JPH05175550A - Multilayer semiconductor film reflector - Google Patents

Abstract

PURPOSE:To suppress the increase of the electric resistance caused by the discontinuity of a band by alternately stacking first semiconductors and second semiconductors different in band gap, and interposing middle layers, which have band gaps intermediate between the first semiconductors and the second semiconductors, between them and stacking these. CONSTITUTION:For a reflector 14, the first semiconductor 32 consisting of a p-AlAs semiconductor, a middle layer 34 consisting of a p-AlyGa1-yAs semiconductor, the second semiconductor 36 consisting of a p-AlyGa1-yAs semiconductor, and a middle substance 38 consisting of a p-AlyGa1-yAs semiconductor are stacked in order repeatedly. These are epitaxially grown continuously by changing the rate of the material gas introduced into a MOCVD device. The mixed crystal ratios of the middle layers 34 and 38 are determined to be values smaller than 1 and larger than the Al mixed ratio of the second semiconductor 36. The band gaps of the middle layers 34 and 38 are smaller than first semiconductor 32 and larger than the second semiconductor 36 consisting of p-AlxGa1-xAs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a semiconductor multilayer film reflecting mirror used for a surface emitting type light emitting diode or a surface emitting laser.

[0002]

2. Description of the Related Art A unit semiconductor layer in which two kinds of semiconductors having different band gaps are stacked is repeatedly stacked,
A semiconductor multilayer film reflecting mirror, which is known as Bragg reflection and reflects incident light by light wave interference, is used for a surface emitting type light emitting diode and a surface emitting laser. Such a reflecting mirror reflects light of a specific wavelength based on the difference in the refractive index of the above-mentioned two types of semiconductors. For example, Al _Z Ga
If the infrared or red light-emitting diode configured in _1-Z As, constructed by alternately laminating AlAs and Al _x Ga _1-x As having a predetermined thickness. The thicknesses t _A and t _G of AlAs and Al _x Ga _1-x As are
The refractive index of the _{n A, Al x Ga 1-} x As the refractive index n _G of,
When the emission wavelength of Al _Z Ga _{1 -Z} As, that is, the central wavelength of the light to be reflected is λ _B , the optical thickness n of those is n.
_{It is determined that A} t _A and n _G t _G are respectively λ _B / 4.

[0003]

However, the semiconductor multilayer film reflecting mirror in which two kinds of semiconductor crystals having different band gaps are alternately laminated in this way has an electric resistance due to the discontinuity of bands at the layer interfaces of both semiconductor crystals. Since it becomes higher, there is a problem that a large operating voltage is required.
This means that in order to prevent light absorption by the GaAs semiconductor, AlAs semiconductor and Al _x semiconductor having a relatively large electric resistance are used.
This is a particular problem when a semiconductor multi-layered film reflection mirror is formed by alternately stacking Ga _{1 -x} As semiconductors.

The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress an increase in electric resistance due to band discontinuity.

[0005]

In order to achieve the above object, the present invention provides a semiconductor multilayer structure in which first semiconductors and second semiconductors having different band gaps are alternately stacked to reflect incident light by light wave interference. In the film reflector, the first semiconductor and the second semiconductor are alternately laminated with an intermediate layer having a band gap intermediate between the first semiconductor and the second semiconductor sandwiched therebetween.

[0006]

With this configuration, since there is an intermediate layer having a band gap in the middle between the first semiconductor and the second semiconductor, there is no band difference between those semiconductors. The continuity is relaxed, the electric resistance is reduced, and the operating voltage of the light emitting diode or the like is reduced.
In order to further alleviate the band discontinuity, the band gap of the intermediate layer is set to the adjacent first semiconductor and second semiconductor layer.
It is also possible to change so that the band gap of the semiconductor is gradually or continuously approached.

When the intermediate layer is provided between the first semiconductor and the second semiconductor as described above, the refractive index of the intermediate layer is different from the refractive index of the first semiconductor and the second semiconductor. May be misaligned. As a simple method for preventing this, it is conceivable to reduce the film thickness of the first semiconductor and the second semiconductor by the film thickness of the intermediate layer. However, when the film thickness of the intermediate layer is relatively large, When the refractive index of the layer deviates from the average value of the refractive indices of the first semiconductor and the second semiconductor, the deviation of the reflection wavelength region cannot be sufficiently prevented.

On the other hand, the optical thickness of the first semiconductor is T
O1, TO2 is the optical thickness of the second semiconductor, TO3 is the total optical thickness of the pair of intermediate layers located above and below the first semiconductor or the second semiconductor, and the central wavelength of the light to be reflected is λ.
_{When B} is set, the first
If the thicknesses of the semiconductor, the second semiconductor, and the pair of intermediate layers are determined,
Even when the thickness of the intermediate layer is relatively large, or when the refractive index of the intermediate layer deviates from the average value of the refractive indices of the first semiconductor and the second semiconductor, it is possible to effectively prevent the deviation of the reflection wavelength range. You can

[0009]

[Number 2] TO1 + (TO3 / 2) = TO2 + (TO3 / 2) = λ B / 4 ··· (1)

Further, the thickness of the unit semiconductor layer of one cycle consisting of the first semiconductor, the intermediate layer, the second semiconductor, and the intermediate layer is constant for all the unit semiconductor layers constituting the semiconductor multilayer mirror. Although it may be present, the thickness of the unit semiconductor layer can be changed continuously or stepwise. In that case, the central wavelength of the reflected light also changes with the change in the thickness of the unit semiconductor layer, so that light in a wide wavelength range is reflected with high reflectance. The deviation of the reflection wavelength range due to the provision of the intermediate layer on the surface becomes almost no problem.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a view for explaining the structure of a surface emitting light emitting diode 10 equipped with a semiconductor multilayer film reflecting mirror according to one embodiment of the present invention. A semiconductor multilayer film reflecting mirror is provided on a p-GaAs substrate 12. (Hereinafter, simply referred to as a reflecting mirror) 14, p-Al
GaAs cladding layer 16, p-GaAs active layer 18, n
-AlGaAs clad layer 20 and n-GaAs cap layer 22 are sequentially stacked, and p-AlGaAs
Cladding layer 16, p-GaAs active layer 18, and n-
The AlGaAs clad layer 20 constitutes a double hetero structure. A negative electrode 26 and a positive electrode 28 are provided on a part of the upper surface 24 of the n-GaAs cap layer 22 and the lower surface of the p-GaAs substrate 12, respectively. By applying a forward voltage between them, Light is emitted from the p-GaAs active layer 18 having the double hetero structure,
The light is extracted from the upper surface 24 of the -GaAs cap layer 22. The reflecting mirror 14 reflects the light traveling toward the p-GaAs substrate 12 side by light wave interference, and thus the light output is improved.

Each semiconductor of the surface emitting light emitting diode 10 is epitaxially grown by using a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, and is made of p-AlGaAs.
The clad layer 16 has a thickness of about 2 μm, the p-GaAs active layer 18 has a thickness of about 0.1 μm, the n-AlGaAs clad layer 20 has a thickness of about 2 μm, and the n-GaAs cap layer 22.
Has a film thickness of about 0.1 μm. Further, the reflecting mirror 14, as shown in FIG. 2, the first semiconductor 32 made of p-AlAs _{semiconductor, p-Al y Ga 1-} y As intermediate layer 34 made of a semiconductor, p-Al _x Ga ₁ the second semiconductor 36 made of _-x as semiconductor, and _{p-Al y Ga 1-y} as unit semiconductor layer 40 and an intermediate layer 38 sequentially laminated made of semiconductor
Is repeatedly laminated, and the epitaxial growth is continuously performed by changing the ratio of the raw material gas introduced into the reaction furnace of the MOCVD apparatus. The Al mixed crystal ratio y of the intermediate layers 34 and 38 is set to a value smaller than 1 and larger than the Al mixed crystal ratio x of the second semiconductor 36, and the band gaps of the intermediate layers 34 and 38 are p−.
Smaller than the first semiconductor 32 made of AlAs semiconductor,
greater than the second semiconductor 36 made of _{p-Al x Ga 1-x} As.

The thickness t ₁ of the first semiconductor 32 and the second
The film thickness t _{3 of the} semiconductor 36 depends on the optical thickness
1, TO2, the total optical thickness of the pair of intermediate layers 34, 38 is TO3, and the central wavelength of the light to be reflected is λ _B ,
It is defined so as to satisfy the expression (1). That is, assuming that the first semiconductor 32 has a refractive index n ₁ , the second semiconductor 36 has a refractive index n ₃ , the intermediate layers 34 and 38 made of the same semiconductor have n ₂ and film thicknesses t ₂ and t _4. , TO1 = t
₁ n ₁ , TO2 = t ₃ n ₃ , TO3 = (t
₂ + t ₄ ) n ₂ , the film thickness t _{1 of} the first semiconductor 32 is
Is calculated according to the following equation (2), and the film thickness t ₃ of the second semiconductor 36 is calculated according to the following equation (3). The unit semiconductor layer 40 made of these semiconductors is t ₁ + t ₂ + t
_The reflecting mirror 14 is configured by repeatedly laminating a predetermined number of layers N with a constant thickness of ₃ + t ₄ = T. The thickness of the intermediate layers 34 and 38 is, for example, 10 to 20 nm.
A relatively small value is preset.

[0015]

Equation 3] _{t 1 = {(λ B /} 4) - (t 2 + t 4) n 2/2} / n 1 ··· (2) t 3 = {(λ B / 4) - (t 2 + t _{4) n 2/2} /} n 3 ··· (3)

In such a surface emitting light emitting diode 10, the first semiconductor 32 and the second semiconductor 3 of the reflecting mirror 14 are provided.
6 and the intermediate layers 34 and 38 having a band gap between them are present, the band discontinuity between these semiconductors is relaxed and the electric resistance is reduced, and the intermediate layers 34 and 38 are reduced. The operating voltage is smaller than that in the case where the device is not provided. Incidentally, as shown in Table 1, the mixed crystal ratio x of the second semiconductor 36 is 0.2, the mixed crystal ratio of the intermediate layers 34 and 38 is y 0.6, and the film thickness t ₂ = T ₄ = 10 nm, the refractive index n ₁ = of the first semiconductor 32, that is, AlAs
2.97, the intermediate layers 34 and 38, that is, Al _0.6 Ga _0.4
As the refractive index n ₂ = 3.22, the second semiconductor 36, that is, Al _0.2 Ga _0.8 As has a refractive index n ₃ = 3.47, and the central wavelength λ _{B of the} light to be reflected is λ _B = 880 nm.
According to the equation, the film thickness t ₁ of the first semiconductor 32 is 63.23 nm.
And the film thickness t ₃ of the second semiconductor 36 is set to 54.12 nm according to the above equation (3).
A semiconductor multilayer film reflecting mirror according to the present invention having 0 layers (N = 20) laminated was manufactured, and an electric current of 100 mA was applied to measure the electric resistance of the reflecting mirror, which was about 1.500Ω and one unit semiconductor layer 40. Then, it was about 0.075Ω. On the other hand, the first semiconductor 32 and the second semiconductor 36 are alternately laminated without providing the intermediate layers 34 and 38, and
The film thicknesses t ₁ and t _{3 of them} are respectively λ _B / 4n ₁ = 7
A conventional semiconductor multilayer film reflecting mirror having 30 unit semiconductor layers laminated with 4.07 nm and λ _B / 4n ₃ = 63.40 nm was manufactured, and an operating current of 100 mA was applied to measure the electric resistance of the reflecting mirror. However, it was about 15.280Ω, and about 0.5093Ω in one unit semiconductor layer.

[0017]

[Table 1]

On the other hand, when the intermediate layers 34 and 38 are provided between the first semiconductor 32 and the second semiconductor 36 as described above, the refractive index n ₂ of the intermediate layers 34 and 38 is the first semiconductor 32 and the second semiconductor 36. Since the refractive indices n ₁ and n ₃ are different from each other, the reflection wavelength range may be shifted. As a simple method for preventing this, the film thickness of the first semiconductor 32 and the second semiconductor 36 is reduced by the film thickness of the intermediate layers 34 and 38, for example, as shown in Table 1 above.
In the conventional product of t ₂ = t ₄ = 10 nm,
In the case of inserting 38, the film thickness t ₁ of the first semiconductor 32 =
With the 74.07-10 = 64.07nm, the thickness t ₃ of the second semiconductor 36 = 63.40-10 = 53.4
It is considered to be 0 nm. By doing so, in the case of the above embodiment in which the refractive index n ₂ of the intermediate layers 34 and 38 is the average value of the refractive indexes n ₁ and n ₃ of the first semiconductor 32 and the second semiconductor 36, Overall optical thickness (T
O1 + TO2 + TO3) becomes λ _B / 2, which is equal to the optical thickness of the unit semiconductor layer 40 of the present embodiment, but the optical thickness (TO1 + TO3 / 2) of the first semiconductor 32 side and the optical thickness of the second semiconductor 36 side are the same. Thickness (TO2 + TO3 / 2) is λ _B
Since there is no deviation in the reflection wavelength range from / 4, the spread of the reflection spectrum decreases as the film thicknesses t ₂ and t ₄ of the intermediate layers 34 and 38 increase. In addition, the refractive indices n ₂ of the intermediate layers 34 and 38 are different from those of the first semiconductor 32 and the second semiconductor
When the refractive indices n ₁ and n ₃ of the semiconductor 36 deviate from the average value, the thicknesses of the first semiconductor 32 and the second semiconductor 36 are reduced by the thicknesses of the intermediate layers 34 and 38 as described above. However, the optical thickness of the first semiconductor 32 side (TO1 + TO3 /
2) and the optical thickness of the second semiconductor 36 (TO2 + TO3 /
2) deviates from λ _B / 4, and the optical thickness (TO1 + TO2 + TO3) of the entire unit semiconductor layer deviates from λ _B / 2, so that not only the spread of the reflection spectrum decreases but also the deviation of the reflection wavelength range becomes remarkable. Become.

[0019] In contrast, the reflector 14 of the present embodiment, the optical thickness n ₂ in consideration of refractive index n ₂ of the intermediate layer 34 and 38
Since the film thickness t ₁ of the first semiconductor 32 and the film thickness t ₃ of the second semiconductor 36 are determined based on (t ₂ + t ₄ ) according to the equations (2) and (3), Despite the difference between the refractive indices n ₁ and n _{3 of the} first semiconductor 32 and the second semiconductor 36 and the refractive indices n ₂ of the intermediate layers 34 and 38, the intermediate layer 3
When the film thicknesses t ₂ and t ₄ of the layers 4, 38 are relatively large, or when the refractive index n ₂ of the intermediate layers 34, 38 is the first semiconductor 32 and the second
Even when the refractive indices n ₁ and n ₃ of the semiconductor 36 deviate from the average value, the deviation of the reflection wavelength region is effectively prevented. Even when materials having different refractive indexes are used for the intermediate layers 34 and 38, if the film thickness is determined according to the equation (1), the deviation of the reflection wavelength region can be effectively prevented.

For example, when the light reflection characteristics of the five types of reflecting mirrors shown in Table 2 were examined by simulation, the results shown in FIGS. 3 to 6 were obtained. The reflectors in Table 2 all have a central wavelength of light to be reflected λ _B = 8
In the case of 80 nm, the reflecting mirrors I and III have the film thickness t ₁ of the first semiconductor 32, the film thickness t ₁ of the first semiconductor 32, and the film thickness t ₁ of the first semiconductor 32 in consideration of the optical thickness of the intermediate layers 34 and 38. 2 The film thickness t _{3 of the} semiconductor 36 is set. Further, in the conventional reflecting mirror, the first semiconductor 32 and the second semiconductor 36 are alternately laminated without providing the intermediate layers 34 and 38, and
The film thicknesses t ₁ and t _{3 of them} are respectively λ _B / 4n ₁ = 7
4.07 nm, λ _B / 4n ₃ = 63.40 nm, and the reflecting mirrors II and IV are the same as those of the conventional reflecting mirrors in the first semiconductor 32, (2) The film thicknesses t ₁ and t ₃ of the semiconductor 36 are thinned.
In calculating the film thickness, the first semiconductor 32, that is, A
lAs has a refractive index n ₁ = 2.97, intermediate layers 34 and 38 have a refractive index n ₂ = 3.31 of Al _0.45 Ga _0.55 As, and second semiconductor 36 have a refractive index n of Al _0.2 Ga _0.8 As.
₃ = 3.47. In addition, the conditions of the above simulation are that light is incident perpendicularly on the reflecting mirror and that light is not absorbed in the reflecting mirror. The incident medium is Al _0.45 Ga _0.55 As, and the medium on the opposite side is GaAs, which is the same as the substrate 12.

[0021]

[Table 2]

As is apparent from FIGS. 3 to 6, in consideration of the optical thicknesses of the intermediate layers 34 and 38, the film thicknesses t ₁ and t ₁ of the first semiconductor 32 are calculated in accordance with the equations (2) and (3). The reflecting mirrors I and III in which the film thickness t ₃ of the second semiconductor 36 is set are
While almost the same reflection characteristics as the conventional reflecting mirror without the intermediate layers 34 and 38 can be obtained, the film thicknesses t ₁ and t _{3 of} the first semiconductor 32 and the second semiconductor 36 are simply equal to the film thicknesses of the intermediate layers 34 and 38. Reflecting mirrors II and IV with a thinner thickness have a reflection wavelength band shifted to the long wavelength side as compared with conventional reflecting mirrors.

As described above, according to the surface-emitting light-emitting diode 10 of this embodiment, the rise of the electric resistance due to the discontinuity of the band is suppressed and the operating voltage is reduced without the deviation of the reflection wavelength region. You can do it.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, in the above embodiment, the unit semiconductor layers 40 having the same thickness T were repeatedly laminated by a predetermined number N, but as shown in FIG. The thickness is continuously changed one by one, a unit semiconductor layer 40 having the same thickness is inserted in the middle as shown in FIG. 7B, or the unit semiconductor layer 40 shown in FIG. As described above, the thickness of the unit semiconductor layer 40 can be changed stepwise. In that case, since the reflection wavelength range is widened, the deviation of the reflection wavelength range due to the insertion of the intermediate layer becomes almost no problem, and the thicknesses of the first semiconductor and the second semiconductor are reduced by the thickness of the intermediate layer. But it doesn't matter. The thickness of the unit semiconductor layer 40 varies depending on whether the first semiconductor 32,
The film thicknesses of the intermediate layer 34, the second semiconductor 36, and the intermediate layer 38 may be changed at the same rate.
Also, the film thickness of the second semiconductor 36 may be simply changed.

Further, although the pair of intermediate layers 34 and 38 have the same composition and the same film thickness in the above embodiment, the intermediate layers 34 and 38 having different compositions and film thicknesses may be provided. In order to further alleviate the band discontinuity, the intermediate layers 34, 38
It is also possible to change the composition, that is, the band gap, in two steps, three steps, or the like, or to change it continuously.

Although the p-type reflecting mirror 14 has been described in the above embodiment, the present invention can be similarly applied to an n-type reflecting mirror, and the first semiconductor 32 can be GaAs. For example, the type and composition of the semiconductor that constitutes the reflecting mirror can be changed appropriately.

Further, although the surface emitting type light emitting diode 10 takes out light from the opposite side of the substrate 12, the present invention can be applied to a surface emitting type light emitting diode taking out light from the substrate 12 side.

Further, the surface emitting light emitting diode 10 of the above-mentioned embodiment has a double hetero structure having the p-GaAs active layer 18, but GaP, InP, InGaAsP.
The present invention can be similarly applied to a surface emitting light emitting diode having a double hetero structure or a single hetero structure made of another compound semiconductor such as, or a surface emitting light emitting diode having a homo structure. It can be similarly applied to other semiconductor devices having a reflecting mirror, such as a surface emitting laser.

Further, in the above-mentioned embodiment, the case where the surface emitting light emitting diode 10 is manufactured by using the MOCVD apparatus has been described, but it is also possible to manufacture it by using other epitaxial growth techniques such as the molecular beam epitaxy method.

Although not illustrated one by one, the present invention can be carried out in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a structure of a surface emitting light emitting diode including a semiconductor multilayer film reflecting mirror according to an embodiment of the present invention.

FIG. 2 is a diagram showing a structure of a semiconductor multilayer film reflecting mirror of the surface emitting light emitting diode of FIG.

FIG. 3 is a diagram showing a light reflection characteristic of a semiconductor multilayer film reflecting mirror according to the present invention in comparison with a conventional product.

FIG. 4 is a diagram showing light reflection characteristics of another semiconductor multilayer film reflecting mirror according to the present invention in comparison with a conventional product.

FIG. 5 is a diagram showing a light reflection characteristic of still another semiconductor multilayer film reflecting mirror according to the present invention in comparison with a conventional product.

FIG. 6 is a diagram showing the light reflection characteristics of still another semiconductor multilayer film reflecting mirror according to the present invention in comparison with a conventional product.

FIG. 7 is a diagram illustrating a specific example in the case of changing the thickness of a unit semiconductor layer forming a semiconductor multilayer film reflecting mirror.

[Explanation of symbols]

 10: surface emitting light emitting diode 14: semiconductor multilayer film reflecting mirror 32: first semiconductor 34, 38: intermediate layer 36: second semiconductor 40: unit semiconductor layer

Claims (4)

[Claims] 1. A semiconductor multi-layered film reflecting mirror in which first semiconductors and second semiconductors having different band gaps are alternately laminated to reflect incident light by light wave interference. A semiconductor multilayer film reflecting mirror, wherein the first semiconductor and the second semiconductor are alternately laminated with an intermediate layer having a bandgap sandwiched therebetween. 2. The intermediate layer has a band gap that is changed so as to approach the band gaps of the first semiconductor and the second semiconductor adjacent to each other stepwise or continuously. Semiconductor multilayer mirror. 3. The optical thickness of the first semiconductor is TO1, the optical thickness of the second semiconductor is TO2, and the optical thickness of a pair of intermediate layers located above and below the first semiconductor or the second semiconductor. Where TO3 is the total wavelength of the light to be reflected and λ _B is the central wavelength of the light to be reflected, the following equation is satisfied: TO1 + (TO3 / 2) = TO2 + (TO3 / 2) = λ _B / 4 The semiconductor multilayer film reflecting mirror according to claim 2. 4. The thickness of a unit semiconductor layer for one period consisting of the first semiconductor, the intermediate layer, the second semiconductor, and the intermediate layer is continuously or stepwise changed. The semiconductor multilayer film reflecting mirror according to.