JP2011192821A - Light emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high power and high efficiency light emitting diode, capable of emitting infrared light having the peak wavelength of ≥850 nm, particularly ≥900 nm. <P>SOLUTION: The light emitting diode includes a DBR reflection layer and a light emitting layer sequentially formed on the substrate. The light emitting layer is characterized by including an active layer having the lamination structure of a well layer expressed with the composition formula (In<SB>X1</SB>Ga<SB>1-X1</SB>)As(0≤X1≤1) and a barrier layer expressed with composition formula (Al<SB>X2</SB>Ga<SB>1-X2</SB>)As(0≤X2≤1) and a first cladding layer and a second cladding layer expressed with the composition formula (Al<SB>X4</SB>Ga<SB>1-X4</SB>)<SB>Y</SB>In<SB>1-Y</SB>P(0≤X4≤1, 0<Y≤1) provided to sandwitch the active layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an infrared light emitting diode having an emission peak wavelength of 850 nm or more, particularly 900 nm or more.

Infrared light emitting diodes are widely used for infrared communication, infrared remote control devices, light sources for various sensors, night illumination, and the like.
In the vicinity of such a peak wavelength, a light emitting diode is known in which a compound semiconductor layer including an AlGaAs active layer is grown on a GaAs substrate by a liquid phase epitaxial method (for example, Patent Documents 1 to 3).
On the other hand, in the case of infrared communication used for transmission / reception between devices, for example, infrared light of 850 to 900 nm is used, and in the case of infrared remote control operation communication, for example, 880 to 880 which is a wavelength band in which the sensitivity of the light receiving unit is high. An infrared ray of 940 nm is used. As an infrared light emitting diode that can be used for both infrared communication and infrared remote control operation communication for terminal devices such as mobile phones that have both functions of infrared communication and infrared remote control operation communication, an effective emission peak wavelength is 880 to 890 nm. One using an AlGaAs active layer containing Ge as an impurity is known (Patent Document 4).
Moreover, what uses an InGaAs active layer is known as an infrared light emitting diode which can have an emission peak wavelength of 900 nm or more (Patent Document 5).

JP-A-6-21507 JP 2001-274454 A Japanese Patent Laid-Open No. 7-38148 JP 2006-190792 A JP 2002-344013 A

However, it is difficult to form a multiple quantum structure with excellent monochromaticity by the method of growing a compound semiconductor layer by a liquid phase epitaxial method.
Further, when an AlGaAs active layer containing Ge as an effective impurity is used, it is difficult to set the emission peak wavelength to 900 nm or more (FIG. 3 of Patent Document 4).
With respect to infrared light emitting diodes using an InGaAs active layer that can have a light emission peak wavelength of 900 nm or more, development of higher light emission efficiency is desired from the viewpoint of further performance improvement, energy saving, and cost.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an infrared light emitting diode that emits infrared light having an emission peak wavelength of 850 nm or more, particularly 900 nm or more, with high output and high efficiency. .

As a result of intensive studies to solve the above problems, the present inventor has obtained an active layer having a multiple quantum well structure composed of a ternary mixed crystal InGaAs well layer and a ternary mixed crystal AlGaAs barrier layer, and this active layer. By adopting a structure including a light emitting part including a sandwiched quaternary mixed crystal AlGaInP clad layer and a DBR reflection layer between the light emitting part and the substrate, high output and high efficiency are 850 nm or more, particularly 900 nm or more. An infrared light-emitting diode that emits infrared light having an emission peak wavelength of 1 was completed.
First, the present inventor adopts a well layer made of InGaAs so as to have an emission peak wavelength of 850 nm or more, particularly 900 nm or more, which is used for infrared communication or the like. Layered.
Further, a quaternary mixed crystal AlGaInP having a good crystallinity was adopted for the clad layer sandwiching the active layer because it does not contain As which has a large band gap and is transparent with respect to the emission wavelength, and easily forms defects.
Furthermore, in an InGaAs / AlGaAs multiple quantum well structure, it is difficult to lattice match the two layers, and the active layer has a strained quantum well structure. The strain quantum well structure has a large effect on the output and monochromaticity of the composition and thickness of InGaAs. By selecting an appropriate composition, thickness and number of pairs, the output of infrared light is significantly higher than that of conventional ones. Got the light.
As a result of further research based on this knowledge, the present inventor has completed the present invention shown in the following configuration.

(1) A light emitting diode comprising a DBR reflective layer and a light emitting unit in order on a substrate,
The light emitting part includes a well layer having a composition formula (In _X1 Ga _1-X1 ) As (0 ≦ X1 ≦ 1) and a barrier layer having a composition formula (Al _X2 Ga _1-X2 ) As (0 ≦ X2 ≦ 1). And a first guide and a second guide comprising a composition formula ( _{AlX3Ga1 -X3} ) _{Y2In1 -Y2P} ; 0≤X3≤1, 0 <Y2≤1) And a composition formula (Al _X4 Ga _1-X4 ) _Y In _1-YP ; 0 ≦ X4 ≦ 1, 0 <Y ≦ sandwiching the active layer through each of the first guide and the second guide A light-emitting diode comprising a first clad layer and a second clad layer made of 1).
(2) The light-emitting diode according to (1), wherein the In composition (X1) of the well layer is 0 ≦ X1 ≦ 0.3.
(3) The light-emitting diode according to (2), wherein the In composition (X1) of the well layer is 0.1 ≦ X1 ≦ 0.3.
(4) The light emitting diode according to any one of (1) to (3), wherein the DBR reflective layer is formed by alternately stacking two to ten pairs of two types of refractive indexes.
(5) The two types of layers having different refractive indices are composed of two types of (Al _Xh Ga _1-Xh ) _{Y 3} In _{1 -Y 3} P (0 <Xh ≦ 1, Y 3 = 0.5), (Al _{Xl Ga 1-xl) Y3 in 1} -Y3 P; 0 ≦ xl <1, Y3 = 0.5) is a combination of, the composition difference ΔX = xh-xl both of Al or greater than or equal to 0.5 (4) The light-emitting diode according to (4) above.
(6) The light emitting diode according to (4), wherein the two types of layers having different refractive indexes are a combination of GaInP and AlInP.
(7) The two types of layers having different refractive indexes are composed of two types of Al _xl Ga _1-xl As (0.1 ≦ xl ≦ 1) and Al _xh Ga _1-xh As (0.1 ≦ xh ≦) having different compositions. The light-emitting diode according to the item (4), which is a combination of 1) and has a composition difference ΔX = xh−xl between both of them being greater than or equal to 0.5.
(8) The light-emitting diode according to any one of (1) to (7), wherein a current diffusion layer is provided on a surface of the light-emitting portion opposite to the DBR reflection layer.

According to said structure, the following effects are acquired.
Infrared light having an emission peak wavelength of 850 nm or more, particularly 900 nm or more can be emitted with high output and high efficiency.
The active layer includes a well layer having a composition formula (In _X1 Ga _1-X1 ) As (0 ≦ X1 ≦ 1) and a barrier layer having a composition formula (Al _X2 Ga _1-X2 ) As (0 ≦ X2 ≦ 1). Since it has a multi-well structure, it is excellent in monochromaticity.
Since the cladding layer has a compositional formula (Al _X Ga _1-X ) _Y In _1-YP ; 0 ≦ X ≦ 1, 0 <Y ≦ 1), the cladding layer is a ternary mixed crystal. Compared with an infrared light emitting diode made of the above, the Al concentration is low and the moisture resistance is improved.
The active layer includes a well layer having a composition formula (In _X1 Ga _1-X1 ) As (0 ≦ X1 ≦ 1) and a barrier layer having a composition formula (Al _X2 Ga _1-X2 ) As (0 ≦ X2 ≦ 1). Since it has a laminated structure, it is suitable for mass production using the MOCVD method. In particular, there is an advantage that the group V element is As and is common, and the switching of the source gas is simple.
Since the DBR reflection film is provided between the light emitting layer and the substrate, it is possible to avoid a decrease in light emission output due to light absorption by the GaAs substrate.

It is a top view of the light emitting diode which is one Embodiment of this invention. It is a figure for demonstrating the active layer which comprises the light emitting diode which is one Embodiment of this invention. It is a graph which shows the correlation with the layer thickness of the well layer of the light emitting diode which is one Embodiment of this invention, and the light emission peak wavelength. It is a graph which shows the correlation with In composition (X1) and the light emission peak wavelength of the well layer of the light emitting diode which is one Embodiment of this invention. It is a graph which shows the correlation with In composition (X1) of the well layer of the light emitting diode which is one Embodiment of this invention, a light emission peak wavelength, and its light emission output. It is a graph which shows the correlation with the number of pairs of the well layer of the light emitting diode which is one Embodiment of this invention, and a barrier layer, and light emission output.

  Hereinafter, a light emitting diode according to an embodiment to which the present invention is applied will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

<Light emitting diode>
FIG. 1 is a schematic cross-sectional view of a light emitting diode according to an embodiment to which the present invention is applied. FIG. 2 is a schematic sectional view of a laminated structure of a well layer and a barrier layer.
The light-emitting diode 100 according to the first embodiment is a light-emitting diode 30 that includes a DBR reflection layer 3 and a light-emitting unit 20 in this order on a substrate 1, and the light-emitting unit 20 has a composition formula (In _X1 Ga _1-1 An active layer 7 having a laminated structure of a well layer 15 made of _X1 ) As (0 ≦ X1 ≦ 1) and a barrier layer 16 made of a composition formula (Al _X2 Ga _1-X2 ) As (0 ≦ X2 ≦ 1); The first guide and the second guide having the composition formula (Al _X3 Ga _1-X3 ) _Y2 In _1-Y2 P; 0 ≦ X3 ≦ 1, 0 <Y2 ≦ 1, and the first guide 6 and the second guide sandwiching the active layer 7 through the respective second guide 8, a composition formula _{(Al X4 Ga 1-X4)} Y in 1-Y P; 0 ≦ X4 ≦ 1,0 <Y ≦ 1) consisting essentially of a first Characterized by having a clad layer 5 and a second clad layer 9 A.

As shown in FIG. 1, the compound semiconductor layer (also referred to as an epitaxial growth layer) 30 has a structure in which a pn junction light emitting unit 20 and a current diffusion layer 10 are sequentially stacked. A known functional layer can be added to the structure of the compound semiconductor layer 30 as appropriate. For example, a contact layer for reducing the contact resistance of an ohmic electrode, a current diffusion layer for planarly diffusing the element driving current over the entire light emitting portion, and conversely, limiting a region through which the element driving current flows. Therefore, a known layer structure such as a current blocking layer or a current confinement layer can be provided.
The compound semiconductor layer 30 is preferably formed by epitaxial growth on a GaAs substrate.

  For example, as shown in FIG. 1, the light emitting unit 20 provided on the n-type substrate has an n-type lower cladding layer (first cladding layer) 5, a lower guide layer 6, an active layer 7 on the DBR reflection layer 3. An upper guide layer 8 and a p-type upper clad layer (second clad layer) 9 are sequentially laminated. That is, the light emitting unit 20 includes a lower clad layer 5 disposed opposite to the upper side and the upper side of the active layer 7 in order to “confine” the carrier (carrier) that causes radiative recombination and light emission in the active layer 7. A so-called double hetero (English abbreviation: DH) structure including the lower guide layer 6, the upper guide layer 8, and the upper cladding layer 9 is preferable in order to obtain high-intensity light emission.

  As shown in FIG. 2, the active layer 7 forms a quantum well structure in order to control the emission wavelength of the light emitting diode (LED). That is, the active layer 7 has a multilayer structure (laminated structure) of a well layer 15 and a barrier layer (also referred to as a barrier layer) 16 having a well layer (also referred to as a well layer) 15 at both ends.

The layer thickness of the active layer 7 is preferably in the range of 0.02 to 2 μm. Further, the conductivity type of the active layer 7 is not particularly limited, and any of undoped, p-type and n-type can be selected. In order to increase the luminous efficiency, it is desirable that the crystallinity is undoped or the carrier concentration is less than 3 × 10 ¹⁷ cm ⁻³ .

  The DBR (Distributed Bragg Reflector) reflective layer 3 has two types of refractive indexes having a thickness of λ / (4n) (λ: wavelength of light to be reflected in vacuum, n: refractive index of layer material). It consists of a multilayer film in which layers are alternately stacked. When the difference between the two types of refractive indexes is large, a high reflectance can be obtained with a multilayer film having a relatively small number of layers. Instead of being reflected on a certain surface as in a normal reflective film, the multilayer film as a whole is characterized in that reflection occurs based on the light interference phenomenon.

The DBR (Distributed Bragg Reflector) reflecting layer 3 is preferably formed by alternately laminating 10 to 50 pairs of two types of layers having different refractive indexes. This is because when the number is 10 pairs or less, the reflectance is too low, so that it does not contribute to an increase in output, and even when the number is 50 pairs or more, the increase in reflectance is small.
Two types of layers having different refractive indexes constituting the DBR (Distributed Bragg Reflector) reflecting layer 3 are two types of (Al _Xh Ga _1-Xh ) _{Y 3} In _{1 -Y 3} P (0 <Xh ≦ 1, Y ₃ ) having different compositions. = 0.5), (Al _Xl Ga _1-Xl ) _Y3 In _1-Y3 P; 0 ≦ Xl <1, Y3 = 0.5), and the Al composition difference ΔX = xh−xl A combination of greater than or equal to 0.5, a combination of GaInP and AlInP, or two types of Al _xl Ga _1-xl As (0.1 ≦ xl ≦ 1) and Al _xh Ga _{1 having} different compositions _-Xh As (0.1 ≦ xh ≦ 1) pair, and the high and efficient reflection is selected from any combination in which the composition difference ΔX = xh−xl of both is greater than or equal to 0.5 This is desirable because the rate is obtained.
A combination of AlGaInP having different compositions is preferable because it does not contain As that easily causes crystal defects, and GaInP and AlInP have the largest refractive index difference among them, so that the number of reflective layers can be reduced and the composition can be switched. Is also preferable because it is simple. Moreover, AlGaAs has an advantage that a large difference in refractive index is easily obtained.

In FIG. 3, the In composition (X1) of the well layer 15 is fixed to 0.1, and the correlation between the layer thickness and the emission peak wavelength is shown. Table 1 shows the values of the points shown in FIG. It can be seen that when the well layer is as thick as 3 nm, 5 nm, and 7 nm, the wavelength monotonously increases to 820 nm, 870 nm, and 920 nm.

FIG. 4 shows the correlation between the emission peak wavelength of the well layer 15 and its In composition (X1) and layer thickness. FIG. 4 shows a combination of the In composition (X1) and the layer thickness of the well layer 15 in which the emission peak wavelength of the well layer 15 is a predetermined wavelength. Specifically, a combination of the In composition (X1) and the layer thickness of the well layer 15 having the emission peak wavelengths of 920 nm and 960 nm, respectively, is shown. FIG. 4 further shows combinations of In composition (X1) and layer thicknesses at other emission peak wavelengths of 820 nm, 870 nm, 985 nm, and 995 nm. Table 2 shows the values of the points shown in FIG.

In the case of an emission peak wavelength of 920 nm, as the In composition (X1) decreases from 0.3 to 0.05, the corresponding layer thickness monotonously increases from 3 nm to 8 nm. A combination with an emission peak wavelength of 920 nm can be easily found.
Further, when the In composition (X1) is 0.1 and the layer thickness is increased to 3 nm, 5 nm, 7 nm, and 8 nm, the emission peak wavelengths are correspondingly increased to 820 nm, 870 nm, 920 nm, and 960 nm. Further, when the In composition (X1) is 0.2, the emission peak wavelength is correspondingly increased to 920 nm and 960 nm when the layer thickness is increased to 5 nm and 6 nm, and when the In composition (X1) is 0.25, When the layer thickness is increased to 4 nm and 5 nm, the emission peak wavelengths are correspondingly increased to 920 nm and 960 nm, and when the In composition (X1) is 0.3, the layer thickness is increased to 3 nm and 5 nm. The emission peak wavelengths are as long as 920 nm and 985 nm.
Furthermore, when the In composition (X1) increases to 0.1, 0.2, 0.25, and 0.3 when the layer thickness is 5 nm, the emission peak wavelengths are increased to 870 nm, 920 nm, 960 nm, and 985 nm. When the In composition (X1) becomes 0.35, the emission peak wavelength becomes 995 nm.

In FIG. 4, it is shown that when a combination of the In composition (X1) with the emission peak wavelengths of 920 nm and 960 nm and the layer thickness is connected, it becomes a substantially straight line. Further, it is presumed that a line connecting a combination of the In composition (X1) having a predetermined emission peak wavelength in the wavelength band from 850 nm to 1000 nm and the layer thickness is also substantially linear. Further, it is assumed that the line connecting the combinations is located at the lower left as the emission peak wavelength is shorter, and located at the upper right as the longer the emission peak wavelength.
Based on the above regularity, the In composition (X1) and the layer thickness having a desired emission peak wavelength of 850 nm or more and 1000 nm or less can be easily found.

FIG. 5 shows the correlation between the In composition (X1), the emission peak wavelength, and the emission output thereof, in which the thickness of the well layer 15 is fixed to 5 nm. Table 3 shows the values of the points shown in FIG.
When the In composition (X1) is increased to 0.12, 0.2, 0.25, 0.3, and 0.35, the emission peak wavelengths are increased to 870 nm, 920 nm, 960 nm, 985 nm, and 995 nm. More specifically, as the In composition (X1) increases from 0.12 to 0.3, the emission peak wavelength increases from 870 nm to 985 nm almost monotonically. However, even if the In composition (X1) is increased from 0.3 to 0.35, the length increases from 985 nm to 995 nm, but the rate of change to long wavelengths is small.
The emission peak wavelength is 870 nm (X1 = 0.12), 920 nm (X1 = 0.2), and 960 nm (X1 = 0.25), and the emission output is a high value of 6.0 mW, which is 985 nm (X1 = 0). .3) has a practically high value of 4.5 mW, but was as low as 1.8 mW at 995 nm (X1 = 0.35).

3 to 5, the well layer 15 preferably has a composition of (In _X1 Ga _{1 -X1} ) As (0 ≦ X1 ≦ 0.3). Said X1 can be adjusted so that it may become a desired light emission peak wavelength.
When the emission peak wavelength is 900 nm or more, 0.1 ≦ X1 ≦ 0.3 is preferable, and when it is less than 900 nm, 0 ≦ X1 ≦ 0.1 is preferable.

  The layer thickness of the well layer 15 is preferably in the range of 3 to 20 nm. More preferably, it is the range of 3-10 nm.

The barrier layer 16 has a composition of (Al _X2 Ga _{1 -X2} ) As (0 ≦ X2 ≦ 1). X is preferably a composition having a band gap larger than that of the well layer 15, and more preferably in the range of 0 to 0.4.
The thickness of the barrier layer 16 is preferably equal to or thicker than the thickness of the well layer 15. Thereby, the luminous efficiency of the well layer 15 can be increased.

FIG. 6 shows the correlation between the number of pairs of well layers and barrier layers and the light emission output when the thickness of the well layer 15 is 5 nm and the In composition (X1) = 0.2. Table 4 shows the values of the points shown in FIG.
It was found that the light emission output was as high as 6.0 mW or more with 1 to 10 pairs, and even 20 pairs had a practically high value of 4.8 mW. If the number of pairs is further increased, it is presumed that the light emission output decreases.

In the multilayer structure of the well layer 15 and the barrier layer 16, the number of pairs in which the well layers 15 and the barrier layers 16 are alternately stacked is not particularly limited. However, based on FIG. The following is preferable. That is, the active layer 7 preferably includes 1 to 10 well layers 15. Here, as a preferable range of the luminous efficiency of the active layer 7, the well layer 15 may be one or more layers, and even one layer is possible. On the other hand, there is a lattice irregularity between the well layer 15 and the barrier layer 16 and the carrier concentration is low. Therefore, if a large number of pairs are used, crystal defects may occur, resulting in a decrease in luminous efficiency or a forward voltage. (V _F ) increases. For this reason, it is preferable that it is 10 pairs or less, and it is more preferable that it is 5 pairs or less.

  The lower guide layer 6 and the upper guide layer 8 are provided on the lower surface and the upper surface of the active layer 7, respectively, as shown in FIG. Specifically, the lower guide layer 6 is provided on the lower surface of the active layer 7, and the upper guide layer 8 is provided on the upper surface of the active layer 7.

The lower guide layer 6 and the upper guide layer 8 have a composition of (Al _X3 Ga _{1 -X3} ) As (0 ≦ X3 ≦ 1). X3 is preferably a composition having a band gap equal to or larger than that of the barrier layer 16, and more preferably in the range of 0.2 to 0.4.

  The lower guide layer 6 and the upper guide layer 8 are provided to reduce the propagation of defects between the lower clad layer 5 and the upper clad layer 9 and the active layer 7, respectively. That is, in the present invention, the group V constituent element of the active layer 7 is arsenic (As), whereas the group V constituent element of the lower cladding layer 5 and the upper cladding layer 9 is phosphorus (P). Defects are likely to occur at the interfaces between the lower cladding layer 5 and the upper cladding layer 9. Propagation of defects to the active layer 7 causes a reduction in the performance of the light emitting diode. In order to effectively reduce the propagation of this defect, the thickness of the lower guide layer 6 and the upper guide layer 8 is preferably 10 nm or more, and more preferably 20 nm to 100 nm.

The conductivity type of the lower guide layer 6 and the upper guide layer 8 is not particularly limited, and any of undoped, p-type, and n-type can be selected. In order to increase the luminous efficiency, it is desirable that the crystallinity is undoped or the carrier concentration is less than 3 × 10 ¹⁷ cm ⁻³ .

  As shown in FIG. 1, the lower cladding layer 5 and the upper cladding layer 9 are provided on the lower surface of the lower guide layer 6 and the upper surface of the upper guide layer 8, respectively.

As the material of the lower cladding layer 5 and the upper cladding layer _9, a semiconductor material _{(Al X4 Ga 1-X4)} Y In 1-Y P (0 ≦ X4 ≦ 1,0 <Y ≦ 1), a barrier layer 15 A material having a larger band gap is preferable, and a material having a larger band gap than the lower guide layer 6 and the upper guide layer 8 is more preferable. As the _material, have a composition X4 is 0.3 to 0.7 of _{(Al X4 Ga 1-X4)} Y In 1-Y P (0 ≦ X4 ≦ 1,0 <Y ≦ 1) preferable. Y is preferably 0.4 to 0.6.

  The lower clad layer 5 and the upper clad layer 9 are configured to have different polarities. The carrier concentration and thickness of the lower clad layer 5 and the upper clad layer 9 can be in a known suitable range, and it is preferable to optimize the conditions so that the luminous efficiency of the active layer 7 is increased. Further, the warpage of the compound semiconductor layer 30 can be reduced by controlling the composition of the lower cladding layer 5 and the upper cladding layer 9.

Specifically, as the lower cladding layer 5, for example, the n-type doped with _{Si ((Al X4b Ga 1-} X4b) Yb In 1-Yb P (0.3 ≦ X4b ≦ 0.7,0.4 ≦ It is desirable to use a semiconductor material comprising Yb ≦ 0.6), the carrier concentration is preferably in the range of 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ , and the layer thickness is preferably in the range of 0.1 to 1 μm. .

On the other hand, as the upper clad layer 9, for example, Mg-doped p-type (Al _X4a Ga _1-X4a ) _Ya In _1- YaP (0.3 ≦ X4a ≦ 0.7, 0.4 ≦ Ya ≦ 0) .6) is preferably used. The carrier concentration is preferably in the range of 2 × 10 ¹⁷ to 2 × 10 ¹⁸ cm ⁻³ , and the layer thickness is preferably in the range of 0.1 to 1 μm.
The polarities of the lower cladding layer 5 and the upper cladding layer 9 can be selected in consideration of the element structure of the compound semiconductor layer 30.

  Further, above the constituent layers of the light emitting unit 20, a contact layer for lowering the contact resistance of the ohmic electrode, a current diffusion layer for planarly diffusing the element driving current throughout the light emitting unit, and conversely A known layer structure such as a current blocking layer or a current confinement layer for limiting the region through which the element driving current flows can be provided.

As shown in FIG. 1, the current spreading layer 10 is provided above the light emitting unit 20. The current spreading layer 10 may be made of a material that is transparent to the emission wavelength from the light emitting unit 20 (active layer 7), such as GaP or GaInP.
The thickness of the current spreading layer 10 is preferably in the range of 0.5 to 20 μm. This is because the current diffusion is insufficient when the thickness is 0.5 μm or less, and the cost for crystal growth to the thickness increases when the thickness is 20 μm or more.

  The p-type ohmic electrode (first electrode) 12 is a low-resistance ohmic contact electrode provided on the main light extraction surface of the light-emitting diode 100, and the n-type ohmic electrode (second electrode) 13 is a substrate of the light-emitting diode 100. It is a low-resistance ohmic contact electrode provided on the side back surface. Here, the p-type ohmic electrode 12 is provided on the surface of the current diffusion layer 10, and for example, an alloy made of AuBe / Au or AuZn / Au can be used. On the other hand, the n-type ohmic electrode 13 can be made of, for example, an alloy made of AuGe or Ni alloy / Au.

<Method for manufacturing light-emitting diode>
Next, the manufacturing method of the light emitting diode 100 of this embodiment is demonstrated using FIG.

(Formation process of compound semiconductor layer)
First, the compound semiconductor layer 30 shown in FIG. 1 is produced. The compound semiconductor layer 30 comprises an n-type GaAs substrate 1 on which a buffer layer 2 made of GaAs, a layer 3a made of GaInP (a layer having a high refractive index) 3a and a layer made of AlInP (a layer having a low refractive index) 3b are alternately arranged. 40 pairs of DBR reflection layers 3, Si-doped n-type lower cladding layer 5, lower guide layer 6, active layer 7, upper guide layer 8, Mg-doped p-type upper cladding layer 9, Mg-doped p A current diffusion layer 10 made of type GaP is sequentially stacked.

As the GaAs substrate 1, a commercially available single crystal substrate manufactured by a known manufacturing method can be used. The surface on which the GaAs substrate 1 is epitaxially grown is preferably smooth. The plane orientation of the surface of the GaAs substrate 1 is easy to epitaxially grow, and a substrate that is turned off within ± 20 ° from the (100) plane and (100) that are mass-produced is desirable from the standpoint of quality stability. Furthermore, the range of the plane orientation of the GaAs substrate 1 is more preferably 15 ° off ± 5 ° from the (100) direction to the (0-1-1) direction.
In this specification, in the notation of Miller index, “-” means a bar attached to the index immediately after that.

The dislocation density of the GaAs substrate 1 is desirably low in order to improve the crystallinity of the compound semiconductor layer 30. Specifically, for example, 10,000 pieces cm ⁻² or less, preferably 1,000 pieces cm ⁻² or less are suitable.

The GaAs substrate 1 may be n-type or p-type. The carrier concentration of the GaAs substrate 1 can be appropriately selected from desired electrical conductivity and element structure. For example, when the GaAs substrate 1 is Si-doped n-type, the carrier concentration is preferably in the range of 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ . On the other hand, when the GaAs substrate 1 is a Zn-doped p-type, the carrier concentration is preferably in the range of 2 × 10 ^{18 to} 5 × 10 ¹⁹ cm ⁻³ .

  The thickness of the GaAs substrate 1 has an appropriate range depending on the size of the substrate. If the thickness of the GaAs substrate 1 is thinner than an appropriate range, the compound semiconductor layer 30 may be broken during the manufacturing process. On the other hand, if the thickness of the GaAs substrate 1 is thicker than an appropriate range, the material cost increases. For this reason, when the substrate size of the GaAs substrate 1 is large, for example, when the diameter is 75 mm, a thickness of 250 to 500 μm is desirable to prevent cracking during handling. Similarly, when the diameter is 50 mm, a thickness of 200 to 400 μm is desirable, and when the diameter is 100 mm, a thickness of 350 to 600 μm is desirable.

  Thus, by increasing the thickness of the substrate according to the substrate size of the GaAs substrate 1, it is possible to reduce the warpage of the compound semiconductor layer 30 caused by the light emitting unit 20. As a result, the temperature distribution during epitaxial growth becomes uniform, so that the in-plane wavelength distribution of the active layer 7 can be reduced. The shape of the GaAs substrate 1 is not particularly limited to a circle, and there is no problem even if it is a rectangle or the like.

  The buffer layer 2 is provided to reduce the propagation of defects between the GaAs substrate 1 and the constituent layers of the light emitting unit 20. For this reason, the buffer layer 2 is not necessarily required if the quality of the substrate and the epitaxial growth conditions are selected. The material of the buffer layer 2 is preferably the same as that of the substrate to be epitaxially grown. Therefore, in the present embodiment, it is preferable to use GaAs for the buffer layer 2 in the same manner as the GaAs substrate 1. The buffer layer 2 may be a multilayer film made of a material different from that of the GaAs substrate 1 in order to reduce the propagation of defects. The thickness of the buffer layer 2 is preferably 0.1 μm or more, and more preferably 0.2 μm or more.

The DBR reflection layer 3 is provided to reflect light traveling in the substrate direction. The material of the DBR reflective layer 3 is preferably transparent with respect to the emission wavelength, and is preferably selected so as to be a combination that increases the difference in refractive index between the two types of materials constituting the DBR reflective layer 3. . In this embodiment, the material of the DBR reflective layer 3 is a combination of AlInP and GaInP, but two types of (Al _Xl Ga _1-Xl ) _0.5 In _0.5 P (0 ≦ xl <1) having different compositions are used. , (Al _Xh Ga _1-Xh ) _0.5 In _0.5 P (0 <xh ≦ 1), and two types of Al _xl Ga _1-xl As (0. It is also possible to select from 1 ≦ xl ≦ 1) and Al _xh Ga _1-xh As (0.1 ≦ xh ≦ 1).

  In the present embodiment, a known growth method such as a molecular beam epitaxial method (MBE) or a low pressure metal organic chemical vapor deposition method (MOCVD method) can be applied. Among these, it is most desirable to apply the MOCVD method which is excellent in mass productivity. Specifically, the GaAs substrate 1 used for the epitaxial growth of the compound semiconductor layer 30 is preferably subjected to a pretreatment such as a cleaning process or a heat treatment before the growth to remove surface contamination or a natural oxide film. The layers constituting the compound semiconductor layer 30 can be stacked by setting a GaAs substrate 1 having a diameter of 50 to 150 mm in an MOCVD apparatus and simultaneously epitaxially growing the layers. As the MOCVD apparatus, a commercially available large-sized apparatus such as a self-revolving type or a high-speed rotating type can be applied.

When the layers of the compound semiconductor layer 30 are epitaxially grown, examples of the group III constituent material include trimethylaluminum ((CH ₃ ) ₃ Al), trimethylgallium ((CH ₃ ) ₃ Ga), and trimethylindium ((CH ₃ ) ₃ In) can be used. Further, as a Mg doping raw material, for example, biscyclopentadienyl magnesium (bis- (C ₅ H ₅ ) ₂ Mg) or the like can be used. Further, as a Si doping material, for example, disilane (Si ₂ H ₆ ) or the like can be used.
In addition, phosphine (PH ₃ ), arsine (AsH ₃ ), or the like can be used as a raw material for the group V constituent element.
As the growth temperature of each layer, when p-type GaP is used as the current diffusion layer 10, 720 to 770 ° C. can be applied, and for the other layers, 600 to 700 ° C. can be applied.
Further, when p-type GaInP is used as the current diffusion layer 10, 600 to 700 ° C. can be applied.
Furthermore, the carrier concentration, layer thickness, and temperature conditions of each layer can be selected as appropriate.

  The compound semiconductor layer 30 produced in this way has a good surface state with few crystal defects despite having the light emitting portion 20. The compound semiconductor layer 30 may be subjected to surface processing such as polishing corresponding to the element structure.

(First and second electrode forming steps)
Next, a p-type ohmic electrode 12 that is a first electrode and an n-type ohmic electrode 13 that is a second electrode are formed.

  Hereinafter, the effect of the present invention will be specifically described with reference to examples. The present invention is not limited to these examples.

  In this example, an example in which a light-emitting diode according to the present invention is manufactured will be specifically described. The light-emitting diode manufactured in this example is an infrared light-emitting diode having an active layer having a quantum well structure of a well layer made of InGaAs and a barrier layer made of AlGaAs. In this example, a light-emitting diode lamp in which a light-emitting diode chip was mounted on a substrate was prepared for characteristic evaluation.

Example 1
In the light emitting diode of Example 1, first, an epitaxial wafer was fabricated by sequentially laminating compound semiconductor layers on a GaAs substrate made of an n-type GaAs single crystal doped with Si. In the GaAs substrate, a plane inclined by 15 ° in the (0-1-1) direction from the (100) plane was used as a growth plane, and the carrier concentration was set to 2 × 10 ¹⁸ cm ⁻³ . The layer thickness of the GaAs substrate was about 0.5 μm. As the compound semiconductor layer, an n-type buffer layer made of GaAs doped with Si, an n-type DBR reflective layer having a 40-pair repeating structure of Si-doped AlInP and GaInP, and Si-doped (Al _0.7 N-type lower clad layer made of Ga _0.3 ) _0.5 In _0.5 P, lower guide layer made of Al _0.4 Ga _0.6 As, (In _0.2 Ga _0.8 ) As / ( Al _0.15 Ga _0.85 ) As three well layers / barrier layers, Al _0.4 Ga _0.6 As upper guide layer, Mg doped (Al _0.7 Ga _0.3 ) p-type upper cladding layer composed of _0.5 in _{0.5 P,} consisting of _{(Al 0.5 Ga} 0.5) an intermediate layer of a thin film made of _{0.5 in} 0.5 P, p-type GaP that Mg-doped A current spreading layer was used.

In this example, a compound semiconductor layer was epitaxially grown on a GaAs substrate having a diameter of 76 mm and a thickness of 350 μm by using a low pressure metal organic chemical vapor deposition apparatus method (MOCVD apparatus) to form an epitaxial wafer. When growing an epitaxial growth layer, trimethylaluminum ((CH ₃ ) ₃ Al), trimethylgallium ((CH ₃ ) ₃ Ga) and trimethylindium ((CH ₃ ) ₃ In) are used as the raw material for the group III constituent element did. Further, biscyclopentadienyl magnesium (bis- (C ₅ H ₅ ) ₂ Mg) was used as a Mg doping material. Further, disilane (Si ₂ H ₆ ) was used as a Si doping material. Further, phosphine (PH ₃ ) and arsine (AsH ₃ ) were used as raw materials for the group V constituent elements. As the growth temperature of each layer, the current diffusion layer made of p-type GaP was grown at 750 ° C. The other layers were grown at 700 ° C.

The buffer layer made of GaAs has a carrier concentration of about 2 × 10 ¹⁸ cm ⁻³ and a layer thickness of about 0.5 μm. The lower cladding layer had a carrier concentration of about 1 × 10 ¹⁸ cm ⁻³ and a layer thickness of about 0.5 μm. The lower guide layer was undoped and had a thickness of about 50 nm. The well layer was undoped (In _0.2 Ga _0.8 ) As with a thickness of about 5 nm, and the barrier layer was undoped (Al _0.15 Ga _0.85 ) As with a thickness of about 10 nm. Three pairs of well layers and barrier layers were alternately laminated. The upper guide layer was undoped and had a thickness of about 50 nm. The upper cladding layer had a carrier concentration of about 8 × 10 ¹⁷ cm ⁻³ and a layer thickness of about 0.5 μm. The intermediate layer had a carrier concentration of about 8 × 10 ¹⁷ cm ⁻³ and a layer thickness of about 50 nm. The current diffusion layer made of GaP has a carrier concentration of about 3 × 10 ¹⁸ cm ⁻³ and a layer thickness of about 10 μm.
Alternating addition, DBR reflection layer and the carrier concentration of about 1 × ¹⁰ 18 ^{cm -3,} and AlInP that were about 71nm thickness, carrier concentration of about 1 × ¹⁰ 18 ^{cm -3,} a thickness of about 67nm was GaInP the 40 pairs were stacked.

  Next, a film was formed on the surface of the current diffusion layer by vacuum deposition so that AuBe was 0.2 μm and Au was 1 μm. Thereafter, patterning was performed using a general photolithography means, and a p-type ohmic electrode was formed as the first electrode. Next, a roughening treatment was performed on the light extraction surface which is a surface other than the electrode portion.

  Next, a second electrode is formed on the back surface of the substrate by vacuum deposition so that AuGe and Ni alloy have a thickness of 0.5 μm, Pt of 0.2 μm, and Au of 1 μm, and an n-type ohmic electrode is formed. Formed. Thereafter, heat treatment was performed at 450 ° C. for 10 minutes to form an alloy, and low resistance p-type and n-type ohmic electrodes were formed.

  Next, a dicing saw was used to cut from the compound semiconductor layer side at 350 μm intervals to form chips. The crushing layer and dirt by dicing were removed by etching with a mixed solution of sulfuric acid and hydrogen peroxide to produce a light emitting diode of Example 1.

  100 light emitting diode lamps each having the light emitting diode chip of Example 1 manufactured as described above mounted on a mount substrate were assembled. This light-emitting diode lamp was manufactured by supporting (mounting) a mount with a die bonder, wire-bonding a p-type ohmic electrode and a p-electrode terminal with a gold wire, and sealing with a general epoxy resin.

Table 1 shows the results of evaluating the characteristics of the light emitting diode (light emitting diode lamp).
As shown in Table 1, when current was passed between the n-type and p-type ohmic electrodes, infrared light having a peak wavelength of 920 nm was emitted. The forward voltage (Vf) when a current of 20 milliamperes (mA) was passed in the forward direction was about 1.2 volts. The light emission output when the forward current was 20 mA was 6.2 mW.

(Example 2)
The light emitting diode of Example 2 was manufactured under the same conditions as in Example 1 except that the configuration of the DBR reflective layer was changed.
Specifically, the DBR reflective layer has (Al _0.9 Ga _0.1 ) _0.5 In _0.5 P with a carrier concentration of about 1 × 10 ¹⁸ cm ^{−3 and a} layer thickness of about 71 nm, and a carrier concentration. (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P with a thickness of about 1 × 10 ¹⁸ cm ⁻³ and a layer thickness of about 68 nm were stacked alternately.
The results of evaluating the characteristics of this light emitting diode (light emitting diode lamp) are as shown in Table 4. Infrared light having a peak wavelength of 920 nm is emitted, and the light emission output (P ₀ ) and forward voltage (V _F ). Were 6.0 mW and 1.2 V, respectively.

(Example 3)
The light emitting diode of Example 3 was manufactured under the same conditions as in Example 1 except that the configuration of the DBR reflective layer was changed.
Specifically, DBR reflective layer was about 1 × ¹⁰ 18 carrier concentration ^{cm -3,} and _Al 0.9 _{Ga 0.1} As that were about 71nm thickness, a carrier concentration of about 1 × ¹⁰ 18 ^{cm -3} 40 pairs of Al _0.1 Ga _0.9 As having a layer thickness of about 64 nm were alternately laminated.
The results of evaluating the characteristics of this light emitting diode (light emitting diode lamp) are as shown in Table 4. Infrared light having a peak wavelength of 920 nm is emitted, and the light emission output (P ₀ ) and forward voltage (V _F ). Were 6.5 mW and 1.1 V, respectively.

(Comparative Example 1)
The light emitting diode of Comparative Example 1 was formed by a liquid phase epitaxial method which is a conventional technique. This is a light emitting diode having a double heterostructure light emitting portion having a light emitting layer of Al _0.01 Ga _0.99 As on a GaAs substrate.

Specifically, the light-emitting diode of Comparative Example 1 was manufactured by forming an n-type upper clad layer made of Al _0.01 Ga _0.99 As on an n-type (100) GaAs single crystal substrate of 50 μm and Al _0. Si luminescent layer made of _0.01 Ga _0.99 As is 20 μm, p-type lower cladding layer made of Al _0.7 Ga _0.3 As is 20 μm, Al _0.25 Ga ₀ transparent to the emission wavelength _A p-type thick film layer made of _.75 As was prepared by a liquid phase epitaxial method so as to be 60 μm. After this epitaxial growth, the GaAs substrate was removed. Next, an n-type ohmic electrode having a diameter of 100 μm was formed on the surface of the n-type AlGaAs upper cladding layer. Next, p-type ohmic electrodes having a diameter of 20 μm were formed on the back surface of the p-type AlGaAs thick film layer at intervals of 80 μm. Next, after cutting with a dicing saw at intervals of 350 μm, the crushed layer was removed by etching to produce a light-emitting diode chip of Comparative Example 1.

Table 1 shows the results of evaluating the characteristics of the light-emitting diode lamp on which the light-emitting diode of Comparative Example 1 was mounted.
As shown in Table 1, when a current was passed between the n-type and p-type ohmic electrodes, infrared light having a peak wavelength of 920 nm was emitted. The forward voltage (Vf) when a current of 20 milliamperes (mA) was passed in the forward direction was about 1.2 volts (V). The light emission output when the forward current was 20 mA was 2 mW. Moreover, the output of any sample of Comparative Example 1 was lower than that of the example of the present invention.

  The light-emitting diode of the present invention can be used as a light-emitting diode product that emits infrared light having an emission peak wavelength of 850 nm or more, particularly 900 nm or more with high output and high efficiency.

DESCRIPTION OF SYMBOLS 1 ... GaAs substrate 2 ... Buffer layer 3 ... DBR reflection layer 3a ... 1st component layer of DBR reflection layer 3b ... 2nd component layer of DBR reflection layer 5 ... Lower part Cladding layer (first cladding layer)
6 ... Lower guide layer (first guide layer)
7 ... Active layer 8 ... Upper guide layer (second guide layer)
9: Upper clad layer (second clad layer)
10 ... current diffusion layer 12 ... p-type ohmic electrode (first electrode)
13 ... n-type ohmic electrode (second electrode)
DESCRIPTION OF SYMBOLS 20 ... Light emission part 30 ... Compound semiconductor layer 100 ... Light emitting diode

Claims (8)

A light-emitting diode comprising a DBR reflective layer and a light-emitting unit on a substrate in order,
The light emitting part includes a well layer having a composition formula (In _X1 Ga _1-X1 ) As (0 ≦ X1 ≦ 1) and a barrier layer having a composition formula (Al _X2 Ga _1-X2 ) As (0 ≦ X2 ≦ 1). And a first guide and a second guide comprising a composition formula ( _{AlX3Ga1 -X3} ) _{Y2In1 -Y2P} ; 0≤X3≤1, 0 <Y2≤1) And a composition formula (Al _X4 Ga _1-X4 ) _Y In _1-YP ; 0 ≦ X4 ≦ 1, 0 <Y ≦ sandwiching the active layer through each of the first guide and the second guide A light-emitting diode comprising a first clad layer and a second clad layer made of 1).   2. The light emitting diode according to claim 1, wherein an In composition (X1) of the well layer is 0 ≦ X1 ≦ 0.3.   3. The light emitting diode according to claim 2, wherein the In composition (X1) of the well layer is 0.1 ≦ X1 ≦ 0.3.   4. The light emitting diode according to claim 1, wherein the DBR reflective layer is formed by alternately stacking 10 to 50 pairs of two types of layers having different refractive indexes. The two types of layers having different refractive indices are composed of two types of (Al _Xh Ga _1-Xh ) _{Y 3} In _{1 -Y 3} P (0 <Xh ≦ 1, Y 3 = 0.5), (Al _Xl Ga _{1− Xl} ) _{Y3In1 -Y3P} ; 0 ≦ Xl <1, Y3 = 0.5), and the difference between the two Al compositions ΔX = xh−xl is greater than or equal to 0.5, The light emitting diode according to claim 4.   The light emitting diode according to claim 4, wherein the two types of layers having different refractive indexes are a combination of GaInP and AlInP. The two types of layers having different refractive indexes are composed of two types of Al _xl Ga _1-xl As (0.1 ≦ xl ≦ 1) and Al _xh Ga _1-xh As (0.1 ≦ xh ≦ 1) having different compositions. The light-emitting diode according to claim 4, wherein the light-emitting diode is a combination, and the difference in composition ΔX = xh−xl between the two Al is greater than or equal to 0.5.   The light emitting diode according to any one of claims 1 to 7, further comprising a current diffusion layer on a surface of the light emitting unit opposite to the DBR reflective layer.

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