JP4402217B2 - Epitaxial substrate for infrared light emitting device and light emitting device produced using the same - Google Patents

Description

【表２】

表１と表２から明らかなように、本発明によれば従来品に比べて発光出力が約３倍高い赤外発光ダイオードを得ることができた。また発光出力のばらつきも減少した。
【００３６】
【発明の効果】
本発明によって、ｎ型ＧａＡｌＡｓ層中のＧｅ濃度を０．１〜３×１０¹⁶ｃｍ^ー3以下に制御することにより、発光出力が向上し、発光出力のばらつきも減少した。
【図面の簡単な説明】
【図１】本発明を実施するに当たり使用したスライドボートの概略図を示す。
【図２】ｎ型クラッド層中のＧｅ濃度とＬＥＤ出力の関係を示す。
【図３】ｐ型活性層に隣接しないｎ型層中のＧｅ濃度とＬＥＤ出力の関係を示す。
【図４】本発明による実施例１で作製されたＬＥＤの構造を示す。
【図５】本発明による実施例２で作製されたＬＥＤの構造を示す。
【符号の説明】
１ ｐ型ＧａＡｓ基板
２ 基板収納溝
３ スライダー
４ スライドボード本体
５ ルツボ
６ ルツボ
７ ルツボ
８ ルツボ
９ ルツボ蓋
１０ ｐ型ＧａＡｓ基板
１１ ｐ型ＧａＡｌＡｓ層
１２ ｐ型ＧａＡｌＡｓクラッド層
１３ ｐ型ＧａＡｌＡｓ活性層
１４ ｎ型ＧａＡｌＡｓクラッド層
１５ ｐ型ＧａＡｓ基板
１６ ｐ型ＧａＡｌＡｓ層
１７ ｐ型ＧａＡｌＡｓクラッド層
１８ ｐ型ＧａＡｌＡｓ活性層
１９ ｎ型ＧａＡｌＡｓクラッド層
２０ 第２のｎ型ＧａＡｌＡｓ層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an epitaxial substrate for producing a high-speed, high-power infrared light-emitting diode used for optical communication and spatial transmission using infrared rays, and an infrared light-emitting device produced from the epitaxial substrate.
[0002]
[Prior art]
A light emitting element (LED) using a Ga _1-X Al _X As (0 <X <1) (hereinafter abbreviated as GaAlAs) compound semiconductor is widely used as a light source for infrared to red. Infrared LEDs are used for optical communication and spatial transmission, but with the increase in the volume of data to be transmitted and the increase in transmission distance, the demand for high-power, high-speed infrared LEDs is increasing. .
[0003]
As is known in the art, in a GaAlAs-based LED, the double heterostructure (hereinafter referred to as DH structure) has a higher output than the single heterostructure, and the output can be further increased by removing the substrate. ing.
[0004]
In order to achieve high output even in high-power and high-speed infrared LEDs, it is indispensable to adopt a DH structure and a type that removes the substrate.
[0005]
In the case of a structure in which the substrate is removed, when the substrate is removed by epitaxially growing only the DH structure, that is, the p-type cladding layer, the p-type active layer, and the n-type cladding layer, the thickness of the product is reduced. At the same time, handling in the fabrication process becomes difficult, and at the same time, the height from the bottom surface of the device fabricated from this epitaxial substrate to the pn junction becomes low, and the paste for adhering the device to the conductor crawls up the device side surface, shorting the pn junction. Problem occurs. In order to prevent this, adding a fourth epitaxial layer to the DH structure to increase the overall thickness after removal of the substrate and the distance from the bottom of the device to the junction is a standard configuration in the substrate removal type structure. ing. The fourth epitaxial layer has a wider band gap than the active layer, and is designed not to absorb the light emitted from the active layer.
[0006]
This fourth epitaxial layer may be added to the n-type cladding side or the p-type cladding side of the DH structure. Further, the fourth epitaxial layer does not have to be a single layer, and a plurality of epitaxial layers may be combined.
[0007]
In infrared LEDs used for optical communication and space transmission, Ge is used as an impurity added to the p-type active layer in order to realize high output and high speed characteristics. The reason why Ge is used as an impurity of the p-type active layer is that diffusion energy is low when Zn, which is generally used as an impurity added to the p-type layer by the epitaxial growth method, is used for the p-type active layer. This is because Zn diffuses into the n-type clad layer and the junction position shifts from the metallurgical interface into the n-cladding layer, and this phenomenon is disadvantageous from the viewpoint of increasing the response speed.
[0008]
[Problems to be solved by the invention]
However, in the high-speed, high-power infrared light emitting diode having the above DH structure, when Ge is used as the dopant of the p-type active layer, there is a phenomenon in which the light emission output varies depending on the production lot even if it is manufactured by the same manufacturing process. In addition, the light output was not sufficient.
[0009]
An object of the present invention is to solve this problem, and to provide an epitaxial substrate for producing a high-output light-emitting element with little variation in light-emission output, and a light-emitting element produced from this epitaxial substrate.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the present inventor has investigated in detail the relationship between various physical properties of the light emitting element and the light emission output, and as a result, the negative correlation between the concentration of Ge contained in the n-type GaAlAs layer and the light emission output. As a result, the present invention was completed. That is, the present invention
[1] p-type cladding layer (Ga _{1 -X1} Al _X1 As, 0 <X1 <1), p-type active layer (Ga _{1 -X2} Al _X2 As, 0 <X2 <1), n-type cladding layer (Ga _{1 -X3} Al _X3 As, 0 <X3 <1), the three layers are in contact with each other in this order, and the main impurity of the p-type active layer is germanium. An epitaxial substrate for an infrared light emitting device, wherein the Ge concentration in the n-type cladding layer is 3 × 10 ¹⁶ cm ⁻³ or less,
[2] Having a second n-type layer (Ga _{1 -X4} Al _X4 As, 0 <X4 <1) in contact with the n-type cladding layer, the Ge concentration in the second n-type layer is 3 × 10 ¹⁶ The epitaxial substrate for infrared light-emitting elements according to [1], which is cm ⁻³ or less,
[3] A light-emitting device manufactured using the infrared light-emitting device epitaxial substrate according to [1] or [2].
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments relating to the first claim of the present invention include a p-type cladding layer (Ga _{1 -X 1} Al _{X 1} As, 0 <X 1 <1), a p-type active layer (Ga ₁ -X ₂ Al _{X 2} As, 0 <X 2 < 1) n-type cladding layer (Ga _{1 -X3} Al _X3 As, 0 <X3 <1) is in this order, and the p-type active layer has a laminated structure in which the main impurity is germanium, The Ge concentration in the layer is 3 × 10 ¹⁶ cm ⁻³ or less. In an embodiment relating to the second claim, the second n-type layer (Ga _{1 -X4} Al _X4 As, 0 <X4 <1) is in contact with the n-type cladding layer of the first embodiment, The Ge concentration in the n-type layer 2 is 3 × 10 ¹⁶ cm ⁻³ or less.
[0012]
Ge is used as an impurity of the p-type active layer, but is not intentionally added to the n-type layer. Accordingly, in the epitaxial layer growth process, the p-type active layer growth Ga solution containing Ge is brought into the n-type layer growth Ga solution, and further, the p-type active layer growth Ga solution containing Ge is brought into the n-type layer. It is considered that the diffusion of Ge into the growth Ga solution is a source of Ge contamination into the n-type layer. A method for preventing the mixing of Ge into the Ga solution will be described using a growth apparatus of the slide boat method as an example.
[0013]
In the slide boat jig shown in FIG. 1, the inside of the substrate storage groove 2 and the inside of the crucibles 5 to 8 are coated with glassy carbon. By coating the portion in direct contact with the Ga solution with glassy carbon, the wettability with the Ga solution is deteriorated, and the Ga solution for p-type active layer growth containing Ge is mixed in the Ga solution for n-type layer growth in the epitaxial growth process. You can prevent it.
[0014]
The crucible lid 9 is made of glassy carbon. This crucible lid is used for the purpose of preventing contamination of dopant impurities from the Ga solution in the crucible, which is different from the evaporation of dopant impurities from the Ga solution in the crucible, but this crucible lid 9 is also a glassy carbon having a low aperture ratio. By making it, the evaporation of Ge from the Ga solution for p-type layer growth and the mixing of Ge into the Ga solution for n-type layer growth can be prevented.
[0015]
Conventionally, the Ge concentration in the n-type epitaxial layer is approximately 5 × 10 ¹⁶ cm ⁻³ or more, but by performing the above method, the Ge concentration in the n-type epitaxial layer is reduced to 3 × 10 ¹⁶ cm ⁻³ or less. It becomes possible to control. Then, by controlling the Ge concentration in the n-type epitaxial layer to 3 × 10 ¹⁶ cm ⁻³ or less by this method, the output of the high-speed, high-power infrared light emitting diode having the DH structure can be made higher than the conventional one. It becomes possible.
[0016]
FIG. 2 shows the relationship between the Ge concentration in the n-type cladding layer of the conventional light emitting diode and the light emitting diode obtained by the present invention and the light emission output.
[0017]
As shown in FIG. 2, the output is almost constant when the Ge concentration in the n-type cladding layer is 1 × 10 ¹⁶ cm ⁻³ or less, but the output starts decreasing when the Ge concentration is higher than 1 × 10 ¹⁶ cm ⁻³ . Then, it was found that the output suddenly decreased when it became higher than 3 × 10 ¹⁶ cm ⁻³ . Therefore, it has been found that high output is obtained when the Ge concentration in the n-type cladding layer is 3 × 10 ¹⁶ cm ⁻³ or less, more preferably 1 × 10 ¹⁶ cm ⁻³ or less.
[0018]
FIG. 3 shows the relationship between the Ge concentration in the n-type layer (second n-type layer) not in contact with the p-type active layer of the conventional light-emitting diode and the light-emitting diode obtained by the present invention and the light-emission output. As shown in FIG. 3, when the Ge concentration in the n-type layer is 1 × 10 ¹⁶ cm ⁻³ or less, the output is almost constant, but when it exceeds 1 × 10 ¹⁶ cm ⁻³ , the output starts decreasing. Then, it was found that the output suddenly decreased when it became higher than 3 × 10 ¹⁶ cm ⁻³ . Accordingly, it has been found that high output is obtained by setting the Ge concentration in the n-type layer not adjacent to the p-type active layer to 3 × 10 ¹⁶ cm ⁻³ or less, more preferably 1 × 10 ¹⁶ cm ⁻³ or less.
[0019]
【Example】
Example 1
An example in which the light emitting device of the present invention is manufactured by a slow cooling liquid phase epitaxial growth method using a slide boat type growth apparatus will be described.
[0020]
FIG. 4 schematically shows the structure of a high-speed, high-power infrared light emitting diode having a DH structure manufactured from the epitaxial substrate described in the present application.
[0021]
FIG. 1 shows a slide boat type growth apparatus used in this embodiment. The GaAs substrate 1 is set in the substrate storage groove 2 of the slider 3. A crucible corresponding to the number of layers to be grown on the GaAs substrate is arranged in the slide boat body 4, and Ga metal, metal Al, and GaAs polycrystal having a suitable composition for growing an epitaxial layer are included in the crucible. A suitable dopant is blended in order to realize the conductivity type and carrier concentration of each epitaxial layer.
[0022]
Actual growth is done as follows. 1 is set in a quartz reaction tube (not shown) and heated to 950 ° C. in a hydrogen stream to dissolve the raw material. Subsequently, the ambient temperature is lowered to 900 ° C., the slider 3 is pushed to the right, and the p-type GaAs substrate 1 is moved below the crucible 5 to come into contact with the melt. Next, the ambient temperature is lowered at a rate of 0.5 ° C./min to grow the first p-type GaAlAs layer shown in FIG. 1 on the p-type GaAs substrate. Thereafter, the four layers of epitaxial layers having different mixed crystal ratios corresponding to FIG. 4 are grown by repeating the movement of the slider and the temperature drop.
[0023]
After the epitaxial growth is completed, the epitaxial substrate is taken out, the surface of the n-type cladding layer 14 in FIG. 4 is protected with an acid-resistant sheet, and the GaAs substrate is selectively removed with an ammonia-hydrogen peroxide-based etchant. Thereafter, gold electrodes (not shown) were formed on both surfaces of the epitaxial substrate, and the elements were separated by dicing, thereby producing an infrared LED as shown in FIG.
[0024]
The Ge concentration in the n-type cladding layer of the high-speed, high-power infrared light-emitting diode having the DH structure obtained in Example 1 was 0.5 to 3 × 10 ¹⁶ cm ⁻³ .
[0025]
(Example 2)
FIG. 5 schematically shows the structure of an infrared light emitting LED produced by the epitaxial substrate described in the present application. Unlike Example 1, the n-type layer is added as a fourth epitaxial layer to the n-cladding layer side of the DH structure.
[0026]
Actual growth was performed using the same jig as in Example 1. At this time, the temperature at which the raw material was dissolved and the temperature at which the p-type GaAs substrate was brought into contact with the melt were set to temperatures suitable for the structure shown in FIG.
[0027]
After the epitaxial growth, the same process as in Example 1 was performed, and a high-speed, high-power infrared light emitting diode having a DH structure as shown in FIG. 5 was produced.
[0028]
The Ge concentration in the n-type cladding layer of the high-speed, high-power infrared light-emitting diode having the DH structure obtained in Example 2 is 0.5 to 3 × 10 ¹⁶ cm ⁻³ and is added to the n-type cladding layer side. The Ge concentration in the second n-type layer was 0.1 to 3 × 10 ¹⁶ cm ⁻³ .
[0029]
In the epitaxial growth shown in the above two examples, all the means for reducing the Ge concentration in the n-type GaAlAs layer described above were implemented. That is, the inside of the substrate storage groove and the inside of the crucible were coated with glassy carbon. The crucible lid was made of glassy carbon.
[0030]
(Comparative Example 1)
A high-speed, high-power infrared light emitting diode having a DH structure having the same structure as that of Example 1 was prepared. However, in the growth of the epitaxial layer according to Comparative Example 1, the means for reducing the Ge concentration in the n-type layer was not particularly performed as in the conventional case.
[0031]
The Ge concentration in the n-type cladding layer of the high-speed, high-power infrared light emitting diode having the DH structure obtained by this comparative example was about 5 to 10 × 10 ¹⁶ cm ⁻³ .
[0032]
(Comparative Example 2)
A high-speed, high-power infrared light emitting diode having a DH structure having the same structure as that of Example 2 was prepared. However, in the growth of the epitaxial layer according to the comparative example 2, the means for reducing the Ge concentration in the n-type layer was not particularly performed as in the prior art.
[0033]
The Ge concentration in the n-type cladding layer of the DH structure high-speed, high-power infrared light-emitting diode obtained by this comparative example was about 5 to 10 × 10 ¹⁶ cm ⁻³ . The Ge concentration in the n-type layer added to the n-cladding layer side was 4 to 7 × 10 ¹⁶ cm ⁻³ .
[0034]
Tables 1 and 2 show the results of measuring the light emission output of the infrared light emitting diodes produced in the above examples and comparative examples.
[0035]
[Table 1]

[Table 2]

As apparent from Tables 1 and 2, according to the present invention, an infrared light emitting diode having a light emission output approximately three times higher than that of the conventional product could be obtained. In addition, the variation in light output was reduced.
[0036]
【The invention's effect】
According to the present invention, by controlling the Ge concentration in the n-type GaAlAs layer to 0.1-3 × 10 ¹⁶ cm ⁻³ or less, the light emission output is improved and the variation of the light emission output is also reduced.
[Brief description of the drawings]
FIG. 1 is a schematic view of a slide boat used for carrying out the present invention.
FIG. 2 shows a relationship between Ge concentration in an n-type cladding layer and LED output.
FIG. 3 shows the relationship between the Ge concentration in the n-type layer not adjacent to the p-type active layer and the LED output.
FIG. 4 shows the structure of an LED fabricated in Example 1 according to the present invention.
FIG. 5 shows the structure of an LED fabricated in Example 2 according to the present invention.
[Explanation of symbols]
1 p-type GaAs substrate 2 substrate housing groove 3 slider 4 slide board body 5 crucible 6 crucible 7 crucible 8 crucible 9 crucible lid 10 p-type GaAs substrate 11 p-type GaAlAs layer 12 p-type GaAlAs cladding layer 13 p-type GaAlAs active layer 14 n P-type GaAlAs cladding layer 15 p-type GaAs substrate 16 p-type GaAlAs layer 17 p-type GaAlAs clad layer 18 p-type GaAlAs active layer 19 n-type GaAlAs clad layer 20 second n-type GaAlAs layer

Claims (2)

On the substrate, less the p-type cladding layer also _{(Ga 1-X1 Al X1 As} , 0 <X1 <1), p -type active layer _{(Ga 1-X2 Al X2 As} , 0 <X2 <1), n -type clad In a method of manufacturing an epitaxial substrate for an infrared light emitting device, including a step of laminating three layers (Ga _{1 -X3} Al _X3 As, 0 <X3 <1) in this order by liquid phase epitaxy and then removing the substrate The liquid phase epitaxial method is performed using a substrate containing groove, a crucible inside, and a crucible lid made of glassy carbon , the main impurity of the p-type active layer is germanium, and the Ge concentration in the n-type cladding layer The manufacturing method of the epitaxial substrate for infrared light emitting elements characterized by being 3 * 10 < ¹⁶ > cm <^-3> or less. A second n-type layer (Ga _{1 -X4} Al _X4 As, 0 <X4 <1) is in contact with the n-type cladding layer, and the Ge concentration in the second n-type layer is 3 × 10 ¹⁶ cm ^−3. The manufacturing method of the epitaxial substrate for infrared light emitting elements of Claim 1 characterized by the following.

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