JP2004096077A - Epitaxial substrate for compound semiconductor light emitting device, method of manufacturing the same, and light emitting device - Google Patents

Abstract

An object is to improve luminous efficiency without impairing a protective function of a light emitting layer.
A p-type layer having a three-layer structure including first to third layers is provided in contact with a light-emitting layer. An n-type AlGaN layer 9 as a first layer functions as a protective layer, a GaN: Mg layer 11 as a third layer functions as a contact layer, and an AlGaN: Mg layer 10 as a second layer is intermediate between these layers. And the intermediate layer is provided. By providing this intermediate layer, even if the thickness of the n-type AlGaN layer 9 is reduced, the InGaN layer 8 can be sufficiently protected from heat during the growth of the layer above it. As a result, the GaN: Mg layer 11 is brought closer to the light emitting layer 7 so that the efficiency of hole injection into the light emitting layer 7 can be increased, and the light emitting efficiency can be improved.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an epitaxial substrate for a compound semiconductor light emitting device, which is formed by laminating nitride-based group III-V compound semiconductor thin films, a method for manufacturing the same, and a light emitting device.
[0002]
[Prior art]
As a material of a light emitting element such as an ultraviolet, blue or green light emitting diode or an ultraviolet, blue or green laser diode, a general formula In_xGa_yAl_zA group 3-5 compound semiconductor represented by N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) is known. Hereinafter, x, y, and z in this general formula may be referred to as an InN mixed crystal ratio, a GaN mixed crystal ratio, and an AlN mixed crystal ratio, respectively. Among the group III-V compound semiconductors, those containing 10% or more of InN at a mixed crystal ratio are particularly important for display applications because the emission wavelength in the visible region can be adjusted according to the InN mixed crystal ratio.
[0003]
By the way, it is known that physical properties of the compound semiconductor greatly change depending on a mixed crystal ratio. For example, a GaAlN-based mixed crystal that does not contain In has excellent thermal stability, and a growth temperature of 1000 ° C. or higher can be used to obtain a good crystal. On the other hand, an InGaAlN-based material containing In does not have sufficient thermal stability depending on the InN mixed crystal ratio, and it is generally practiced to grow the compound semiconductor at a relatively low temperature of about 800 ° C. Has been done. For this reason, an InGaAlN-based mixed crystal growth layer, which is important as a growth layer constituting a light-emitting layer of a light-emitting element in the visible light region, is grown at a low temperature, and thermal stability is often insufficient.
[0004]
On the other hand, after the light emitting layer is grown, a p-type layer is grown thereon. However, since the growth of the p-type layer needs to be at a higher growth temperature, it is thermally unstable from this high growth temperature. In order to protect a certain light-emitting layer, a method of once growing a heat-resistant protective layer on the light-emitting layer and then growing a p-type layer on the protective layer at a high growth temperature has been adopted.
[0005]
This protective layer is an important layer that has a significant effect on not only the above-described protective function of the light emitting layer but also the light emitting characteristics of the light emitting element. That is, holes are effectively injected from the p-type layer formed on the protective layer into the light emitting layer, and the electrons injected into the light emitting layer from the lower side of the light emitting layer and the holes cause emission recombination deeply. Are involved. Therefore, in order to increase the efficiency of injecting holes from the p-type layer into the light emitting layer, it is desirable that the protective layer has p-type conductivity or n-type conductivity with a low carrier concentration.
[0006]
However, when the protective layer containing Al is grown at the same temperature as the growth temperature of the light-emitting layer, the protective layer does not have sufficient crystallinity and contains many crystal defects and usually exhibits n-type conductivity with a high carrier concentration. . For this reason, there is a problem that the efficiency of injecting holes into the light emitting layer is reduced, and it is difficult to obtain high light emitting efficiency.
[0007]
That is, the growth conditions of the protective layer and the p-type layer need to be optimized from the two viewpoints of strengthening the protective function and maintaining the hole injection efficiency. Therefore, the protective layer thermally protects the light emitting layer. At the same time, it is required to control conductivity in order to efficiently inject holes from the p-type layer into the light emitting layer while maintaining high crystal quality.
[0008]
In order to solve this requirement, conventionally, (1) a method of growing a p-type GaN layer after growing an AlGaN protective layer and then raising the temperature to a growth temperature of a p-type GaN layer (contact layer); A method is known in which the protective layer is a GaN layer that does not contain Al and can be grown at a low temperature, thereby improving the crystallinity of the protective layer and slightly lowering the background-type carrier concentration.
[0009]
[Problems to be solved by the invention]
However, according to the conventional method (1), the protective layer needs to have a certain thickness or more in order to prevent thermal degradation during the growth of the p-type GaN layer (contact layer). There is a problem that the junction interface is separated from the light emitting layer, and the efficiency of hole injection into the light emitting layer is reduced.
[0010]
Further, as the Al composition decreases, the function of the AlGaN layer as a protective layer decreases. Therefore, in the case of the conventional method (2) using GaN as the protective layer, the film thickness must also be increased. However, improvement in luminous efficiency cannot be expected.
[0011]
An object of the present invention is to provide an epitaxial substrate for a compound semiconductor light-emitting device, a method for manufacturing the same, and a light-emitting device using the same, which can solve the above-mentioned problems in the prior art.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide an epitaxial substrate for a compound semiconductor light emitting device and a method of manufacturing the same, which can enhance the efficiency of hole injection into the light emitting layer without impairing the protective function of the light emitting layer by the protective layer. Another object of the present invention is to provide a light emitting element.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides an intermediate layer between a protective layer and a p-type layer so that a sufficient protective function can be obtained even when the protective layer is thinned. Thereby, the p-type layer is brought closer to the light emitting layer, the hole injection efficiency is increased, and the luminous efficiency is improved.
[0014]
According to the first aspect of the present invention, in the epitaxial substrate for a compound semiconductor light emitting device including the light emitting layer having a double hetero structure having a pn junction, the layer structure on the p-type layer side provided in contact with the light emitting layer is as follows. In order from the layer in contact with the light emitting layer, In_xAl_yGa_zAn n-type first layer represented by N (x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1);_uAl_vGa_wA p-type second layer represented by N (u + v + w = 1, 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1);_pAl_qGa_rA p-type third layer represented by N (p + q + r = 1, 0 ≦ p ≦ 1, 0 ≦ q ≦ 1, 0 ≦ r ≦ 1), and these three layers are stacked in contact with each other. There has been proposed an epitaxial substrate for a compound semiconductor light emitting device, characterized in that:
[0015]
According to a second aspect of the present invention, in the first aspect, the first layer has a thickness d.₁(Å) is 5 ≦ d₁≦ 200, and the thickness d of the second layer₂(Å) is 5 ≦ d₂An epitaxial substrate for a compound semiconductor light emitting device having a range of ≦ 30000 is proposed.
[0016]
According to a third aspect of the present invention, there is provided a method for manufacturing an epitaxial substrate for a compound semiconductor light emitting device according to the first or second aspect,
Growth temperature T of the first layer₁And the growth temperature T of the second layer₂Between
T₁≤T₂
A method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device, characterized by satisfying the following relationship, is proposed.
[0017]
According to the invention of claim 4, in the invention of claim 3, the growth temperature T of the second layer is set.₂(° C.) and the thickness d of the second layer₂Between (式) and
5 ≦ d₂≦ 30000 (900 ≦ T₂≤ $ 1150)
T₂≧ 0.4d₂+700 (700 ≦ T₂<$ 900)
A method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device, wherein the second layer is grown so as to satisfy the relationship represented by
[0018]
According to the invention of claim 5, in the invention of claim 3 or 4, after the growth of the first layer is completed, the second layer and the third layer are formed by a regrowth method. A method for manufacturing an epitaxial substrate for a compound semiconductor light emitting device is proposed.
[0019]
According to the invention of claim 6, a light emitting device using the epitaxial substrate for a compound semiconductor light emitting device according to claim 1 or 2 is proposed.
[0020]
According to a seventh aspect of the present invention, there is provided a light emitting device manufactured by using the manufacturing method according to the third, fourth or fifth aspect.
[0021]
According to the invention of claim 8, in the epitaxial substrate for a compound semiconductor light emitting device including a light emitting layer having a double hetero structure having a pn junction,
The layer structure on the p-type layer side provided in contact with the light-emitting layer has an order of In from the layer in contact with the light-emitting layer._xAl_yGa_zAn n-type first layer represented by N (x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1);_uAl_vGa_wAn n-type second layer represented by N (u + v + w = 1, 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1);_pAl_qGa_rA p-type third layer represented by N (p + q + r = 1, 0 ≦ p ≦ 1, 0 ≦ q ≦ 1, 0 ≦ r ≦ 1), and these three layers are stacked in contact with each other There has been proposed an epitaxial substrate for a compound semiconductor light emitting device, wherein
[0022]
According to the ninth aspect, in the eighth aspect, the p-type dopant concentration of the second layer is 1 × 10 5.¹⁷cm^-3More than 1 × 10²¹cm^-3And the n-type carrier concentration of the second layer is 1 × 10¹⁹cm^-3The following epitaxial substrate for compound semiconductor light emitting device is proposed.
[0023]
According to the invention of claim 10, in the invention of claim 8 or 9, the thickness d of the first layer is d.₁(Å) is 5 ≦ d₁≦ 200, and the thickness d of the second layer₂(Å) is 5 ≦ d₂An epitaxial substrate for a compound semiconductor light emitting device having a range of ≦ 500 is proposed.
[0024]
According to the eleventh aspect, in the method for manufacturing an epitaxial substrate for a compound semiconductor light emitting device according to the eighth, ninth, or tenth aspect,
Growth temperature T of the first layer₁And the growth temperature T of the second layer₂Between
T₁≤T₂
A method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device, characterized by satisfying the following relationship, is proposed.
[0025]
According to a twelfth aspect, in the eleventh aspect, the growth temperature T of the second layer is set.₂(° C) and layer thickness d₂Between (式) and
T₂≧ 0.4d₂+ 700 (5 ≦ d₂≦ 500)
1150 ≧ T₂≧ 700
A method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device, wherein the second layer is grown so as to satisfy the relationship represented by
[0026]
According to a thirteenth aspect of the present invention, in the eleventh or twelfth aspect, the second layer and the third layer are formed by a regrowth method after the growth of the first layer is completed. A method for manufacturing an epitaxial substrate for a compound semiconductor light emitting device is proposed.
[0027]
According to a fourteenth aspect of the present invention, there is provided a light emitting device using the compound semiconductor light emitting device epitaxial substrate according to the eighth, ninth, or tenth aspect.
[0028]
According to a fifteenth aspect of the present invention, there is provided a light emitting device manufactured using the manufacturing method of the eleventh, twelfth, or thirteenth aspect.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
[0030]
FIG. 1 is a layer structure diagram of a light-emitting element showing an example of an embodiment of the present invention. The light emitting device shown in FIG. 1 is manufactured using the epitaxial substrate for a compound semiconductor light emitting device according to the present invention.
[0031]
The layer structure of the light emitting device 20 will be described. On the sapphire substrate 1, a low-temperature GaN buffer layer 2, an n-type GaN: Si layer 3, an n-type GaN: Si layer 4, and a GaN layer 5 are formed by MOVPE (Metal Organic Vapor Phase). The layers are sequentially stacked by epitaxial growth according to the (Epitaxy) method. An AlGaN layer 6 is formed on the GaN layer 5, and a light emitting layer 7 is formed on the AlGaN layer 6. The AlGaN layer 6 and the light emitting layer 7 are also sequentially stacked by epitaxial growth by MOVPE.
[0032]
In this embodiment, a sapphire substrate is used as a substrate. However, there is no particular limitation on a substrate to be used. In addition to sapphire, for example, SiC, a GaN substrate having a reduced dislocation density by buried growth, a GaN substrate on Si , A free standing GaN substrate, an AlN substrate, or the like can be used. The buffer layer is not limited to the low-temperature GaN buffer layer. For example, a low-temperature AlN buffer, a low-temperature AlGaN buffer, a low-temperature InGaAlN buffer, or the like can be used.
[0033]
The light emitting layer 7 has a double hetero structure having a pn junction formed by growing an InGaN layer 8 on a multiple quantum well structure in which an InGaN layer 7A and a GaN layer 7B are repeatedly formed to have four composition lengths. The growth temperature of the InGaN layer 8 is 780 ° C. On the light-emitting layer 7, a layer on the p-type layer side of a three-layer structure including a first layer, a second layer, and a third layer is provided in contact with the light-emitting layer 7. That is, in the present embodiment, the layer structure on the p-type layer side provided in contact with the light-emitting layer 7 includes an n-type AlGaN layer (first layer) 9 and an AlGaN: Mg layer in order from the layer in contact with the light-emitting layer 7. (A second layer) 10 and a GaN: Mg layer (a third layer) 11, and these three layers are stacked in contact with each other as shown in the figure.
[0034]
Here, the first layer is an n-type AlGaN layer 9 grown by MOVPE at the same temperature as 780 ° C., which is the growth temperature of the InGaN layer 8. The second layer is an AlGaN: Mg layer 10, which is grown by MOVPE at 1000 ° C. higher than the growth temperature of the n-type AlGaN layer 9. The third layer is a GaN: Mg layer 11, which is grown by MOVPE at 1040 ° C., which is higher than the growth temperature of the AlGaN: Mg layer 10.
[0035]
In the present embodiment, the AlGaN: Mg layer 10 as the second layer and the GaN: Mg layer 11 as the third layer are p-type layers having low resistance. An ohmic n-electrode 12 is provided on the n-type GaN: Si layer 4, and an ohmic p-electrode 13 is provided on the GaN: Mg layer 11.
[0036]
The light emitting element 20 has the above-described layer structure. The light emitting element 20 is manufactured first by manufacturing an epitaxial substrate for a compound semiconductor light emitting element in which the above-described layer structure is formed on the sapphire substrate 1. It was manufactured in the form as shown in FIG. 1 using an epitaxial substrate.
[0037]
The light-emitting element 20 is provided with a three-layer structure including the first to third layers on the p-type layer side in contact with the light-emitting layer 7, thereby protecting the n-type AlGaN layer 9 as the first layer. The GaN: Mg layer 11, which is the third layer, functions as a contact layer, and the AlGaN: Mg layer 10, which is the second layer, is provided between them to form an intermediate layer. As a result, even if the thickness of the n-type AlGaN layer 9 is reduced, the InGaN layer 8 can be sufficiently protected from heat during the growth of the layer above it, whereby the GaN: Mg layer 11 , The efficiency of hole injection into the light emitting layer 7 can be increased, and the luminous efficiency can be improved.
[0038]
In the embodiment shown in FIG. 1, the conductivity of the AlGaN: Mg layer 10 as the second layer is p-type, but the conductivity of the second layer is not limited to p-type. , N-type. The second layer can be an n-type compound semiconductor layer by changing the growth conditions. Even when the n-type AlGaN: Mg layer is used as the second layer instead of the p-type AlGaN: Mg layer 10, the InGaN layer is formed in the same manner as in the embodiment shown in FIG. 7A and 8 can be effectively protected from heat during the growth of the layer above them, and the efficiency of hole injection into the light-emitting layer 7 can be increased to improve the luminous efficiency.
[0039]
Next, each layer on the p-type layer side including the first to third layers will be generally described.
[0040]
Since the first layer is a layer provided on the p-type layer side of the light-emitting layer 7, it is originally desirable to have p-type or low-concentration n-type conductivity in order to improve luminous efficiency. However, the growth temperature of the first layer is usually set to the same relatively low temperature (780 ° C. in the present embodiment) as that of the light emitting layer 7 so as not to deteriorate the crystallinity of the light emitting layer 7 containing In having low heat resistance. Therefore, it has n-type conductivity due to n-type carriers considered to be derived from crystal defects without doping. It is practically very difficult to compensate for n-type charges by using a p-type dopant to form a low-concentration n-type or p-type layer due to a low growth temperature.
[0041]
It is also known as a so-called memory effect that the p-type dopant material easily remains in the reaction furnace and may adversely affect the quality of a light-emitting layer formed by growth subsequent to growth using the p-type dopant material. . Therefore, it is necessary to design a reactor having a small memory effect of the p-type dopant and use a plurality of furnaces including a furnace using the p-type dopant material and a furnace not using the p-type dopant material for mainly growing the light emitting layer. It is effective to carry out crystal growth. Since the n-type AlGaN layer 9 as the first layer is a protective layer that grows next to the light-emitting layer 7, it is preferable that the n-type AlGaN layer 9 be grown in a furnace that does not use a p-type dopant material. If the p-type dopant material is not used, the first layer is likely to be n-type for the above-described reason. Therefore, in the present embodiment, the n-type AlGaN layer 9 as the first layer is n-type. However, as can be seen from the above description, the conductivity of the first layer can be p-type depending on the crystal growth conditions.
[0042]
If the Al composition of the first layer is too high, crystallinity such as surface flatness is impaired. If the Al composition is too low, the protective function is reduced, the required layer thickness is increased, and the light emission efficiency is impaired. It is preferable that the Al composition be approximately in the range of 0 to 0.5. The preferable range of the Al composition depends on the layer thickness of the first layer and the growth temperature of the second layer. The smaller the thickness of the first layer and the higher the growth temperature of the second layer, the higher the Al composition. To increase the protection function.
[0043]
If the thickness of the first layer is too large, the crystallinity is impaired, and the hole injection efficiency is reduced, so that the luminous efficiency is reduced. If the thickness is too small, the protective function is reduced and the luminescent layer is deteriorated. There is a range. The thickness of the first layer is preferably in the range of approximately 5 ° to 200 °. The preferable range of the layer thickness depends on the Al composition of the first layer and the growth temperature of the second layer. The smaller the Al composition of the first layer, the larger the layer thickness in order to exhibit a sufficient protective function. It is necessary to increase the layer thickness as the growth temperature of the second layer increases, in order to prevent deterioration of the light emitting layer due to high temperature.
[0044]
Next, the second layer will be described. The Al composition of the second layer is preferably higher from the viewpoint of improving carrier emission properties by making carrier confinement effective so that the potential barrier in the conduction band can be increased with respect to the light emitting layer. However, if the Al composition of the second layer is too high, the crystallinity is impaired, and it becomes difficult to realize p-type or low-concentration n-type, thereby impairing hole injection efficiency. Therefore, the Al composition of the second layer has a preferable range. The Al composition of the second layer is preferably in the range of approximately 0.001 to 0.3. The preferable range of the Al composition depends on the growth temperature, the supply amount of the p-type dopant, and the layer thickness. The lower the growth temperature, the more likely it becomes n-type due to crystal defects, and the lower the hole injection efficiency. To prevent this, it is necessary to keep the Al composition small and maintain good crystallinity. Similarly, the smaller the supply amount of the p-type dopant, the more easily it becomes n-type and the lower the hole injection efficiency. To prevent this, it is necessary to reduce the Al composition to suppress the n-type crystal. . As the layer thickness increases, the crystallinity may decrease due to an increase in strain due to lattice mismatch. Therefore, it is necessary to reduce the Al composition to prevent this.
[0045]
Next, the thickness of the second layer will be described. The second layer constitutes a second layer of a three-layered p-type layer provided on the light-emitting layer 7 side of the p-type layer, and the conductivity of the second layer is n-type. As described above, any p-type may be used. Therefore, here, the layer thickness of the second layer will be described while differentiating between the case where the conductivity of the second layer is n-type and the case where the conductivity of the second layer is p-type.
[0046]
If the layer thickness of the second layer is n-type, if the layer thickness is too large, the crystal quality is likely to be reduced, and the efficiency of hole injection into the light emitting layer 7 is reduced, which may impair the light emission efficiency. Basically, thinner is better, and there is a preferable range of the layer thickness. Also in the case where the second layer is p-type, if the layer thickness is too large, the crystal quality is impaired, so there is a preferable range of the layer thickness. However, in the case of the p-type, the influence on the luminous efficiency is not so remarkable as in the case of the n-type. Preferred layer thickness d for n-type₂Is approximately 5 to 500 degrees. Preferred layer thickness d for p-type₂Is approximately 5 to 30,000. Here, the layer thickness d₂If the thickness is too small, it will be difficult to ensure reproducibility in production, so a thickness of about 5 mm is considered necessary. The upper limit in the case of the n-type is experimentally determined as a range in which a decrease in optical output due to a decrease in hole injection efficiency does not increase. The upper limit in the case of the p-type is determined from the requirement that the crystal quality does not decrease or the range that the production efficiency does not decrease.
[0047]
The preferable range of the thickness of the second layer depends on the growth temperature of the second layer, the Al composition, and the supply amount of the p-type dopant. In the case of the n-type, the lower the growth temperature, the lower the supply amount of the p-type dopant, and the higher the Al composition, the higher the n-type carrier concentration, the lower the efficiency of hole injection into the light-emitting layer, and the lower the luminous efficiency. In some cases, the layer thickness must be reduced to prevent this. The x-axis is the layer thickness d of the second layer₂, The y-axis is the growth temperature T of the second layer₂Then, a region represented by the following equation is a preferable range of the layer thickness and the growth temperature of the second layer in the case of n-type.
5 ≦ d₂≤ 500
T₂≧ 0.4d₂+700
1150 ≧ T₂≧ 700
[0048]
In the case of the p-type, as the growth temperature is lower and the Al composition is higher, the crystal quality may be reduced. Therefore, it is necessary to reduce the layer thickness so as not to lower the luminous efficiency. The x-axis is the layer thickness d of the second layer₂, The y-axis is the growth temperature T of the second layer₂Then, a region represented by the following equation is a preferable range of the layer thickness and the growth temperature of the second layer in the case of the p-type.
0.4d₂+700 ≦ T₂≦ 1150 (5 ≦ d₂≦ 500)
900 ≦ T₂≦ {1150} (500 ≦ d₂≤30000)
A more preferable range of the thickness and the growth temperature of the second layer in the case of the p-type is a region represented by the following equation.
0.4d₂+700 ≦ T₂≦ 1100 (5 ≦ d₂≦ 500)
900 ≦ T₂≦ {1100} (500 ≦ d₂≤30000)
[0049]
Next, the conductivity control, carrier concentration, and growth temperature of the second layer will be described. Again, for the same reason as in the description of the layer thickness of the second layer, the case where the conductivity of the second layer is n-type and p-type is divided as necessary. The conductivity control of the second layer, the carrier concentration, and the growth temperature will be described.
[0050]
As described above, the conductivity of the second layer may be p-type or n-type. When the conductivity of the second layer is p-type, the preferred range of the carrier concentration is not particularly limited, and may be any range that can be technically realized.¹⁶cm³~ 1 × 10²⁰cm³It is. When the conductivity of the second layer is n-type, the preferable range of the carrier concentration is as small as possible so as not to impair the hole injection efficiency.¹⁴cm³~ 1 × 10¹⁹cm³, Preferably 1 × 10¹⁴cm³~ 1 × 10¹⁸cm³It is.
[0051]
The carrier concentration is controlled by the growth temperature, the II / III ratio (the supply ratio of the p-type dopant and the group III source, or the p-type dopant supply amount when the group III source supply is constant), and the V / III ratio (the group III 原料 source). And the ratio of the V group material).
[0052]
Regardless of whether the second layer is p-type or n-type, the higher the growth temperature is, the better the crystal quality is, and thus the easier it is to control the carrier concentration. In particular, in the case of n-type, the higher the growth temperature, the smaller the supply amount of p-type dopant required for conductivity control.
[0053]
The preferred ranges of the II / III ratio and the preferred V / III ratio are generally limited to numerical values because they greatly vary depending on conditions such as the shape and size of the reactor, the flow pattern of the raw material gas, the growth temperature and the pressure. There is no point in doing it. As a general tendency, the higher the growth temperature, the more preferable the range of the II / III ratio spreads to the smaller side.
[0054]
Next, the growth temperature of the second layer will be described in more detail. The growth temperature of the second layer is preferably as close as possible to the growth temperature of the light emitting layer 7 in order to maintain the protective function of the n-type AlGaN layer 9 as the first layer and not harm the light emitting layer 7. A higher growth temperature is better for improving the crystal quality and controlling the conductivity of the second layer, and therefore there is a preferable temperature range for the growth temperature of the second layer. The preferred temperature range is generally from 700 ° C to 1150 ° C.
[0055]
The preferable growth temperature range of the second layer changes depending on the thickness and the Al composition of the first layer, the Al composition of the second layer, and the supply amount of the p-type dopant. As the thickness of the first layer is larger and the Al composition of the first layer is larger, the function of protecting the light emitting layer is enhanced. Therefore, the preferable growth temperature range of the second layer is shifted to a higher side, and the second layer is Can be made into higher quality crystals. On the other hand, the higher the Al composition of the second layer, the more difficult the conductivity control becomes. Therefore, as the Al composition of the second layer increases, the preferable range of the growth temperature of the second layer is such that the conductivity control becomes more difficult. It is necessary to shift to a higher growth temperature side, which makes it easier. In addition, as the supply amount of the p-type dopant in the second layer is reduced, it becomes more difficult to obtain p-type in the second layer. Therefore, in order to obtain p-type or low-concentration n-type, the preferable growth temperature of the second layer is increased. There is a need to.
[0056]
When a light-emitting element is manufactured using a Group 3-5 compound semiconductor, a doping step of a p-type dopant is an indispensable step. However, the p-type dopant raw material remains in the reactor and causes a so-called memory effect, which adversely affects the next growth. Specifically, when a new substrate is set in the reactor and the next epitaxial growth step is performed, the crystallinity of the light emitting layer formed on this substrate due to the remaining p-type dopant material in the previous step In addition to the above, problems such as difficulty in controlling the p-type concentration are caused.
[0057]
In order to avoid these problems caused by the memory effect, an epitaxial substrate having a light emitting device structure as shown in FIG. A growth method, a so-called regrowth method can be used.
[0058]
Specifically, when manufacturing an epitaxial substrate for a compound semiconductor light emitting device having the layer structure shown in FIG. 1, after growing the n-type AlGaN layer 9 as the first layer, the substrate is once taken out of the reaction furnace, By growing the AlGaN: Mg layer 10 and subsequent layers, which are the second layer, in another reactor using a p-type dopant material, it is possible to avoid a memory effect and to produce an epitaxial substrate stably having good characteristics. it can.
[0059]
The GaN: Mg layer 11 formed as the third layer is a p-type layer for making ohmic contact with the n-type GaN layer 13. The significance of the present invention of providing a three-layered p-type layer on the InGaN layer 8 is that the n-type AlGaN layer 9 and the AlGaN: Mg layer, which are the first layer and the second layer, as described above. The tenth structure and growth conditions are to be defined, and the layers formed after the third layer may have any structure. Therefore, for example, the GaN: Mg layer 11 may have a single-layer structure, but may have a stacked structure including a plurality of layers with different p-type carrier concentrations or a stacked structure including a plurality of layers with different compositions. Further, a stacked structure in which the outermost surfaces of a plurality of layers are p-type thin film layers of high concentration may be used.
[0060]
【Example】
(Example 1)
The light emitting device having the layer structure shown in FIG. 1 was manufactured as follows by forming a film on a sapphire substrate by crystal growth using the MOVPE method. First, a sapphire substrate 1 is prepared, and an epitaxial substrate for a compound semiconductor light emitting device is manufactured. The sapphire substrate 1 is set in a MOVPE growth furnace, and NH₃And MO (TMG) and silane as raw materials,₂Was used as a carrier gas to grow a GaN thin film layer as a low-temperature GaN buffer layer 2, followed by growing an n-type GaN: Si layer 3 at 1040 ° C.
[0061]
Thereafter, the sapphire substrate 1 is once taken out of the MOVPE growth furnace, subjected to a predetermined inspection, returned to the MOVPE growth furnace again, and₃And MO (TMG, TMA, TMI) and silane as raw materials,₂Is used as a carrier gas to form an n-type GaN: Si layer 4 on the n-type GaN: Si layer 3 at a growth temperature of 1040 ° C., and further, an undoped GaN layer 5 on the n-type GaN: Si layer 4. Formed. After the formation of the undoped GaN layer 5, the reactor temperature was lowered to 780 ° C.₂Was used as a carrier gas to form an AlGaN layer 6, and further, an InGaN layer 8 was grown on a stack of four sets of an InGaN layer 7A and a GaN layer 7B to form a light emitting layer 7. After the growth of the InGaN layer 8, an n-type AlGaN layer 9 having an Al composition of 0.15 (undoped but n-type layer) was grown as the first layer by 110 °, and the substrate was taken out of the MOVPE growth furnace.
[0062]
Next, this substrate was set in another MOVPE growth furnace,₃And MO as raw materials, N₂Was used as a carrier gas, and an AlGaN: Mg layer 11 having an Al composition of 0.05 was grown as a second layer. Here, the supply amount of the Mg raw material EtCp2Mg was set at 600 sccm, and after growing at 250 ° C. at 1000 ° C., the reactor temperature was increased to 1040 ° C., and the GaN: Mg layer 11 was grown as the third layer. An epitaxial substrate for a compound semiconductor light emitting device was taken out of the growth furnace.
[0063]
The epitaxial substrate for a compound semiconductor light emitting device manufactured as described₂The AlGaN: Mg layer 10 (second layer) and the GaN: Mg layer 11 (third layer) were turned into low-resistance p-type layers by performing a heat treatment at 800 ° C. for 20 minutes in an atmosphere.
[0064]
Next, a p-electrode pattern was formed on the surface by photolithography, NiAu was deposited by vacuum evaporation, an electrode pattern was formed by lift-off, and a heat treatment was performed to produce an ohmic p-electrode 13. Next, a mask pattern was formed by photolithography, and etching was performed by dry etching so that the n-layer was exposed. After removing the mask, an n-electrode pattern was formed on the dry-etched surface by photolithography, Al was deposited by vacuum evaporation, and an electrode pattern was formed by lift-off to obtain an n-electrode 12. The electrode area of the p electrode 13 was 3.14 × 10^-4cm²It is.
[0065]
As described above, first, an epitaxial substrate for a compound semiconductor light emitting device is manufactured, and then a compound semiconductor light emitting device is manufactured using the epitaxial substrate, and voltage is applied to the light emitting device thus obtained to emit light in a wafer state. When the characteristics were examined, the luminous intensity was 1505 mcd at 20 mA in the forward direction, the leakage current was 0.25 nA at a reverse bias of 5 V, and excellent light emitting characteristics were exhibited.
[0066]
In order to evaluate the conductivity of the second layer grown under the above conditions, a second layer under the same growth conditions as described above was grown by about 0.3 μm on a sample obtained by growing undoped GaN on a sapphire substrate by about 3 μm. did. The conductivity type and carrier concentration of this sample were evaluated by a CV measurement method using an electrolytic solution.¹⁸cm^-3Met.
[0067]
(Examples 2 to 8, Comparative Examples 1 to 3)
A light emitting device was manufactured in the same manner as in Example 1 except that the growth temperature, the layer thickness, the Al composition, and the Mg supply amount were changed variously under the growth conditions of the AlGaN: Mg layer. FIG. 2 shows the growth conditions and characteristics of these light emitting devices.
In Examples 4, 6, 7, and 8, AlGaN: Mg, which is the second layer, is doped with a p-type dopant, but shows n-type conductivity and an n-type carrier concentration of 1 × 10¹⁹cm^-3The following is the content of claim 9.
[0068]
Here, in Comparative Example 1, the value of the layer thickness d of the second layer was set to 750 ° out of a suitable range, and the luminous intensity at this time was the same as that of Example except that the conditions other than the layer thickness were the same. It can be seen that it is significantly inferior to No. 4. That is, it can be seen that the luminous intensity is reduced to about 1/4 by increasing the thickness of the second layer from 250 ° to 750 ° three times.
[0069]
In Comparative Example 2, the layer thickness was increased to 750 °. Compared with Example 5 in which the growth conditions were the same except for the layer thickness, it was found that the luminous intensity was reduced to about １ ／. .
[0070]
In Comparative Example 3, the layer thickness was increased to 750 °. Compared with Example 6 in which the growth conditions other than the layer thickness were the same, it was found that the luminous intensity was reduced to about １ ／. .
[0071]
FIG. 3 shows the luminous intensity of the data shown in FIG. 2 when the Mg supply amount is 600 sccm and the Al composition is 0.05, the layer thickness (Å) is plotted on the horizontal axis, and the growth temperature (° C.) is plotted on the vertical axis. ) To make a graph. The numbers in the circles are luminous intensity (mcd).
[0072]
The luminous intensity of Example 2 is 405 mcd, and the luminous intensity of Example 6 is 334 mcd, which is substantially equal. The data in the area below this line segment has a luminous intensity that is not practical. Therefore, when the growth temperature is T and the layer thickness is d, the empirical formula indicating the upper region including this line segment is:
T-800 ≧ 2 (d-250) / 5
Becomes Thus, the relationship between T and d is
T ≧ 0.4d + 700
Can be represented by
[0073]
That is, it is necessary to grow the second layer at a growth temperature equal to or more than 0.4 times the layer thickness d and 700 or more in order to secure good luminous intensity. .
[0074]
(Examples 9 to 16)
Next, Examples 9 to 16 of the present invention will be described. In Examples 9 to 16, the AlGaN layer 9 having an Al composition of 0 was used as the first layer, the first layer was an n-type GaN layer, and the layer thickness was 180 °. Example of a light-emitting element manufactured under the same conditions as in Example 1 except that the growth temperature, the Al composition, and the Mg supply amount were variously changed among the growth conditions of the AlGaN: Mg layer 10 as the layer. It is.
[0075]
FIG. 4 shows the growth conditions (growth temperature (° C.), film thickness (Å), Al composition, Mg supply amount (sccm)) of the second layer for each of Examples 9 to 16, and the second layer. Characteristics (conductivity type and carrier concentration (cm^-3)) And the measured values of the light emission characteristics (luminous intensity (mcd)) for each example. In Examples 9 to 16, the second layer was grown so that the growth temperature was equal to or higher than a value obtained by adding 700 to 0.4 times the layer thickness d. In Examples 13 to 16, AlGaN: Mg as the second layer is doped with a p-type dopant, but shows n-type conductivity and an n-type carrier concentration of 1 × 10¹⁹cm^-3The following is the content of claim 9. From the respective luminescence characteristic data measured for Examples 9 to 16, it is understood that all of them have luminous intensity sufficient for practical use.
[0076]
【The invention's effect】
According to the present invention, as described above, the layer structure of the p-type layer provided in contact with the light-emitting layer is changed between the protective layer (first layer) and the p-type layer (third layer). The two-layer structure is inserted to optimize the layer structure, and by optimizing the growth conditions, the crystal structure near the pn junction is maintained without impairing the function of protecting the light emitting layer. Properties can be improved and holes can be easily injected. Therefore, even if the thickness of the protective layer is reduced, a sufficient protective function can be obtained, and the hole injection efficiency can be increased and the luminous efficiency can be improved. .
[Brief description of the drawings]
FIG. 1 is a layer structure diagram illustrating an example of an embodiment of the present invention.
FIG. 2 is a view showing data of Examples 1 to 8 and Comparative Examples 1 to 3 of the present invention.
FIG. 3 is a graph showing a relationship between a layer thickness of a second layer, a growth temperature, and light emission characteristics based on the data shown in FIG. 2;
FIG. 4 is a view showing data of Examples 9 to 16 of the present invention.
[Explanation of symbols]
1 Sapphire substrate
7 Light emitting layer
9 n-type AlGaN layer
10% AlGaN: Mg layer
11 GaN: Mg layer
20mm light emitting element

Claims (15)

An epitaxial substrate for a compound semiconductor light emitting device having a light emitting layer having a double hetero structure having a pn junction,
The layer structure of the contact with the light-emitting layer p-type layer side to be provided with, in order from the layer in contact with the light emitting _{layer, In x Al y Ga z N} (x + y + z = 1,0 ≦ x ≦ 1,0 ≦ y ≦ 1, a n-type first layer represented by 0 ≦ z ≦ _1), in _{in u Al v Ga w n (} u + v + w = 1,0 ≦ u ≦ 1,0 ≦ v ≦ 1,0 ≦ w ≦ 1) a second layer of p-type _represented, the p-type represented by _{in p Al q Ga r N (} p + q + r = 1,0 ≦ p ≦ 1,0 ≦ q ≦ 1,0 ≦ r ≦ 1) 3. An epitaxial substrate for a compound semiconductor light-emitting device, comprising: a plurality of layers; and the three layers being stacked in contact with each other. The layer thickness d ₁ (Å) of the first layer is in the range of 5 ≦ d ₁ ≦ 200, and the layer thickness d ₂ (Å) of the second layer is in the range of 5 ≦ d ₂ ≦ 30000. The epitaxial substrate for a compound semiconductor light emitting device according to claim 1. A method for producing an epitaxial substrate for a compound semiconductor light emitting device according to claim 1 or 2,
Between the growth temperature T ₂ of the second layer and the growth temperature T ₁ of the first layer, the following equation T ₁ ≦ T ₂
The method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device, wherein the following relationship is satisfied. Between the growth temperature T ₂ (° C.) of the second layer and the thickness d ₂ (の 間 に) of the _second layer, the following equation 5 ≦ d ₂ ≦ 30000 (900 ≦ T ₂ ≦ 1150)
T ₂ ≧ 0.4d ₂ +700 (700 ≦ T ₂ <900)
4. The method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device according to claim 3, wherein the second layer is grown such that a relationship represented by the following expression is satisfied. 5. The method for manufacturing an epitaxial substrate for a compound semiconductor light emitting device according to claim 3, wherein after the growth of the first layer is completed, the second layer and the third layer are formed by a regrowth method. . A light emitting device using the compound semiconductor light emitting device epitaxial substrate according to claim 1. A light-emitting element manufactured by using the manufacturing method according to claim 3. An epitaxial substrate for a compound semiconductor light emitting device having a light emitting layer having a double hetero structure having a pn junction,
The layer structure of the contact with the light-emitting layer p-type layer side to be provided with, in order from the layer in contact with the light emitting _{layer, In x Al y Ga z N} (x + y + z = 1,0 ≦ x ≦ 1,0 ≦ y ≦ 1, a n-type first layer represented by 0 ≦ z ≦ _1), in _{in u Al v Ga w n (} u + v + w = 1,0 ≦ u ≦ 1,0 ≦ v ≦ 1,0 ≦ w ≦ 1) a second layer n-type _represented, the p-type represented by _{in p Al q Ga r n (} p + q + r = 1,0 ≦ p ≦ 1,0 ≦ q ≦ 1,0 ≦ r ≦ 1) 3. An epitaxial substrate for a compound semiconductor light-emitting device, comprising: three layers, wherein the three layers are stacked in contact with each other. The p-type dopant concentration of the second layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²¹ cm ⁻³ or less, and the n-type carrier concentration of the second layer is 1 × 10 ¹⁹ cm ⁻³ or less. The epitaxial substrate for a compound semiconductor light emitting device according to claim 8, wherein The thickness d ₁ (Å) of the first layer is in the range of 5 ≦ d ₁ ≦ 200, and the thickness d ₂ (Å) of the second layer is in the range of 5 ≦ d ₂ ≦ 500. The epitaxial substrate for a compound semiconductor light emitting device according to claim 8 or 9. A method for producing an epitaxial substrate for a compound semiconductor light emitting device according to claim 8, 9 or 10,
Between the growth temperature T ₂ of the second layer and the growth temperature T ₁ of the first layer, the following equation T ₁ ≦ T ₂
The method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device, wherein the following relationship is satisfied. Between the growth temperature T ₂ (° C.) of the _second layer and the layer thickness d ₂ (Å), the following equation T ₂ ≧ 0.4d ₂ +700 (5 ≦ d ₂ ≦ 500)
1150 ≧ T ₂ ≧ 700
The method for manufacturing an epitaxial substrate for a compound semiconductor light emitting device according to claim 11, wherein the second layer is grown such that a relationship represented by the following expression is satisfied. The method of manufacturing an epitaxial substrate for a compound semiconductor light emitting device according to claim 11 or 12, wherein after the growth of the first layer is completed, the second layer and the third layer are formed by a regrowth method. . A light emitting device using the epitaxial substrate for a compound semiconductor light emitting device according to claim 8, 9, or 10. A light-emitting element manufactured by using the manufacturing method according to claim 11.

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