JP2016207869A - Epitaxial wafer, and light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial wafer capable of improving luminous efficiency of a light emitting part made of an AlGaInP based material in an emission wavelength region of not less than 670 nm and not more than 690 nm.SOLUTION: This epitaxial wafer has a luminous layer in which a first conductivity type clad layer formed by a compound semiconductor expressed by a composition formula (ALGa)InP (provided, 0≤x≤1, 0≤y≤1), an active layer, and a second conductivity type clad layer, the emission wavelength of the luminous layer is not less than 670 nm and not more than 690 nm, the active layer has a quantum well structure in which a well layer and a barrier layer are alternately laminated, and the composition of the barrier layer is 0.20≤x≤0.45, 0<y<1.SELECTED DRAWING: Figure 1

Description

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

  A cultivation method using illumination by a light emitting diode capable of energy saving, long life, and miniaturization has attracted attention. From the research results so far, the effect of red light in the region of 660 to 670 nm has been confirmed as one of the emission wavelengths suitable for light sources for plant growth (photosynthesis), and in particular, the light with an emission wavelength of 660 nm is It is a desirable light source because of its high photosynthesis reaction efficiency. On the other hand, since light absorption of green plants has a peak at 680 nm, light having an emission wavelength of 680 nm is expected as a light source with higher reaction efficiency of photosynthesis.

In a compound semiconductor light-emitting diode including a light-emitting layer made of an AlGaInP ((Al _x Ga _1-x ) _y In _1-y P: 0 ≦ x ≦ 1, 0 <y ≦ 1) -based material, Ga _0.5 Although the wavelength of the light emitting layer having the composition of In _0.5 P is the longest, the light emission wavelength (peak wavelength) obtained with this light emitting layer is around 650 nm. For this reason, a region having a wavelength longer than 650 nm is realized by using a strained light emitting layer. However, as the emission wavelength is lengthened, the amount of strain increases, so that crystal defects inside the light emitting layer increase, making it difficult to achieve practical use and increase efficiency.

  In order to solve these problems, in Patent Document 1, in a laminated structure in which a strained light emitting layer and a barrier layer are alternately stacked in an active layer, light is emitted by applying a strain opposite to the strained light emitting layer to the barrier layer. A method of obtaining high luminous efficiency by relaxing the strain generated in the layer and suppressing the generation of crystal defects inside the strained light emitting layer is disclosed. Further, in Patent Document 2, in a stacked structure in which an active layer is alternately stacked with a strained light emitting layer and a barrier layer, the number of strained light emitting layers is 1 to 7 and the film thickness is 250 nm or less, and the amount of strain is reduced. Thus, a method for obtaining high luminous efficiency is disclosed.

JP 2012-018986 A JP 2012-039049 A

  As described above, Patent Documents 1 and 2 are disclosed for the problem of obtaining high light emission efficiency in a wavelength region where the emission wavelength is 650 nm or more. However, when the emission wavelength is 670 nm or more, the amount of distortion increases. For this reason, crystal defects in the light emitting layer increase, and it cannot be said that high light emission efficiency can be obtained.

  From the above, in the light-emitting element using the AlGaInP-based material, it is necessary to optimize the structural parameters of the active layer in order to improve the light emission efficiency particularly in the wavelength region where the emission wavelength is 670 nm or more.

  The present invention has been made in view of the above problems, and an epitaxial wafer capable of improving the light emission efficiency of a light emitting portion made of an AlGaInP-based material in a light emission wavelength region of 670 nm or more and 690 nm or less in a light emitting diode. The purpose is to provide.

In order to achieve the above object, the present invention provides a compound semiconductor represented by a composition formula (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1). An epitaxial wafer having a light emitting layer formed by laminating a first conductive type cladding layer, an active layer, and a second conductive type cladding layer, wherein the light emitting layer has an emission wavelength of 670 nm or more and 690 nm or less, An epitaxial wafer characterized in that the active layer has a quantum well structure in which well layers and barrier layers are alternately stacked, and the composition of the barrier layers is 0.20 ≦ x ≦ 0.45 and 0 <y <1 I will provide a.

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

  The present invention also provides a light emitting diode manufactured using the above epitaxial wafer.

  If it is such a light emitting diode, it can be set as the light emitting diode from which a high luminous efficiency is acquired in the area | region of 670-690 nm of light emission wavelengths.

  As described above, with the epitaxial wafer of the present invention, high light emission efficiency can be obtained in a light emitting diode having an emission wavelength of 670 to 690 nm. Moreover, if it is a light emitting diode of this invention, it can be set as the light emitting diode from which a high luminous efficiency is obtained in the area | region of 670-690 nm of light emission wavelengths.

It is typical sectional drawing which shows an example of embodiment of the epitaxial wafer of this invention. It is typical sectional drawing which shows an example of embodiment of the light emitting diode of this invention. It is process sectional drawing which shows an example of the method of manufacturing the light emitting diode of this invention. It is a figure which shows the relationship between Al composition x of a barrier layer and PL intensity | strength in case luminescence wavelength is 680 nm.

  As described above, in the light emitting device using the AlGaInP-based material, it is necessary to optimize the structural parameters of the active layer in order to improve the light emission efficiency particularly in the wavelength region where the emission wavelength is 670 nm or more.

Therefore, the present inventors have intensively studied an epitaxial wafer that can improve the light emission efficiency of the light emitting layer made of an AlGaInP-based material in the region where the emission wavelength is not less than 670 nm and not more than 690 nm. As a result, by setting the composition of the barrier layer to 0.20 ≦ x ≦ 0.45 and 0 <y <1 in the composition formula of (Al _x Ga _1-x ) _y In _1-y P, the emission wavelength is 670. It has been found that high luminous efficiency can be obtained in a light emitting diode of ˜690 nm, and the present invention has been made.

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

  First, the epitaxial wafer of the present invention will be described with reference to FIG.

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

  Specifically, the epitaxial wafer 10 is obtained by epitaxially growing a first conductivity type etching stop layer 13, a first conductivity type contact layer 14, and a light emitting portion 28 in this order on a GaAs substrate 12. The light emitting unit 28 includes a first conductivity type current spreading layer 15, a light emitting layer 27 provided on the first conductivity type current spreading layer 15, and a second conductivity type current spreading layer 19 provided on the light emitting layer 27. Have.

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

Here, for example, the first conductivity type is p-type, and the second conductivity type is n-type. In this case, specifically, the first conductivity type etching stop layer 13 is p- (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 <y <1), the first conductivity Type contact layer 14 is p-GaAs, and first conductivity type current spreading layer 15 is p- (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 <y <1), The first conductivity type cladding layer 16 is p- (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 <y <1), and the well layer 17a in the quantum well active layer 17 is _{i-Ga y in 1-y} P ( where 0 <y <1), the barrier layer 17b in the quantum well active layer 17 is _{i- (Al x Ga 1-x} ) y in 1-y P ( where, 0. 2 ≦ x ≦ 0.45,0 <y < 1), the second-conductivity-type cladding layer 18 is _{n- (Al x Ga 1-x} ) y In 1-y P However, 0 ≦ x ≦ 1,0 <y <1), the second conductivity type current diffusion layer 19 is n-GaP layer. In this case, the Ga composition y of the well layer 17a of the quantum well active layer 17 can be varied so as to have a desired emission wavelength. Since the epitaxial wafer of the present invention has an emission wavelength of 670 nm or more and 690 nm or less, the Ga composition y of the well layer 17a of the quantum well active layer 17 is set so that the emission wavelength is 670 nm or more and 690 nm or less.

  The epitaxial wafer of the present invention is high in a light emitting diode having an emission wavelength of 670 to 690 nm by setting the composition of the barrier layer 17b of the quantum well active layer 17 to 0.20 ≦ x ≦ 0.45 and 0 <y <1. Luminous efficiency can be obtained.

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

  As shown in FIG. 2, the light-emitting diode 11 of the present embodiment includes a light-emitting portion 28, a first ohmic wire electrode 20 and a pad electrode (not shown) on the first conductivity type side (for example, p-type side), a second It has a second ohmic wire electrode 21 on the conductive type side (for example, n-type side), a transparent oxide film layer 22, a reflective metal layer 23, a bonding metal layer 24, a conductive support substrate 25, and a conductive ohmic electrode 26. Yes. The light emitting diode 11 includes a conductive support substrate 25, a bonding metal layer 24, a reflective metal layer 23, a transparent oxide film layer 22, and a light emitting portion 28 provided in this order. The first ohmic thin wire electrode 20 and the pad The electrode is provided on the light emitting portion 28 via the first conductivity type contact layer 14, the second ohmic wire electrode 21 is provided in the transparent oxide film layer 22, and the conductive ohmic electrode 26 is connected to the conductive support substrate 25. It is provided on the lower surface. First conductive type current spreading layer 15, light emitting layer 27 (first conductive type cladding layer 16, quantum well active layer 17 and second conductive type cladding layer 18) constituting light emitting unit 28, second conductive type current spreading layer 19 is the same as that shown in FIG. Further, the first ohmic wire electrode 20 and the second ohmic wire electrode 21 are arranged at positions that do not overlap each other when viewed from above.

  2 is manufactured using the epitaxial wafer 10 of FIG. 1, as will be described later. If it is a light emitting diode like FIG. 2, it can be set as the light emitting diode from which a high luminous efficiency is acquired in the area | region of 670-690 nm of light emission wavelengths.

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

A semiconductor stacked structure of a plurality of AlGaInP-based materials is formed on the n-GaAs substrate 12 shown in FIG. 1 by the MOVPE method. Specifically, on the n-GaAs substrate 12, a p-type etching stop layer 13 made of p-Ga _0.5 In _0.5 P, a p-type contact layer 14 made of p-GaAs, and p- (Al _0.4 Ga _{0.6) 0.5} in _0.5 and p-type current diffusion layer 15 made of _P, a p-type cladding layer 16 made of _{p-Al 0.5 in} 0.5 _P, an undoped Ga _{0 .3} In _0.7 P well layer 17a (film thickness 8 nm) and undoped (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P barrier layer 17b (film thickness 7.7 nm) A quantum well active layer 17 having a pair number of 4 (5 well layers and 4 barrier layers) (described in the case of an emission wavelength of 680 nm), an n-type cladding layer 18 made of n-Al _0.5 In _0.5 P, The n-type current diffusion layer 19 made of n-GaP is sequentially formed by the MOVPE method. It is deposited. Thereby, an epitaxial wafer 10 as shown in FIG. 1 is formed.

Here, the raw materials used in the MOVPE method are organometallic compounds such as trimethylgallium (TMGa), triethylgallium (TEGa), trimethylaluminum (TMAl), trimethylindium (TMIn), arsine (AsH ₃ ), and phosphine (PH ₃ A hydride gas such as) can be used. Furthermore, monosilane (SiH ₄ ) can be used as the n-type dopant material, and biscyclopentadienyl magnesium (Cp ₂ Mg) can be used as the p-type dopant material. In addition, hydrogen selenide (H ₂ Se), disilane (Si ₂ H ₆ ), diethyl tellurium (DETe), or dimethyl tellurium (DMTe) can also be used as an n-type dopant material. And dimethyl zinc (DMZn) or diethyl zinc (DEZn) can also be used as a raw material of a p-type dopant.

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

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 an n-type second ohmic wire electrode 21 is formed in the transparent oxide film layer 22. (See FIG. 3A and FIG. 3B). Specifically, for example, a SiO ₂ film is formed as the transparent oxide film layer 22 using a plasma CVD (Chemical Vapor Deposition) apparatus, and then an opening is formed in the transparent oxide film layer 22 using a photolithography method and an etching method. Provide. More specifically, an opening is provided by removing the transparent oxide film layer 22 in a region where the resist pattern is not formed using a hydrofluoric acid-based etchant as an etchant. Subsequently, an AuSi alloy, which is a material constituting the n-type second ohmic wire electrode 21, is formed in the opening using a vacuum deposition 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 using a vacuum deposition method or a sputtering method. Thereby, the reflective metal layer 23 is formed (see FIG. 3C). In addition, the material which comprises the reflective metal layer 23 can select the material with a high reflectance with respect to the wavelength of the said light according to the wavelength of the light which the quantum well active layer 17 emits. Thereby, the semiconductor multilayer structure 29 is obtained.

Next, as a conductive ohmic bonding metal layer 24, Ti as a contact electrode, Ni as a barrier layer, and Au as a bonding layer are deposited on a conductive support substrate 25 (for example, a Si substrate) by vacuum deposition. The support substrate 30 is prepared using The support substrate 30 and the semiconductor multilayer structure 29 shown in FIG. 3C are bonded to form a mechanically and electrically connected junction structure 31 (see FIG. 3D). Here, the wafers are bonded by bringing the inside of the bonding apparatus to a predetermined pressure, and then applying pressure to the overlapped semiconductor laminated structure 29 and the support substrate 30 through a jig and heating them to a predetermined temperature. Specifically, the pressure is 90 N / cm ² and the temperature is 350 ° C. for 30 minutes.

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

  Next, an ohmic electrode on the p-type side is formed at a predetermined position by using a photolithography method and a vacuum vapor deposition method (see FIG. 3F). The p-type ohmic electrode is formed by a circular electrode (not shown) and a thin wire electrode 20, and is formed by evaporating, for example, Ti, AuBe, and Au in this order. In this case, the p-type ohmic electrode is formed at a position that does not overlap the n-type second ohmic electrode 21 when viewed from above. Next, the p-type contact layer 14 made of p-GaAs is removed by etching using the p-type ohmic electrode as a mask. Alternatively, the p-type current diffusion layer 15 can be roughened using the p-type ohmic electrode as a mask. Further, after removing the p-type contact layer 14, a roughening treatment can be performed using a predetermined etchant.

  Next, a conductive ohmic electrode 26 is formed on substantially the entire back surface of the conductive support substrate 25 by a vacuum deposition method (see FIG. 3G). The back ohmic electrode 26 is formed by evaporating Ti and Au on the bottom surface of the conductive support substrate 25 in this order. Thereafter, an alloying process is performed, which is an alloying process for forming each ohmic electrode in electrical bonding. As an example, heat treatment is performed at 400 ° C. for 5 minutes in a nitrogen atmosphere as an inert atmosphere. Thereby, the joined structure 31 ′ is formed.

  Then, using a dicing apparatus having a dicing blade, the junction structure 31 ′ is element-isolated. Thereby, a plurality of light emitting diodes 11 as shown in FIG. 2 are formed.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these Examples.

(Example 1-9, Comparative Example 1-7)
In Example 1-9 and Comparative Example 1-7, in the step of laminating a plurality of semiconductor layers on the n-GaAs substrate 12 having a diameter of 50 mm by the MOVPE method, the barrier layer 17b ((Al _x in _{Ga 1-x) y in 1} -y P, and a _{y = 0.5 (Al x Ga 1} -x) 0.5 in 0.5 P) Al composition x of 0.1 to 0.6 of In the well layer 17a ((Al _x Ga _1-x ) _y In _1-y P, the desired wavelengths (that is, 670 nm, 680 nm, and 690 nm) are changed for each Al composition. The only difference was that the Ga composition y of Ga _y In _1-y P) = 0 was changed, and in other steps, an epitaxial wafer was manufactured according to the manufacturing method described above. Here, the Ga compositions y of Examples 1-9 and Comparative Examples 1-7 are as shown in 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 emission wavelength is 680 nm (Example 1-3, Comparative Example 1-3). Here, the PL (Photo Luminescence) method is based on measuring the spectrum of light emitted when electron-hole pairs are generated by light irradiation and recombined through various processes. This is a method for measuring the doping amount of impurities and the like. Since the PL intensity, half-value width, etc. of the epitaxial wafer can determine the crystallinity of the material, the magnitude of the PL intensity can know the magnitude of the brightness in the element state.

  As can be seen from FIG. 4, the PL intensity becomes maximum when the Al composition x of the barrier layer 17b is around 0.4, and the PL intensity gradually decreases as the Al composition x of the barrier layer 17b decreases. As the Al composition is reduced, the amount of strain is also reduced, but at the same time, the effect of confining carriers is reduced, resulting in a decrease in strength. On the other hand, 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 strength decreases extremely. Many hillocks due to crystal defects were observed on the epitaxial wafer surface at this time.

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

  Using the epitaxial wafers of Example 1-9 and Comparative Example 1-7, light emitting diodes were produced according to the production method as described above.

  About the produced light emitting diode, the peak wavelength and luminous efficiency were measured. The results are shown in Table 2. Here, the luminous efficiency is calculated by luminous efficiency (%) = output (mW) / input power (mW), and when the Al composition x of the barrier layer 17b is 0.4, the value is “1”. The ratio is shown.

  As can be seen from Table 2, when the Al composition x is 0.5 or more, a large number of hillocks are generated on the surface of the epitaxial wafer, so that the surface unevenness becomes too large and the semiconductor multilayer structure 29 and the support substrate 30 cannot be joined. , Device formation (production of light emitting diode) could not be performed. In the range where the Al composition x that can be made into an element is in the range of 0.1 to 0.45, the luminous efficiency tends to be the same as the PL intensity result, and in Comparative Examples 1, 4, and 6, it is 0.90 or less. On the other hand, in Example 1-9, it is improved with 0.94-1.00.

  Further, when the Al composition x is 0.5 or more (Comparative Examples 2, 3, 5, and 7), it is estimated that the light emission efficiency is considerably lowered from the result of FIG. .

  That is, in Example 1-9, by setting the Al composition x of the barrier layer 17b to 0.2 or more and 0.45 or less, the emission layer has a light emission wavelength of 670 to 690 nm in which the distortion amount of the light emission layer is increased. Since internal crystal defects can be suppressed, the light emission efficiency was improved as compared with Comparative Example 1-7, and an epitaxial wafer capable of producing a light emitting diode having high light emission efficiency could be obtained.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

10 ... epitaxial wafer, 11 ... light emitting diode,
12 ... GaAs substrate (n-GaAs substrate),
13 ... 1st conductivity type etching stop layer (p-type etching stop layer),
14 ... First conductivity type contact layer (p-type contact layer),
15 ... First conductivity type current spreading layer (p-type current spreading layer),
16 ... 1st conductivity type clad layer (p-type clad layer),
17 ... quantum well active layer, 17a ... well layer, 17b ... barrier layer,
18 ... second conductivity type cladding layer (n-type cladding layer),
19 ... Second conductivity type current spreading layer (n-type current spreading layer),
20 ... 1st ohmic thin wire electrode (thin wire electrode), 21 ... 2nd ohmic thin wire electrode,
22 ... Transparent oxide layer, 23 ... Reflective metal layer, 24 ... Bonding metal layer,
25 ... conductive support substrate, 26 ... conductive ohmic electrode, 27 ... light emitting layer,
28 ... Light-emitting part, 29 ... Semiconductor laminated structure, 30 ... Support substrate,
31, 31 '... Joining structure.

About the produced light emitting diode, the peak wavelength and luminous efficiency were measured. The results are shown in Table 2. Here, the luminous efficiency (au) is calculated as luminous efficiency (%) = output (mW) / input power (mW), and is a value when the Al composition x of the barrier layer 17b is 0.4. The ratio is shown as “1”.

Claims (2)

First conductivity type cladding layer and active layer made of a compound semiconductor represented by a composition formula (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) An epitaxial wafer having a light emitting layer on which a second conductivity type clad layer is laminated, wherein the light emitting layer has an emission wavelength of 670 nm or more and 690 nm or less,
The active layer has a quantum well structure in which well layers and barrier layers are alternately stacked, and the composition of the barrier layer is 0.20 ≦ x ≦ 0.45, 0 <y <1 Wafer. A light-emitting diode manufactured using the epitaxial wafer according to claim 1.

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