JP2002214428A - Semiconductor multilayer film reflecting mirror and semiconductor luminous element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy a diffraction condition (the sum of optical thicknesses is 1/2 of maximum absorption wavelength λ0) and to ensure a high reflectance even when the optical thickness of a layer having a higher absorption coefficient is made smaller in a multilayer film reflecting mirror obtained by stacking pairs of semiconductor layers different from each other in refractive index and absorption coefficient. SOLUTION: Each semiconductors is selected from AlxGa1-xAs (0<=x<=1) and (AlyGa1-y)zIn1-zP (0<=y<=1 and 0<=z<=1), a first semiconductor layer comprises a semiconductor having a higher absorption coefficient at wavelength λ0 than that of a second semiconductor layer and the optical thickness n1d1 of the first layer is made smaller than λ0/4. The optical thickness ratio n1d1/n2d2 of the first layer to the second layer is preferably in the range of 0.3-0.8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor multilayer mirror and a semiconductor light emitting device, and more particularly, to a semiconductor multilayer mirror having a high reflectance and a semiconductor light emitting device having a high light emission luminance.

2. Description of the Related Art An important component of a semiconductor light emitting device such as a light emitting diode or a laser diode is a semiconductor multilayer film reflecting mirror which reflects incident light of a specific wavelength by light wave interference. The semiconductor multilayer film reflecting mirror is configured such that two semiconductor layers having different refractive indices are repeatedly laminated to reflect incident light of a specific wavelength by an optical interference effect known as Bragg reflection.

FIG. 7 shows a typical structure of a semiconductor multilayer mirror. GaAs layer 1 and AlIn on GaAs substrate 3
P layers 2 are alternately stacked. When the thickness of the GaAs layer 1 is d ₁ , the refractive index is n ₁ , the thickness of the AlInP layer 2 is d ₂ , and the refractive index is n ₂ , n ₁ d ₁ = n ₂ d ₂ = λ _0/4 (λ ₀ is the maximum wavelength of the reflected light) (1) The following relationship is established. That is, the optical thicknesses n ₁ d ₁ and n ₂ d ₂ of the two layers (1 and 2) are equal,
The ratio n ₁ d ₁ / n ₂ d ₂ is 1. In FIG. 8, the thickness of each layer indicates the optical thickness in relation to the maximum wavelength λ _{0 of the} reflected light.

[0003] A multilayer reflection comprising a pair of a first layer (incident side) having a thickness d ₁ and a refractive index n ₁ and a second layer (substrate side) having a thickness d ₂ and a refractive index n _2. The reflectance R of the mirror is represented by the following equation (2) (N is the number of stacked two-layer pairs). R = [[(n ₁ / n ₂ ) ^2N −1] / [(n ₁ / n ₂ ) ^2N +1]] ² (2) That is, the reflectance R increases as the ratio of the refractive indexes of the two layers increases. . Further, the number N of pairs of two layers required to obtain the same reflectance may be small.

[0004]

In order to construct a multilayer mirror having the typical structure shown in FIG. 7, a combination of substances which are lattice-matched to the substrate and have a large refractive index ratio is required. Combinations of such substances are limited. Among them, GaAs and GaInP have a large refractive index, but have a large light absorption coefficient in a visible light region, so that a sufficiently large reflectance cannot be obtained. AlGaInP and AlInP
Although light absorption is extremely small, a high reflectance cannot be obtained and the width of the reflection spectrum is narrow because the refractive index ratio is small in these combinations. In any case, the number N of layers must be increased in order to obtain a high reflectance.

[0005] Increasing the number of layers N not only increases the time and cost for manufacturing, but also narrows the width of the reflection spectrum. When used as a light emitting element, it is necessary to increase a driving voltage.

In order to obtain a high reflectivity in a multilayer mirror composed of a combination of semiconductor layers having a large refractive index ratio, it is important to reduce the light absorption of each semiconductor layer. For this reason, light absorption is reduced by reducing the optical thickness of the semiconductor layer having the larger light absorption coefficient. However, at the same time, the optical thickness of the two semiconductor layers cannot be kept equal (the ratio is 1: 1), that is, the reflectance is lowered due to deviation from the diffraction condition. From the above, when the decrease in the reflectance due to the deviation of the ratio of the optical thickness of the semiconductor layer from the diffraction condition exceeds the effect of reducing the light absorption in the semiconductor layer, as a result, the reflectivity of the multilayer mirror is reduced. When the effect of reducing the light absorption exceeds the decrease in reflectance due to the deviation of the ratio of the optical thickness of the semiconductor layer from the diffraction condition,
It is expected that the reflectance of the multilayer mirror will be improved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor multi-layered film mirror comprising a pair of semiconductor layers having different refractive indices and light absorption coefficients which are repeatedly laminated, and the optical characteristics of a layer having a larger light absorption coefficient among the pair of semiconductor layers. The effect of reducing the light absorption by reducing the target thickness is higher by appropriately deviating from the diffraction conditions so that the effect of reducing the optical absorption of the semiconductor layer exceeds the decrease in the reflectance due to the deviation of the optical thickness ratio from the diffraction conditions. An object of the present invention is to realize a semiconductor multilayer film reflecting mirror capable of obtaining a reflectance.

Another object of the present invention is to provide a semiconductor multi-layered film mirror comprising a plurality of pairs of semiconductor layers having different refractive indices and different light absorption coefficients, which have very small light absorption but cannot obtain a large refractive index ratio. It is another object of the present invention to provide a semiconductor multilayer mirror capable of avoiding a decrease in the width of the reflection spectrum and obtaining a high reflectance without increasing the number N of layers even with a combination of semiconductor layers.

Another object of the present invention is to realize a semiconductor multilayer film reflecting mirror which can avoid an increase in the time and cost required for manufacturing accompanying an increase in the number N of layers.

Still another object of the present invention is to provide a semiconductor multi-layered film reflecting mirror composed of a combination of semiconductor layers which has a very small light absorption but does not provide a large refractive index ratio.
High reflectance without increasing the number of layers, and avoiding a narrow reflection spectrum width, an increase in manufacturing cost, and an increase in required driving voltage due to an increase in the number of stacked layers N. The realization of an element.

[0011]

According to the present invention, in order to achieve the above object, a pair of semiconductor layers having different refractive indices and light absorption coefficients are repeatedly laminated to form the first and second semiconductor layer pairs. the sum of the optical thickness of the second semiconductor layer is λ _0/2 (λ
₀ is the maximum wavelength of reflected light), and the first and second semiconductor layers are made of Al _x Ga _{1 -x} A
s layer (0 ≦ x ≦ 1) and (Al _y Ga _1-y ) _z In _1-z
P layer (0 ≦ y ≦ 1, 0 ≦ z ≦ 1), the first semiconductor layer has a larger light absorption coefficient at the maximum wavelength of reflected light than the second semiconductor layer, and has an optical thickness of λ. characterized in that from _0/4 small.

When the thickness of the first semiconductor layer is d ₁ and its refractive index is n ₁ , the thickness of the second semiconductor layer is d ₂ and its refractive index is n ₂ , the first semiconductor layer And the optical thicknesses of the second semiconductor layer are n ₁ d ₁ and n ₂ d ₂ , respectively.
The sum of the optical thicknesses of the semiconductor layers forming the pair is n ₁ d ₁ +
n ₂ d ₂ . The sum of the optical thickness of each of the semiconductor layers constituting the pair is equal to λ _0/2, the formula (3). _{n 1 d 1 + n 2 d} 2 = λ 0/2 (3) optical thickness of the first semiconductor layer and the lambda _0/4 less than the formula (4). _{n 1 d 1 <λ 0/} 4 (4)

According to the present invention, in order to achieve the above object, a pair of semiconductor layers having different refractive indices and light absorption coefficients are repeatedly laminated, and the first and second semiconductor layers constituting the pair of semiconductor layers are stacked. equal to the optical thickness of the sum is lambda _0/2 (lambda ₀ is reflected light maximum wavelength), in the semiconductor multilayer reflector, the first and second semiconductor layer, Al _x Ga _1-x As layer (0
≦ x ≦ 1) is selected from and _{(Al y Ga 1-y)} z In 1-z P layer (0 ≦ y ≦ 1,0 ≦ z ≦ 1), the first semiconductor layer, the reflected light maximum wavelength λ larger light absorption coefficient than the second semiconductor layer at _0, with that optical thickness is smaller than lambda _0/4, further optical thickness of the first semiconductor layer, the optical second semiconductor layer The ratio to the thickness is 0.3
From 0.8 to 0.8. That is, using the same definition as in the equations (3) and (4), n ₁ d ₁ / n ₂ d ₂ = p 0.3 ≦ p ≦ 0.8 (5) At this time, the optical property of the first semiconductor layer Although the target thickness is smaller than the second semiconductor layer, the light absorption coefficient of the first semiconductor layer at the maximum wavelength of the reflected light is larger than the second semiconductor layer.

Further, in the present invention, in order to achieve the above object, a semiconductor multilayer film reflecting mirror in which pairs of semiconductor layers having different refractive indices and light absorption coefficients are repeatedly laminated, and the first and second layers constituting the pair of semiconductor layers are formed. second semiconductor layer optical thickness of sum lambda _0/2 of (lambda ₀ is reflected light maximum wavelength) is equal to, in the semiconductor light emitting device, the first and second semiconductor layers is Al _x
Ga _1-x As layer (0 ≦ x ≦ 1) and (Al _y G
a _1-y ) _z In _1-z P layer (0 ≦ y ≦ 1, 0 ≦ z ≦ 1), and the first semiconductor layer has a light absorption coefficient at a reflected light maximum wavelength λ ₀ of the second layer. greater than the semiconductor layer, wherein the optical thickness is less than λ _0/4.

The second semiconductor layer (hereinafter, referred to as a second layer) having an optical thickness of the first semiconductor layer (hereinafter, referred to as a first layer).
The optimum value of the ratio to the optical thickness varies depending on the material of each layer, the steepness of the interface, and the like. For example, the first layer is GaAs,
When the second layer is composed of AlInP, this ratio p is equal to 0.1.
Particularly preferred is 4 to 0.6, with 0.5 giving maximum reflectivity.

The multilayer reflector of the present invention is a general MOVP.
Not only the E method but also other epitaxial growth techniques such as MBE (Molecular Beam Epitaxy) can be used. The multilayer reflector of the present invention can be applied to a soft X-ray reflector. The light emitting device of the present invention is used as a light emitting diode or a laser diode.

[0017]

Embodiments of the present invention will be described below.
On a GaAs substrate, a multilayer reflector in which a combination of 10 pairs of an AlInP layer and a GaAs layer is laminated is formed by MOVPE.
Made by the method. The sum of the optical thicknesses of the two layers of each pair is λ ₀
/ 2 and the ratio was set to a constant value of 0.5. That is, the thickness d ₁ of the GaAs layer, the refractive index n ₁ ,
The thickness d ₂ and the refractive index n _{2 of the} AlInP layer are expressed by the formula (3) (0
Fulfills the relation _{n 1 d 1 + n 2 d} 2 = λ 0/2 shown in reference 012 Section), related in the following equation _{(6) n 1 d 1 /} n 2 d 2 = 0.5 (6) I met it. In order to simultaneously satisfy the relationship between Expressions (3) and (6), the relationship between n ₁ d ₁ and n ₂ d ₂ with λ ₀ is as follows. _{n 1 d 1 = λ 0/} 6, n 2 d 2 = λ 0/3

FIG. 1 shows a cross section of a semiconductor multilayer mirror according to the present invention. GaAs layer 1 and AlIn on GaAs substrate 3
Ten pairs (partially omitted in the drawing) of the combinations of the P layers 2 are stacked. The thickness of each layer indicates the optical thickness in relation to the maximum wavelength λ _{0 of the} reflected light.

FIG. 2 is a sectional view of the semiconductor multilayer mirror shown in FIG.
Ratio of optical thickness n ₁ d ₁ between aAs layer 1 and AlInP layer 2
It shows the reflectance when / n ₂ d ₂ is changed from 0 to 1 in steps of 0.1.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
The multilayer reflector was manufactured by laminating 10 pairs of the lInP layer 2 and the GaAs layer 1 alternately by the MOVPE method. GaAs
The thickness d ₁ of the layer 1, the refractive index n _1, the thickness of the AlInP layer 2 d
_2, the refractive index n _2, and to satisfy the relationship of Equation (6) fulfills the relationship shown in equation (3). _{(N 1 d 1 + n 2} d 2 = λ 0/2, n 1 d 1 / n 2 d
_{2 = 0.5, n 1 d 1} = λ 0/6, n 2 d 2 = λ 0 /
3)

FIG. 3 shows a wavelength of 300 n of the multilayer mirror.
The reflectance in the range from m to 800 nm is shown. The maximum reflectance was 85%, and the half width at the maximum was 58 nm.

A light emitting diode having the structure shown in FIG. 4 was manufactured using the multilayer reflector of the embodiment. The light emitting output of this light emitting diode is 1.6 mW, and the forward operating voltage is 1.8 V.
(20 mA conduction).

FIG. 4 shows a cross section of a light emitting diode using the multilayer mirror of the embodiment. The light emitting diode 10 has n
-GaAs substrate 11, n-AlInP layer 2 and n-GaAs
a multilayer reflector 12 composed of a pair of s-layers 1 and n-AlG
aAs cladding layer 13, p-GaAs active layer 14, p-
An AlGaAs clad layer 15 and a p-GaAs cap layer 16 are stacked and configured. n-AlGaAs
Clad layer 13, p-GaAs active layer 14, p-AlG
The aAs cladding layer 15 forms a double hetero structure. A positive electrode 17 is provided on a part of the upper surface of the p-GaAs cap layer 16, and a negative electrode 18 is provided on the lower surface of the n-GaAs substrate 11.

FIG. 5 shows a cross section of a part of the multilayer mirror 12 of a light emitting diode using the multilayer mirror of the embodiment. The multilayer mirror 12 is composed of the n-GaAs layer 1 and the n-Al
Is composed of a pair of InP layer 2, the optical thickness of the n-GaAs layer 1 is optical thickness of λ _0/6, n-AlInP layer 2 lambda
_0/3 .

When a voltage is applied between the positive electrode 17 and the negative electrode 18, the p-GaAs active layer 14 emits light, and the p-GaAs active layer 14 emits light.
Light is extracted from the upper surface of the As cap layer 16. The light traveling toward the substrate is reflected by the multilayer mirror 12,
Increase light output.

FIG. 6 shows the light emission output of a light emitting diode using the multilayer mirror of the present invention. The light emitting diode is shown in FIG.
The same structure as that of FIG.
Ratio of optical thickness n ₁ d ₁ between aAs layer 1 and AlInP layer 2
/ N ₂ d ₂ was changed from 0 to 1 in steps of 0.1 (other conditions are the same). The ratio n ₁ d ₁ / n ₂ d ₂ is about 0.5.
At 6, the light emission output showed the maximum.

Comparative Example GaAs layer 1 and AlInP layer 2
The optical thickness _{n 1 d 1, n 2 d} 2 and the λ _0/4 (n
Except for ₁ d ₁ / n ₂ d ₂ = 1), a multilayer mirror was manufactured with the same basic structure, composition and method as in Example 1. The structure of the multilayer mirror corresponds to the structure of FIG.

FIG. 8 shows a multi-layer reflecting mirror of a comparative example having a wavelength of 3
The reflectance in the range from 00 nm to 800 nm is shown. The maximum reflectance was 75%, and the half width at the maximum was 60 nm. 3 and 8, it is understood that the multilayer mirror of the present invention has a higher reflectance than the multilayer mirror of the comparative example.

A light emitting diode was manufactured using the multilayer mirror of the comparative example. The structure of the light emitting diode is the same as that of FIG. 4 except for the multilayer mirror. The light emitting output of this light emitting diode is 1.3 mW, and the forward operating voltage is 1.8 V (20 m
A energized). Since the light emitting output of the light emitting diode using the multilayer reflector in the example was 1.6 mW, it was about 20% larger than the light emitting diode using the multilayer reflector in the comparative example. There was no difference between the forward operating voltages of the two (1.8).
V).

[0030]

According to the semiconductor multilayer reflector of the present invention, in a semiconductor multilayer reflector in which semiconductor layers having different refractive indexes and different light absorption coefficients are repeatedly laminated, the light absorption coefficient It is possible to obtain a high reflectivity by reducing the optical thickness of the larger layer, and the resulting effect of lowering the light absorption outweighs the effect of lowering the light reflectivity by deviating from the diffraction conditions. it can.

According to the multilayer mirror of the present invention, a semiconductor multilayer mirror formed by repeatedly stacking pairs of semiconductor layers having different refractive indices and light absorption coefficients has a large refractive index.
Even if a combination of semiconductor layers having a large light absorption coefficient in the visible light region (for example, GaAs or GaInP) is used, high reflectance can be obtained.

According to the multilayer mirror of the present invention, in a semiconductor multilayer mirror in which pairs of semiconductor layers having different refractive indices and light absorption coefficients are repeatedly laminated, light absorption is small.
Combination of semiconductor layers having a small refractive index ratio (for example, Al
Even if GaInP or AlInP) is used, it is possible to avoid a decrease in the width of the reflection spectrum due to an increase in reflectance.

According to the semiconductor multilayer mirror of the present invention, a combination of semiconductor layers having a large refractive index but a large light absorption coefficient in the visible light region or a semiconductor layer having a small light absorption but a small refractive index ratio is used. Even if the combination is used for a multilayer mirror, a high reflectance can be obtained without increasing the number N of semiconductor layers, so that various disadvantages associated with increasing the number N of pairs of semiconductor layers can be obtained. Can be avoided. That is,
Increasing the number N of layers increases the time and cost for manufacturing and reduces the width of the reflection spectrum. However, according to the multilayer mirror of the present invention, these disadvantages can be avoided.

According to the semiconductor light emitting device of the present invention, a combination of a semiconductor layer having a large refractive index and a large light absorption coefficient in the visible light region or a combination of semiconductor layers having a small light absorption and a small refractive index ratio is used. Even when used for a film reflecting mirror, a high reflectance can be obtained without increasing the number N of stacked semiconductor layers, so that various disadvantages associated with increasing the number N of stacked semiconductor layers can be avoided. That is, when the number N of stacked layers increases, the number of crystal interfaces increases, so that crystallinity often decreases,
The driving voltage of the light emitting element increases. Also, by increasing the number of layers N, the time and cost for manufacturing increase and the width of the spectrum becomes narrower. However, according to the semiconductor light emitting device of the present invention, these disadvantages can be avoided.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of a semiconductor multilayer mirror according to the present invention;

FIG. 2 is a graph showing the reflectance of the semiconductor multilayer mirror of the present invention;

FIG. 3 is a graph showing the relationship between the reflectance and the wavelength of the semiconductor multilayer mirror of the present invention.

FIG. 4 is an explanatory sectional view of a semiconductor light emitting device of the present invention.

FIG. 5 is a partial cross-sectional explanatory view of a multilayer reflector portion of the semiconductor light emitting device of the present invention.

FIG. 6 is a graph showing a light emission output of a light emitting diode (semiconductor light emitting device of the present invention) using the semiconductor multilayer film reflecting mirror of the present invention.

FIG. 7 is an explanatory cross-sectional view of a conventional semiconductor multilayer mirror;

FIG. 8 is a graph showing the relationship between the reflectance and wavelength of a conventional semiconductor multilayer mirror.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs layer 2 AlInP layer 3 GaAs substrate 10 Light emitting diode 11 n-GaAs substrate 12 Multilayer reflector 13 n-AlGaAs cladding layer 14 p-GaAs active layer 15 p-AlGaAs cladding layer 16 p-GaAs cap layer 17 + electrode 18 -Electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H01L 21/027 H01L 21/30 531A F term (Reference) 2H042 DA08 DA12 DB02 DE07 2H048 FA05 FA09 FA15 FA22 FA24 GA04 GA11 GA24 GA35 GA51 GA62 5F041 AA03 CA04 CA12 CA34 CA35 CA36 CB15 5F046 GB01

Claims (7)

[Claims] 1. A refractive index and made by a pair of optical absorption coefficient different semiconductor layers repeatedly stacked, the sum of the optical thickness of the first and second semiconductor layers constituting the pair λ _0/2 ( wherein λ ₀ is the maximum wavelength of the reflected light, wherein the first and second semiconductor layers are Al _x Ga _{1 -x} As layers (0 ≦ x ≦ 1) and (Al _y Ga _1-y). ) _Z In _1-z P
The first semiconductor layer has a larger light absorption coefficient at the maximum wavelength of reflected light than the second semiconductor layer, and an optical thickness of λ.
_A semiconductor multilayer film reflecting mirror characterized by being smaller than 0/4. 2. The method according to claim 1, wherein a ratio of an optical thickness of the first semiconductor layer to an optical thickness of the second semiconductor layer is in a range from 0.3 to 0.8. The semiconductor multi-layer film reflecting mirror according to claim 1. 3. The semiconductor device according to claim 1, wherein said first and second semiconductor layers are formed of Al _x
Ga _1-x As layer (0 ≦ x <1) and (Al _y G
a _1-y ) _z In _1-z P layer (0 <y ≦ 1, 0 <z <1), wherein the ratio is in the range of 0.4 to 0.6. A semiconductor multilayer mirror according to claim 2. Wherein said first semiconductor layer is a GaAs layer, said second semiconductor layer, Al _z In _1-z P layer (0 <
4. The semiconductor multilayer mirror according to claim 2, wherein z <1). 5. A multi-layer reflector in which pairs of semiconductor layers having different refractive indices and light absorption coefficients are repeatedly laminated, and first and second semiconductors constituting the pair of semiconductor layers of the multi-layer reflector. the sum of the optical thickness of lambda _0/2 layer (lambda ₀ is reflected light maximum wavelength) is equal to, in the semiconductor light emitting device, the first and second semiconductor layers is Al _x Ga _1-x As layer (0 ≦ x ≦ 1) and _{(Al y Ga 1-y)} z In 1-z P
The first semiconductor layer has a larger light absorption coefficient at the maximum wavelength of reflected light than the second semiconductor layer, and an optical thickness of λ.
_A semiconductor light emitting device characterized by being smaller than 0/4. 6. A method according to claim 1, wherein a ratio of an optical thickness of the first semiconductor layer to an optical thickness of the second semiconductor layer is in a range from 0.3 to 0.8. A semiconductor light emitting device according to claim 5. 7. The semiconductor device according to claim 1, wherein the first semiconductor layer is a GaAs layer.
Said second semiconductor layer is _{Al z In 1-z P (} 0 <z <1)
7. The semiconductor light emitting device according to claim 6, which is a layer.