TWI721841B - Infrared LED components - Google Patents

Abstract

The subject of the present invention is to realize an infrared LED element that emits light with a wavelength exceeding 1000 nm and improves light extraction efficiency more than before. The solution is an infrared LED element, which is characterized by: a substrate, which is made of InP, and shows that the concentration of n-type dopants is 1×10 ¹⁷ /cm ³ or more, but less than 3×10 ¹⁸ /cm ³ ; The first semiconductor layer, which is formed on the upper layer of the substrate, shows n-type; the active layer, which is formed on the upper layer of the first semiconductor layer; and the second semiconductor layer, which is formed on the upper layer of the active layer, shows p-type; the first electrode, which is formed on the surface of the substrate, on the first surface opposite to the side on which the first semiconductor layer is formed; the second electrode, which is formed on the upper layer of the second semiconductor layer, When viewed from the first direction orthogonal to the surface of the substrate, it is formed only on a part of the surface of the second semiconductor layer, and the main emission wavelength is 1000 nm or more.

Description

Infrared LED components

The present invention relates to an infrared LED element, and particularly to an infrared LED element with an emission wavelength of 1000 nm or more.

In the past, as a light-emitting element that uses an infrared region of 1000 nm or more as a light-emitting wavelength, the development of a laser element for communication and measurement has been widely progressed. On the other hand, LED elements in such a wavelength range are not very useful so far, and the development has not progressed compared to laser elements.

For example, Patent Document 1 below discloses that a GaAs-based light-emitting element can generate light with a wavelength of 0.7 to 0.8 μm (700 to 800 nm). However, in order to generate light with a longer wavelength of about 1.3 μm (1300 nm), InP-based light-emitting elements are required. In particular, Patent Document 1 discloses that a p-type InP substrate is used as a growth substrate, and a p-type cladding layer, an active layer, and an n-type cladding layer, which are lattice-matched to InP crystals, are epitaxially grown in sequence, and then electrodes are formed. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 4-282875 [Patent Document 2] Japanese Patent Publication No. 6-103759 [Patent Document 3] Japanese Patent No. 3084364

(The problem to be solved by the invention)

As mentioned above, LED elements with emission wavelengths exceeding 1000 nm are not very industrially used, and their development has not progressed. In response to this, in recent years, the demand for LED elements in such a wavelength band has also increased from the market, and LED elements with higher light intensity have been demanded.

In view of the above-mentioned problems, the present invention provides an infrared LED element with an emission wavelength exceeding 1000 nm, with the purpose of improving the light extraction efficiency more than before. (Means to solve the problem)

As a light-emitting element with a light-emitting wavelength of more than 1000 nm, the development of laser elements is still the main advancement in history as described above. From the viewpoint of improving the luminous efficiency, in order to increase the luminous intensity in the active layer, methods for injecting a large current have been reviewed so far. For example, in the field of semiconductor lasers using InP substrates, increasing the dopant concentration of InP is also used to reduce the resistivity of the substrate and increase the current density that can be injected into the active layer.

If we learn from the development of semiconductor lasers so far, we can think that for InP-based LED elements, in order to supply a large current to the active layer through the InP substrate, a high concentration of dopant is injected into the InP substrate. However, according to the intensive research conducted by the inventor(s) of the present invention, it has been confirmed that once the dopant concentration of the InP substrate is increased, the amount of light taken out decreases. For this reason, the inventor(s) of the present invention speculate that by increasing the dopant concentration of the InP substrate, the expansion of the current flowing in the substrate in the direction parallel to the substrate surface (hereinafter referred to as the "lateral direction") will be affected. Suppress, as a result, current will be concentrated in a limited area in the active layer, and the area that contributes to light emission in the active layer will be reduced.

In view of the above-mentioned novel insights of the inventor(s), the present invention is an infrared LED element characterized by: an infrared LED element characterized by: a substrate, which is made of InP and displays n-type The dopant concentration is 1×10 ¹⁷ /cm ³ or more but less than 3×10 ¹⁸ /cm ³ ; The first semiconductor layer is formed on the upper layer of the aforementioned substrate and shows n-type; the active layer is formed On the upper layer of the aforementioned first semiconductor layer; and the second semiconductor layer, which is formed on the upper layer of the aforementioned active layer, exhibiting p-type; the first electrode, which is formed on the surface of the aforementioned substrate, and is formed with the aforementioned The first surface on the side opposite to the side of the first semiconductor layer; the second electrode, which is formed on the upper layer of the second semiconductor layer, is formed only on the first direction orthogonal to the surface of the substrate The main emission wavelength of a part of the surface of the second semiconductor layer is 1000 nm or more.

When the n-type semiconductor layer, active layer, and p-type semiconductor layer are epitaxially grown on an n-type InP substrate, the p-type semiconductor layer has a large absorption coefficient, so the p-type semiconductor layer needs to be grown as thinly as possible. Therefore, if a p-side electrode is provided on the upper surface of the p-type semiconductor layer, and an n-side electrode is provided on the opposite side (rear surface) of the semiconductor layer of the InP substrate, and a voltage is applied between the two electrodes, the current will tend to concentrate on the p side Right below the electrode. In this case, the active layer directly below the p-side electrode emits stronger light, and the area contributing to light emission in the active layer is narrowed. The emitted light is easily absorbed by the p-side electrode, resulting in a decrease in light extraction efficiency.

In addition, as described above, once the current is concentrated in a specific place, Joule heat increases, defects in the active layer increase, and light is absorbed in the defects, so there is also a problem that the light extraction efficiency is more likely to decrease.

In compound semiconductor light-emitting devices, several methods have been known for countermeasures against concentration of current paths. For example, Patent Document 2 discloses a technique of forming a thick film in a position of the upper layer of the active layer to form a semiconductor layer that is transparent to the generated light. In addition, Patent Document 3 discloses a method of forming a transparent electrode between the active layer and the upper electrode.

However, infrared LED elements with emission wavelengths exceeding 1000 nm, that is, InP-based (GaInAsP-based) infrared LED elements, have a problem of increased defect density due to the increase in film thickness and degradation of crystal quality. In addition, in the p-type semiconductor layer, the absorption coefficient may be large as described above. In view of these points, even if the method described in Patent Document 2 is applied as it is to an infrared LED element with a light emission wavelength exceeding 1000 nm, the effect of improving the light extraction efficiency cannot be obtained. In addition, In, which is a component of the semiconductor layer of the GaInAsP-based infrared LED element, is a rare metal that is heavily produced in the region. Therefore, increasing the thickness of the semiconductor layer causes other problems such as ensuring the stability of raw materials and increasing manufacturing costs.

In addition, as described in Patent Document 3, the technique of using a transparent electrode such as ITO to disperse the current in the horizontal direction is widely used in semiconductor light-emitting elements whose emission wavelengths are in the visible light region. However, ITO generally used as a transparent electrode absorbs infrared light whose emission wavelength exceeds 1000 nm. Therefore, even if the method described in Patent Document 3 is applied as it is to an infrared LED element whose emission wavelength exceeds 1000 nm, the effect of improving the light extraction efficiency cannot be obtained.

As a result of intensive research, the inventor(s) found a new finding. In an infrared LED element whose main emission wavelength is 1000nm or more, if the n-type dopant concentration ratio of an InP-containing substrate is reduced in order to reduce resistance When the conventional concentration of doping is further reduced, the effect of dispersing the current in the lateral direction (direction parallel to the surface of the substrate) can be obtained. That is, according to the infrared LED element of the present invention described above, since the n-type dopant concentration of the substrate is set to 1×10 ¹⁷ /cm ³ or more, a slightly lower value less than 3×10 ¹⁸ /cm ³ Therefore, as a result of the relative increase in the resistivity of the substrate relative to the second semiconductor layer showing the p-type, electrons in the substrate easily move in the lateral direction, and the current flowing in the active layer can be expanded in the lateral direction.

The resistivity in the semiconductor layer is determined by the carrier concentration, and the carrier concentration almost depends on the dopant concentration. Here, the p-type second semiconductor layer generally increases the dopant concentration to approach the upper limit of implantability from the viewpoint of functioning as a cladding layer for the active layer. For example, its concentration is 5×10 ¹⁷ / cm ³ or more, 3×10 ¹⁸ /cm ³ or less. In contrast, the n-type dopant concentration of the substrate is as described above, 1×10 ¹⁷ /cm ³ or more and less than 3×10 ¹⁸ /cm ³ , and the p-type dopant concentration of the second semiconductor layer is equal to or less than . As a result, the resistivity of the substrate, that is, the n-side, is relatively higher than the resistivity of the second semiconductor layer, that is, the p-side.

Regarding the first direction, it does not matter if the thickness of the substrate is 10 times or more the thickness of the second semiconductor layer.

As described above, in an infrared LED element with an emission wavelength exceeding 1000 nm, once the thickness of the p-type semiconductor layer (second semiconductor layer) is increased, the absorption coefficient is large, so the light extraction efficiency is reduced. Therefore, as much as possible It is desirable to thin the film thickness, and it is usually set to about several μm. On the other hand, since InP has extremely high cleavage properties, from the viewpoint of ensuring independence, the thickness of the substrate must be at least 50 μm or more, preferably 150 μm or more, and more preferably 200 μm or more.

In this way, when the thickness of the substrate is more than 10 times the thickness of the second semiconductor layer, the thickness of the substrate is thick. Therefore, by intentionally lowering the concentration of the n-type dopant of the substrate, the current flows horizontally in the substrate. The effect of direction expansion will be significant. As a result, the effect of spreading the current flowing in the active layer in the horizontal direction is more exhibited, and the light extraction efficiency is improved.

In addition, from the viewpoint of housing the infrared LED element in a general package, the thickness of the substrate is preferably 700 μm or less, and more preferably 400 μm or less.

Even if the second electrode is formed only on a part of the area of the surface of the second semiconductor layer, in the first direction, at least a part of the area where the second electrode is not formed is the same as the area where the first electrode is formed. At least a part of the area is okay.

According to the above configuration, the first electrode formed on the first surface side of the substrate and the second electrode formed on the opposite surface (referred to as the "second surface") side are arranged in relation to the first A position that is completely out of the opposite direction. As a result, the effect of spreading the current flowing between the first electrode and the second electrode in the horizontal direction is further improved.

In addition, by forming the second electrode on a partial area of the surface of the second semiconductor layer, not only the side surface of the substrate but also the surface related to the second semiconductor layer can be used as a light extraction surface, and light extraction efficiency can be improved.

In the above-mentioned structure, it does not matter if the first electrode arranged on the first surface side of the substrate is formed only on a part of the first surface of the substrate. In this case, the non-formation area of the first electrode and the second electrode is set as opposed to the first direction, and the non-formation area of the second electrode and the first electrode is set to be opposed to the first direction. ideal.

The second electrode is provided with a plurality of partial electrodes having a lattice shape or a comb shape extending in different directions on the surface of the second semiconductor layer, and the separation distance between the adjacent partial electrodes is 100 μm or less It's okay.

By setting the n-type dopant concentration of the substrate to 1×10 ¹⁷ /cm ³ or more and less than 3×10 ¹⁸ /cm ³ , the current dispersion length can be made 50 μm or more. Here, the term “dispersion length” means the distance from the horizontal direction of the second electrode to the position where the luminance in the vicinity of the second electrode shows a half of the luminance.

By setting the separation distance between the partial electrodes to 100 μm or less, the currents flowing from the plurality of separated partial electrodes overlap each other. As a result, the current can flow in the active layer across a wide range in the horizontal direction.

It does not matter if the dopant of the aforementioned substrate contains Sn. As mentioned above, ^{when doping InP with a dopant concentration of 1×10 17} /cm ³ or more but less than 3×10 ¹⁸ /cm ³ , Sn can be contained in the dopant to reduce crystal defects. The density is reduced.

Even if it is assumed that the area where the first electrode is not formed on the first surface of the substrate is made of a material having a higher reflectivity to the light generated in the active layer than the first electrode It's okay to have a reflective layer.

According to the above configuration, especially in infrared LED elements in which the side surface of the substrate or the surface on the second electrode side is used as the light extraction surface, even if the light travels in a direction different from the extraction surface, it can return to the substrate. Therefore, the reduction in extraction efficiency will be suppressed.

It does not matter if the reflective layer includes one or more materials contained in the group consisting of Ag, Ag alloy, Au, and Al.

The infrared LED element has a dielectric layer made of a material having a refractive index smaller than that of the substrate by 0.2 or more in the region where the first electrode is not formed even if it is set on the first surface of the substrate. It’s okay to either.

According to such a configuration, total reflection is likely to occur in the boundary between the substrate and the specific area. As a result, especially in the infrared LED element where the side surface of the substrate or the surface on the second electrode side is used as the light extraction surface, even if the light travels in a different direction from the extraction surface, it can return to the substrate, so it can be extracted. The reduction in efficiency will be suppressed.

The aforementioned dielectric layer does not matter if it contains one or more materials contained in the group _{consisting of SiO 2} , SiN, Al ₂ O _{3, ZnO, and ITO.}

Moreover, it does not matter if the said board|substrate is a surface other than the said 1st surface and the 2nd surface on the opposite side of the said 1st surface, ie, the side surface which has unevenness|corrugation. Since the refractive index of InP is 3.0 or more, which shows an extremely large value, the refractive index difference between the substrate and the air becomes large, and light is difficult to take out. For this reason, by providing uneven portions on the side surface of the substrate, total reflection on the side surface is less likely to occur, and light extraction efficiency can be improved.

In addition, if the uneven portion is formed on the surface of the second semiconductor layer, there is a region where the thickness of the second semiconductor layer is reduced, and therefore, the effect of spreading the current in the lateral direction may be reduced. From such a viewpoint, it is desirable that the surface of the second semiconductor layer is not formed with uneven portions.

In particular, when the substrate has a thickness of 10 times or more with respect to the thickness of the semiconductor layer, since the surface area of the side surface increases, most of the light generated by the active layer is taken out from the side surface of the substrate. Therefore, in order to suppress the total reflection on the side surface and improve the light extraction efficiency, it is desirable to provide the uneven portion on the side surface. [Effects of the invention]

According to the infrared LED element of the present invention, in the region where the emission wavelength exceeds 1000 nm, the light extraction efficiency is improved more than before.

The embodiment of the infrared LED element of the present invention will be described with reference to the drawings. In addition, the following drawings are schematic representations, and the size ratio on the drawing does not necessarily match the actual size ratio. In addition, there are also cases where the size ratio is inconsistent between the drawings.

In this specification, the description of "GaInAsP" means a mixed crystal of Ga, In, As, and P, and the description of the composition ratio is abbreviated. The same applies to other descriptions such as "AlGaInAs".

In this specification, the expression "layer B is formed on the upper layer of layer A", of course, refers to the case where layer B is directly formed on the surface of layer A, but it also includes the case where layer B is formed on the surface of layer A via a thin film. Happening. In addition, the term "thin film" here means a layer with a film thickness of 10 nm or less, and it does not matter if it is a layer with a thickness of 5 nm or less.

[First Embodiment] The structure of the first embodiment of the infrared LED element of the present invention will be described.

"structure" Fig. 1 is a cross-sectional view schematically showing the structure of the infrared LED element of the present embodiment. The infrared LED element 1 shown in FIG. 1 includes a substrate 3 and a semiconductor layer 10 formed on the upper layer of the substrate 3. In addition, the infrared LED element 1 is provided with electrodes (21, 22, 23) for injecting current.

1 is a schematic cross-sectional view corresponding to the case where the infrared LED element 1 is cut along the XZ plane at a predetermined position. Hereinafter, refer to the XYZ coordinate system attached to FIG. 1 as appropriate. According to the coordinate system shown in Fig. 1, the Z direction corresponds to the "first direction".

In addition, FIG. 2 is an example of a schematic plan view when the infrared LED element 1 is viewed from the +Z direction. For the convenience of description, the illustration of the electrode 23 is omitted in FIG. 2.

(Substrate 3) In this embodiment, the substrate 3 is made of InP doped with n-type impurities. In this case, the n-type corresponds to the "first conductivity type". As the n-type impurity material doped in the substrate 3, Sn, Si, S, Ge, Se, etc. can be used, and Sn is particularly preferable.

The thickness (length in the Z direction) of the substrate 3 is 50 μm or more and 700 μm or less. Since InP has extremely high cleavage properties, it is necessary to set the thickness of the substrate 3 to at least 50 μm from the viewpoint of ensuring independence. In addition, from the viewpoint of housing the infrared LED element 1 in a general package, the thickness of the substrate 3 needs to be 700 μm or less. The thickness of the substrate 3 is desirably 150 μm or more, and more desirably 200 μm or more. In addition, the thickness of the substrate 3 is desirably 400 μm or less.

The dopant concentration of the n-type impurity of the substrate 3 is 1×10 ¹⁷ /cm ³ or more, less than 3×10 ¹⁸ /cm ³ , and more preferably 3×10 ¹⁷ /cm ³ or more, 3×10 ¹⁸ /cm ³ Hereinafter, it is particularly desirable to be 5×10 ¹⁷ /cm ³ or more and 3×10 ¹⁸ /cm ³ or less. In addition, when Sn is used as a dopant, although the impurity is implanted at the dopant concentration in the above-mentioned numerical range, the quality of the InP crystal constituting the substrate 3 can be particularly maintained in a good state.

The above-mentioned dopant concentration is a slightly lower value when compared with the case where doping is generally performed to improve the conductivity of an InP substrate. Therefore, from the viewpoint of suppressing excessively high resistance of the substrate 3 itself, it is desirable to set the thickness of the substrate 3 to 700 μm or less. For example, if the current density is 150 A/cm ² , the substrate 3 having a thickness of 700 μm or more will have a potential difference of 0.1 V or more due to internal resistance. As will be described later with reference to FIG. 4B, using the driving voltage of the infrared LED element 1, for example, about 1.0V as a reference, a potential difference of 10% or more will be generated in the substrate 3, which is not ideal. In contrast, for example, in the case of the substrate 3 having a thickness of 400 μm, the potential difference due to the internal resistance is 0.06V, which is suppressed to less than 0.1V.

In addition, the substrate 3 is constituted by doping the above-mentioned n-type impurity into the crystal of InP, but it does not matter even if it is mixed with a small amount of other impurities (for example, less than 1%).

(Semiconductor layer 10) In this embodiment, the semiconductor layer 10 is formed on the surface 3b of the substrate 3. The face 3b corresponds to the "second face".

In the example shown in FIG. 1, the semiconductor layer 10 includes a first semiconductor layer 11, an active layer 12, and a second semiconductor layer (13, 14), and these layers are laminated.

The first semiconductor layer 11 is formed on the second surface 3b of the substrate 3. The first semiconductor layer 11 is an InP layer doped with n-type impurities, and constitutes the n-type cladding layer of the infrared LED element 1. The n-type dopant concentration of the first semiconductor layer 11 is desirably 1×10 ¹⁷ /cm ³ or more, 5×10 ¹⁸ /cm ³ or less, and more desirably 5×10 ¹⁷ /cm ³ or more, 4×10 ¹⁸ / cm ³ or less. As the n-type impurity material doped in the first semiconductor layer 11, Sn, Si, S, Ge, Se, etc. can be used, and Si is particularly desirable.

As described later, the active layer 12 generates infrared light whose main emission wavelength is 1000 nm or more and less than 1800 nm. The first semiconductor layer 11 is made of a material that does not absorb light in such a wavelength band, and can be appropriately selected from a material that can be epitaxially grown by lattice matching with the substrate 3 made of InP. For example, as the first semiconductor layer 11, in addition to InP, materials such as GaInAsP and AlGaInAs may also be used.

The film thickness of the first semiconductor layer 11 is 0.1 μm or more and 10 μm or less, preferably 0.5 μm or more and 5 μm or less.

The active layer 12 is formed on the upper layer (position in the +Z direction) of the first semiconductor layer 11. The active layer 12 is composed of a material that generates infrared light whose main emission wavelength is 1000 nm or more and less than 1800 nm. The active layer 12 is capable of generating light of a target wavelength, and is appropriately selected from a material that can be lattice-matched with the substrate 3 made of InP and grow epitaxially. For example, the active layer 12 may have a single-layer structure of GaInAsP, InGaAs, or AlGaInAs, or it may include a well layer made of GaInAsP, InGaAs, or AlGaInAs, and a GaInAsP whose band gap energy is larger than that of the well layer. The MQW (Multiple Quantum Well) structure of the barrier layer formed by InGaAs, AlGaInAs or InP is also OK.

The active layer 12 does not matter even if it is doped n-type or p-type, and it does not matter even if it is not doped. When it is doped into n-type, for example, Si can be used as a dopant.

When the active layer 12 has a single-layer structure, the film thickness of the active layer 12 is 100 nm or more and 2000 nm or less, preferably 500 nm or more and 1500 nm or less. In addition, when the active layer 12 has an MQW structure, the well layer and the barrier layer having a film thickness of 5 nm or more and 20 nm or less are laminated in a range of 2 cycles or more and 50 cycles or less.

The second semiconductor layer (13, 14) is formed on the upper layer of the active layer 12 (position in the +Z direction). The second semiconductor layers (13, 14) are all doped with p-type impurities. The second semiconductor layer 13 is a p-type cladding layer constituting the infrared LED element 1, and the second semiconductor layer 14 is a p-type contact layer constituting the infrared LED element 1. The second semiconductor layer 14 is a layer that is doped with a high concentration in order to ensure electrical connection with the second electrode 21 described later. However, when the electrical connection can be sufficiently ensured, even if the second semiconductor layer 14 is omitted, the second electrode 21 may directly contact the second semiconductor layer 13 constituting the p-type cladding layer.

As an example, the second semiconductor layer 13 constituting the p-type cladding layer is made of Zn-doped InP, and the second semiconductor layer 14 constituting the p-type contact layer is made of Zn-doped GaInAsP.

The p-type dopant concentration of the second semiconductor layer 13 constituting the p-type cladding layer is desirably 8×10 ¹⁷ /cm ³ or more, 3×10 ¹⁸ /cm ³ or less, and more desirably 1×10 ¹⁸ /cm ³ Above, 3×10 ¹⁸ /cm ³ or less. In addition, the p-type dopant concentration of the second semiconductor layer 14 constituting the p-type contact layer is desirably 5×10 ¹⁷ /cm ³ or more, 3×10 ¹⁸ /cm ³ or less, and more desirably 1×10 ¹⁸ /cm ³ or more, 3×10 ¹⁸ /cm ³ or less. In addition, as a diffusion prevention layer of Zn doped in the second semiconductor layer (13, 14), even a layer with a low p-type dopant concentration is between the active layer 12 and the second semiconductor layer (13, 14) It's okay.

As the p-type impurity material doped in the second semiconductor layer (13, 14), Zn, Mg, Be, etc. can be used. Zn or Mg is preferable, and Zn is particularly preferable. In addition, the materials of the p-type dopant constituting the second semiconductor layer 13 of the p-type cladding layer and the p-type dopant constituting the second semiconductor layer 14 of the p-type contact layer may be the same or may be different.

(Electrodes 21, 22, 23) The infrared LED element 1 has electrodes (21, 22, 23).

A first electrode 22 is formed on the first surface 3a of the substrate 3. The first electrode 22 makes ohmic contact with the first surface 3a of the substrate 3. The first electrode 22 is made of materials such as AuGe/Ni/Au, Pt/Ti, Ge/Pt, etc. As an example, it does not matter if it is provided with a plurality of such materials. In addition, in this specification, the notation of "X1/X2" used when describing materials means that a layer made of X1 and a layer made of X2 are laminated.

A second electrode 21 is formed on the surface of the second semiconductor layer 14. The second electrode 21 realizes ohmic contact with the surface of the second semiconductor layer 14. The second electrode 21 is made of materials such as Au/Zn/Au, AuZn, AuBe, and the like. As an example, it does not matter if it is provided with a plurality of such materials.

A pad electrode 23 is formed on the surface of the second electrode 21. The pad electrode 23 is formed as an area for connecting the bonding wire. The pad electrode 23 is made of Ti/Au, Ti/Pt/Au, etc., for example.

In the example shown in FIG. 2, the second electrode 21 has an electrode region 21 b in which the pad electrode 23 is arranged, and an electrode region 21 a linearly extending from the electrode region 21 b. The electrode region 21a is provided for the purpose of spreading current in a direction parallel to the XY plane.

(Concave and convex part 41) In this embodiment, uneven portions 41 are formed on the side surface of the substrate 3. Here, the side surface of the substrate 3 refers to the surface of the substrate 3 other than the two surfaces (3a, 3b) parallel to the XY plane as shown in FIG. 1. When the substrate 3 has a substantially rectangular parallelepiped shape, the substrate 3 has four side surfaces, and uneven portions 41 are formed on these side surfaces.

The uneven portion 41 is configured such that the maximum value of the height difference is 0.5 times or more the emission wavelength, and the interval between the protrusions and the recesses is 0.7 times or more the emission wavelength. As an example, the maximum value of the height difference of the uneven portion is 0.5 μm or more, preferably 3 μm or less, and more preferably 0.8 μm or more, and 2 μm or less. In addition, the distance between the protrusions and the recesses, that is, the pitch of the uneven portions 41 is 0.8 μm or more, preferably 4 μm or less, and more preferably 1.4 μm or more, and 3 μm or less.

"Production method" An example of the method of manufacturing the infrared LED element 1 described above will be described with reference to each of FIGS. 3A to 3I. Figures 3A to 3I are cross-sectional views of one of the processes in the manufacturing process.

(Step S1) As shown as FIG. 3A, in order to prepare a 1 × 10 ¹⁷ / cm ³ or more, the dopant concentration of the n-type impurity doped InP less than ³ × 10 ¹⁸ / cm 3 is formed between the substrate 3 .

(Step S2) As shown in FIG. 3A, the substrate 3 is transported into a MOCVD (Metal Organic Chemical Vapor Deposition) device, and the semiconductor layer 10 including the first semiconductor layer 11, the active layer 12, and the second semiconductor layer (13, 14) is sequentially deposited The crystal grows on the second surface 3b side of the substrate 3. In this step S2, the type and flow rate of the raw material gas, the processing time, the environmental temperature, etc. are appropriately adjusted in accordance with the material or film thickness of the layer to be grown.

Examples of materials for each semiconductor layer 10 are as described above. As an example, the semiconductor layer 10 is formed by this epitaxial growth process. The semiconductor layer 10 includes: a first semiconductor layer 11 made of Si-doped InP, an active layer 12 made of GaInAsP, and a semiconductor layer 10 made of GaInAsP. The second semiconductor layer 13 is made of InP and the second semiconductor layer 14 is made of Zn-doped GaInAsP. Through this process, an epitaxial wafer in which the semiconductor layer 10 is formed on the surface of the substrate 3 is obtained.

(Step S3) epitaxial wafer taken out from the MOCVD apparatus, are formed by photolithography process (photolithography) method to pattern resist mask on the surface of the second semiconductor layer 14. Then, after forming the material (for example, Au/Zn/Au) of the second electrode 21 into a film using a vacuum vapor deposition apparatus, the resist mask is peeled off by a lift-off method. Then, for example, alloying treatment (annealing treatment) is performed by heat treatment at 450° C. for 10 minutes, whereby the second electrode 21 is formed on the upper surface of the second semiconductor layer 14 as shown in FIG. 3B.

(Step S4) Among the surfaces of the substrate 3, the surface on the side where the semiconductor layer 10 is formed is coated with a resist for protection, and the surface opposite to this surface, namely the first surface 3a, is subjected to grinding and polishing treatment, and according to the hydrochloric acid system. Wet etching treatment of etchant. Thereby, the thickness of the substrate 3 is adjusted (refer to FIG. 3C). The thickness of the substrate 3 is set to 50 μm or more and 700 μm or less as described above, for example, it is set to 250 μm. Then, the resist as a protective film is removed with an organic solvent.

(Step S5) As shown in FIG. 3D, on the first surface 3a side of the substrate 3, a vacuum evaporation device is used to form the first electrode 22 forming material (for example, AuGe/Ni/Au) into a film, for example, at 450°C, The alloy treatment (annealing treatment) is carried out by heating treatment for 10 minutes, whereby the first electrode 22 is formed.

(Step S6) As shown in FIG. 3E, on the upper surface of the second electrode 21, a pad electrode 23 made of Ti/Au, for example, is formed by a lithography process method, a vacuum evaporation method, and a lift-off method.

(Step S7) As shown in FIG. 3F, mesa etching for separation is performed for each component. Specifically, in a state where the non-etched area in the surface of the second semiconductor layer 14 is masked by a resist patterned by a lithography process, the process is performed by a mixture of bromine and methanol. Wet etching treatment. Thereby, a part of the second semiconductor layer (13, 14), the active layer 12 and the first semiconductor layer 11 in the unmasked area will be removed.

(Step S8) As shown in FIG. 3G, after the wafer subjected to the mesa etching process is attached to the dicing base 31, a blade cutting device is used to divide the components along the dicing line. Furthermore, with the expansion device, the cutting base 31 to which the infrared LED element 1 is attached is expanded, and a gap is provided between the adjacent infrared LED elements 1.

(Step S9) As shown in FIG. 3H, the dicing seat 31 to which the infrared LED element 1 is attached is immersed in an acidic etching solution containing hydrochloric acid to form a concave-convex shape on the side surface of the infrared LED element 1. In this step S9, the uneven portion 41 is formed on the side surface of the substrate 3, and the uneven portion 42 is formed on the side surface of the semiconductor layer 10.

In addition, although it is not shown in FIG. 3H, it does not matter that uneven portions are formed on the upper surface of the second semiconductor layer 14 by this step S9.

(Step S10) The infrared LED element 1 is removed from the cutting base 31. As a result, it becomes the state shown in FIG. 1.

(Step S11) As shown in FIG. 3I, for example, on a TO-18 type stem 35, the first electrode 22 side of the infrared LED element 1 is bonded via silver paste 34 (Die bonding), and after thermal curing, the bonding The pad electrode 23 is electrically connected to the wire 36. In addition, in this step S11, it does not matter even if solder is used instead of the silver paste 34. The solder is a material such as AuSn or SnAgSu.

"effect" Once a voltage is applied between the first electrode 22 and the second electrode 21 of the infrared LED element 1 manufactured through the process of steps S1 to S11, a current flows in the active layer 12 to emit light. Among this light, the light traveling in the +Z direction is taken out from the surface of the second semiconductor layer 14 to the outside. In addition, the light traveling in the -Z direction is taken out from the side surface to the outside through the substrate 3.

Here, the uneven portion 41 is formed on the side surface of the substrate 3, so the amount of light that is totally reflected on the side surface of the substrate 3 and returned to the inside of the substrate 3 is suppressed.

In addition, the dopant concentration of the substrate 3 is 1×10 ¹⁷ /cm ³ or more and less than 3×10 ¹⁸ /cm ³ , if it is doped with the purpose of reducing the resistivity of the substrate in the field of semiconductor lasers For comparison, it is a low concentration. By setting the dopant concentration to a value within such a range, the current flowing in the substrate 3 is expanded in the lateral direction (direction parallel to the XY plane). As a result, the current flows in the active layer 12 In the wide range, the light-emitting area will be expanded, which can improve the light extraction efficiency.

4A and 4B show the values of the luminous intensity and the dispersion length of a plurality of infrared LED elements 1 manufactured through the process of steps S1 to S11 under the condition that the dopant concentration of the substrate 3 is different , To graph the relationship with dopant concentration. Fig. 4A is a graph showing the relationship between dopant concentration and luminous intensity. Figure 4B is a graph showing the relationship between dopant concentration and dispersion length

In more detail, FIG. 4A is the result of evaluating the luminous intensity of the infrared LED element 1 manufactured by making the substrate 3 different in the dopant concentration of the substrate 3 when a current of 50 mA is injected into the luminous intensity for each dopant concentration. Chartist.

In addition, FIG. 4B is defined by measuring the distance between the point where the brightness is highest and the point where the brightness is reduced by 1/2 in a state where each of the infrared LED elements 1 manufactured by different dopant concentrations of the substrate 3 emits light. The results of "dispersion length" are graphed for each dopant concentration. The dispersion length is to capture the surface of the infrared LED element 1 while actually making each infrared LED element 1 emit light. Based on the imaging result, the brightness corresponding to the surface position is converted into a numerical value, and it is derived from the comparison result of the numerical value corresponding to the position. Value.

According to FIG. 4A, it is confirmed that in the range of the dopant concentration of the substrate 3 above 1×10 ¹⁷ /cm ³ and below 1×10 ¹⁹ /cm ³ , as the dopant concentration of the substrate 3 decreases, the emission intensity rise. In addition, according to FIG. 4B, it is confirmed that as the dopant concentration of the substrate 3 decreases, the dispersion length increases. From the above results, as described in the section "Means to Solve the Problem", by setting the dopant concentration of the substrate 3 to 1×10 ¹⁷ /cm ³ or more, less than 3×10 ¹⁸ /cm ^{Within the range of 3} , it can be considered that the current flowing in the substrate 3 will be expanded in the horizontal direction, and accordingly, the current flowing in the active layer 12 will also be expanded in the horizontal direction, and the luminous efficiency will be improved.

According to the result of FIG. 4B, the dispersion length can be set to 50 μm or more. Therefore, in order to flow a current in a wide range in the active layer 12, when the second electrode 21 is provided with a separation distance d1 (see FIG. 2), it is desirable to set the separation distance to 100 μm or less.

In addition, the shape of the second electrode 21 shown in FIG. 2 is just an example, and in this embodiment, the shape of the second electrode 21 included in the infrared LED element 1 is arbitrary. For example, as shown in FIG. 5, the second electrode 21 has an electrode region 21b in which the pad electrode 23 is arranged, and an electrode region 21a connected to the electrode region 21b and extending linearly. Even if the electrode region 21a has a lattice shape It's okay. In this case, it is also desirable that the separation distance d1 between the electrode regions 21a constituting the grid is 100 μm or less, for example.

[Other implementation forms] Hereinafter, another embodiment of the infrared LED element 1 will be described.

<1> As shown in FIG. 6, it does not matter if the first electrode 22 is formed on a partial region of the first surface 3 a of the substrate 3. In this case, at least a part of the first electrode 22 is related to the Z direction, and it is ideal to be arranged to oppose a region where the second electrode 21 is not formed. That is, it is desirable to arrange each electrode (21, 22) so that at least a part of the region B1 where the first electrode 22 is formed faces the Z direction with respect to the region A2 where the second electrode 21 is not formed. As a result, the current is expanded in the horizontal direction (the direction parallel to the XY plane), the current flows in a wide range in the active layer 12, and the luminous intensity is increased.

In addition, by setting the region B2 where the first electrode 22 is not formed as a gap, the difference in refractive index becomes extremely large at the boundary interface between the substrate 3 and the region B2. As a result, the light traveling in the -Z direction in the substrate 3 is easily totally reflected on the -Z side surface (first surface 3a) of the substrate 3, and the amount of light extracted from the light extraction surface such as the side surface of the substrate 3 increases. .

When the infrared LED element 1 shown in FIG. 6 is manufactured, the first electrode 22 only needs to be patterned during the execution of the above-mentioned step S5. In more detail, after forming a patterned resist mask by a lithography process, a vacuum evaporation device is used to form a film of the material (for example, AuGe/Ni/Au) of the first electrode 22, which is then lifted off. The resist mask is peeled off. Then, an alloy treatment (annealing treatment) was performed by heat treatment at 450° C. for 10 minutes, thereby forming the first electrode 22. The subsequent steps are common to the above-mentioned embodiment, so the description is omitted.

For the infrared LED element 1 shown in FIG. 6, when the crystal is bonded to the stem 35 via the silver paste 34 as in FIG. 3I, the silver paste 34 will enter the gap B2 shown in FIG. 6. As a result, the above-mentioned large refractive index difference between the substrate 3 and the void B2 cannot be obtained. However, the silver particles contained in the silver paste 34 entering the gap B2 have a high reflectivity for infrared light, so it is still possible to reflect the light traveling in the -Z direction in the substrate 3 in the +Z direction. function.

In addition, in the infrared LED element 1 shown in FIG. 6, since a step is formed on the first surface 3a side of the substrate 3, it does not matter if the first electrode 22 is connected to the package substrate with solder during mounting. . The solder is a material such as AuSn or SnAgSu. In this case, the gap B2 is still left. Therefore, as described above, a large refractive index difference can be provided between the substrate 3 and the gap B2, so it is easy to make the light traveling in the -Z direction in the substrate 3 all on the first surface 3a. reflection.

<2> In FIG. 6, it does not matter if the reflective layer 25 is formed in the region B2 where the first electrode 22 is not formed (see FIG. 7).

The reflective layer 25 may be any material that exhibits high reflectance for infrared light of 1000 nm or more but less than 1800 nm, and is composed of, for example, materials such as Ag, Ag alloy, Au, and Al. Compared with the materials of the first electrode 22, these materials have higher reflectivity for infrared light. In addition, the reflectance of the reflective layer 25 with respect to infrared light is preferably 50% or more, and more preferably 70% or more.

When the infrared LED element 1 shown in FIG. 7 is manufactured, it is only necessary to separately form the patterned first electrode 22 and the patterned reflective layer 25 during the execution of the above-mentioned step S5.

<3> In FIG. 6, it does not matter if the dielectric layer 26 is formed in the region B2 where the first electrode 22 is not formed (see FIG. 8).

The dielectric layer 26 only needs to be a material with a lower refractive index than the substrate 3 made of InP, and is made of materials such as SiO ₂ , SiN, Al ₂ O ₃ , ITO, and ZnO, for example. These materials all show a refractive index that is 0.2 or more smaller than the refractive index of InP. Therefore, it is realized that a refractive index difference of total reflection easily occurs at the interface between the substrate 3 and the dielectric layer 26.

When the infrared LED element 1 shown in FIG. 8 is manufactured, it is only necessary to form the patterned first electrode 22 and the patterned dielectric layer 26 during the execution of the above-mentioned step S5. _{For example, after the dielectric layer 26 made of SiO 2} is formed on the entire surface by the plasma CVD method, a resist mask patterned by a lithography process is used to perform a wet etching process with a BHF solution , And the patterning process of the dielectric layer 26 is performed. Then, the first electrode 22 is formed in the opening area of the dielectric layer 26.

In addition, the infrared LED element 1 shown in FIG. 8 can be mounted by the method of step S11 as described above. In this case, since the silver paste 34 intervenes in the lower layer of the dielectric layer 26, the Ag particles contained in the silver paste 34 function as a reflective member.

Furthermore, as shown in FIG. 9, it does not matter if the reflective layer 25 is formed so as to cover the surfaces of the dielectric layer 26 and the first electrode 22.

<4> In the above-mentioned embodiment, it is demonstrated that the side surface of the board|substrate 3 with which the infrared LED element 1 is equipped has the uneven|corrugated part 41 formed. However, it does not matter if the substrate 3 does not necessarily have the uneven portion 41 on the side surface (see FIG. 10). In this case, as shown in FIG. 10, it does not matter if the uneven portion 42 is not formed on the side surface of the semiconductor layer 10.

<5> In the infrared LED element 1 described in the above embodiment, among the surfaces of the semiconductor layer 10, the light extraction surface parallel to the XY plane, that is, the surface of the second semiconductor layer 14 may also have irregularities. .

<6> In the above-mentioned embodiment, the second semiconductor layer 14 as the p-type contact layer is formed on the upper surface of the second semiconductor layer 13 as the p-type cladding layer, and the second semiconductor layer 14 is formed on the surface of the second semiconductor layer 14 In the case of the second electrode 21. However, as long as contact is made to the second electrode 21, even if the contact is It does not matter if the conductivity type of the layer is n-type. In this case, the second electrode 21 is formed on the upper layer of the second semiconductor layer 13 via a thin n-type contact layer.

1: Infrared LED components

3: substrate

3a: The first side of the substrate

3b: The second side of the substrate

10: Semiconductor layer

11: The first semiconductor layer

12: Active layer

13,14: Second semiconductor layer

21: second electrode

22: first electrode

23: Pad electrode

25: reflective layer

26: Dielectric layer

28: Passivation film

31: Cutting seat

34: Silver paste

35: stem

41: Concave and convex part

42: Concave and convex part

Fig. 1 is a cross-sectional view schematically showing the structure of the first embodiment of the infrared LED element of the present invention. [Fig. 2] is an example of a schematic plan view when the infrared LED element shown in Fig. 1 is viewed from the +Z direction. [Fig. 3A] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3B] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3C] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3D] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3E] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3F] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3G] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3H] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 3I] is a cross-sectional view for explaining one process of the method of manufacturing the infrared LED element shown in Fig. 1. [Fig. [Fig. 4A] is a graph showing the relationship between the dopant concentration of the substrate and the luminous intensity in the infrared LED element manufactured through the process of steps S1 to S11. [FIG. 4B] is a graph showing the relationship between the dopant concentration of the substrate and the dispersion length in the infrared LED element manufactured through the process of steps S1 to S11. Fig. 5 is a plan view schematically showing another structure of the first embodiment of the infrared LED element of the present invention. Fig. 6 is a cross-sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention. Fig. 7 is a cross-sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention. Fig. 8 is a cross-sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention. Fig. 9 is a cross-sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention. Fig. 10 is a cross-sectional view schematically showing the structure of another embodiment of the infrared LED element of the present invention.

1: Infrared LED components

3: substrate

3a: The first side of the substrate

3b: The second side of the substrate

10: Semiconductor layer

11: The first semiconductor layer

12: Active layer

13,14: Second semiconductor layer

21: second electrode

22: first electrode

23: Pad electrode

41: Concave and convex part

42: Concave and convex part

Claims (9)

An infrared LED element characterized by: a substrate containing InP, showing that the concentration of n-type dopants is 1×10 ¹⁷ /cm ³ or more but less than 3×10 ¹⁸ /cm ³ ; the first semiconductor layer , Which is formed on the upper layer of the aforementioned substrate, showing n-type; the active layer, which is formed on the upper layer of the aforementioned first semiconductor layer; and the second semiconductor layer, which is formed on the upper layer of the aforementioned active layer, showing p Type; The first electrode, which is formed on the surface of the substrate, and the first surface on the side opposite to the side on which the first semiconductor layer is formed; The second electrode, which is formed on the second semiconductor layer The upper layer, when viewed from the first direction orthogonal to the surface of the substrate, is formed only on a part of the surface of the second semiconductor layer, and the main emission wavelength is 1000nm or more. The second electrode is only covered by In a part of the area formed on the surface of the second semiconductor layer, with respect to the first direction, at least a part of the area where the second electrode is not formed and at least a part of the area where the first electrode is formed are opposed to each other. The infrared LED element according to claim 1, wherein, in the first direction, the thickness of the substrate is 10 times or more than the thickness of the second semiconductor layer. The infrared LED element according to claim 1 or 2, wherein the thickness of the substrate is 150 μm or more and 400 μm or less. The infrared LED element according to claim 1 or 2, wherein the second electrode has a plurality of partial electrodes having a lattice shape or a comb shape extending in different directions on the surface of the second semiconductor layer, The separation distance between the adjacent partial electrodes is 100 μm or less. The infrared LED element according to claim 1 or 2, wherein the dopant of the substrate contains Sn. The infrared LED element according to claim 3, wherein the second electrode has a plurality of partial electrodes in a lattice shape or a comb shape extending in different directions on the surface of the second semiconductor layer, The separation distance between the adjacent partial electrodes is 100 μm or less. The infrared LED element according to claim 3, wherein the dopant of the substrate contains Sn. The infrared LED element according to claim 4, wherein the dopant of the substrate contains Sn. The infrared LED element according to claim 6, wherein the dopant of the substrate contains Sn.

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