TWI437729B - Light-emitting diode - Google Patents

Description

Light-emitting diode

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

Infrared light-emitting diodes have been widely used in infrared communication, infrared remote control devices, various sensor light sources, and night illumination.

In the vicinity of such a peak wavelength, a compound semiconductor layer containing an AlGaAs active layer is grown on a light-emitting diode of a GaAs substrate by liquid phase epitaxy (for example, Patent Documents 1 to 3).

On the other hand, in the case of infrared communication used for transmitting and receiving messages between machines, for example, using infrared rays of 850 to 900 nm, in the case of infrared remote control operation, a wavelength band having a high sensitivity of the light receiving portion, for example, 880 to 940 is used. Infrared rays of nm. As an infrared light-emitting diode that can be used for both infrared communication and infrared remote control operation communication for terminals such as mobile phones that have both infrared communication and infrared remote control operation communication, it is known that the wavelength of the illuminating peak is 880. An AlGaAs active layer containing Ge in a substantial impurity of 890 nm (Patent Document 4).

In addition, as an infrared light-emitting diode which can have an emission peak wavelength of 900 nm or more, an InGaAs active layer is conventionally used (Patent Document 5).

[Previous Technical Literature] Patent literature

Patent Document 1: Japanese Patent Publication No. 6-21507

Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-274454

Patent Document 3: Japanese Patent Laid-Open No. Hei 7-38148

Patent Document 4: Japanese Laid-Open Patent Publication No. 2006-190792

Patent Document 5: Japanese Laid-Open Patent Publication No. 2002-344013

However, in the method of growing the compound semiconductor layer by the liquid phase epitaxy method, it is difficult to form a multiple quantum structure having excellent monochromaticity.

In the case where an AlGaAs active layer containing Ge in a substantially pure substance is used, it is difficult to make the emission peak wavelength 900 nm or more (Patent Document 4, FIG. 3).

Infrared light-emitting diodes using an InGaAs active layer having an emission peak wavelength of 900 nm or more are expected to have higher luminous efficiency from the viewpoint of further improving performance, energy saving, and cost.

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

The inventors of the present invention have been made to solve the above problems, and as a result of continuous research, a high-output/high-efficiency emission of 850 nm or more is achieved by forming a structure including a light-emitting portion and a DBR reflection layer between the light-emitting portion and the substrate. - In particular, an infrared light-emitting diode having an emission peak wavelength of 900 nm or more is completed; wherein the light-emitting portion has a multi-quantum well structure composed of a 3-dos mixed crystal InGaAs well layer and a 3-ary mixed crystal AlGaAs barrier layer The active layer and the AlGaInP cladding layer of the 4-membered mixed crystal of the active layer.

First, the inventors of the present invention used a well layer composed of InGaAs to have a luminescence peak wavelength of 850 nm or more, particularly 900 nm or more used for infrared communication or the like, as a multiple quantum for improving monochromaticity and output. The active layer of the well structure.

Further, AlGaInP, which is a 4-component mixed crystal, is used in a coating layer which is sandwiched between active layers, has a large band gap and is transparent to an emission wavelength, and has good crystallinity because it does not contain As which is liable to cause defects.

Further, in the multiple quantum well structure of InGaAs/AlGaAs, it is difficult to make a two-layer lattice rule, and the active layer becomes a skew quantum well structure. From such a skewed quantum well structure, the output of the InGaAs and the thickness of the output or the effect on the monochromaticity are also large, and the selection of the appropriate composition, thickness, and number of pairs results in a particularly high output and high output. Infrared light of power.

The inventors of the present invention conducted further studies based on such findings, and thus completed the present invention shown in the following structures.

(1) A light-emitting diode characterized by having a DBR reflective layer and a light-emitting diode of a light-emitting portion sequentially on a substrate, the light-emitting portion having a composition formula (In _X1 Ga _1-X1 ) As (0) X1 1) The well layer formed by the composition formula (Al _X2 Ga _1-X2 ) As (0 X2 1) The active layer of the laminated structure of the barrier layer formed by the composition formula (Al _X3 Ga _1-X3 ) As (0 X3 1) a first light guiding layer and a second light guiding layer, and a composition formula in which the first light guiding layer and the second light guiding layer are interposed therebetween and sandwiching the active layer (Al _X4 Ga _{1 -X4} ) _Y In _1-Y P(0 X4 1, 0 < Y 1) The first cladding layer and the second cladding layer.

(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 the item (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 composed of two layers having different refractive indices of two to ten pairs of alternating layers.

(5) The light-emitting diode according to the item (4), wherein the two kinds of layers having different refractive indices are different in composition (Al _Xh Ga _1-Xh ) _Y3 In _1-Y3 P (0<Xh) 1, Y3 = 0.5), (Al _X1 Ga _1-X1 ) _Y3 In _1-Y3 P (0 A combination of X1<1 and Y3=0.5), the composition difference of Al of both ΔX=Xh-X1 is larger or equal to 0.5.

(6) The light-emitting diode according to (4), wherein the two layers having different refractive indices are a combination of GaInP and AlInP.

(7) The light-emitting diode according to the item (4), wherein the two kinds of layers having different refractive indices are two kinds of Al _x1 Ga _1-x1 As (0.1) X1 1), Al _xh Ga _1-xh As (0.1 Xh In the combination of 1), the composition difference ΔX=xh-x1 of the two is greater 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 the above configuration, the following effects are obtained.

High-output ‧ high-efficiency emission of infrared light with an emission peak wavelength of 850 nm or more, especially 900 nm or more.

Because the active layer is composed of the composition formula (In _X1 Ga _1-X1 ) As (0 X1 1) The well layer formed by the composition formula (Al _X2 Ga _1-X2 ) As (0 X2 1) The structure of the multiple well structure of the barrier layer formed, which has excellent monochromaticity.

Because the cladding layer is composed of a 4-ary mixed crystal (Al _X Ga _1-X ) _Y In _1-Y P (0 X1 1, 0 < Y 1) The structure is such that the Al concentration is lower and the moisture resistance is improved as compared with the infrared light-emitting diode composed of a three-component mixed crystal.

Because the active layer has a compositional formula (In _X1 Ga _1-X1 ) As (0 X1 1) The well layer formed by the composition formula (Al _X2 Ga _1-X2 ) As (0 X2 1) The laminated structure of the barrier layer formed is suitable for mass production by the MOCVD method. In particular, the group V elements are commonly referred to as As, and the switching of the material gas is a simple advantage.

Since the structure of the DBR reflection film is provided between the light-emitting layer and the substrate, it is possible to prevent the light-emitting output from being lowered due to light absorption by the GaAs substrate.

Hereinafter, a light-emitting diode according to an embodiment of the present invention will be described in detail using the drawings. In addition, the illustrations used in the following description are for the purpose of facilitating the understanding of the features, and it is convenient to enlarge the parts which become the features, and the dimensional ratios and the like of the respective structural elements are not limited to the same as the actual ones.

<Light Emitting Diode>

Fig. 1 is a schematic cross-sectional view showing a light-emitting diode according to an embodiment of the present invention. In addition, FIG. 2 is a schematic cross-sectional view showing a laminated structure of a well layer and a barrier layer.

The light-emitting diode 100 according to the first embodiment is provided with a DBR reflective layer 3 and a light-emitting diode 30 of the light-emitting portion 20 in this order, and the light-emitting portion 20 has a composition formula (In _X1 Ga _1-X1). )As(0 X1 1) The well layer 15 formed by the composition formula (Al _X2 Ga _1-X2 ) As (0 X2 1) The active layer 7 of the laminated structure of the barrier layer 16 formed by the composition formula (Al _X3 Ga _1-X3 ) As (0) X3 1) a composition formula (Al) in which the first light guiding layer and the second light guiding layer are formed, and the first light guiding layer 6 and the second light guiding layer 8 are interposed therebetween to sandwich the active layer 7 _X4 Ga _1-X4 ) _Y In _1-Y P(0 X4 1, 0 < Y 1) The first cladding layer 5 and the second cladding layer 9 which are formed.

As shown in FIG. 1, the compound semiconductor layer (also referred to as an epitaxial growth layer) 30 has a structure in which a light-emitting portion 20 of a pn junction type and a current diffusion layer 10 are sequentially laminated. In the configuration of the compound semiconductor layer 30, a conventional functional layer can be added as appropriate. For example, a contact layer for reducing the contact resistance of the ohmic electrode and a current diffusion layer for planarly diffusing the element drive current to the entire light-emitting portion can be provided; instead, the region through which the element drive current flows is limited A conventional layer structure such as a current blocking layer or a current confinement layer.

Further, the compound semiconductor layer 30 is preferably formed by epitaxial growth and formed on a GaAs substrate.

For example, as shown in Fig. 1, the light-emitting portion 20 provided on the n-type substrate has an n-type lower cladding layer (first cladding layer) 5 and a lower light guide layer sequentially laminated on the DBR reflective layer 3. The layer 6, the active layer 7, the upper light guiding layer 8, and the p-type upper cladding layer (second cladding layer) 9 are formed. That is, the light-emitting portion 20 is preferably included in the lower side of the active layer 7 in order to obtain high-intensity light emission for the purpose of causing the radiation recombination carrier and the "lighting" of the light into the active layer 7. The structure of the lower cladding layer 5, the lower light guiding layer 6, and the upper light guiding layer 8 and the upper cladding layer 9 disposed on the upper side is a so-called double variation (English abbreviated as DH).

As shown in Fig. 2, the active layer 7 is used to control the emission wavelength of the light-emitting diode (LED) to constitute a quantum well structure. That is, the active layer 7 has a multilayer structure (stacked structure) of the well layer 15 and the 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, and more preferably in the range of 0.05 to 1 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 improve the luminous efficiency, it is desirable to be an undoped or a carrier concentration of less than 3 × 10 ¹⁷ cm ^{-3 which} is excellent in crystallinity.

DBR (Distributed Bragg Reflector) reflective layer 3 is composed of alternating layers with a film thickness of λ/(4n) (λ: in order to reflect the wavelength of light in vacuum, n: refractive index of layer material), 2 A multilayer film composed of layers having different refractive indices. When the reflectance is such that the difference between the two refractive indices is large, a high reflectance is obtained with a multilayer film having a small number of layers. It is characterized in that it does not reflect on a certain surface as in the case of a general reflection film, and the entire multilayer film is reflected by the interference phenomenon of light.

The DBR (Distributed Bragg Reflector) reflective layer 3 is preferably composed of two layers having different refractive indices of the alternating layers 10 to 50, and is preferably composed of a pair of layers 20 to 40. In the case of 10 or less, since the reflectance is too low, it does not contribute to an increase in output; even if it is 50 pairs or more, the reflectance is further increased to be small.

Two layers having different refractive indices constituting the DBR (Distributed Bragg Reflector) reflective layer 3 are desirably made of two kinds of compositions (Al _Xh Ga _{1 ) in} order to obtain high efficiency and high reflectance. _-Xh ) _Y3 In _1-Y3 P(0<Xh 1, Y3 = 0.5), (Al _X1 Ga _1-X1 ) _Y3 In _1-Y3 P (0 a combination of Xh<1 and Y3=0.5), the difference in the composition of the two ΔX=Xh-X1 is larger or equal to 0.5; or the combination of GaInP and AlInP; or the composition of the two Al _x1 Ga _1-x1 As (0.1 X1 1), Al _xh Ga _1-xh As (0.1 Xh 1) Pairwise, the difference between the two components △X=xh-x1 is selected from any of the combinations that are larger or equal to 0.5.

The combination of different compositions of AlGaInP is preferable because it does not contain As which is prone to crystal defects, and since GaInP and AlInP take the largest difference in refractive index, the number of reflective layers can be reduced, and the replacement of the composition is also simple. . Further, the AlGaAs system has an advantage that a large refractive index difference can be easily obtained.

In Fig. 3, it is shown that the In composition (X1) of the well layer 15 is fixed at 0.1, showing the correlation between the layer thickness and the wavelength of the luminescence peak. The values shown in Table 1 are shown in Table 1. When the well layer is thickened to 3 nm, 5 nm, and 7 nm, the wavelength is monotonically grown to 820 nm, 870 nm, and 920 nm.

Figure 4 shows the relationship between the luminescence peak wavelength of the well layer 15 and its In composition (X1) and layer thickness. Fig. 4 is a graph showing the combination of the In composition (X1) of the well layer 15 and the layer thickness of the well layer 15 with the illuminating peak wavelength of the well layer 15. Specifically, a combination of the In composition (X1) and the layer thickness of the well layer 15 having a structure in which the emission peak wavelengths are 920 nm and 960 nm, respectively, is displayed. Further, in Fig. 4, the combination of In composition (X1) and layer thickness at other emission peak wavelengths of 820 nm, 870 nm, 985 nm, and 995 nm is shown. The values at the points shown in Fig. 4 are shown in Table 2.

When the illuminating peak wavelength is 920 nm, if the In composition (X1) is decreased from 0.3 to 0.05, since the layer thickness corresponding to this is monotonously thickened from 3 nm to 8 nm, it can be easily found by the same industry. It becomes a combination of the illuminating peak wavelength of 920 nm.

In addition, when the In composition (X1) is 0.1, when the layer thickness is increased to 3 nm, 5 nm, 7 nm, and 8 nm, the wavelength of the luminescence peak becomes 820 nm, 870 nm, and 920 nm. 960 nm. In addition, when the In composition (X1) is 0.2, when the layer thickness is increased to 5 nm or 6 nm, the wavelength of the luminescence peak becomes 920 nm and 960 nm, and when the composition of In (X1) is 0.25. When the layer thickness is increased to 4 nm and 5 nm, the wavelength of the luminescence peak is 920 nm and 960 nm, and when the composition of In (X1) is 0.3, the thickness of the layer is increased to 3 At nm and 5 nm, the wavelength of the luminescence peak is 920 nm and 985 nm.

In addition, when the layer thickness is 5 nm, if the In composition (X1) is increased to 0.1, 0.2, 0.25, and 0.3, the wavelength of the luminescence peak becomes 870 nm, 920 nm, 960 nm, and 985 nm; When the composition (X1) is increased to 0.35, the luminescence peak wavelength becomes 995 nm.

In Fig. 4, when the combination of the In composition (X1) and the layer thickness at which the emission peak wavelength is 920 nm and 960 nm is connected, the display is approximately straight. Further, it is presumed that the line connecting the In composition (X1) and the layer thickness which are the predetermined emission peak wavelengths in the wavelength band of 850 nm or more and up to 1000 nm is also approximately linear. Further, it is presumed that the shorter the wavelength of the illuminating peak of the line connecting the combinations, the lower the lower the left side, and the longer the upper side is located on the upper right side.

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.

In Fig. 5, the In composition (X1) in which the layer thickness of the well layer 15 is fixed at 5 nm is shown to be related to the wavelength of the luminescence peak and its luminescence output. The values at the points shown in Fig. 5 are shown in Table 3.

When the composition of In (X1) is increased to 0.12, 0.2, 0.25, 0.3, and 0.35, the wavelength of the luminescence peak becomes 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 luminescence peak wavelength increases approximately monotonically from 870 nm to 985 nm. However, even if the In composition (X1) is increased from 0.3 to 0.35, although the length is changed from 985 nm to 995 nm, the rate of change for the long wavelength becomes small.

In addition, the illuminating peak wavelength is 870 nm (X1 = 0.12), 920 nm (X1 = 0.2), and 960 nm (X1 = 0.25), and the illuminating output is as high as 6.0 mW; even at 985 nm (X1 = 0.3) In the case of practical use, it has a value of up to 4.5 mW; in the case of 995 nm (X1 = 0.35), it is as low as 1.8 mW.

According to Figures 3 to 5, the well layer 15 preferably has (In _X1 Ga _1-X1 ) As (0) X1 The composition of 0.3). Adjusting the above X1 enables the desired wavelength of light emission.

When the wavelength of the luminescence peak is 900 nm or more, it is preferably 0.1. X1 0.3; below 900 nm, preferably 0 X1 0.1.

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

The barrier layer 16 has (Al _X2 Ga _1-X2 ) As (0 X2 1) The composition. The above X2 is preferably formed to have a band gap larger than that of the well layer 15, and more preferably in the range of 0 to 0.4.

The layer thickness of the barrier layer 16 is preferably equal to or thicker than the layer thickness of the well layer 15, whereby the luminous efficiency of the well layer 15 can be improved.

In Fig. 6, when the layer thickness of the well layer 15 is 5 nm and the In composition (X1) = 0.2, the logarithm of the well layer and the barrier layer is correlated with the light emission output. The values at the points shown in Fig. 6 are shown in Table 4.

From the pair of 1 to 10 pairs, it is known that the luminous output has a value of up to 5.5 mW or more, and even 20 pairs have a practically sufficiently high value of 4.8 mW. It is speculated that when the number of pairs is further increased, the luminescence output will decrease.

In the multilayer structure of the well layer 15 and the barrier layer 16, the number of pairs of the alternate well layer 15 and the barrier layer 16 is not particularly limited, and according to Fig. 6, it is preferably one pair or more and ten pairs or less. That is, in the active layer 7, the well layer 15 preferably contains from 1 to 10 layers. Here, the luminous efficiency of the active layer 7 is a suitable range, and the well layer 15 is one layer or more, and even one layer is possible. On the other hand, the lattice irregularity exists between the well layer 15 and the barrier layer 16, and because the carrier concentration is low, if many pairs are formed, crystal defects will occur to lower the luminous efficiency or to make the forward voltage (V _F ) increase. Therefore, it is preferably 10 pairs or less, more preferably 5 pairs or less.

As shown in FIG. 2, the lower light guiding layer 6 and the upper light guiding layer 8 are respectively disposed on the lower surface and the upper surface of the active layer 7. Specifically, a lower light guiding layer 6 is provided on the lower surface of the active layer 7, and an upper light guiding layer 8 is provided on the upper surface of the active layer 7.

The lower light guiding layer 6 and the upper light guiding layer 8 have (Al _X3 Ga _1-X3 ) As (0) X3 1) The composition. The energy band gap of the above X3 is preferably made equal to or larger than the barrier layer 16, and more preferably in the range of 0.2 to 0.4.

The lower light guiding layer 6 and the upper light guiding layer 8 are respectively provided for reducing the transmission of defects between the lower cladding layer 5 and the upper cladding layer 9 and the active layer 7. That is, in the present invention, the group V structural element of the active layer 7 is arsenic (As), and the lower cladding layer 5 and the V group structural element of the upper cladding layer 9 are phosphorus (P) in the active layer 7 The interface with the lower cladding layer 5 and the upper cladding layer 9 is liable to cause defects. The transfer of the defects of the active layer 7 causes a decrease in the performance of the light-emitting diode. In order to effectively reduce the transmission of the defect, the layer thickness of the lower light guiding layer 6 and the upper light guiding layer 8 is preferably 10 nm or more, more preferably 20 nm to 100 nm.

The conductivity type of the lower light guiding layer 6 and the upper light guiding layer 8 is not particularly limited, and any of undoped, p-type, and n-type can be selected. In order to improve the luminous efficiency, it is desirable to be an undoped or a carrier concentration of less than 3 × 10 ¹⁷ cm ^{-3 which} is excellent in crystallinity.

As shown in Fig. 1, the lower cladding layer 5 and the upper cladding layer 9 are respectively disposed on the lower surface of the lower light guiding layer 6 and the upper surface of the upper light guiding layer 8.

The material of the lower cladding layer 5 and the upper cladding layer 9 is (Al _X4 Ga _1-X4 ) _Y In _1-Y P (0). X4 1, 0 < Y The semiconductor material of 1) is preferably a material having a larger band gap than the barrier layer 15, and more preferably a material having a larger band gap than the lower light guiding layer 6 and the upper light guiding layer 8. The above material preferably has (Al _X4 Ga _1-X4 ) _Y In _1-Y P(0 X4 1, 0 < Y 1) X4 is a composition of 0.3 to 0.7. Further, Y is preferably made to be 0.4 to 0.6.

The lower cladding layer 5 and the upper cladding layer 9 are configured to have different polarities. Further, the carrier concentration and thickness of the lower cladding layer 5 and the upper cladding layer 9 can be within a suitable range, and it is preferred to optimize the conditions to improve the luminous efficiency of the active layer 7. Further, by controlling the composition of the lower cladding layer 5 and the upper cladding layer 9, the bending of the compound semiconductor layer 30 can be reduced.

Specifically, it is desirable that the lower cladding layer 5 is made of, for example, an n-type (Al _X4b Ga _1-X4b ) _Yb In _1-Yb P (0.3) doped with Si. X4b 0.7, 0.4 Yb 0.6) The semiconductor material formed. Further, 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, it is desirable that the upper cladding layer 9 is made of, for example, Mg-doped p-type (Al _X4a Ga _1-X4a ) _Ya In _1-Ya P (0.3 X4a 0.7, 0.4 Ya 0.6) The semiconductor material formed. Further, 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.

Further, 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 structural layer of the light-emitting portion 20, a contact layer for reducing the contact resistance of the ohmic electrode, a current diffusion layer for diffusing the element drive current planarly to the entire light-emitting portion, and the like may be provided. A conventional layer structure such as a current blocking layer or a current confinement layer in a region where the element drive current is limited.

As shown in FIG. 1, the current diffusion layer 10 is provided above the light-emitting portion 20. The current diffusion layer 10 is a material transparent to the light emission wavelength from the light-emitting portion 20 (active layer 7), and for example, GaP or GaInP can be used.

Further, the thickness of the current diffusion layer 10 is preferably in the range of 0.5 to 20 μm. When it is 0.5 μm or less, current diffusion is insufficient, and when it is 20 μm or more, the cost is increased in order to grow crystals until the thickness thereof.

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

<Method of Manufacturing Light Emitting Diode>

Next, a method of manufacturing the light-emitting diode 100 of the present embodiment will be described using FIG.

(Step of forming a compound semiconductor layer)

First, as shown in Fig. 1, a compound semiconductor layer 30 is formed. The compound semiconductor layer 30 is formed on the n-type GaAs substrate 1, and a buffer layer 2 made of GaAs, a layer composed of GaInP (a layer having a large refractive index) 3a and a layer composed of AlInP are sequentially laminated. a layer (a layer having a small refractive index) 3b, a DBR reflective layer 3, a Si-doped n-type lower cladding layer 5, a lower light guiding layer 6, an active layer 7, an upper light guiding layer 8, and Mg doping The p-type upper cladding layer 9 is obtained by a current diffusion layer 10 composed of Mg-doped p-type GaP.

As the GaAs substrate 1, a commercially available single crystal substrate obtained by a conventional production method can be used. It is desirable that the surface of the GaAs substrate 1 whose epitaxial growth is smooth is smooth. From the viewpoint of quality stability, it is desirable that the surface orientation of the surface of the GaAs substrate 1 is easily epitaxially grown, and the substrate is produced in a (100) plane and offset (100) ± 20°. Further, the range of the plane orientation of the GaAs substrate 1 is more preferably shifted by 15° ± 5° from the (100) direction toward the (0-1-1) direction.

Also, in the specification of the present invention, in the indication of the Miller index, "-" means a horizontal line attached to its subsequent index.

The difference in the discharge density of the GaAs substrate 1 is to improve the crystallinity of the compound semiconductor layer 30, and the lower the ratio, the better. Specifically, for example, it is suitably 10,000 cm ^-2 or less, and more desirably 1,000 cm ^-2 or less.

The GaAs substrate 1 may be either n-type or p-type. The carrier concentration of the GaAs substrate 1 can be appropriately selected from the desired conductivity and device structure. For example, in the case where the GaAs substrate 1 is an n-type doped with Si, the carrier concentration is preferably in the range of 1 × 10 ¹⁷ to 5 × 10 ¹⁸ cm ^-3 . To this end, in the case where Zn is doped to the p-type of the GaAs substrate 1, 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 a suitable range in accordance with the size of the substrate. If the thickness of the GaAs substrate 1 is thin, the crack in the process of the compound semiconductor layer 30 is feared. On the other hand, if the thickness of the GaAs substrate 1 is thick, the material cost will increase. Therefore, in the case where the substrate size of the GaAs substrate 1 is large, for example, in the case of a diameter of 75 mm, in order to prevent cracking during operation, a thickness of 250 to 500 μm is desirable. Similarly, in the case of a diameter of 50 mm, a thickness of 200 to 400 μm is desired; in the case of a diameter of 100 mm, a thickness of 350 to 600 μm is desired.

In this manner, by increasing the thickness of the substrate in accordance with the substrate size of the GaAs substrate 1, the bending of the compound semiconductor layer 30 caused by the light-emitting portion 20 can be reduced. Thereby, the wavelength distribution in the plane of the active layer 7 can be made small in order to make the temperature distribution in epitaxial growth uniform. Further, the shape of the GaAs substrate 1 is not particularly limited to a circular shape, and there is no problem even if it is a rectangle or the like.

The buffer 2 is provided to reduce the defect transmission of the structural layers of the GaAs substrate 1 and the light-emitting portion 20. Therefore, if the quality of the substrate or the epitaxial growth conditions are selected, the buffer layer 2 is not necessarily required. Further, the material of the buffer layer 2 is preferably made of the same material as the substrate on which the epitaxial growth is performed. Therefore, in the present embodiment, similarly to the GaAs substrate 1, GaAs is preferably used in the buffer layer 2. Further, in the buffer layer 2, a multilayer film made of a material different from the GaAs substrate 1 can be used to reduce the transmission 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 reflective layer 3 is used to reflect the light set in the direction of the substrate. The material of the DBR reflective layer 3 is preferably selected so as to be transparent to the light-emitting wavelength and to be a combination of the refractive index difference between the two materials constituting the DBR reflective layer 3. In the present embodiment, the material of the DBR reflective layer 3 is a combination of AlInP and GaInP, but it can also be composed of two kinds of (Al _X1 Ga _1-X1 ) _0.5 In _0.5 P (0). X1<1), (Al _Xh Ga _1-Xh ) _0.5 In _0.5 P(0<Xh 1) to choose, in addition, can also be composed of two different types of Al _x1 Ga _1-x1 As (0.1 X1 1), Al _xh Ga _1-xh As (0.1 Xh 1) to choose.

In the present embodiment, a conventional growth method such as a molecular line epitaxy method (MBE method) or a reduced pressure metalorganic chemical vapor deposition method (MOCVD method) can be employed. Among them, the MOCVD method having excellent mass productivity is most desirable. Specifically, the GaAs substrate 1 used for epitaxial growth of the compound semiconductor layer 30 is desirably subjected to a pretreatment such as a cleaning step or a heat treatment before growth to remove surface contamination or a natural oxide film. Each of the layers constituting the compound semiconductor layer 30 can be mounted in an MOCVD apparatus with a GaAs substrate 1 having a diameter of 50 to 150 mm, and is epitaxially grown to be laminated. Further, the MOCVD apparatus can be a commercially available large-scale apparatus such as a self-propelled transformation or a high-speed rotation type.

When the epitaxial growth of each layer of the compound semiconductor layer 30 is carried out, a raw material of the group III constituent element can be, for example, trimethylaluminum ((CH ₃ ) ₃ Al), trimethylgallium ((CH ₃ ) ₃ Ga), and three. Methyl indium ((CH ₃ ) ₃ In). Further, as the doping raw material of Mg, for example, biscyclopentadienyl magnesium (bis-(C ₅ H ₅ ) ₂ Mg) or the like can be used. Further, as the doping raw material of Si, for example, dioxane (Si ₂ H ₆ ) or the like can be used.

Further, as a raw material of the group V structural element, phosphine (PH ₃ ), hydrazine (AsH ₃ ) or the like can be used.

Further, in the case where p-type GaP is used as the current diffusion layer 10, the growth temperature of each layer can be 720 to 770 ° C, and in the case of other layers, 600 to 700 ° C can be employed.

Further, in the case where p-type GaInP is used as the current diffusion layer 10, 600 to 700 ° C can be employed.

Further, the carrier concentration, layer thickness, and temperature conditions of each layer can be appropriately selected.

The compound semiconductor layer 30 obtained in this manner can obtain a good surface state with few crystal defects even though it has the light-emitting portion 20. Further, the compound semiconductor layer 30 may be subjected to surface processing such as polishing in accordance with the element structure.

(Step of forming the first and second electrodes)

Next, a p-type ohmic electrode 12 of the first electrode and an n-type ohmic electrode 13 of the second electrode are formed.

[Examples]

Hereinafter, the effects of the present invention will be specifically described using examples. Further, the present invention is not limited by the embodiments.

In the present embodiment, an example of producing a light-emitting diode according to the present invention will be specifically described. Further, in the light-emitting diode system obtained in the present embodiment, an infrared light-emitting diode having an active layer composed of a quantum well structure consisting of a well layer made of InGaAs and a barrier layer made of AlGaAs. In the present embodiment, a light-emitting diode lamp in which a light-emitting diode wafer is mounted on a substrate is produced for characteristic evaluation.

(Example 1)

In the light-emitting diode system of the first embodiment, an epitaxial wafer was first formed by sequentially laminating a compound semiconductor layer on a GaAs substrate made of a Si-doped n-type GaAs single crystal.

The GaAs substrate has a surface which is inclined by 15° from the (100) plane toward the (0-1-1) direction as a growth surface, and has a carrier concentration of 2 × 10 ¹⁸ cm ^-3 . Further, the layer thickness of the GaAs substrate was made to be about 0.5 μm. The compound semiconductor layer is an n-type buffer layer composed of GaAs doped with GaAs, an n-type DBR reflective layer of 40 pairs of Si-doped AlInP and GaInP, and Si-doped (Al _0.7 Ga _0.3 ) _0.5 An n-type lower cladding layer composed of In _0.5 P, a lower light guiding layer composed of Al _0.4 Ga _0.6 As, and a well composed of three pairs of (In _0.2 Ga _0.8 )As/(Al _0.15 Ga _0.85 ) As a layer/barrier layer, an upper light guiding layer composed of Al _0.4 Ga _0.6 As, a p-type upper cladding layer composed of Mg-doped (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, and (Al _0.5 Ga _0.5 An intermediate layer of a film composed of _0.5 In _0.5 P and a current diffusion layer made of Mg-doped p-type GaP.

In the present embodiment, a compound semiconductor layer was epitaxially grown on a GaAs substrate having a diameter of 76 mm and a thickness of 350 μm using a reduced-pressure organic metal chemical vapor deposition apparatus (MOCVD apparatus) to form an epitaxial wafer. When the epitaxial growth layer is grown, the raw materials of the group III constituent elements are trimethylaluminum ((CH ₃ ) ₃ Al), trimethylgallium ((CH ₃ ) ₃ Ga), and trimethyl indium (( CH ₃ ) ₃ In). Further, as the doping raw material of Mg, biscyclopentadienyl magnesium (bis-(C ₅ H ₅ ) ₂ Mg) can be used. Further, dioxane (Si ₂ H ₆ ) can be used as the doping material for Si. Further, as a raw material of the group V structural element, phosphine (PH ₃ ) or hydrazine (AsH ₃ ) can be used. Further, as a growth temperature of each layer, a current diffusion layer composed of p-type GaP was grown at 750 °C. The other layers were grown at 700 °C.

The buffer layer composed of GaAs has a carrier concentration of about 2 × 10 ¹⁸ cm ^-3 and a thickness of about 0.5 μm. The lower cladding layer has a carrier concentration of about 1 × 10 ¹⁸ cm ^-3 and a thickness of about 0.5 μm. The lower light guiding layer is made undoped and has a layer thickness of about 50 nm. The well layer is made of (In _0.2 Ga _0.8 )As which is undoped and has a layer thickness of about 5 nm, and the barrier layer is made of (Al _0.15 Ga _0.85 ) As which is undoped and has a layer thickness of about 10 nm. In addition, the well layer and the barrier layer are alternately laminated. The upper light guiding layer is undoped and has a layer thickness of about 50 nm. The upper cladding layer has a carrier concentration of about 8 × 10 ¹⁷ cm ^-3 and a thickness of about 0.5 μm. The intermediate layer has a carrier concentration of about 8 × 10 ¹⁷ cm ^-3 and a thickness of about 50 nm. The current diffusion layer composed of GaP has a carrier concentration of about 3 × 10 ¹⁸ cm ^-3 and a thickness of about 10 μm.

Further, the DBR reflective layer is an alternating layer 40 having a carrier concentration of about 1 × 10 ¹⁸ cm ^-3 , a thickness of about 71 nm of AlInP, and a carrier concentration of about 1 × 10 ¹⁸ cm ^-3 , so that the thickness becomes GaInP of about 67 nm.

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

Next, on the back surface of the substrate as the second electrode, AuGe and Ni alloy were formed into a film having a thickness of 0.5 μm, Pt was 0.2 μm, and Au was set to 1 μm, and a film was formed by a vacuum deposition method to form an n-type ohmic electrode. Thereafter, the film was heat-treated at 450 ° C for 10 minutes to form a low-resistance p-type and n-type ohmic electrode.

Subsequently, cutting and wafer formation were performed at intervals of 350 μm from the side of the compound semiconductor layer using a die cutter. The light-emitting diode of Example 1 was produced by etching and removing the fracture layer and the dirt caused by the die cutting using a sulfuric acid/hydrogen peroxide mixed solution.

A light-emitting diode lamp in which the light-emitting diode wafer of the first embodiment fabricated as described above was mounted on a mounting substrate was assembled. The LED lamp mounting is supported (mounted) by a die bond, and the p-type ohmic electrode and the p-electrode terminal are bonded by a gold wire, and then sealed by a general epoxy resin.

The results of evaluating the characteristics of this light-emitting diode (light-emitting diode lamp) are shown in Table 5.

As shown in Table 5, after flowing a current between the n-type and p-type ohmic electrodes, infrared light having a peak wavelength of 920 nm was emitted. The forward voltage (Vf) at a current of 20 microamperes (mA) in the forward direction becomes about 1.2 volts. The luminous output when the forward current is 20 mA is 6.2 mW.

Measuring current = 20 mA

(Example 2)

The light-emitting diode system of Example 2 was produced under the same conditions as in Example 1 except that the structure of the DBR reflective layer was changed.

Specifically, the DBR reflective layer is an alternating layer 40 which has a carrier concentration of about 1×10 ¹⁸ cm ⁻³ , a layer thickness of about 71 nm (Al _0.9 Ga _0.1 ) _0.5 In _0.5 P , and a carrier concentration of about 1 ×10 ¹⁸ cm ^-3 , layer thickness about 68 nm (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P.

The results of evaluating the characteristics of the light-emitting diode (light-emitting diode lamp) are as shown in Table 4, and the infrared light having a peak wavelength of 920 nm is emitted, and the light-emitting output (P ₀ ) and the forward voltage (V _F ) are respectively It is 6.0 mW, 1.2 V.

(Example 3)

The light-emitting diode system of Example 3 was produced under the same conditions as in Example 1 except that the structure of the DBR reflective layer was changed.

Specifically, the DBR reflective layer is an alternating layer 40 such that the carrier concentration is about 1×10 ¹⁸ cm ⁻³ , the layer thickness is about 71 nm, Al _0.9 Ga _0.1 As, and the carrier concentration is about 1×10 ¹⁸ cm ^{− 3.} Al _0.1 Ga _0.9 As with a layer thickness of about 64 nm.

The results of evaluating the characteristics of the light-emitting diode (light-emitting diode lamp) are as shown in Table 4, and the infrared light having a peak wavelength of 920 nm is emitted, and the light-emitting output (P ₀ ) and the forward voltage (V _F ) are respectively It is 6.5 mW and 1.1 V.

(Comparative Example 1)

The light-emitting diode system of Comparative Example 1 was formed by a liquid phase epitaxy method of a conventional technique. It is changed to a light-emitting diode having a double heterostructure light-emitting portion having Al _0.01 Ga _0.99 As as a light-emitting layer on a GaAs substrate.

Specifically, the light-emitting diode of Comparative Example 1 was formed on an n-type (100) plane GaAs single crystal substrate, and the n-type upper cladding layer composed of Al _0.01 Ga _0.99 As was 50 μm. The Si-doped light-emitting layer composed of Al _0.01 Ga _0.99 As is 20 μm, the p-type lower cladding layer composed of Al _0.7 Ga _0.3 As is 20 μm, and is transparent to the emission wavelength by Al _0.25 Ga _0.75 As The p-type thick film layer was formed to have a liquid crystal epitaxy method in a manner of 60 μm. After the epitaxial growth, the GaAs substrate is 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, on the back surface of the p-type AlGaAs thick film layer, a p-type ohmic electrode having a diameter of 20 μm was formed at intervals of 80 μm. Next, after cutting at 350 nm intervals by a die cutter, the fracture layer was removed by etching to obtain a light-emitting diode wafer of Comparative Example 1.

The results of evaluating the characteristics of the light-emitting diode lamp of the light-emitting diode of Comparative Example 1 are shown in Table 5.

As shown in Table 5, after flowing a current between the n-type and p-type ohmic electrodes, infrared light having a peak wavelength of 920 nm was emitted. In addition, the forward voltage (Vf) at a current of 20 microamperes (mA) in the forward direction is about 1.2 volts (V). In addition, the luminous output when the forward current was 20 mA was 2 mW. Further, in comparison with the examples of the present invention, the output of any of the samples of Comparative Example 1 was low.

[Possibility of industrial use]

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

1. . . GaAs substrate

2. . . The buffer layer

3. . . DBR reflective layer

3a. . . The first structural layer of the DBR reflective layer

3b. . . The second structural layer of the DBR reflective layer

5. . . Lower cladding layer (first cladding layer)

6. . . Lower light guiding layer (first light guiding layer)

7. . . Active layer

8. . . Upper light guiding layer (2nd light guiding layer)

9. . . Upper cladding layer (second cladding layer)

10. . . Current diffusion layer

12. . . P-type ohmic electrode (first electrode)

13. . . N-type ohmic electrode (second electrode)

20. . . Light department

30. . . Compound semiconductor layer

100. . . Light-emitting diode

Fig. 1 is a plan view showing a light-emitting diode according to an embodiment of the present invention.

Fig. 2 is a view for explaining a pattern of an active layer constituting a light-emitting diode according to an embodiment of the present invention.

Fig. 3 is a graph showing the correlation between the layer thickness of the well layer of the light-emitting diode of one embodiment of the present invention and the wavelength of the luminescence peak.

Fig. 4 is a graph showing the correlation between the In composition (X1) of the well layer of the light-emitting diode of one embodiment of the present invention and the wavelength of the luminescence peak.

Fig. 5 is a graph showing the relationship between the In composition (X1) of the well layer of the light-emitting diode of one embodiment of the present invention and the luminescence peak wavelength and its luminescence output.

Fig. 6 is a view showing the layer thickness of the well layer of the light-emitting diode according to the embodiment of the present invention and the number of pairs of the barrier layer and the light emission output.

1. . . GaAs substrate

2. . . The buffer layer

3. . . DBR reflective layer

3a. . . The first structural layer of the DBR reflective layer

3b. . . The second structural layer of the DBR reflective layer

5. . . Lower cladding layer (first cladding layer)

6. . . Lower light guiding layer (first light guiding layer)

7. . . Active layer

8. . . Upper light guiding layer (2nd light guiding layer)

9. . . Upper cladding layer (second cladding layer)

10. . . Current diffusion layer

12. . . P-type ohmic electrode (first electrode)

13. . . N-type ohmic electrode (second electrode)

20. . . Light department

30. . . Compound semiconductor layer

100. . . Light-emitting diode

Claims (6)

A light-emitting diode characterized by having a DBR reflective layer and a light-emitting diode of a light-emitting portion sequentially on a substrate, the light-emitting portion having: a composition formula (In _X1 Ga _1-X1 ) As (0.1 X1 0.3) The well layer formed by the composition formula (Al _X2 Ga _1-X2 ) As (0 X2 1) The active layer of the laminated structure of the barrier layer formed by the composition formula (Al _X3 Ga _1-X3 ) As (0 X3 1) a first light guiding layer and a second light guiding layer, and a composition formula in which the first light guiding layer and the second light guiding layer are interposed therebetween and sandwiching the active layer (Al _X4 Ga _{1 -X4} ) _Y In _1-Y P(0.3 X4 0.7, 0.4 Y 0.6) The first cladding layer and the second cladding layer which are formed have an emission wavelength of 900 nm or more and 985 nm or less. The light-emitting diode of claim 1, wherein the DBR reflective layer is composed of two layers having different refractive indices of two to ten pairs of alternating layers. For example, in the light-emitting diode of claim 2, wherein the two kinds of layers having different refractive indices are different in composition (Al _Xh Ga _1-Xh ) _Y3 In _1-Y3 P (0<Xh) 1, Y3 = 0.5), (Al _X1 Ga _1-X1 ) _Y3 In _1-Y3 P (0 A combination of X1<1 and Y3=0.5), the composition difference of Al of both ΔX=Xh-X1 is larger or equal to 0.5. The light-emitting diode of claim 2, wherein the two layers having different refractive indices are a combination of GaInP and AlInP. The light-emitting diode of claim 2, wherein the two types of layers having different refractive indices are two different compositions of Al _x1 Ga _1-x1 As (0.1 X1 1), Al _xh Ga _1-xh As (0.1 Xh In the combination of 1), the composition difference ΔX=xh-x1 of the two is greater or equal to 0.5. The light-emitting diode according to claim 1, wherein a current diffusion layer is provided on a surface of the light-emitting portion opposite to the DBR reflection layer.