JP2006324507A - Manufacturing method of light emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting diode having a high light intensity whose surface is so made coarse as to improve the taking-out efficiency of its light to the external, by the etching means for making effectively coarse the surface of the light emitting diode including GaAsP mixed crystal layers formed on a GaP substrate. <P>SOLUTION: A manufacturing method of the light emitting diode, wherein there are formed on a GaP substrate 1 GaAs<SB>x</SB>P<SB>1-x</SB>(0<x<1) layers 3, 4 and nitrogen-doped GaAs<SB>x</SB>P<SB>1-x</SB>(0<x<1) layers 5, 6 having a pn-junction 10 in between them, is performed by following processes (1), (2). In the process (1), its surface is etched chemically by using the mixed liquid containing iodic acid, hydrofluoric acid, nitric acid, and acetic acid. In the process (2), its surface is etched chemically by using at least either one of (a) hydrochloric acid having a temperature not lower than 20°C, (b) hydrofluoric acid, and (c) the mixed liquid of hydrofluoric acid and sulfuric acid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a GaAsP-based light emitting diode using a nitrogen-doped GaAsP layer formed on a GaP substrate as a light emitting layer.

A nitrogen-doped GaAs _x P _1-x (0 <x <1) layer (hereinafter sometimes referred to as “GaAsP mixed crystal layer” or “GaAsP light emitting layer”) formed on the GaP substrate is referred to as a light emitting layer. The GaAsP-based light emitting diode can change the wavelength of emitted light from the red wavelength region near 650 nm to the yellow wavelength region near 580 nm by changing the mixed crystal ratio y. Widely used as a light source.

  As a method for improving the light intensity of the light emitting diode, there are a method for increasing the internal quantum efficiency and a method for increasing the light extraction efficiency. Among these, the latter is achieved by suppressing loss due to light absorption inside the light emitting diode, or suppressing light loss due to being not extracted to the outside due to total reflection on the light emitting surface.

  As a method of suppressing total reflection on the light emitting surface, a method of roughening the surface of the light emitting diode (including all surfaces of the substrate surface, the light emitting layer surface, and the side surface) is known. As a method for roughening the surface of the light emitting diode, chemical etching with an etching solution is effective in terms of cost and simplicity.

Conventionally, as a surface roughening method by etching a light emitting diode, for example, for a GaAsP mixed crystal layer, a surface roughening is performed by using an etching solution containing Br ₂ or I ₂ and nitric acid, hydrogen fluoride, and acetic acid. A method to do this has been proposed (Patent Document 1). On the other hand, a roughening method using hydrochloric acid is disclosed for a GaP light emitting device chip (Patent Document 2). In fact, roughening treatment with only hydrochloric acid cannot be expected to improve the light extraction efficiency sufficiently. Therefore, after roughing the surface by lapping, treatment with aqua regia, sulfuric acid, etc. There has also been proposed a method (Patent Document 3).
JP 2000-196141 A JP-A-4-354382 Japanese Patent Laid-Open No. 10-652111

  However, in a light emitting diode having a plurality of layers having different compositions, including a GaAsP mixed crystal layer formed on a GaP substrate, the effect of roughening by etching, that is, the outside of the light emitting diode The improvement of the light extraction efficiency was insufficient.

For example, when roughening with Br ₂ or I ₂ described in Patent Document 1 and an etching solution containing nitric acid, hydrogen fluoride, and acetic acid, the GaAsP layer is roughened to some extent, but a GaP substrate or GaP The surface of the GaAsP layer having a high composition was not sufficiently roughened, and the light extraction efficiency was not improved so much. Etching with hydrochloric acid alone disclosed in Patent Document 2 is effective for roughening the GaP substrate, but roughening of the GaAsP layer is insufficient, and the effect of improving the light extraction efficiency is low.

  The method of processing with an etching solution after performing rough surface processing by lapping performed in Patent Document 3 is preferable in terms of processing time and cost because a machining process called lapping increases in addition to the etching process. In addition, there has been a demand for a simple method capable of roughening the entire surface of the light-emitting diode only by a processing step using an etching solution.

  The present invention is intended to solve such problems, and the surface of a light-emitting diode chip including a GaAsP mixed crystal layer formed on a GaP substrate is efficiently roughened, and the light extraction efficiency to the outside is remarkably improved. It is an object of the present invention to provide a method for manufacturing a light emitting diode with high light intensity.

  As a result of intensive studies on various etching solutions and combinations thereof in order to roughen both the GaP substrate and the GaAsP mixed crystal layer, the present inventors have found that a specific acidic etching solution is a GaP substrate or a GaAsP mixed crystal. Properly roughen the layer, and perform etching in two stages by appropriately combining these etchants, and further eliminate the influence of the previous etchant between the two stages of the etching process. It has been found that the light output of the light emitting diode is remarkably improved by interposing the process.

That is, in the method for manufacturing a light emitting diode according to the present invention, a GaAs _x P _1-x (0 <x <1) layer on a GaP substrate and a nitrogen-doped GaAs _x P _1-x (0 < x <1) A method for manufacturing a light-emitting diode comprising a step of chemically etching a surface of a light-emitting diode chip formed with a layer, wherein the etching step comprises the following steps (1) and (2) in this order or They are included in the reverse order (claim 1).
Step (1): Step of etching using a mixed solution containing iodic acid, hydrofluoric acid, nitric acid and acetic acid Step (2): (a) hydrochloric acid at 20 ° C. or higher, (b) hydrofluoric acid, and ( c) A step of etching using one or more acids selected from the group consisting of a mixture of hydrofluoric acid and sulfuric acid.

  In this method, it is preferable to include a step of treating with an alkali between the steps (1) and (2) or between the steps (2) and (1).

  The mixed solution containing iodic acid, hydrofluoric acid, nitric acid and acetic acid is 1 to 30000 mol of hydrofluoric acid, 1 to 20000 mol of nitric acid, and 50 to 80,000 acetic acid with respect to 1 mol of iodic acid. It is preferable to contain a mole (claim 3).

  According to the method for manufacturing a light emitting diode of the present invention, an acidic etching solution capable of roughening the surface of a GaP substrate or a GaAsP mixed crystal layer is selected and used in combination, whereby a GaAsP mixed solution is formed on the GaP substrate. It is possible to roughen the entire surface of the light emitting diode on which the crystal layer is formed into an appropriate fine shape, and it is possible to manufacture a light emitting diode with high light extraction efficiency.

  DESCRIPTION OF EMBODIMENTS Embodiments of the present invention will be described in detail below with reference to the drawings. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is the gist thereof. Unless specified above, the following contents are not specified.

  First, a light emitting diode manufactured according to the present invention will be described with reference to FIG.

  FIG. 1 is a schematic cross-sectional view showing an embodiment of a light-emitting diode having a roughened surface obtained by the method of the present invention.

In this light emitting diode, on a GaP substrate 1, a GaP layer 2, a GaAsP composition change layer (layer in which _x changes in GaAs _x P _1-x (0 <x <1)) 3, a GaAsP constant composition layer (GaAs _x P _1-x (0 <x <1) and x is constant layer) 4, n-type nitrogen doped GaAsP layer (GaAs _x P _1-x (0 <x <1) layer and x is constant) 5, A p-type nitrogen-doped GaAsP layer (GaAs _x P _1-x (0 <x <1) layer where x is constant) 6 is sequentially laminated in this order. In general, x in the GaAsP composition constant layer and x in the nitrogen-doped GaAsP layer are the same, but may be different to correct the warpage of the wafer. Further, a p-side electrode 7 is formed on the surface of the p-type nitrogen-doped GaAsP layer 6 opposite to the n-type nitrogen-doped GaAsP layer 5, and on the surface opposite to the surface on which each layer of the GaP substrate 1 is formed. An n-side electrode 8 is formed. Reference numeral 10 denotes a pn junction at the interface between the n-type nitrogen-doped GaAsP layer 5 and the p-type nitrogen-doped GaAsP layer 6.

  The GaAsP composition change layer 3 may be formed directly on the GaP substrate 1, but a GaP layer 2 having the same composition as the substrate 1 is formed between the substrate 1 and the GaAsP composition change layer 3 with a thickness of 0.1. It is preferable that the thickness is about 100 μm, preferably about 0.1 to 15 μm because misfit transition can be suppressed and high light output can be stably obtained.

  The GaAsP composition change layer 3 is a layer in which the lattice constant is changed by changing the mixed crystal ratio of GaP and GaAs. The GaAsP composition change layer 3 is arbitrarily set so as to relax the difference in lattice constant between the GaP layer 2 and the GaAsP constant composition layer 4. Can be provided. For example, GaAsP whose composition is changed in the layer thickness direction so that the lattice constant substantially coincides with GaP at the interface with GaP and substantially coincides with the lattice constant with GaAsP constant composition layer 4 at the interface with GaAsP constant composition layer 4. It is preferable to obtain the GaAsP constant composition layer 4 with few crystal defects by forming the composition change layer 3.

  The GaAsP composition changing layer 3 is not only a layer whose composition changes continuously in the layer thickness direction, but also has a lattice constant intermediate between the lattice constant of the GaAsP constant composition layer 4 and the lattice constant of GaP. Therefore, even if the composition changes in a plurality of steps in the layer thickness direction, for example, it can be regarded as the GaAsP composition change layer 3 regardless of the form of the composition change.

The thickness of the GaAsP composition change layer 3 is preferably 1 to 100 μm, more preferably 10 to 80 μm. Further, the carrier concentration of the composition change layer 3 is 0.5 × 10 ¹⁷ to 30 × 10 ¹⁷ cm ⁻³ , preferably 0.8 × 10 ¹⁷ cm ^{−3 to} 20 × 10 ¹⁷ cm ⁻³ , and on average 1 × 10 ¹⁷ to 8 × 10 ¹⁷ cm ⁻³ is preferable in that the forward voltage when an LED is formed is lowered and good crystallinity is obtained. When the carrier concentration exceeds 30 × 10 ¹⁷ cm ⁻³ , the crystallinity of the GaAsP composition change layer 3 is deteriorated, crystal defects are generated on the surface of the epitaxial layer, and the light output of the LED is reduced.

The constant GaAsP composition layer 4 is usually arbitrarily provided between the GaAsP composition change layer 3 and the n-type nitrogen-doped GaAsP layer 5 as a layer having the same GaAsP composition as the light emitting layer, that is, a layer having the same lattice constant as the light emitting layer. be able to. The layer thickness of the GaAsP constant composition layer 4 is preferably 10 to 70 μm, more preferably 10 to 30 μm. The carrier concentration of the GaAsP constant composition layer 4 is 0.5 × 10 ¹⁷ to 30 × 10 ¹⁷ cm ⁻³ , preferably 0.8 × 10 ¹⁷ cm ^{−3 to} 20 × 10 ¹⁷ cm ^−3. 2 × 10 ¹⁷ to 8 × 10 ¹⁷ cm ⁻³ is preferable in that the forward voltage when the LED is formed is lowered and good crystallinity is obtained.

  The total thickness of the GaAsP composition change layer 3 and the GaAsP composition constant layer 4 is preferably 30 to 130 μm.

  If the thickness of each of the GaAsP composition changing layer 3 and the constant GaAsP composition layer 4 and the total layer thickness are both smaller than the above range, the effect obtained by providing them cannot be obtained, and the thickness is larger than the above range. Although there are few problems, it is disadvantageous in terms of cost.

Each of the n-type nitrogen doped GaAsP layer 5 and the p-type nitrogen doped GaAsP layer 6 is a nitrogen-doped GaAsP light emitting layer, and a pn junction 10 is formed at the interface. Nitrogen doping can be performed, for example, using NH ₃ when forming the GaAsP layer. As a method for forming a pn junction, for example, layers 2 to 6 (layers 5 and 6 are non-doped) are grown on the substrate 1 by an arbitrary method, and then a p-type dopant such as Zn is used as a diffusion source. There is a method of forming a pn junction at the interface between the layer 5 and the layer 6 by performing the thermal diffusion and converting the surface layer portion of the GaAsP layer to a p-type with a predetermined thickness to form the layer 6. At this time, since the surface layer portion on the GaP substrate 1 side is also p-type, the portion that has become p-type by lapping is removed, and then the electrodes 7 and 8 are formed.

  The formation method of the layers 2 to 6 is preferably selected from vapor phase epitaxial growth methods, and specifically, either halogen transport method or metal organic vapor phase growth method (MOCVD) is selected. . The halogen transport method having at least one halogen compound raw material as a raw material is advantageous because a high-purity epitaxial layer is obtained and mass productivity is high, and a hydride vapor phase method is particularly common.

Note that _x in the GaAsP constant composition layer (GaAs _x P _1-x (0 <x <1)) and the nitrogen-doped GaAsP layer (GaAs _x P _1-x (0 <x <1)) is preferably 0.45 < x <1.

  The p-side electrode 7 and the n-side electrode 8 can be formed, for example, by depositing a conductive material mainly composed of gold on the surface of the p-type nitrogen-doped GaAsP layer 6 and the surface of the GaP substrate 1. .

  The light emitting diode chip before the surface roughening treatment is manufactured by forming each layer and forming the electrodes 7 and 8 on the GaP substrate as described above, and then cutting into a desired shape by dicing. In addition, when a mechanical damage layer arises in a cut surface by dicing, it is preferable to process with the liquid mixture of a sulfuric acid, hydrogen peroxide, and water, and to remove a mechanical damage layer.

In the light emitting diode manufacturing method of the present invention, the surface of the light emitting diode chip thus obtained is roughened by chemical etching through the following two-stage etching steps (1) and (2).
Step (1): Step of etching using a mixed solution containing iodic acid, hydrofluoric acid, nitric acid and acetic acid Step (2): (a) hydrochloric acid at 20 ° C. or higher, (b) hydrofluoric acid, and ( c) A step of etching using one or more acids selected from the group consisting of a mixture of hydrofluoric acid and sulfuric acid.

Step (1) is a step of etching using a mixed solution containing iodic acid, hydrofluoric acid, nitric acid and acetic acid. The acid mixing ratio and etching time used here differ optimally depending on the emission wavelength of the light emitting diode to be manufactured and the surface orientation to be etched, and the conditions under which the maximum luminance can be obtained vary depending on the individual product. Can be adjusted. For example, the molar mixing ratio of iodic acid, hydrofluoric acid, nitric acid, and acetic acid solution is preferably 1 to 30000 hydrofluoric acid (HF) and nitric acid (HNO ₃ ) with respect to iodic acid (HIO ₃ ) 1. ) In the range of 1 to 20000 and acetic acid (CH ₃ COOH) in the range of 50 to 80000, more preferably HIO ₃ : HF: HNO ₃ : CH ₃ COOH = 1: 10 to 10000: 10 to 10000: 100 to 50000 (molar ratio) ), Particularly preferably in the range of 1:70 to 7000: 40 to 4000: 400 to 40,000 (molar ratio). In addition, it is preferable to make these into an aqueous solution having a total concentration of 10% by weight or more, particularly 50% by weight or more, and particularly 75% by weight or more. The etching time is usually set in the range of 5 seconds to 10 minutes. If this total concentration is too low, the time required for etching becomes long. The upper limit of the total concentration is appropriately determined from the availability of chemicals and operability in handling. In addition, there is no restriction | limiting in particular about the temperature of this liquid mixture, Usually, 5-45 degreeC, Preferably it is about 15-35 degreeC (practically room temperature around 25 degreeC) grade. In this step (1), the GaAsP layer is mainly etched.

  Step (2) is a step of etching using any one of (a) hydrochloric acid, (b) hydrofluoric acid, and (c) a mixture of hydrofluoric acid and sulfuric acid.

  Here, the temperature of (a) hydrochloric acid is 20 ° C. or higher, preferably 40 ° C. or higher and lower than 90 ° C., more preferably 50 ° C. or higher and lower than 80 ° C. When the temperature of hydrochloric acid is lower than this range, sufficient etching cannot be performed, and when the temperature is high, it is not preferable in terms of safety in terms of work. It is preferable to use concentrated hydrochloric acid having a concentration of about 20 to 40% by weight.

  (B) Hydrofluoric acid is preferably used in an aqueous solution of less than 70% by weight, particularly 30 to 65% by weight. If the concentration of hydrofluoric acid is lower than this range, sufficient etching cannot be performed. There is no restriction | limiting in particular about the temperature of this hydrofluoric acid, Usually, it is about 15-35 degreeC (practically room temperature around 25 degreeC).

  Moreover, there is no restriction | limiting in particular about the temperature of the liquid mixture of (c) hydrofluoric acid and a sulfuric acid, Usually, it is about 15-70 degreeC.

  Although the etching time of process (2) is arbitrary, it is 30 seconds or more, for example, Preferably it is 1 minute or more, More preferably, it is 10 minutes or more and is less than 1 hour. If this etching time is too short, roughening will be insufficient, and if it is too long, roughening will proceed too much, resulting in an adverse effect, and light output will be reduced. In this step (2), the GaP substrate and the GaAsP layer having a large GaP composition are mainly etched.

  Specifically, the etching steps (1) and (2) are performed by immersing the light emitting diode chip using an etching solution having a predetermined composition and temperature.

  Either of these etching steps (1) and (2) may be performed first. Even if step (2) is performed after step (1), step (1) is performed after step (2). ) May be performed, and an equivalent effect can be obtained in any case.

  In any case, if the etchant component used in the immediately preceding etching process remains on the surface of the light emitting diode chip, a good rough surface cannot be formed by etching in the next process. It is preferable to perform a treatment for removing the residual acid component in the immediately preceding etching step. There is no particular limitation on the method of this treatment, and a method of washing away residual acid components by washing with water or the like can be adopted, but it is preferable to perform a neutralization treatment using an alkali. A neutralization process can be performed by processing the etching surface using the aqueous alkali solution containing 1 type, or 2 or more types of alkalis, such as potassium hydroxide, sodium hydroxide, and ammonia. Washing with running water using ultrapure water or the like may be performed before and / or after this neutralization step.

  In particular, when (a) hydrochloric acid is used in step (2), step (2) is performed first, and then step (1) is performed, hydrochloric acid remains in the concave portions of the rough surface roughened by etching. By doing so, the etching action by the mixed liquid in the step (2) may be hindered, and therefore, the neutralization step is preferably performed between the step (2) and the step (1). When step (1) is performed first and step (2) is performed later, the problem of etching inhibition due to such residual components is small, but a better rough surface is formed by interposing the neutralization step. Can be preferred.

  The alkali used for the neutralization treatment is preferably an alkali of about 0.1 to 5N because efficient neutralization cannot be performed if it is too weak.

  Specifically, the neutralization treatment with alkali is performed by immersing the light-emitting diode chip that has undergone the previous etching step in an alkaline aqueous solution.

  After the etching process according to the present invention, in order to remove an acid component remaining on the surface of the light emitting diode, it may be washed with running ultrapure water as necessary. Further, after washing with running water, neutralization is performed using ammonia water, and washing with ultrapure water is performed again, whereby the acid component can be removed more efficiently. The end of the ultrapure water cleaning can be determined with good reproducibility, for example, by monitoring the conductivity of the waste water at the outlet of the cleaning tank.

  The light-emitting diode obtained by the roughening treatment by the etching process in which the two-stage etching process, preferably the neutralization process with an alkali between the two-stage etching processes, is preferably performed on the entire surface except for the electrode forming portion. It is a rough surface including fine irregularities having a non-arc-shaped cross-sectional shape and continuous with the irregularities. Here, the non-arc-shaped fine irregularities mean non-granular irregularities in which the fine irregularities are not simply a collection of granular irregularities having an arc-shaped cross section, but non-arc-shaped irregularities.

  It is known that the light extraction efficiency is generally improved and the light intensity is improved when the surface of the light emitting diode has a fine unevenness as compared with the case where the surface is a mirror surface. The inventors have found a phenomenon that the light intensity is remarkably improved when the unevenness includes a portion having a non-arc shape and the unevenness is continuous as compared with the case where the fine unevenness has an arcuate cross section. In particular, among these irregularities, it is effective for improving the brightness that the density of the irregularities in which a surface called facet reflecting the crystal plane orientation is projected is high.

  According to the method of the present invention, the rough surface of the surface of the light emitting diode on which such unevenness is formed has an average roughness (Ra) in the range of 5 to 450 nm and a root square existing in an area of 10 nm × 10 nm. The number (N) of protrusions having a height equal to or higher than the average roughness (RMS) is preferably in the range of 10 or more and less than 1000. If Ra and N are smaller than the above range, the effect of improving the light extraction efficiency due to the roughening is not sufficient, and even if it is large, the light extraction efficiency to the outside tends to decrease.

  Next, the present invention will be described more specifically with reference to experimental examples, examples, and comparative examples. However, the present invention is not limited to the description of the following examples unless it exceeds the gist.

  In the following description, the light-emitting diode chip before the roughening provided for the etching process is manufactured as follows.

<Light emitting diode chip manufacturing method>
A GaP layer with a thickness of 3 μm, a GaAsP composition change layer with a thickness of 23 μm (a layer in which x increases continuously from 0 to x in GaAs _x P _1-x ) on a GaP substrate using a hydride vapor phase method, After sequentially epitaxially growing a 12 μm thick GaAsP composition constant layer (GaAs _x P _1-x layer) and a 20 μm thick nitrogen-doped GaAsP layer (GaAs _y P _1-y layer), a P-type impurity using ZnAs ₂ as a diffusion source Then, a pn junction was formed by diffusing Zn from a surface to a depth of 4 μm at a temperature of 760 ° C. in a quartz ampule together with Zn. Next, the substrate side was lapped to roughen the surface and etched with aqua regia etchant to remove damage, and the back surface was semi-mirror finished to a thickness of 280 μm. Subsequently, front and back electrodes were formed by vacuum deposition. Circular electrodes with a diameter of 120 μm were deposited on the surface at intervals of 350 μm, and circular electrodes with a diameter of 50 μm were deposited on the back surface at intervals of 70 μm in the vertical and horizontal directions. If a double-sided mask is used here, the front and back electrodes can be formed at predetermined positions. Dicing was performed in accordance with the front electrodes at intervals of 350 μm, and the position was determined by looking at the front electrodes from the etching surface between the back electrodes on the back surface through the epitaxial wafer, and half dicing was performed leaving 50 μm. Further, dicing damage was removed with an etching solution of sulfuric acid and hydrogen peroxide. By sticking to an adhesive sheet and performing braking, a square pillar-shaped light emitting diode chip having a height of 254 μm × 254 μm and a height of 280 μm was completed.

The composition ratio of the GaAsP light emitting layer for each light emission color is as follows.
Red light emitting diode: GaAs _0.45 P _0.55
Orange light emitting diode: GaAs _0.35 P _0.65
Soft orange light emitting diode: GaAs _0.25 P _0.75
Yellow light emitting diode: GaAs _0.1 P _0.9

  In the following Examples and Comparative Examples, the average relative luminance of the roughened light emitting diode was determined as follows.

<Average relative luminance>
For each light emitting diode, in order to reduce the influence of the in-plane distribution of the wafer before and after the surface roughening, the light emitting diode of 254 μm × 254 μm size is taken out from the designated area of 1 cm × 1 cm, and each chip operates by 5 chips. The light output at a current of 20 mA was measured, and the ratio of the average value of the light output of the light-emitting diode after roughening to the average value of the light output of the light-emitting diode before roughening was calculated.

  In the following experimental examples, examples, and comparative examples, details of the chemicals used for the etching treatment are as follows.

<Drugs used>
Iodic acid: 0.1N aqueous solution Nitric acid: 69% aqueous solution Hydrofluoric acid: 49% aqueous solution Hydrochloric acid: 36% aqueous solution Acetic acid: 99.7% aqueous solution Citric acid: 1.0N aqueous solution Tartaric acid: 1.0 Normal aqueous solution

Example 1
The light-emitting diode chip was immersed in hydrochloric acid at 65 ° C. and etched for 15 minutes (step (2)), then pulled up, immersed in 1.0N aqueous potassium hydroxide solution for 5 minutes, and then 14 L / min. The remaining acid component on the surface is removed by washing with ultrapure water at a flow rate of 5 minutes (neutralization step), and then iodic acid, hydrofluoric acid, nitric acid and acetic acid are removed from HIO ₃ : HF: HNO ₃ : Etching is performed for 2 to 3 minutes by immersing in a mixed solution at a temperature of 25 ° C. mixed at a ratio of CH ₃ COOH = 1: 720: 389: 3553 (molar ratio) to a total concentration of 87.3% by weight. (Step (1)).
The resulting roughened light emitting diode was examined for average relative luminance, and the results are shown in Table 1.

Example 2
In Example 1, the process (2) and the process (1) were replaced, and the etching process was performed in the same manner except that the process (1), the neutralization process, and the process (2) were performed in this order. The average relative luminance of the roughened light emitting diode was examined, and the results are shown in Table 1.

Comparative Example 1
Etching was conducted in the same manner except that only step (2) of Example 1 was performed, and the average relative luminance of the obtained roughened light emitting diode was examined. The results are shown in Table 1.

Comparative Example 2
Etching was conducted in the same manner except that only step (1) of Example 1 was performed, and the average relative luminance of the obtained roughened light emitting diode was examined. The results are shown in Table 1.

  From Table 1, it can be seen that according to the present invention, a light-emitting diode having excellent light extraction efficiency and high luminance is provided.

  Scanning electron micrographs of the surface of the GaP substrate and the surface of the GaAsP light emitting layer (nitrogen doped GaAsP layer) of the light emitting diodes obtained in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIGS. However, with respect to the surface of the GaP substrate, since it is difficult to perform observation with a scanning electron microscope after forming the GaAsP light emitting layer on the GaP substrate, a (100) n-type GaP substrate without a separate GaAsP light emitting layer is prepared, A scanning electron micrograph of the (100) plane is taken for this GaP substrate etched in the same procedure. Thus, even a GaP substrate before the formation of the GaAsP light emitting layer can be subjected to a surface roughening process equivalent to that of the GaP substrate after the formation of the GaAsP light emitting layer, so that the surface roughness of the GaP substrate of the light emitting diode is simulated. Can be adopted as.

  The following is clear from FIGS.

  In Comparative Example 1 (FIG. 4) in which only etching with hydrochloric acid in the step (2) is performed, the GaP substrate is extremely roughened, but the degree of roughening of the CaAsP light emitting layer is low. Further, in Comparative Example 2 (FIG. 5) in which only the etching with the iodic acid mixed acid solution in the step (1) is performed, the surface of the GaAsP light emitting layer is roughened, but the GaP substrate is not roughened.

  As described above, when only one of the steps (1) and (2) is performed, both the GaP substrate and the GaAsP light emitting layer cannot be roughened efficiently. The brightness is low.

  On the other hand, in Examples 1 and 2 in which both steps (1) and (2) were performed, both the GaP substrate and the GaAsP light emitting layer were roughened to a good rough surface. It will be understood that there is no particular restriction on the order of (2), and either may be performed first.

Examples 3 and 4
Etching was performed in the same manner as in Examples 1 and 2 except that the neutralization step with 1.0N potassium hydroxide aqueous solution was not performed, and only water washing was performed for 5 minutes, and GaP of the obtained roughened light emitting diode was obtained. Scanning electron micrographs of the surface of the substrate and the GaAsP light emitting layer are shown in FIGS.

Example 5
Etching was performed in the same manner as in Example 3 except that washing was performed for 15 minutes, and scanning electron micrographs of the surface of the GaP substrate and the GaAsP light emitting layer of the obtained roughened light emitting diode are shown in FIG.

  6-8, the GaP substrate and the GaAsP light emitting layer are both roughened only by washing with water between step (2) and step (1) or between step (1) and step (2). Although the surface of the GaAsP light emitting layer can be roughened, the surface of the GaAsP light-emitting layer has a small degree of roughening, that is, if the acid in the former etching solution remains, the etching with the latter etching solution is inhibited. 2) is performed first, and the etching inhibition when hydrochloric acid remains is large. Therefore, there is a residual acid in the previous stage between step (1) and step (2) or between step (2) and step (1). It is preferable to sufficiently remove the components, and for that purpose, it is understood that neutralization with an alkali is preferable to washing with water.

Experimental example 1
As a preliminary experiment for roughening according to the present invention, a light emitting diode chip was immersed in an etching solution having the composition and temperature shown in Table 2 for 1 minute to perform etching treatment, and the presence or absence of roughening was investigated. Indicated.

  As can be seen from Table 2, a mixed acid etching solution of iodic acid / hydrofluoric acid / nitric acid / hydrochloric acid can roughen the GaAsP light-emitting layer, but cannot roughen the GaP substrate. (No. 2). If the nitric acid in this mixed acid etching is removed, the GaAsP light emitting layer cannot be roughened (No. 1), and even if hydrofluoric acid is changed to hydrochloric acid, hydrochloric acid is further added to this mixed acid etching solution. However, it cannot be roughened (Nos. 3 to 5), and even if a carboxylic acid heavier than acetic acid is used, it cannot be roughened (Nos. 6 and 7).

  Therefore, it is preferable to use a mixed acid etching solution of iodic acid / hydrofluoric acid / nitric acid / hydrochloric acid for roughening the GaAsP light emitting layer, and in this mixed acid system, only a rough surface of the GaAsP light emitting layer can be formed. Since it is impossible to roughen both the GaAsP light-emitting layer and the GaP substrate with other etching solutions, it can be seen that it is necessary to separately roughen the GaP substrate.

It is the schematic diagram of the cross section which shows embodiment of the light emitting diode by which the surface obtained by the method of this invention was roughened. It is a scanning electron micrograph of the surface of the roughened light emitting diode obtained in Example 1, (a) A figure is a GaAsP light emitting layer surface, (b) A figure is a photograph of the GaP substrate surface. It is a scanning electron micrograph of the surface of the roughened light emitting diode obtained in Example 2, (a) A figure is a GaAsP light emitting layer surface, (b) A figure is a photograph of the GaP substrate surface. It is a scanning electron micrograph of the surface of the roughened light emitting diode obtained by the comparative example 1, (a) A figure is a GaAsP light emitting layer surface, (b) A figure is a photograph of the GaP substrate surface. It is a scanning electron micrograph of the surface of the roughened light emitting diode obtained by the comparative example 2, (a) A figure is a GaAsP light emitting layer surface, (b) A figure is a photograph of the GaP substrate surface. It is a scanning electron micrograph of the surface of the roughening light emitting diode obtained in Example 3, (a) A figure is a GaAsP light emitting layer surface, (b) A figure is a photograph of the GaP substrate surface. It is a scanning electron micrograph of the surface of the roughened light emitting diode obtained in Example 4, (a) A figure is a GaAsP light emitting layer surface, (b) A figure is a photograph of the GaP substrate surface. It is a scanning electron micrograph of the surface of the roughened light emitting diode obtained in Example 5, (a) A figure is a GaAsP light emitting layer surface, (b) A figure is a photograph of the GaP substrate surface.

Explanation of symbols

1 GaP substrate 2 GaP layer 3 GaAsP composition change layer 4 GaAsP constant composition layer 5 n-type nitrogen doped GaAsP layer 6 p-type nitrogen doped GaAsP layer 7 p-side electrode 8 n-side electrode 10 pn junction

Claims (3)

On a GaP substrate, _{GaAs x P 1-x (0} <x <1) layer and the nitrogen-doped _{GaAs x P 1-x (0} <x <1) layer and the formed light-emitting diode having a pn junction therein In a method of manufacturing a light emitting diode having a step of chemically etching the surface of a chip
The etching step includes the following steps (1) and (2) in this order or in the reverse order.
Step (1): Step of etching using a mixed solution containing iodic acid, hydrofluoric acid, nitric acid and acetic acid Step (2): (a) hydrochloric acid at 20 ° C. or higher, (b) hydrofluoric acid, and ( c) A step of etching using one or more acids selected from the group consisting of a mixture of hydrofluoric acid and sulfuric acid.   2. The method of manufacturing a light emitting diode according to claim 1, further comprising a step of treating with an alkali between the steps (1) and (2) or the steps (2) and (1).   The mixed liquid containing iodic acid, hydrofluoric acid, nitric acid and acetic acid according to claim 1 or 2, wherein 1 to 30000 mol of hydrofluoric acid and 1 to 20000 mol of nitric acid with respect to 1 mol of iodic acid, A method for producing a light-emitting diode, comprising 50 to 80,000 mol of acetic acid.

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