JP2010206220A - Epitaxial wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial wafer having a structure of a p-type layer optimal for enabling a further improved light output and formation of a desirable Ohmic electrode. <P>SOLUTION: The epitaxial wafer has at least a substrate and an n-type layer and a p-type layer on the n-type layer, which are formed by epitaxial growth on the substrate. In this epitaxial wafer, the n-type layer and the p-type layer are of GaAsP or GaP, and the p-type layer has at least a first p-type layer and a second p-type layer formed above the first p-type layer, in which a carrier concentration of the first p-type layer measures 5×10<SP>16</SP>to 3×10<SP>17</SP>per cm<SP>3</SP>and a carrier concentration of the second p-type layer measures 7×10<SP>18</SP>to 3×10<SP>19</SP>per cm<SP>3</SP>, and a silicon concentration of each of the n-type and the p-type layers measures 1×10<SP>14</SP>to 1.5×10<SP>15</SP>per cm<SP>3</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an epitaxial wafer, and specifically to a semiconductor epitaxial wafer for a light emitting diode (hereinafter referred to as LED).

  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 a light-emitting element as it is. Therefore, a desired emission wavelength is obtained on the substrate. Therefore, the layer having the composition is epitaxially grown. 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. 5 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 epitaxial layer 22 on the n-type GaP substrate 21. In this case, a composition-change GaAsP layer 22a 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 and the epitaxial layer does not occur. A constant composition N-doped GaAsP layer 22c doped with nitrogen (N) is formed as a trap. In subsequent processing steps, high concentration of zinc is diffused by thermal diffusion to form a p-type layer 23 of about 4 to 10 μm on the surface of the epitaxial layer. Thereby, a good ohmic contact can be stably obtained.

Here, since the thermal diffusion method can process several tens to hundreds of epitaxial wafers at a time and is advantageous in terms of cost, in general, only the n-type layer is grown by vapor deposition and then thermal diffusion is performed. A p-type layer is formed by the method.
As a result, an LED can be stably obtained, but the carrier concentration of the p-type layer at the pn junction becomes too high, increasing the light absorption, leading to a decrease in the light output of the LED. In addition, the pn junction is damaged by heat and the crystal quality of the epitaxial layer is deteriorated. Although these problems can be solved by significantly lowering the diffusion temperature, the thickness of the p-type layer becomes too thin, and it is difficult to obtain good ohmic contact due to a decrease in the carrier concentration on the surface.

Therefore, the p-type layer has a structure composed of two layers, a first p-type layer and a second p-type layer, and the carrier concentration of the first p-type layer is 5 × 10 ^{17 to} 5 × 10 ¹⁸ / cm ^3. An epitaxial wafer is disclosed that achieves good ohmic contact and improved light output of the LED by forming an electrode on the surface of the second p-type layer with a carrier concentration of 5 × 10 ¹⁸ / cm ³ or more (patent) Reference 1). Also, the carrier concentration of the first p-type layer is 5 × 10 ^{16 to} 2.2 × 10 ¹⁸ / cm ^3, the carrier concentration of the second p-type layer is 5 × 10 ^{17 to} 4.5 × 10 ¹⁸ / cm ³ , and ( An epitaxial wafer in which the carrier concentration of the second p-type layer) ≧ 2 × (carrier concentration of the first p-type layer) is also disclosed (see Patent Document 2).

Japanese Patent No. 3143040 JP 2001-36136 A

  An object of the present invention is to provide an epitaxial wafer having an optimum p-type layer structure that enables further improvement of light output and formation of a good ohmic electrode as compared with the above-described epitaxial wafer.

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, and 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 the carrier concentration of the first p-type layer is 5 ×. Provided is an epitaxial wafer characterized in that 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ and the carrier concentration of the second p-type layer is 7 × 10 ^{18 to} 3 × 10 ¹⁹ / cm ³ .

As described above, in the present invention, the carrier concentration of the first p-type layer of the epitaxial wafer having at least the p-type layer and the n-type layer composed of the first p-type layer and the second p-type layer is set to 5 × 10 ^{16 to} 3 × 10 ^17. / Cm ³ , and the carrier concentration of the second p-type layer is 7 × 10 ^{18 to} 3 × 10 ¹⁹ / cm ³ .
By setting the carrier concentration of the first p-type layer in the above range, an optimum pn junction surface for obtaining a higher light output can be formed, and thus the light output can be improved as compared with the conventional case.
Moreover, since the fall of the carrier concentration on the surface can be suppressed by setting the carrier concentration of the second p-type layer in the above range, a good ohmic electrode can be stably formed. Therefore, generation | occurrence | production and increase of the forward voltage variation when it is set as LED can be suppressed. Moreover, since it can be set as the carrier concentration range which can suppress that light absorption increases, it can be set as the epitaxial wafer which improved the optical output.

The p-type layer has a third p-type layer between the first p-type layer and the second p-type layer, and the carrier concentration of the third p-type layer is 3 × 10 ¹⁷ to 1 × 10 ¹⁸ / cm. ³ is preferable.
As described above, by providing the third p-type layer having the carrier concentration in the above range between the first p-type layer and the second p-type layer, the carrier concentration distribution in the p-type layer is further improved in light output. Distribution can be obtained, and thus the light output can be further improved when the LED is used.

The silicon concentration of the n-type layer and the p-type layer is preferably 1 × 10 ^{14 to} 1.5 × 10 ¹⁵ / cm ³ .
Thus, by setting the silicon concentration as an impurity within the above range, the lifetime of the carrier can be improved, and the decrease in light emission luminance can be suppressed, and thus a higher quality LED. The epitaxial wafer can be made as follows.

The first p-type layer preferably has a concentration distribution in which the carrier concentration gradually increases in the concentration range of 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ from the substrate side to the surface side.
As described above, the carrier concentration of the first p-type layer is not rapidly increased, but is gradually increased in the concentration range of 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ , thereby causing a difference in lattice constant. By further suppressing the occurrence of lattice distortion, it is possible to suppress the crystallinity of the first p-type layer from being lowered, and thus the manufacturing yield can be improved.

Moreover, it is preferable that the layer thickness of the said 1st p-type layer is 4-50 micrometers.
By setting the thickness of the first p-type layer in the range of 4 to 50 μm in this way, a sufficient current diffusion layer can be secured in the case of an LED, and thus the current is sufficiently spread. Can be further increased.

The n-type layer and the p-type layer may be GaAs _1-x P _x (0.45 <x <1), and the substrate may be GaP.
As described above, since the epitaxial wafer of the present invention has a carrier concentration distribution structure that can improve the optical output as compared with the conventional one, it is conventionally used as an n-type layer or a p-type layer as described above. The composition can be made of GaAsP with a good composition, and the substrate can be made of GaP, which is highly useful.

Further, it is preferable that at least one of the n-type layer and the p-type layer 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. It can be an epitaxial wafer.

The p-type dopant of the p-type layer may be zinc, magnesium, or both.
Examples of the p-type dopant include zinc and magnesium. An organometallic compound such as dimethylzinc (DMZn) can be supplied into the reactor. A high carrier concentration can be obtained, and the configuration of the carrier concentration and the layer thickness of the present invention can be realized only by vapor phase growth.

The n-type layer and the p-type layer are preferably formed by a hydride method.
Thus, an epitaxial wafer having a high-purity and high-quality n-type layer and p-type layer can be obtained by forming an epitaxial wafer having an n-type layer and a p-type layer formed by a hydride method that is rich in mass productivity. it can.

  As described above, since the epitaxial wafer of the present invention has a structure in which the p-type layer of the epitaxial wafer having a pn junction has at least two stages of carrier concentration, a high light output is achieved by suppressing the carrier concentration on the pn junction side. Can be obtained. Further, by increasing the carrier concentration on the surface side (the second p-type layer side), it is possible to obtain a concentration range in which good ohmic contact can be obtained. Can be.

It is the schematic which shows an example of a structure of the epitaxial wafer of this invention. It is a figure when the optical output with respect to the carrier concentration of the 1st p-type layer at the time of making the epitaxial wafer of the Example and comparative example of this invention into LED is evaluated. It is the figure which showed the relationship with the electric current when a voltage is applied to the electrode of the surface of the epitaxial wafer of the Example of this invention, and a comparative example. It is the relationship of the afterglow rate with respect to the light emission time at the time of making the epitaxial wafer in an Example into LED. It is the schematic which shows an example of a structure of the conventional epitaxial wafer.

Hereinafter, the present invention will be described more specifically.
As described above, the development of an epitaxial wafer having an optimum p-type layer structure capable of further improving the light output and forming a good ohmic electrode as compared with the prior art has been awaited.

  Therefore, as a result of intensive studies, the present inventors can stably realize a good ohmic contact by optimizing the carrier concentration, which is the biggest factor that determines the characteristics of the LED, and more than ever. It was discovered that the light output of the LED was improved by 30% or more, and the present invention was completed.

  Hereinafter, the present invention will be described in detail with reference to FIG. 1, but the present invention is not limited thereto. FIG. 1 is a schematic view showing an example of the configuration of the epitaxial wafer of the present invention.

In FIG. 1, an epitaxial wafer 10 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. The n-type layer 12 and the p-type layer 13 are made of GaAsP or GaP. The p-type layer 13 includes at least a first p-type layer 13a and a second p-type layer 13b above the first p-type layer 13a. Have. The carrier concentration of the first p-type layer 13a is in the range of 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ , and the carrier concentration of the second p-type layer 13b is 7 × 10 ^{18 to} 3 × 10 ¹⁹ / cm ^3. Yes.
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.

Thus, in an epitaxial wafer having an n-type layer and a p-type layer composed of at least a first p-type layer and a second p-type layer, the carrier concentration of the first p-type layer is 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm. ^3. The carrier concentration of the second p-type layer is set to 7 × 10 ^{18 to} 3 × 10 ¹⁹ / cm ³ .
By setting the carrier concentration of the first p-type layer 13a to 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ , a pn junction surface capable of obtaining a higher light output can be obtained. The emission intensity can be increased compared to the conventional case. When the carrier concentration of the first p-type layer 13a is smaller than 5 × 10 ¹⁶ / cm ³ or larger than 3 × 10 ¹⁷ / cm ³ , the emission intensity cannot be increased sufficiently. The carrier concentration is in the above range.
In addition, by setting the carrier concentration of the second p-type layer 13b to 7 × 10 ^{18 to} 3 × 10 ¹⁹ / cm ³ , good ohmic contact can be obtained when the electrode is formed. When the carrier concentration of the second p-type layer 13b is smaller than 7 × 10 ¹⁸ / cm ³ , good ohmic contact cannot be obtained, and when it is larger than 3 × 10 ¹⁹ / cm ^3, it is difficult to produce an epitaxial wafer. Therefore, the carrier concentration of the second p-type layer 13b is in the above range.

  The substrate 11 desirably has a structure of at least a single crystal substrate 11a and a substrate buffer layer 11b. With such a structure, when the n-type layer 12 is formed on the substrate 11 by the epitaxial growth method, the composition of the substrate 11 and the n-type layer 12 is different, so that crystal defects due to the difference in lattice constant are introduced. It can be suppressed.

Here, as shown in FIG. 1B, the third p-type having a carrier concentration of 3 × 10 ¹⁷ to 1 × 10 ¹⁸ / cm ³ between the first p-type layer 13 a and the second p-type layer 13 b of the p-type layer 13. It may have a layer 13c.
Thus, by providing the third p-type layer having a carrier concentration in the range of 3 × 10 ¹⁷ to 1 × 10 ¹⁸ / cm ³ between the first p-type layer and the second p-type layer, The carrier concentration distribution can be a distribution that can further improve the light output, and thus the light output can be improved when the LED is used.

Further, the silicon concentration of the n-type layer 12 and the p-type layer 13 can be in the range of 1 × 10 ^{14 to} 1.5 × 10 ¹⁵ / cm ³ .
Thus, the carrier lifetime can be improved by setting the silicon concentration as an impurity within the above-described range. Moreover, the fall of light-emitting luminance can be suppressed, Therefore It can be set as the epitaxial wafer which can be set as LED with higher quality and long life.
With respect to the method of adjusting the silicon concentration within the above range, for example, as disclosed in Japanese Patent Application Laid-Open No. 2002-255696, the moisture content of HCl gas introduced into the reaction vessel may be 5 ppm or less immediately before the introduction. Can be mentioned.

Furthermore, the first p-type layer 13a has a concentration distribution in which the carrier concentration gradually increases in the concentration range of 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ from the substrate 11 side toward the surface side of the epitaxial wafer 10. Can do.
Thus, the carrier concentration of the first p-type layer is not increased rapidly, but is gradually increased, thereby further suppressing the occurrence of lattice distortion due to the difference in lattice constant, thereby reducing the first p-type layer. It can suppress that the crystallinity of a layer falls and can further improve an optical output.

And the layer thickness of the 1st p-type layer 13a can be made into the range of 4-50 micrometers.
By setting the thickness of the first p-type layer in the range of 4 to 50 μm in this way, the current can be sufficiently expanded when the LED is used, so that the light output can be further increased.

The n-type layer 12 and the p-type layer 13 are GaAs _1-x P _x (0.45 <x <1), and the substrate 11 can be made of GaP.
Thus, the epitaxial wafer of the present invention has a carrier concentration distribution structure that can improve the optical output as compared with the conventional one, and other configurations can be the same as the conventional one. 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, at least one of the n-type layer 12 and the p-type layer 13 can be 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. It can be an epitaxial wafer.

Furthermore, the p-type dopant of the p-type layer 13 can be zinc or magnesium, or both.
Although it does not specifically limit as a p-type dopant, Zinc, magnesium, etc. are mentioned. For example, it can dope by supplying organometallic compounds, such as a dimethyl zinc (DMZn), in a reactor. A high carrier concentration can be obtained, and the configuration of the carrier concentration and the layer thickness of the present invention can be realized only by vapor phase growth.

The n-type layer 12 and the p-type layer 13 can be formed by a hydride method.
Vapor phase epitaxy is effective for metal organic vapor phase (MO-CVD), molecular beam epitaxy (MBE), halogen transport, etc., but the hydride method is particularly suitable for mass production and yields high purity crystals. This is preferable.

  Thus, according to the epitaxial wafer of the present invention, since the p-type layer of the epitaxial wafer having a pn junction has a structure having at least two stages of carrier concentrations, a high light output is achieved by suppressing the carrier concentration on the pn junction side. Can be obtained. In addition, a good ohmic contact can be obtained by increasing the carrier concentration on the surface side (second p-type layer side). From the above, when the LED is used, the light output can be strong.

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. As the GaP substrate, tellurium (Te) is added at ³ to 10 × 10 ¹⁷ / cm ^{3, and a} GaP substrate having a diameter of 50 mm and a surface deviated by 10 ° in the [011] direction from the (100) plane is used. Were placed on the holder at the same time, and the holder was rotated three 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 kept constant at 800 ° C. and 930 ° C., respectively, GaAs _1-x P _{x having} a peak emission wavelength of 585 ± 10 nm The vapor phase growth of the epitaxial film was started.

First, hydrogen sulfide gas (H ₂ S), which is an n-type impurity diluted with hydrogen gas to a concentration of 50 ppm, is introduced at a rate of 328 sccm per minute to generate 118 sccm per minute as a group III element component raw material of the periodic table. High-purity hydrogen chloride gas (HCl) was blown into the Ga reservoir in the quartz boat at a rate of 118 sccm per minute and was blown out from the upper surface of the Ga reservoir. On the other hand, while introducing high-purity hydrogen phosphide gas (PH ₃ ) at 49 sccm per minute as a group V element component of the periodic table, a GaP buffer layer as the first layer is grown on the GaP single crystal substrate for 45 minutes. I let you.

Next, without changing the introduction amount of HCl, the introduction amount of high-purity hydrogen arsenide gas (AsH ₃ ) is gradually increased from 0 sccm per minute to 4.7 sccm per minute, and at the same time, the introduction amount of H ₂ S is increased. A second GaAs _1-x P _x epitaxial layer was grown on the first GaP buffer layer over 42 minutes (n-type layer−) at a rate of 191 sccm / min, the amount of PH ₃ introduced was reduced to 47 sccm / min. Composition change layer).

Next, without changing the introduction amounts of HCl, AsH ₃ , and PH ₃ , the introduction amount of H ₂ S is gradually decreased from 191 sccm / min to 65 sccm / min, and the third GaAs _1-x P is added over 32 minutes. _{An x} epitaxial layer was grown on the second GaAs _1-x P _x epitaxial layer (n-type layer-constant composition layer).

For the next 30 minutes, the introduction amount of HCl, PH ₃ , AsH ₃ is not changed, and the introduction amount is gradually increased to 161 sccm per minute for addition of nitrogen iso-electronic trap, and high purity ammonia gas (NH ₃ ) is added. And at the same time, the introduction of H ₂ S gas was stopped, and then the fourth GaAs _1-x P _x epitaxial layer was grown on the third GaAs _1-x P _x epitaxial layer (n-type layer— Nitrogen concentration increasing layer). The nitrogen doping amount at this time was 3 × 10 ¹⁸ / cm ³ .

Introducing the fifth GaAs _1-x P _x epitaxial layer on the fourth GaAs _1-x P _x epitaxial layer while introducing the same amount of HCl, PH ₃ , AsH ₃ and NH _{3 for} the next 30 minutes. Growing (n-type layer-nitrogen concentration constant composition layer).

Then, for the next 40 minutes, without changing the amount of HCl, PH ₃ , AsH ₃ , and NH ₃ , DMZn gas diluted to 0.4% with H ₂ gas was introduced as a p-type dopant at 1.7 sccm per minute. A sixth p-type GaAs _1-x P _x epitaxial layer was grown on the fifth GaAs _1-x P _x epitaxial layer (first p-type layer).

Then, in the final 30 minutes, the seventh p-type GaAs ₁ was introduced without changing the amount of HCl, PH ₃ , AsH ₃ , while the DMZn gas introduction rate was 200 sccm / min and the introduction of NH ₃ was stopped. the _-x P _x epitaxial layer is grown to a 6 _{GaAs 1-x P} x epitaxial layer on to complete the vapor phase growth (a 2p-type layer).
The film thicknesses of the first p-type layer and the second p-type layer were 6 μm and 4 μm, respectively.
The carrier concentration of the p-type layer was 2.3 × 10 ¹⁷ / cm ^{3 for} the first p-type layer and 2 × 10 ¹⁹ / cm ³ for the second p-type layer.

The produced epitaxial wafer was evaluated as follows.
First, in order to evaluate the carrier concentration in the p-type layer of the produced epitaxial wafer, the following evaluation was performed.
A chip of about 1 cm square was cut out from the central portion of the produced epitaxial wafer, and the thickness of the p-type layer was measured by SEM. Thereafter, electrodes were attached to the four corners of the cut chip, and the carrier concentration was measured by Hall measurement. In addition, an electrical characteristic curve was created to evaluate ohmic properties.
Next, in order to evaluate the light output, the following procedure was evaluated.
The produced epitaxial wafer was taken out and backside lapping was performed. Thereafter, an n-type electrode was formed on the back surface of the wafer, and a p-type electrode was formed on the epilayer on the surface. And it cut | disconnected to Chip size with a 300 micrometer pitch. Thereafter, a total of 6 chips were taken out from the outer peripheral side of the wafer in the vicinity of 5 mm (OF portion and anti-OF portion) and 2 from 3 locations in the center of the wafer. A lamp was produced from the removed chip. Thereafter, the omnidirectional light output was measured with an integrating sphere when a direct current of 20 mA was passed through a lamp manufactured at room temperature and normal humidity. The afterglow ratio is measured by applying 95 mA DC current at room temperature and normal humidity to the lamp for which measurement of the omnidirectional light output has been completed. The output was measured by using an integrating sphere and compared with the value immediately after the previous production.

(Example 2-4, Comparative Example 1-3)
In Example 1, the carrier concentration of the first p-type layer is 5 × 10 ¹⁶ / cm ³ (Example 2), 1.5 × 10 ¹⁷ / cm ³ (Example 3), and 3 × 10 ¹⁷ / cm ^{3, respectively.} (Example 4), 6 × 10 ¹⁷ / cm ³ (Comparative Example 1), 3 × 10 ¹⁶ / cm ³ (Comparative Example 2), DMZn gas to be 1 × 10 ¹⁸ / cm ³ (Comparative Example 3) An epitaxial wafer was prepared under the same conditions as in Example 1 except that the first p-type layer was formed by adjusting the amount of introduced, and the same evaluation was performed. FIG. 2 shows the result of evaluating the optical output of each epitaxial wafer at this time.

As shown in FIG. 2, when the first p-type layer has a carrier concentration of 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ and each of the epitaxial wafers of Example 2-4 is an LED, the emission intensity is 0. The emission intensity exceeded 04 mW, and the emission intensity was higher than that of Comparative Example 1 (0.035 mW) and Comparative Example 3 (0.027 mW), which are conventional ranges. In addition, it was found that the emission intensity of the LED was weakened in the emission intensity (0.035 mW) of Comparative Example 2 where the carrier concentration was 3 × 10 ¹⁶ / cm ³ because the carrier concentration of the layer was low. .

(Examples 5, 6, 7 and Comparative Example 4)
In Example 1, the carrier concentration of the second p-type layer is 1 × 10 ¹⁹ / cm ³ (Example 5), 7 × 10 ¹⁸ / cm ³ (Example 6), and 3 × 10 ¹⁹ / cm ³ (implementation). Example 7) Epitaxial wafer under the same conditions as in Example 1 except that the second p-type layer was formed by adjusting the amount of DMZn gas introduced so as to be 5 × 10 ¹⁸ / cm ³ (Comparative Example 4). The same evaluation was performed. At this time, the electrical characteristic curve of each epitaxial wafer is shown in FIG.

Thus, when the carrier concentration of the second p-type layer is in the range of 7 × 10 ^{18 to} 3 × 10 ¹⁹ / cm ³ , a good ohmic electrode can be stably formed when an LED is formed. I understood. On the other hand, it was found that a good ohmic electrode could not be produced in Comparative Example 4 outside the above range.

(Example 8)
In Example 1, the amount of DMZn gas introduced when forming the first p-type layer was increased from 0.8 sccm / min to 4 sccm / min, and epitaxial growth was performed for 39 min. Thereafter, before forming the second p-type layer, the third p-type layer was formed by epitaxial growth for 40 minutes with the amount of DMZn gas introduced fixed at 4 sccm per minute. Thereafter, an epitaxial wafer was produced under the same conditions as in Example 1 except that the DMZn gas to be introduced was increased from 4 sccm / min to 200 sccm / min and the second p-type layer was formed for 40 minutes, and the same evaluation was performed. .

The carrier concentration of the p-type layer of Example 8 is 1 × 10 ¹⁷ / cm ^{3 for} the first p-type layer, 2 × 10 ¹⁹ / cm ^{3 for} the second p-type layer, and 5 × 10 ¹⁷ / cm for the ^third p-type layer. ³ . The thickness of each layer was 3 μm for the first p-type layer, 4 μm for the second p-type layer, and 10 μm for the third p-type layer.
The chip output when the epitaxial wafer of Example 8 is an LED is 0.067 (mW), about 1.4 times that of the epitaxial wafer of Example 1, and Comparative Example 1 which is a conventional epitaxial wafer. Is about 1.9 times, and it has been found that the light output when an LED is formed can be further improved by providing a third p-type layer between the first p-type layer and the second p-type layer.

Moreover, the figure which showed the relationship of the afterglow rate with respect to the light emission time at the time of making the epitaxial wafer of Example 1 and Example 8 into LED is shown in FIG.
As described above, it was found that the LEDs using the epitaxial wafers of Example 1 and Example 8 both have a slightly increased emission intensity even when the emission time exceeds 150 hours, and slightly increase. Therefore, according to the epitaxial wafer of this invention, it turned out that it can be set as high quality LED which can endure use for a long time.

  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.

DESCRIPTION OF SYMBOLS 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 layer, 13b ... second p-type layer, 13c ... third p-type layer,
21 ... GaP substrate, 22 ... n-type layer, 22a ... composition-change GaAsP layer, 22b ... constant composition GaAsP layer, 22c ... constant composition N-doped GaAsP layer, 23 ... p-type layer.

Claims (8)

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, and the p-type layer has at least a first p-type layer and a second p-type layer above the first p-type layer,
The carrier concentration of the first p-type layer is 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ , the carrier concentration of the second p-type layer is 7 × 10 ^{18 to} 3 × 10 ¹⁹ / cm ³ , and the n-type layer The epitaxial wafer, wherein the silicon concentration of the layer and the p-type layer is 1 × 10 ^{14 to} 1.5 × 10 ¹⁵ / cm ³ . The p-type layer has a third p-type layer between the first p-type layer and the second p-type layer, and the carrier concentration of the third p-type layer is 3 × 10 ¹⁷ to 1 × 10 ¹⁸ / cm ³ . The epitaxial wafer according to claim 1, wherein the epitaxial wafer is provided. The first p-type layer has a concentration distribution in which a carrier concentration gradually increases in a concentration range of 5 × 10 ^{16 to} 3 × 10 ¹⁷ / cm ³ from the substrate side to the surface side. The epitaxial wafer according to claim 2.   4. The epitaxial wafer according to claim 1, wherein a thickness of the first p-type layer is 4 to 50 μm. 5. The n-type layer and the p-type layer are GaAs _1-x P _x (0.45 <x <1), and the substrate is GaP. The epitaxial wafer according to claim 1.   The epitaxial wafer according to any one of claims 1 to 5, wherein at least one of the n-type layer and the p-type layer is doped with nitrogen.   The epitaxial wafer according to any one of claims 1 to 6, wherein the p-type dopant of the p-type layer is zinc, magnesium, or both.   The epitaxial wafer according to any one of claims 1 to 7, wherein the n-type layer and the p-type layer are formed by a hydride method.

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