TWI672827B - Epitaxial wafer and light-emitting diode - Google Patents

Abstract

The invention provides an epitaxial wafer, which can improve the luminous efficiency of a light-emitting portion composed of an AlGaInp-based material in a range of an emission wavelength of 670 nm to 690 nm. The epitaxial wafer of the present invention includes a light emitting layer, a first conductive type cladding layer and an active layer composed of a compound semiconductor represented by a chemical formula (Al _x Ga _1-x ) _y In _1-y P. And a second conductive type cladding layer, wherein 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, the light emitting layer has a light emission wavelength of 670 nm to 690 nm, and the active layer is a well layer and a barrier layer A quantum well structure formed by cross-layering, the composition of the barrier layer is 0.20 ≦ x ≦ 0.45, and 0 <y <1.

Description

Epitaxial wafer and light emitting diode

The invention relates to an epitaxial wafer and a light emitting diode manufactured using the epitaxial wafer.

A cultivation method using light-emitting diodes that are energy-saving, long-lived, and can be miniaturized has attracted attention. From the results of research so far, as a light source suitable for plant breeding (photosynthesis), the effect of red light in the range of 660 to 670nm has been confirmed. In particular, light with a wavelength of 660nm has a highly satisfactory light synthesis reaction efficiency. . On the other hand, the absorption of light by green plants has a peak at 680 nm, so an optical system with a light emission wavelength of 680 nm is expected as a light source with higher reaction efficiency in light synthesis.

In a light-emitting diode of a compound semiconductor having a light-emitting layer composed of an AlGaInP ((Al _x Ga _1-x ) _y In _1-y P, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) series material, although The wavelength of the light-emitting layer having a composition of Ga _0.5 In _0.5 P is the longest, but the light-emitting wavelength (peak wavelength) obtained by the light-emitting layer is around 650 nm. Therefore, a wavelength range longer than 650 nm is achieved by using a strained light emitting layer. However, as the emission wavelength becomes longer, the amount of strain increases accordingly. As a result, crystal defects in the light-emitting layer increase, which makes it difficult to be practical and efficient.

In order to solve these problems, in the method described in Patent Document 1, in the multilayer structure in which the active layer is a strained light-emitting layer and a barrier layer that are alternately laminated, a strain in the reverse direction of the strained light-emitting layer is applied to the barrier layer to reduce the light emission. The strain generated in the layer suppresses the occurrence of crystal defects in the strained light-emitting layer, thereby obtaining high light-emitting efficiency. Furthermore, in the method described in Patent Document 2, the active layer is a laminated structure in which the strained light emitting layer and the barrier layer are alternately laminated, the number of layers of the strained light emitting layer is 1 to 7, and the film thickness is 250 nm or less, so that the strain amount is reduced Thereby, high luminous efficiency is obtained. [Prior Art Literature] [Patent Literature]

[Patent Document 1] JP 2012-18986 [Patent Document 2] JP 2012-039049

[Problems to be solved by the invention]

As described above, although patent documents 1 and 2 describe the problem of obtaining high luminous efficiency in a wavelength range of 650 nm or more, when the emission wavelength is 670 nm or more, the amount of strain increases. The internal crystal defects increase, and it cannot be said that high luminous efficiency will be obtained.

For the above reasons, among light-emitting devices using an AlGaInP-based material, it is necessary to optimize the parameters of the structure of the active layer, particularly in order to improve the luminous efficiency in the wavelength range of 670 nm or more.

In view of the above-mentioned problems, an object of the present invention is to provide an epitaxial wafer that can improve the light-emitting portion of a light-emitting portion made of an AlGaInP-based material in a range of 670 nm or more and 690 nm or less of a light emitting diode. Luminous efficiency. [Technical means to solve problems]

To achieve the above object, the present invention provides an epitaxial wafer including a light-emitting layer. The light-emitting layer consists of a chemical formula (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is formed by laminating a first conductive type cladding layer, an active layer, and a second conductive type cladding layer composed of a compound semiconductor represented by the compound semiconductor, and the light emitting layer has a light emission wavelength of 670 nm or more and Below 690nm. The active layer is a quantum well structure in which a well layer and a barrier layer are alternately laminated. The composition of the barrier layer is 0.20 ≦ x ≦ 0.45, and 0 <y <1.

By thus structuring the composition of the barrier layer to 0.20 ≦ x ≦ 0.45, 0 <y <1, and a light emitting diode having a light emission wavelength of 670 to 690 nm, high light emission efficiency can be obtained.

Furthermore, the present invention provides a light emitting diode, which is manufactured using the above epitaxial wafer.

With such a light-emitting diode, a light-emitting diode having a high light-emitting efficiency in a range of a light-emitting wavelength of 670 to 690 nm can be obtained. [Contrast with the effect of the prior art]

As described above, the epitaxial wafer of the present invention can obtain high light emitting efficiency in a light emitting diode system having a light emitting wavelength of 670 to 690 nm. Furthermore, if it is the light-emitting diode of the present invention, it can be used as a light-emitting diode with a high light-emitting efficiency in the range of 670 to 690 nm.

As described above, a light-emitting element using an AlGaInP-based material must optimize the parameters of the structure of the active layer, especially in order to improve the light-emitting efficiency in a wavelength range of 670 nm or more.

For this reason, the present inventors have worked hard on epitaxial wafers that can improve the light emission efficiency of a light emitting layer made of an AlGaInP-based material in a range of 670 nm to 690 nm. As a result, it was found that by setting the composition of the barrier layer in the chemical formula of (Al _x Ga _1-x ) _y In _1-y P to be 0.20 ≦ x ≦ 0.45, 0 <y <1, the light emission wavelength can be 670 ~ 690nm The light-emitting diode obtained high luminous efficiency, and completed the present invention.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

First, an epitaxial wafer according to the present invention will be described with reference to FIG. 1.

As shown in FIG. 1, the epitaxial wafer 10 of this embodiment includes a pn junction type light emitting portion 28 provided on a GaAs substrate 12. The light emitting portion 28 includes a quantum well active layer 17 as a part of the light emitting layer. .

Specifically, the epitaxial wafer 10 is formed by sequentially epitaxially growing the first conductive type etch stop layer 13, the first conductive type contact layer 14, and the light emitting portion 28 on the GaAs substrate 12. The light emitting section 28 includes a first conductive type current diffusion layer 15, a light emitting layer 27 provided on the first conductive type current diffusion layer 15, and a second conductive type current diffusion layer 19 provided on the light emitting layer 27.

The light emitting layer 27 includes a first conductive type cladding layer 16, a quantum well active layer 17 provided on the first conductive type cladding layer 16, and a second conductive type cladding layer provided on the quantum well active layer 17. 18. The quantum well active layer 17 is formed by alternately stacking a well layer 17a and a barrier layer 17b.

Here, for example, the first conductivity type is a p-type, and the second conductivity type is an n-type. In this case, in detail, the first conductive type etching stop layer 13 is p- (Al _x Ga _1-x ) _y In _1-y P (however, 0 ≦ x ≦ 1, 0 <y <1), and the first conductive type The type contact layer 14 is p-GaAs, and the first conductive type current diffusion layer 15 is p- (Al _x Ga _1-x ) _y In _1-y P (however, 0 ≦ x ≦ 1, 0 <y <1), The first conductive type cladding layer 16 is p- (Al _x Ga _1-x ) _y In _1-y P (however, 0 ≦ x ≦ 1, 0 <y <1), and the well in the quantum well active layer 17 The layer 17a is i-Ga _y In _1-y P (however, 0 <y <1), and the barrier layer 17 b in the quantum well active layer 17 is i- (Al _x Ga _1-x ) _y In _1-y P (However, 0.2 ≦ x ≦ 0.45, 0 <y <1), and the second conductive type coating layer 18 is n- (Al _x Ga _1-x ) _y In _1-y P (however, 0 ≦ x ≦ 1, 0 <y <1), and the second conductivity type current diffusion layer 19 is an n-GaP layer. In this case, the Ga composition y of the well layer 17a of the quantum well active layer 17 can be changed to a desired emission wavelength. The light emission wavelength of the epitaxial wafer of the present invention is 670 nm to 690 nm. Therefore, the Ga composition y of the well layer 17a of the quantum well active layer 17 is set so that the light emission wavelength is 670 nm to 690 nm.

In the epitaxial wafer of the present invention, the composition of the barrier layer 17b of the quantum well active layer 17 is 0.20 ≦ x ≦ 0.45, and 0 <y <1, so that the light emitting diode having a light emission wavelength of 670 to 690 nm can obtain high light emission. effectiveness.

Next, a light-emitting diode of the present invention will be described with reference to FIG. 2.

As shown in FIG. 2, the light-emitting diode 11 according to this embodiment includes a light-emitting portion 28, a first ohmic wire electrode 20 on a first conductivity type side (for example, a p-type side), and a pad electrode (not shown). The second ohmic line electrode 21 on the second conductive type side (for example, the n-type side), the transparent oxide film layer 22, the reflective metal layer 23, the bonding metal layer 24, the conductive support substrate 25, and the conductive ohmic electrode 26. The light emitting diode 11 is a bonding metal layer 24, a reflective metal layer 23, a transparent oxide film layer 22, and a light emitting portion 28, a first ohmic wire electrode 20, and a pad electrode system on the conductive support substrate 25 in this order. The first conductive type contact layer 14 is provided on the light emitting portion 28, the second ohmic line electrode 21 is provided in the transparent oxide film layer 22, and the conductive ohmic electrode 26 is provided under the conductive support substrate 25. On the surface. The first conductive type current diffusion layer 15, the light emitting layer 27 (the first conductive type cladding layer 16, the quantum well active layer 17, and the second conductive type cladding layer 18) and the second conductive type current diffusion layer constituting the light emitting portion 28 The 19 series is the same as that shown in FIG. 1. In addition, the first ohmic linear electrode 20 and the second ohmic linear electrode 21 are arranged at positions that do not overlap each other when viewed from above.

The light emitting diode 11 shown in FIG. 2 is manufactured using the epitaxial wafer 10 shown in FIG. 1 as described later. The light-emitting diode shown in FIG. 2 can be a light-emitting diode having a high light-emitting efficiency in a range of a light-emitting wavelength of 670 to 690 nm.

Next, an example of a method for manufacturing an epitaxial wafer according to the present invention will be described.

By the MOVPE method, a semiconductor multilayer structure of a plurality of AlGaInP-based materials is formed on the n-GaAs substrate 12 shown in FIG. 1. Specifically, by the MOVPE method, a p-type etch stop layer 13 composed of p-Ga _0.5 In _0.5 P and a p-type contact layer 14 composed of p-GaAs are sequentially deposited on the n-GaAs substrate 12. , P-type current diffusion layer 15 composed of p- (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P, p-type cladding layer 16 composed of p-Al _0.5 In _0.5 P, and self-doped Ga _0.3 In _The number of pairs of well layers 17a (film thickness 8nm) of _0.7 P and barrier layer 17b (film thickness 7.7nm) of no impurity (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P is 4 (number of well layers 5, Number of barrier layers 4) Quantum well active layer 17 (where the emission wavelength is described as 680 nm), n-type cladding layer 18 composed of n-Al _0.5 In _0.5 P, and n-type current diffusion composed of n-GaP Layer 19. Thereby, an epitaxial wafer 10 as shown in FIG. 1 is formed.

Here, as raw materials for the MOVPE method, organic metal compounds such as trimethylgallium (TMGa), triethylgallium (TEGa), trimethylaluminum (TMAl), and trimethylindium (TMIn) can be used, and Hydride gases such as arsenide (AsH ₃ ) and phosphine (PH ₃ ). Furthermore, as the raw material of the n-type impurity, silane (SiH ₄ ) can be used, and as the raw material of the p-type impurity, dimagnesium (Cp ₂ Mg) can be used. In addition, as a raw material of the n-type impurity, hydrogen selenide (H ₂ Se), disilane (Si ₂ H ₆ ), diethyl tellurium (DETe), or dimethyl tellurium (DMTe) may be used. Then, as a raw material of the p-type impurity, dimethyl zinc (DMZn) or diethyl zinc (DEZn) may be used.

Next, an example of a method of manufacturing the light-emitting diode of the present invention will be described with reference to FIG. 3.

First, a transparent oxide film layer 22 is formed on the surface of the n-type current diffusion layer 19 of the epitaxial wafer 10 formed as described above, and a second ohmic line electrode 21 on the n-type side is formed in the transparent oxide film layer 22. (Refer to Figure 3 (a) and Figure 3 (b)). Specifically, after forming a transparent oxide film layer 22 (for example, a SiO ₂ film) using a plasma CVD (Chemical Vapor Deposition) device, an opening is provided in the transparent oxide film layer 22 using a photolithography method and an etching method. More specifically, an opening is provided by removing a transparent oxide film layer 22 in a region where a resist pattern is not formed using a hydrofluoric acid-based etchant as an etching solution. Next, an AuSi alloy of a material constituting the second ohmic wire-shaped electrode 21 on the n-type side is formed in the opening portion by a vacuum evaporation method.

Next, an Al layer as a reflective layer, a Ti layer as a barrier layer, and an Au layer as a bonding layer are formed by a vacuum evaporation method or a sputtering method. Thereby, the reflective metal layer 23 is formed (refer to FIG. 3 (c)). In addition, as a material constituting the reflective metal layer 23, a material having a high reflectance with respect to a wavelength of light emitted from the quantum well active layer 17 may be selected. Thereby, a semiconductor laminated structure 29 is obtained.

Next, using a vacuum evaporation method, Ti as a contact electrode, Ni as a barrier layer, and Au as a bonding layer are applied on a conductive support substrate 25 (for example, a Si substrate) as a contact ohmic bonding metal layer 24. Is formed, and the support substrate 30 is prepared. By bonding this support substrate 30 to the semiconductor multilayer structure 29 shown in FIG. 3 (c), a bonding structure 31 that is mechanically and electrically connected is formed (see FIG. 3 (d)). Here, the wafer bonding is performed by applying a predetermined pressure in the bonding device, and then applying pressure to the overlapped semiconductor multilayer structure 29 and the support substrate 30 through a jig, and heating the wafer to a predetermined temperature. Specifically, it was performed at a pressure of 90 N / cm ² and a temperature of 350 ° C for 30 minutes.

Next, the GaAs substrate 12 is selectively removed completely from the bonding structure 31 with an etchant for GaAs etching, and the p-type etch stop layer 13 made of p-Ga _0.5 In _0.5 P is exposed. As an etchant for GaAs etching, a mixed liquid of ammonia water and hydrogen peroxide is taken as an example. Next, the etching stop layer 13 is removed from the bonding structure 31 from which the GaAs substrate has been removed by etching using a specific etchant (see FIG. 3 (e)). When the etching stopper layer 13 is formed of a compound semiconductor of an AlGaInP-based material, an etchant containing hydrochloric acid can be used as a predetermined etchant.

Next, a p-type ohmic electrode is formed at a specific position by a photolithography method and a vacuum evaporation method (refer to FIG. 3 (f)). The ohmic electrode on the p-type side is formed by a disk electrode (not shown) and the linear electrode 20, and is formed by, for example, vapor deposition in the order of Ti, AuBe, and Au. In this case, the ohmic electrode system on the p-type side is formed at a position that does not overlap with the second ohmic linear electrode 21 when viewed from above. Next, as the ohmic electrode on the p-type side, the p-type contact layer 14 made of p-GaAs is etched and removed. In addition, as the ohmic electrode covering the p-type side, the p-type current diffusion layer 15 may be subjected to a surface roughening treatment. After the p-type contact layer 14 is removed, a surface roughening treatment may be performed using a predetermined etchant.

Next, a conductive ohmic electrode 26 is formed on approximately the entire surface of the back surface of the conductive support substrate 25 by a vacuum evaporation method (refer to FIG. 3 (g)). The ohmic electrode 26 on the rear surface is formed on the bottom surface of the conductive support substrate 25 in the order of Ti and Au and by vapor deposition. Thereafter, an alloy treatment is applied to form an alloying treatment for electrically connecting the respective ohmic electrodes. As an example, the heat treatment is performed at 400 ° C. for 5 minutes under a nitrogen atmosphere as an inert atmosphere. Thereby, the joint structure 31 'is formed.

Then, the bonding structure 31 'is divided into elements by a cutting device having a cutting blade. Thereby, a plurality of light-emitting diodes 11 as shown in FIG. 2 are formed.

Hereinafter, the present invention will be described more specifically by showing examples and comparative examples, but the present invention is not limited to these examples.

[Examples 1-9 and Comparative Examples 1-7] Examples 1-9 and Comparative Examples 1-7 were processed by laminating a plurality of semiconductor layers on an n-GaAs substrate 12 having a diameter of 50 mm by the MOVPE method. Only in the barrier layer 17b of the quantum well active layer 17 (of (Al _x Ga _1-x ) _y In _1-y P, y = 0.5 (Al _x Ga _1-x ) _0.5 In _0.5 P) Al The composition x changes from 0.1 to 0.6, and the Ga composition y of the well layer 17a (of (Al _x Ga _1-x ) _y In _1-y P, x = 0 Ga _y In _1-y P) The point where the desired wavelength (that is, 670 nm, 680 nm, and 690 nm) is changed for each Al composition is different. The other processes are to produce epitaxial wafers according to the manufacturing method described above. Here, Ga compositions y of Examples 1-9 and Comparative Examples 1-7 are as shown in Table 1.

[Table 1]

FIG. 4 shows the relationship between the Al composition x of the barrier layer 17b and the PL intensity of the epitaxial wafer when the light emission wavelength is 680 nm (Examples 1-3 and Comparative Examples 1-3). Here, the PL (Photo Luminescence) method is a method that generates electron hole pairs through the irradiation of light, and then combines them through various processes, and then measures the spectrum of light emission at this time, and then determines the band gap, The crystallinity of materials, the amount of impurities, etc. Since the crystallinity of the material can be determined by the PL intensity and the full width at half maximum of the epitaxial wafer, the magnitude of the PL intensity can be used to determine the approximate brightness in the element state.

As can be seen from FIG. 4, when the Al composition x of the barrier layer 17 b is around 0.4, the PL intensity is the largest, and as the Al composition x of the barrier layer 17 b becomes smaller, the PL intensity gradually decreases. Although the Al composition becomes smaller, the strain amount will also become smaller, but at the same time, the limitation effect of the carrier becomes smaller, and a decrease in strength occurs. In addition, when the Al composition is 0.5 or more, the amount of strain increases and the crystal defects inside the light-emitting layer increase, so that the intensity extremely decreases. The surface of the epitaxial wafer at this time has a lot of bumps caused by crystal defects observed.

Table 2 shows the Al composition x of the barrier layer 17b of Example 1-9 and Comparative Example 1-7 and the surface state of the epitaxial wafer.

Using the epitaxial wafers of Examples 1-9 and Comparative Examples 1-7, light-emitting diodes were manufactured according to the manufacturing method described above.

The produced light-emitting diode was measured for peak wavelength and luminous efficiency. The results are shown in Table 2. Here, the luminous efficiency (au) is calculated by the luminous efficiency (%) = output (mW) / input power (mW), and the value when the Al composition x in the barrier layer 17b is 0.4 is defined as " 1 "ratio.

[Table 2]

As can be seen from Table 2, when the Al composition x is 0.5 or more, a large number of bumps are generated on the surface of the epitaxial wafer, and the surface unevenness becomes too large, and the bonding of the semiconductor multilayer structure 29 and the support substrate 30 cannot be performed, and Componentization (production of light-emitting diodes). Within the range of possible Al composition x from 0.1 to 0.4, the luminous efficiency tends to have the same tendency as the PL intensity result. For Comparative Examples 1, 4, and 6 of 0.90 or less, Examples 1 to 9 improved to 0.94 to 1.00.

In addition, when the Al composition x is 0.5 or more (Comparative Examples 2, 3, 5, and 7), even if elementization is possible, it is estimated from the results of FIG. 4 that the luminous efficiency is extremely low.

That is, in Example 1-9, by making the Al composition x of the barrier layer 17b 0.2 or more and 0.45 or less, the crystal defects in the light-emitting layer can be suppressed within the light-emitting wavelength range of 670 to 690 nm in which the strain amount of the light-emitting layer becomes large. Therefore, compared with the comparative example, it can be seen that the luminous efficiency is improved, and an epitaxial wafer that can be used to make a light emitting diode with high luminous efficiency can be obtained.

The present invention is not limited to the embodiments described above. The above embodiment is an example, and anyone who has substantially the same structure as the technical idea described in the patent application scope of the present invention and produces the same effect is included in the technical scope of the present invention no matter what.

10‧‧‧Epistar Wafer

11‧‧‧light-emitting diode

12‧‧‧GaAs substrate (n-GaAs substrate)

13‧‧‧ The first conductive type etch stop layer (p-type etch stop layer)

14‧‧‧ the first conductive contact layer (p-type contact layer)

15‧‧‧ the first conductivity type current diffusion layer (p-type current diffusion layer)

16‧‧‧The first conductive type cladding layer (p-type cladding layer)

17‧‧‧ Quantum Well Active Layer

17a‧‧‧well

17b‧‧‧Bundles

18‧‧‧Second conductive type cladding layer (n-type cladding layer)

19‧‧‧Second conductivity type current diffusion layer (n-type current diffusion layer)

20‧‧‧ the first ohm linear electrode (linear electrode)

21‧‧‧Second ohm wire electrode

22‧‧‧ transparent oxide film

23‧‧‧Reflective metal layer

24‧‧‧ bonding metal layer

25‧‧‧ conductive support substrate

26‧‧‧Conductive ohmic electrode

27‧‧‧Light-emitting layer

28‧‧‧Lighting Department

29‧‧‧Semiconductor multilayer structure

30‧‧‧ support substrate

31、31’‧‧‧joining structure

FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of an epitaxial wafer according to the present invention. Fig. 2 is a schematic cross-sectional view showing an example of an embodiment of a light emitting diode of the present invention. FIG. 3 is a process cross-sectional view showing an example of a method of manufacturing the light-emitting diode of the present invention. FIG. 4 is a graph showing the relationship between the Al composition x and the PL intensity of the barrier layer at a light emission wavelength of 680 nm.

Claims (2)

An epitaxial wafer includes: a light-emitting layer, a first conductive type cladding layer composed of a compound semiconductor represented by a chemical formula (Al _x Ga _1-x ) _y In _1-y P, an active layer Layer and a second conductive type cladding layer are laminated, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, the light-emitting layer has a light emission wavelength of 670 nm to 689 nm, wherein the active layer is a well The barrier layer and the barrier layer are layered quantum well structures. The composition of the barrier layer is 0.20 ≦ x ≦ 0.45, and 0 <y <1. A light-emitting diode is manufactured using the epitaxial wafer according to claim 1.