JP5310369B2 - Epitaxial wafer and light emitting diode - Google Patents

Description

  The present invention relates to an epitaxial wafer and a light emitting diode, and more specifically to an epitaxial wafer that can suppress cratering from occurring in a crystal in a wire bonding step.

In recent years, compound semiconductors are widely used as optical semiconductor element materials. As the semiconductor material, a material obtained by epitaxially growing a desired semiconductor crystal layer on a single crystal substrate is used. This is because a crystal that is currently available and used as a substrate has many defects and low purity, so that it is difficult to use it as it is as a light emitting element. Therefore, a layer having a composition for obtaining a desired emission wavelength is epitaxially grown on the substrate. As this epitaxial growth layer, a ternary mixed crystal layer is mainly used.
For epitaxial growth, vapor phase growth or liquid phase growth is usually used. In the vapor phase growth method, epitaxial growth is performed by a method in which a graphite or quartz holder is placed in a quartz reactor to hold a substrate, and a raw material gas is flowed and heated.

  Since III-V compound semiconductors have band gaps corresponding to visible and infrared wavelengths, they are applied to light-emitting elements. Among them, GaAsP and GaP are particularly widely used as LED materials.

Taking GaAs _1-x P _x as an example, GaAs _1-x P _x (0.45 <x <1) emits light by doping nitrogen (N) as an iso-electronic trap that captures conduction electrons. The light output as a diode can be improved about 10 times. Therefore, GaAs _1-x P _x (0.45 <x <1) grown on the GaP substrate is usually doped with nitrogen.

FIG. 5A shows a conventional configuration example of a GaAsP epitaxial wafer.
In the vapor phase growth method, a source gas is flowed into the reactor to grow the n-type layer 22 on the n-type GaP substrate 21. In this case, a composition-change GaAsP layer whose composition is changed stepwise is provided as an intermediate layer so that lattice distortion due to the difference in lattice constant between the substrate 21 and the n-type layer 22 does not occur. A constant composition nitrogen concentration increasing GaAsP layer and a constant composition nitrogen doped GaAsP layer doped with nitrogen (N) are formed as electronic traps.
Thereafter, a good ohmic contact can be stably obtained by epitaxially growing the p-type layer 23 having a structure composed of the first p-type layer 23b and the second p-type layer 23d (see, for example, Patent Document 1). In addition, the epitaxial wafer 20 can achieve high brightness.

JP-A-8-335715

However, in the wire bonding process when manufacturing a light-emitting diode using an epitaxial wafer having such a structure, a phenomenon (hereinafter referred to as cratering) occurs in which the electrodes on the p-type layer formed by epitaxial growth are swept away by the crystal. doing.
The light emitting diode in which the crater is generated has a problem that the yield is lowered because energization (and thus light emission) itself is impossible.

  The present invention has been made in view of the above problems, and provides an epitaxial wafer and a light-emitting diode that can reduce the occurrence of cratering in the wire bonding process when assembling the light-emitting diode, and thus can improve the yield. The purpose is to do.

  In order to solve the above problems, in the present invention, in an epitaxial wafer having at least a substrate, an n-type layer formed by epitaxial growth on the substrate, and a p-type layer on the n-type layer, the n-type layer and The p-type layer is GaAsP or GaP, the p-type layer has at least a first p-type layer, and a second p-type layer above the first p-type layer and having a high carrier concentration, and further, the n-type layer A first p-type carrier concentration increasing layer in which the p-type carrier concentration gradually increases between the first p-type layer and the first p-type layer; and a p-type carrier concentration in which the p-type carrier concentration gradually increases between the first p-type layer and the second p-type layer. An epitaxial wafer characterized by having a 2p type carrier concentration increasing layer is provided.

As described above, the first p-type carrier concentration increasing layer in which the p-type carrier concentration gradually increases is provided between the n-type layer and the first p-type layer, and the p-type is provided between the first p-type layer and the second p-type layer. The epitaxial wafer has a structure in which a second p-type carrier concentration increasing layer in which the carrier concentration gradually increases is provided.
As a result, the p-type carrier concentration does not increase rapidly from the n-type layer to the first p-type layer or from the first p-type layer to the second p-type layer, and the lattice distortion caused by the difference in lattice constants. And the accompanying crystal defects can be suppressed. Therefore, the crystal of the entire p-type layer becomes an epitaxial wafer better than the conventional one, and the generation rate of cratering generated in the wire bonding process can be made smaller than before.
In addition, since lattice distortion and crystal defects can be reduced, the light emission luminance and the light emission lifetime can be improved.
The “gradual increase” in the present invention includes not only a continuous (linear) increase but also a step-like (step-like) increase.

Here, in the first p-type carrier concentration increasing layer, the concentration increase rate of the p-type carrier is preferably 2 × 10 ¹⁶ to 2 × 10 ¹⁷ cm ⁻³ / μm.
Thus, if the increasing rate of the p-type carrier concentration of the first p-type carrier concentration increasing layer is 2 × 10 ¹⁶ to 2 × 10 ¹⁷ cm ⁻³ / μm, the p-type carrier concentration does not increase rapidly. The deterioration of the crystallinity at the interface between the n-type layer and the p-type layer is suppressed, and the epitaxial wafer has a good crystallinity. Moreover, it can suppress that the thickness of an increase layer becomes unnecessarily thick, and can make productivity high.

In the second p-type carrier concentration increasing layer, the concentration increase rate of the p-type carrier is preferably 3 × 10 ^{17 to} 3 × 10 ¹⁸ cm ⁻³ / μm.
Thus, if the increasing rate of the p-type carrier concentration of the second p-type carrier concentration increasing layer is within the above range, the crystallinity between the first p-type layer and the second p-type layer is good and the productivity is high. A high epitaxial wafer can be obtained.

The second p-type layer preferably has a carrier concentration of 0.6 to 1.0 × 10 ¹⁹ cm ⁻³ .
Thus, by setting the carrier concentration of the second p-type layer to 0.6 to 1.0 × 10 ¹⁹ cm ⁻³ , the crystallinity of the second p-type layer may be maintained in a good state. In addition, it is possible to obtain an epitaxial wafer suitable for the manufacture of a light emitting diode in which the occurrence of cratering is further suppressed and the characteristics such as light emission luminance are good.

Furthermore, it is preferable that the layer thickness of the first p-type carrier concentration increasing layer is 2 to 6 μm, and the layer thickness of the second p-type carrier concentration increasing layer is 5 to 15 μm.
Thus, by setting the thicknesses of the first p-type carrier concentration increasing layer and the second p-type carrier concentration increasing layer within the above-described range, it takes less time to form the p-type carrier concentration increasing layer and the productivity. Can be high. Further, the concentration of the p-type carrier is not rapidly increased, and the epitaxial wafer has good crystallinity.

In addition, the present invention provides a light emitting diode manufactured using the epitaxial wafer according to the present invention.
As described above, the epitaxial wafer of the present invention has a rate of occurrence of cratering in the wire bonding step that has been suppressed as compared with the prior art, and has good emission luminance and emission lifetime characteristics. A light emitting diode manufactured using such an epitaxial wafer has better light emission characteristics and higher yield than the conventional one.

  As described above, according to the present invention, an epitaxial wafer in which the crystallinity of the p-type layer is greatly improved as compared with the conventional one is obtained, and by using such an epitaxial wafer, cratering occurs in the wire bonding process. The rate can be greatly reduced compared to the conventional case. Further, the crystallinity is better than the conventional one, and the light emission luminance and the light emission life characteristics can be improved.

It is the figure which showed an example of the outline of the epitaxial wafer of this invention. It is the figure which showed the incidence rate of the crater ring of the light emitting diode produced from the Example of this invention and the epitaxial wafer of Comparative Examples 1-3. It is the figure which compared the light emission intensity of the light emitting diode of an Example and Comparative Examples 1-3 by setting the light emission intensity of the light emitting diode of an Example to 100. FIG. It is the figure which compared the light emission lifetime of the light emitting diode of an Example and Comparative Examples 1-3 by setting the light emission lifetime of the light emitting diode of an Example to 100. FIG. It is the figure which showed an example of the outline of the conventional epitaxial wafer. It is an observation image of the light emitting diode chip | tip which the crater ring generate | occur | produced in the wire bonding process.

Hereinafter, the present invention will be described more specifically.
As described above, the development of an epitaxial wafer and a light emitting diode that can reduce the occurrence of cratering in the wire bonding process at the time of assembling the light emitting diode and thereby improve the yield has been awaited.

Therefore, the present inventor conducted various investigations on the structure of the epitaxial wafer used for the light emitting diode in which cratering occurred and the structure of the chip after wafer dicing.
As a result, as shown in FIG. 6, as a result of observing a plurality of light emitting diode chips in which cratering has occurred, the depth of the portion that has been removed due to the occurrence of cratering is mainly between the first p-type layer and the second p-type layer. It was inferred that cratering was occurring because it was near the interface or near the interface between the n-type layer and the first p-type layer.

  Therefore, as a result of intensive studies on the structure of the epitaxial wafer for improving the crystal weakness in the vicinity of the interface between the first p-type layer and the second p-type layer and in the vicinity of the interface between the n-type layer and the first p-type layer, A p-type carrier concentration increasing layer in which the p-type carrier concentration is gradually increased is provided between the n-type layer and the first p-type layer, and the p-type carrier concentration is also gradually increased between the first p-type layer and the second p-type layer. The idea was to provide a p-type carrier concentration increasing layer to suppress the deterioration of crystallinity due to a sudden increase in the amount of p-type carriers in the vicinity of these interfaces and to improve the crystallinity.

  And by producing light-emitting diode chips from an epitaxial wafer with such a structure, it is generated due to the height of the bonding force in the wire bonding process or the reason that the Au ball at the time of bonding is off the electrode center and hits the crystal surface. It was difficult to suppress the crater ring, but it was discovered that the occurrence of crater ring derived from the structure of the epitaxial wafer can be substantially suppressed, and the present invention has been completed.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a view showing an example of an outline of an epitaxial wafer of the present invention.
As shown in FIG. 1, an epitaxial wafer 10 of the present invention has at least a substrate 11, an n-type layer 12 formed on the substrate 11 by epitaxial growth, and a p-type layer 13 on the n-type layer 12. doing.
The n-type layer 12 and the p-type layer 13 are made of GaAsP or GaP, and the p-type layer 13 is at least above the first p-type layer 13b and the first p-type layer 13b and has a high carrier concentration. And a second p-type layer 13d.
Further, between the n-type layer 12 and the first p-type layer 13b, the p-type carrier concentration increasing layer 13a in which the p-type carrier concentration gradually increases, and the p-type between the first p-type layer 13b and the second p-type layer 13d. And a second p-type carrier concentration increasing layer 13c in which the type carrier concentration gradually increases.
The n-type layer 12 includes at least a composition change layer 12a, a constant composition layer 12b, a nitrogen concentration increasing layer 12c, and a nitrogen concentration constant layer 12d.

  In the case of an epitaxial wafer having such a structure, a lattice is caused by a difference in p-type carrier concentration between the n-type layer and the first p-type layer or a difference in p-type carrier concentration between the first p-type layer and the second p-type layer. Crystal defects caused by strain can be suppressed. Therefore, the crystallinity from the n-type layer to the p-type layer can be made better than before, and the rate of cratering that occurs in the wire bonding process can be improved. At the same time, the light emission luminance and the light emission life characteristics can be improved.

  Here, the substrate 11 preferably has a structure of at least a single crystal substrate 11a and a substrate buffer layer 11b formed by an epitaxial growth method. With such a structure, when the n-type layer 12 is formed on the substrate 11 by the epitaxial growth method, the introduction of crystal defects inherent in the substrate 11 into the n-type layer 12 and the p-type layer 13 is suppressed. can do.

In addition, the carrier concentration of the second p-type layer 13d can be set to 0.6 to 1.0 × 10 ¹⁹ cm ⁻³ .
Thereby, the crystallinity of the second p-type layer can be made better, and an epitaxial wafer that can further suppress the occurrence of cratering can be obtained.

The concentration increase rate of the p-type carrier of the first p-type carrier concentration increasing layer 13a is in the range of 2 × 10 ¹⁶ to 2 × 10 ¹⁷ cm ⁻³ / μm, more preferably 4 × 10 ¹⁶ to 1 × 10 ¹⁷ cm ^−. It can be in the range of ³ / μm.
As a result, the concentration of the p-type carrier between the n-type layer and the first p-type layer is not abruptly increased, and the increase rate can be suppressed from becoming too gradual. Therefore, the crystallinity at the interface between the n-type layer and the first p-type layer becomes better, the rate of cratering can be further reduced, and the light emission luminance and light emission lifetime characteristics can be further improved. And it can be manufactured efficiently.

Furthermore, the layer thickness of the first p-type carrier concentration increasing layer 13a can be set to 2 to 6 μm.
As a result, the formation of the layer does not take time and the productivity is high. Furthermore, the concentration increase rate of the p-type carrier does not become abrupt, deterioration of crystallinity can be suppressed, and the effect of suppressing cratering can be further enhanced.

Also, the concentration increase rate of the p-type carrier in the second p-type carrier concentration increasing layer 13c is in the range of 3 × 10 ^{17 to} 3 × 10 ¹⁸ cm ⁻³ / μm, more preferably 5 × 10 ^{17 to} 1.5 ×. The range can be 10 ¹⁸ cm ⁻³ / μm.
As a result, the concentration of the p-type carrier between the first p-type layer and the second p-type layer is not abruptly increased, and it is possible to suppress the increase rate from becoming unnecessarily gradual. Accordingly, the crystallinity of the p-type layer is further improved, the cratering rate and the light emission lifetime characteristics can be further improved, and the production efficiency does not have to be lowered.

The layer thickness of the second p-type carrier concentration increasing layer 13c can be 5 to 15 μm.
As a result, the formation of the layer does not take a long time, and the rate of increase in the concentration of the p-type carrier can be suppressed from becoming abrupt. Therefore, it is possible to obtain an epitaxial wafer with high productivity and good crystallinity.

Furthermore, the n-type layer 12 and the p-type layer 13 are preferably GaAs _1-x P _x (0.45 <x <1), and the substrate 11 is preferably made of GaP.
Thus, in the epitaxial wafer of the present invention, the rate of occurrence of cratering is reduced as compared with the conventional one, and the light output can be improved, but other configurations are the same as the conventional one. Therefore, the n-type layer and the p-type layer can be made of GaAsP having the above composition, and the substrate can be made of GaP. Therefore, high quality can be achieved with a simple configuration.

Further, it is desirable that at least one of the n-type layer 12 and the p-type layer 13 is doped with nitrogen.
Thus, by doping at least one of the n-type layer and the p-type layer with nitrogen as an iso-electronic trap that captures conduction electrons, the light output as a light-emitting diode can be improved by about 10 times. Can be an epitaxial wafer.

And it is desirable that the p-type carrier of the p-type layer 13 is zinc, magnesium, or both.
Although it does not specifically limit as a p-type carrier, Zinc, magnesium, etc. are mentioned. For example, it can dope by supplying organometallic compounds, such as a dimethyl zinc (DMZn), in a reactor. Thereby, a high carrier concentration can be obtained, and the structure of the epitaxial wafer of the present invention can be easily realized only by vapor phase growth.

  Furthermore, a light emitting diode manufactured using the epitaxial wafer of the present invention in which the rate of occurrence of cratering in such a wire bonding process is suppressed as compared with that of the present invention, and the light emission luminance and light emission lifetime characteristics are also good. In comparison, the characteristics as a light-emitting diode are good, the occurrence of cratering is small, and the yield is high.

The epitaxial wafer of the present invention as described above can be manufactured by the manufacturing method as described below, but the present invention is not limited to these.
In the manufacturing method shown below, the case where the n-type layer and the p-type layer are made of GaAsP and GaP is used for the substrate has been described. However, the present invention is not limited to this, and the n-type layer and the p-type layer are not limited to this. GaP can also be used.

First, a GaP single crystal substrate 11a and high-purity gallium (Ga) are respectively installed at predetermined locations in an epitaxial reactor equipped with a Ga reservoir quartz boat.
Next, nitrogen (N ₂ ) gas is introduced into the reactor, and after sufficiently replacing and removing air, high-purity hydrogen (H ₂ ) is introduced as a carrier gas, and the flow of N ₂ is stopped for the temperature raising step. enter.
After confirming that the temperature of the Ga-containing quartz boat installation part and the installation part of the single crystal substrate 11a is kept constant at a predetermined temperature, the gas phase of the GaP epitaxial film having the same composition as the single crystal substrate 11a is confirmed. Start growing.

First, an n-type carrier doping gas is introduced into the reactor, and high-purity hydrogen chloride gas (HCl) is added to the Ga reservoir in the quartz boat to generate GaCl as a Group III element component raw material of the periodic table. Blow and blow out from the surface of the Ga reservoir.
On the other hand, the substrate buffer layer 11b as the first layer was grown on the single crystal substrate 11a while introducing high-purity hydrogen phosphide gas (PH ₃ ) as a Group V element component of the periodic table.

Next, the introduction amount of the high purity hydrogen arsenide gas (AsH ₃ ) is started without changing the introduction amount of HCl, and then the introduction amount is gradually increased. At the same time, the introduction amount of the n-type carrier doping gas and PH ₃ is increased. The n-type composition change layer 12a (GaAs _1-x P _x epitaxial layer) to be the second layer is grown on the substrate buffer layer 11b.

Next, the introduction amount of the n-type carrier doping gas is gradually decreased without changing the introduction amounts of HCl, PH ₃ , and AsH ₃ , and the n-type constant composition layer 12b (GaAs _{1− x} P _x epitaxial layer) is grown on the composition change layer 12a.

Next, without changing the introduction amount of HCl, PH ₃ , AsH ₃ , the nitrogen doping gas was introduced to the nitrogen iso-electronic trap addition, and the introduction of the n-type carrier doping gas was stopped at the same time. Thus, an n-type nitrogen concentration increasing layer 12c to be a fourth layer is grown on the constant composition layer 12b.

Next, the n-type nitrogen concentration constant layer 12d to be the fifth layer is grown on the nitrogen concentration increasing layer 12c without changing the introduction amounts of HCl, PH ₃ , AsH ₃ , and nitrogen doping gas.

Then, without changing the introduction amount of HCl, PH ₃ , AsH ₃ , and nitrogen doping gas, introduction is started while increasing the introduction amount of the p-type carrier doping gas to dope the p-type carrier, A GaAs _1-x P _x first p-type carrier concentration increasing layer 13a to be a sixth layer is grown on the nitrogen concentration constant layer 12d.
As a result, the stress in the crystal due to the difference in lattice constant caused by the difference in p-type carrier concentration at the interface between the n-type layer and the first p-type layer can be reduced, and the occurrence of cratering can be suppressed. The light emission luminance and the light emission life characteristics can be improved.
Note that the method for increasing the introduction amount of the p-type carrier doping gas at this time is not particularly limited, and the introduction amount may be linear, stepped, or curved.

Thereafter, the p-type GaAs _{1 serving as} the seventh layer is formed without changing the introduction amount of the HCl, PH ₃ , AsH ₃ , and p-type carrier doping gas, and while gradually reducing the introduction amount of the nitrogen doping gas. _-x P _x epitaxial layer (second 1p-type layer 13b) is grown on the 1p-type carrier concentration increases layer 13a.

Next, the p-type GaAs _1-x P _x second p, which becomes the eighth layer, while gradually increasing the introduction amount of the p-type carrier doping gas without changing the introduction amounts of HCl, PH ₃ , AsH ₃ . A type carrier concentration increasing layer 13c is grown on the first p type layer 13b.
This can reduce the stress in the crystal due to the difference in the lattice constant due to the difference in the p-type carrier concentration at the interface between the first p-type layer and the second p-type layer, suppress the occurrence of cratering, and emit light. Luminance and light emission lifetime characteristics can be improved.
Note that the method for increasing the introduction amount of the p-type carrier doping gas at this time is also not particularly limited, and the introduction amount may be linear, stepped, or curved.

Finally, the p-type GaAs _1-x P _x epitaxial layer (second p-type layer 13d) serving as the ninth layer is formed in the first layer without changing the amount of introduction of HCl, PH ₃ , AsH ₃ , and p-type carrier doping gas. By growing on the 2p-type carrier concentration increasing layer 13c and terminating the vapor phase growth, the epitaxial wafer 10 in which the crystallinity from the n-type layer to the p-type layer is significantly improved as compared with the prior art can be obtained. .
The carrier concentration of the second p-type layer 13d is set higher than that of the first p-type layer 13b.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, of course, this invention is not limited to these.
Example 1
A GaP substrate and high-purity gallium (Ga) were respectively installed at predetermined locations in an epitaxial reactor equipped with a Ga reservoir quartz boat. The GaP substrate has tellurium (Te) added in an amount of ³ to 10 × 10 ¹⁷ / cm ³ , is circular with a diameter of 50 mm, and has a surface deviated by 10 ° in the [011] direction from the (100) surface. These were simultaneously placed on the holder, and the holder was rotated 3 times per minute. Next, after introducing nitrogen (N ₂ ) gas into the reactor for 20 minutes and sufficiently replacing and removing air, high-purity hydrogen (H ₂ ) is introduced as a carrier gas at 6500 sccm / min, and the flow of N ₂ is changed. Stopped temperature rising process. After confirming that the temperatures of the Ga-containing quartz boat installation part and the GaP single crystal substrate installation part were maintained at a constant temperature, vapor phase growth of the GaAs _1-x P _x epitaxial film was started.

First, an n-type carrier doping gas diluted with hydrogen gas is introduced, and high purity hydrogen chloride gas (HCl) is added to the Ga reservoir in the quartz boat to generate GaCl as a group III element component raw material of the periodic table. And blown out from the surface of the Ga reservoir. On the other hand, a GaP buffer layer as a first layer was grown on a GaP single crystal substrate while introducing high purity hydrogen phosphide gas (PH ₃ ) as a group V element component of the periodic table.

Next, the introduction amount of the high purity hydrogen arsenide gas (AsH ₃ ) is started without changing the introduction amount of HCl, and then the introduction amount is gradually increased, and at the same time, the introduction amount of PH ₃ is decreased, A _first GaAs _1-x P _x epitaxial layer was grown on the first GaP buffer layer (n-type layer-composition change layer).

Next, the introduction amount of the n-type carrier doping gas is gradually decreased without changing the introduction amounts of HCl, PH ₃ , and AsH ₃ , and the third GaAs _1-x P _x epitaxial layer is formed as the second layer. It is grown in the _{GaAs 1-x P} x epitaxial layer (n-type layer - constant composition layer).

Thereafter, high purity ammonia gas (NH ₃ ) is introduced to the nitrogen iso-electronic trap for addition without changing the introduction amount of HCl, PH ₃ , AsH ₃ , and at the same time, n-type carrier doping gas after stopped introduced was grown fourth layer _{GaAs 1-x P} x epitaxial layer of the third layer _{GaAs 1-x P} x epitaxial layer of (n-type layer - the nitrogen concentration increases layer).

_{Next, HCl,} PH _3, while introducing without changing the amount of _{AsH 3,} NH 3, the fifth layer _{GaAs 1-x P} x epitaxial layer of the fourth layer _{GaAs 1-x P} x epitaxial layer of Growing (n-type layer-nitrogen concentration constant composition layer).

Next, without changing the introduction amount of HCl, PH ₃ , AsH ₃ , NH ₃ , DMZn gas diluted to 0.4% with H ₂ gas was gradually ramped up to a predetermined flow rate as a p-type carrier doping gas. However, the first p-type carrier concentration increasing layer of the sixth layer was grown on the GaAs _1-x P _x epitaxial layer of the fifth layer.

Then, the p-type GaAs _1-x P _x epitaxial layer ( _first layer) of the seventh layer is formed without changing the amounts of HCl, PH ₃ , AsH ₃ , DMZn, and while gradually reducing the amount of NH ₃ gas introduced. 1p-type layer) was grown on the first p-type carrier concentration increasing layer of the sixth layer.

Next, in a state where the DMZn flow rate is gradually increased by ramping without changing the introduction amounts of HCl, PH ₃ and AsH _{3 and} the introduction of NH ₃ is stopped, the second p-type carrier concentration increasing layer of the eighth layer is formed. A seventh layer of p-type GaAs _1-x P _x epitaxial layer was grown.

Finally, the amount of DMZn gas introduced is fixed without changing the amounts of HCl, PH ₃ , and AsH ₃ , and the ninth p-type GaAs _1-x P _x epitaxial layer (second p-type layer) is formed as the first layer. An epitaxial wafer was manufactured by growing on the eight layers of the second p-type carrier concentration increasing layer and terminating the vapor phase growth.
The layer thickness of the first p-type carrier concentration increasing layer was 4 μm, the layer thickness of the first p-type layer was 8 μm, the layer thickness of the second p-type carrier concentration increasing layer was 10 μm, and the layer thickness of the second p-type layer was 4 μm.

  Then, electrode formation, dicing, molding, etc. were performed with respect to the produced epitaxial wafer, and the light emitting diode was manufactured.

The manufactured light emitting diode was evaluated as shown below.
First, the electrode formation surface on the p-type layer side after wire bonding was observed, and the presence or absence of cratering was evaluated. The result is shown in FIG. FIG. 2 is a diagram showing the rate of occurrence of cratering of light emitting diodes produced from epitaxial wafers of Examples and Comparative Examples 1 to 3 described later, and the vertical axis indicates cratering out of 1 million light emitting diodes. It represents the number of light emitting diodes generated.
Next, the light emission luminance of the manufactured light emitting diode was evaluated. The result is shown in FIG. FIG. 3 is a graph comparing the light emission intensities of the light emitting diodes of Examples and Comparative Examples 1 to 3 to be described later.
And the light emission lifetime of the manufactured light emitting diode was evaluated. The result is shown in FIG. FIG. 4 is a diagram comparing the light emitting lifetimes of the light emitting diodes of the example and comparative examples 1 to 3 described later, and is a relative value when the example is 100.

(Comparative Example 1)
In Example 1, the first p-type carrier concentration increasing layer and the second p-type carrier concentration increasing layer are not formed, but the thickness of the first p-type layer is 8 μm and the thickness of the second p-type layer is 4 μm. An epitaxial wafer 20 including a GaP substrate 21, an n-type layer 22, a first p-type layer 23b, and a second p-type layer 23d as shown in FIG. A diode was manufactured. And evaluation similar to Example 1 was performed.

(Comparative Example 2)
In Example 1, the first p-type carrier concentration increasing layer is not formed, the thickness of the first p-type layer is 8 μm, the thickness of the second p-type carrier concentration increasing layer is 10 μm, and the thickness of the second p-type layer is 4 μm. A GaP substrate 21, an n-type layer 22, a first p-type layer 23b ', a p-type carrier concentration increasing layer 23e, and a second p-type layer as shown in FIG. An epitaxial wafer 20 ′ composed of 23d ′ was manufactured, a light emitting diode was manufactured in the same manner, and the same evaluation as in Example 1 was performed.

(Comparative Example 3)
In Example 1, the second p-type carrier concentration increasing layer is not formed, the thickness of the first p-type layer is 8 μm, the thickness of the first p-type carrier concentration increasing layer is 4 μm, and the thickness of the second p-type layer is 4 μm. A GaP substrate 21, an n-type layer 22, a p-type carrier concentration increasing layer 23e ′, a first p-type layer 23b ″, and a second p are formed in the same manner as in Example 1 except that An epitaxial wafer 20 ″ made of the mold layer 23d ″ was manufactured, a light emitting diode was manufactured in the same manner, and the same evaluation as in Example 1 was performed.

  As shown in FIG. 2, in the light emitting diode of the example, the rate of occurrence of crater was 2 ppm, whereas in Comparative Example 1, it was 47 ppm, in Comparative Example 2, 19 ppm, and in Comparative Example 3, 33 ppm. It was found that by providing both the type carrier concentration increasing layer and the second p-type carrier concentration increasing layer, the occurrence of cratering can be greatly suppressed, and one of them is not very effective.

  Further, as shown in FIG. 3, when the light emitting luminance of the light emitting diode of the example is 100, the light emitting diode of the comparative example 1 is 92, the comparative example 2 is 97, and the comparative example 3 is 94. Thus, it has been found that the emission luminance can be improved by providing the p-type carrier concentration increasing layer both at the interface between the n-type layer and the first p-type layer and at the interface between the first p-type layer and the second p-type layer.

  As shown in FIG. 4, when the light emitting lifetime of the light emitting diode of the example is 100, the light emitting diode of the comparative example 1 is 90, the comparative example 2 is 95, the comparative example 3 is 93, and the first p-type carrier concentration. It has been found that by providing both the increase layer and the second p-type carrier concentration increase layer, the emission lifetime can be significantly improved as well as the occurrence rate of cratering.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

10: Epitaxial wafer,
11 ... Substrate, 11a ... Single crystal substrate, 11b ... Substrate buffer layer,
12 ... n-type layer, 12a ... composition change layer, 12b ... constant composition layer, 12c ... nitrogen concentration increasing layer, 12d ... nitrogen concentration constant layer,
13 ... p-type layer, 13a ... first p-type carrier concentration increasing layer, 13b ... first p-type layer, 13c ... second p-type carrier concentration increasing layer, 13d ... second p-type layer,
20, 20 ', 20''... epitaxial wafer, 21 ... GaP substrate, 22 ... n-type layer, 23 ... p-type layer, 23b, 23b', 23b "... first p-type layer, 23d, 23d ', 23d''... second p-type layer, 23e, 23e' ... p-type carrier concentration increasing layer.

Claims (7)

At least in an epitaxial wafer having a substrate, an n-type layer formed by epitaxial growth on the substrate, and a p-type layer on the n-type layer,
The n-type layer and the p-type layer are GaAsP or GaP, the p-type layer has at least a first p-type layer, and a second p-type layer above the first p-type layer and having a high carrier concentration,
Furthermore, a first p-type carrier concentration increasing layer in which a p-type carrier concentration gradually increases between the n-type layer and the first p-type layer, and a p-type carrier between the first p-type layer and the second p-type layer. An epitaxial wafer comprising a second p-type carrier concentration increasing layer having a gradually increasing concentration. 2. The epitaxial wafer according to claim 1, wherein the first p-type carrier concentration increasing layer has a p-type carrier concentration increasing rate of 2 × 10 ¹⁶ to 2 × 10 ¹⁷ cm ⁻³ / μm. 3. The second p-type carrier concentration increasing layer according to claim 1, wherein the p-type carrier concentration increasing rate is 3 × 10 ^{17 to} 3 × 10 ¹⁸ cm ⁻³ / μm. Epitaxial wafer. 4. The epitaxial wafer according to claim 1, wherein the second p-type layer has a carrier concentration of 0.6 to 1.0 × 10 ¹⁹ cm ⁻³ .   5. The epitaxial wafer according to claim 1, wherein a thickness of the first p-type carrier concentration increasing layer is 2 to 6 μm.   6. The epitaxial wafer according to claim 1, wherein a thickness of the second p-type carrier concentration increasing layer is 5 to 15 μm.   A light-emitting diode manufactured using the epitaxial wafer according to any one of claims 1 to 6.

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