that the improvement of the light emission output and the reduction of the forward voltage can be achieved by applying the present invention. It was.

1 is a cross-sectional structure diagram of a semiconductor light emitting device showing an embodiment of the present invention. 1 is a cross-sectional structure diagram of a semiconductor light emitting device showing an embodiment of the present invention. 1 is a cross-sectional structure diagram of a semiconductor light emitting device showing an embodiment of the present invention. It is a cross-section figure of the epitaxial wafer produced in the middle of manufacture of a semiconductor light emitting element. It is sectional structure drawing of the conventional semiconductor light-emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor light-emitting device 2 1st electrode 3 1st electrode side contact layer 4 Light extraction layer 5 1st clad layer 6 Active layer 7 2nd clad layer 8 Intervening layer 9 Reflective metal film layer side contact layer 10 Oxide layer 11 Reflective metal Film layer 12 Metal adhesion layer 13 Support substrate 14 Second electrode 15 Ohmic contact junction 23 First light extraction layer 24 Second light extraction layer

Claims (23)

A plurality of semiconductor layers including an active layer that generates light sandwiched between first and second cladding layers and a light extraction layer that forms a main surface on the first cladding layer side, the light extraction layer partially A first electrode that covers the surface, a second electrode that covers the opposite surface of the main surface, a reflective metal film layer that reflects light between the second cladding layer and the second electrode, and activity of the reflective metal film layer In a semiconductor light emitting device having an oxide layer in contact with the layer side and an ohmic contact junction partly formed in the oxide layer,
The light extraction layer is composed of a plurality of layers having different composition ratios, and irregularities for making the main surface rough are formed over the plurality of layers, and the outermost layer among the plurality of layers forming the light extraction layer A semiconductor light emitting device characterized in that the slope of the uneven surface is smaller than that of the outer layer . 2. The semiconductor light emitting device according to claim 1 , wherein a material of an outermost layer among the plurality of layers constituting the light extraction layer has a smaller Al composition ratio than a material of the next outer layer. 3. The semiconductor light emitting element according to claim 1 , wherein the outermost layer among the plurality of layers constituting the light extraction layer has a band gap energy smaller than the next outer layer. Materials of the layers that constitute the light extraction layer, respectively _{(Al X Ga 1-X)} Y In 1-Y P, however, is represented by 0.3 ≦ X ≦ 1,0.4 ≦ Y ≦ 0.6 The semiconductor light-emitting device according to claim 1 , wherein The semiconductor light emitting element according to claim 1 , wherein the sum of the layer thicknesses of the light extraction layer and the first cladding layer is 800 to 5300 nm. 6. The semiconductor light emitting element according to claim 1 , wherein the material of the light extraction layer has a higher refractive index than the material of the first cladding layer. The first electrode side that covers the same portion as the first electrode between the light extraction layer and the first electrode, has a lower band gap energy than the active layer, and is opaque to the light from the active layer The semiconductor light-emitting device according to claim 1, further comprising a contact layer. 8. The semiconductor light emitting element according to claim 7 , wherein the first electrode side contact layer has a thickness of 5 to 200 nm. 8. The semiconductor light emitting element according to claim 1 , wherein the material of the plurality of layers constituting the light extraction layer has an Al composition ratio larger than that of the material of the active layer. Materials of the layers that constitute the light extraction layer, respectively _{(Al X Ga 1-X)} Y In 1-Y P, however, is represented by 0.3 ≦ X ≦ 1,0.4 ≦ Y ≦ 0.6 , the material of the active layer is _{(Al X Ga 1-X)} Y in 1-Y P, however, is characterized by being represented by 0 ≦ X ≦ 0.5,0.4 ≦ Y ≦ 0.6 The semiconductor light-emitting device according to claim 1 . 11. The semiconductor light emitting device according to claim 1 , wherein the active layer has a multiple quantum well structure or a strained multiple quantum well structure composed of 20 to 160 well layers. The semiconductor light-emitting element according to claim 1, further comprising an undoped layer on the second cladding layer side between the active layer and the second cladding layer. 13. The semiconductor light emitting device according to claim 12 , wherein the material of the second cladding layer side undoped layer has a higher Al composition ratio than the material of the active layer. 14. The semiconductor light emitting element according to claim 12 , wherein the material of the second cladding layer side undoped layer has a band gap energy larger than that of the material of the active layer. The material of the second cladding layer side undoped layer is _{(Al X Ga 1-X)} Y In 1-Y P, however, is represented by 0.3 ≦ X ≦ 1,0.4 ≦ Y ≦ 0.6, the claim material of the active layer has a _{(Al X Ga 1-X)} Y in 1-Y P, but characterized by being represented by 0 ≦ X ≦ 0.5,0.4 ≦ Y ≦ 0.6 12 The semiconductor light emitting element in any one of -14 . 16. The semiconductor light emitting element according to claim 1 , wherein the outermost layer of the plurality of layers constituting the light extraction layer has a thickness of 50 to 1000 nm. A support substrate between the plurality of semiconductor layers and the second electrode, the claims material of the supporting substrate is Si, GaAs, Ge, Cu, Mo, W, and characterized in that either CuW The semiconductor light emitting element in any one of 1-16 . It has a reflective metallic film layer side contact layer between the oxide layer and the second cladding layer, claim material of the reflective metal film layer side contact layer, characterized in that mainly GaP 1 to 17 Any one of the semiconductor light-emitting devices. There is an intervening layer between the reflective metal film layer side contact layer and the second cladding layer, and the material of the intervening layer is Ga _X In _1-X P, where 0.6 ≦ X <1 The semiconductor light-emitting device according to claim 18 . The reflective metal film layer side contact layer has three layers having different material additives, and the material of the layer in contact with the intervening layer among these three layers is Mg, and the layer is in contact with the oxide layer. 20. The semiconductor light emitting device according to claim 18 , wherein the material of the layer is Zn, and the material of the intermediate layer between the two layers is free of an active additive. The layer thickness d at the non-ohmic contact junction of the oxide layer is:
Reference layer thickness dst = odd constant α × wavelength λp of light from the active layer
/ (4 × refractive index n of the light at the non-ohmic contact junction)
And within the range of ± 30% with respect to the reference layer thickness dst represented by the relational expression, and the layer thickness in the ohmic contact junction of the oxide layer is equal to the layer thickness in the non-ohmic contact junction The semiconductor light emitting element according to claim 1 . Between the light extraction layer and the first cladding layer, a high Al composition ratio than the light extraction layer, and any claim 1 to 21, characterized in that the band gap energy is large insertion layer is inserted A semiconductor light emitting device according to any one of the above. Claims, characterized in that the material of the insertion layer is represented by _{(Al X Ga 1-X)} Y In 1-Y P, but 0.4 <X ≦ 1,0.4 ≦ Y ≦ 0.6 22. The semiconductor light emitting device according to 22 .

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