JPH0786638A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To provide a high luminance LED that makes it possible to form a semiconductor multilayer reflecting film having a high reflection factor and a wide reflection band for the improvement of light extraction efficiency, and enables the reduction of heterochromatic wavelength stray light. CONSTITUTION:ALED consists of a n-type GaAs substrate 101, a n-type semiconductor multilayer reflecting film, composed of a semiconductor thin film, formed on the substrate 101; and an InGaAlP double heterostructure section formed on the semiconductor multilayer reflecting film, composed of an active layer 105 sandwiched by a n-type cladding layer 104 and a p-type cladding layer 106, wherein light is extracted through the opposite surface to the substrate 101. The semiconductor multilayer reflecting film is formed with a first Bragg reflector 102 on the substrate 101 side, having wide reflection band characteristics and absorption losses; and a second Bragg reflector 103 on the double hetero-structure side, having a high reflection factor and transparent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device using an InGaAlP semiconductor material.

[0002]

2. Description of the Related Art In recent years, a light emitting diode (LED) has been widely used as a light source for a display device in optical communication and optical information processing equipment. Generally, in an LED, the emission intensity and the response speed are important characteristics, and in particular, the display LED is required to emit light with high brightness.

InGaAlP materials exclude nitrides I
It has the largest direct transition type band gap in the II-V group compound semiconductor mixed crystal, and is attracting attention as a light emitting device material in the 0.5 to 0.6 μm band. In particular, a pn substrate with GaAs and a light emitting part made of InGaAlP that lattice-matches the substrate.
The junction LED is capable of high-luminance light emission from red to green as compared with a conventional LED using an indirect transition type material such as GaP or GaAsP. However, since the GaAs substrate gives absorption loss to this wavelength band, all the light emitted from the active layer to the substrate side is absorbed by the substrate and cannot be extracted to the outside.

FIG. 7 shows a cross section of the structure of a conventional LED having an InGaAlP light emitting portion. In the figure, 1 is n-GaA
s substrate, 2 is n-InGaAlP clad layer, 3 is In
GaAlP active layer, 4 p-InGaAlP clad layer, 5 n-InGaAlP current blocking layer, 6 p-Ga
AlAs current diffusion layer, 7 is a p-GaAs contact layer,
Reference numeral 8 is a p-side electrode made of AuZn, and 9 is an n-side electrode made of AuGe.

The mixed crystal composition is set so that the energy gap of the InGaAlP active layer 3 is smaller than that of the clad layers 2 and 4, and the light and carriers are used as the active layer 3.
It has a double hetero structure that is confined in. Also, p
-The composition of the GaAlAs current diffusion layer 6 is InGaAlP.
It is set to be substantially transparent to the wavelength of light emitted from the active layer 3.

In the structure of FIG. 7, the active layer 3 has a thickness of 0.
2 μm undoped In _0.5 (Ga _1-x Al _x ) _0.5
When P (x = 0.4), the conductivity type was n-type, and the carrier concentration was about 1 to 5 × 10 ¹⁶ cm ⁻³ . At this time, the emission wavelength was 565 nm (green), and the emission efficiency was about 0.15% at DC 20 mA. Also, x =
At 0.3, the emission wavelength is 585 nm (yellow), and the emission efficiency is as low as about 0.6% at DC 20 mA.
The characteristic merit over the aAsP system was not always found. On the other hand, when x = 0.2, the emission wavelength is 6
20 nm (daily color), the luminous efficiency is about 3.0% at 20 mA DC, and Ga becomes an absorber for the emission wavelength.
The luminous efficiency higher than that of the GaAlAs system was obtained without removing the As substrate 1.

As described above, even in the LED using InGaAlP having a direct transition type band gap, the luminous efficiency in the short wavelength region (green emission) was not always sufficiently high.

The light emission efficiency of the LED is determined by the internal quantum efficiency and the light extraction efficiency, of which the light extraction efficiency is greatly influenced by the device structure. As described above, the light emitted from the active layer to the substrate side is absorbed by the GaAs substrate and cannot be extracted to the outside of the device. In particular, in the short wavelength region where the luminous efficiency is low, there is great significance to improve this. As a measure against the absorption of light in the substrate, it has been attempted to provide a reflective film (Bragg type reflecting mirror) formed of a semiconductor multilayer film between the active layer and the substrate (Japanese Patent Application No. 2-
No. 217079).

In order to sufficiently obtain the effect of the reflective film formed by this semiconductor multilayer film, it was necessary to increase the reflectance and widen the reflection band in order to increase the manufacturing tolerance. However, it has been extremely difficult to combine these two characteristics in terms of the characteristics and structure of the constituent materials. Further, in the LED of the double hetero structure InGaAlP, the end face light on the long wavelength side of 10 to 15 nm with respect to the surface emission wavelength becomes stray light, and red light for yellow emission and yellow light for green emission are mixed. Was there. That is, the LED of the double heterostructure InGaAlP emits two colors, which has been a serious problem in practical use for display.

[0010]

As described above, the In
In a semiconductor light emitting device having a light emitting portion made of GaAlP, a method of extracting light emitted from the active layer to the substrate side to the outside of the element using a semiconductor multilayer reflection film is used, but the reflectance is high and the manufacturing tolerance is high. It is difficult to obtain a wide reflection band for increasing the wavelength, and stray light from the end face exists.

The present invention has been made in consideration of the above circumstances, and an object thereof is to improve the light extraction efficiency by producing a semiconductor multilayer reflective film having a high reflectance and a wide reflection band. Another object of the present invention is to provide a high-brightness semiconductor light emitting device capable of reducing the stray light of different color wavelength.

[0012]

The essence of the present invention is to have characteristics of a high reflectance and a wide reflection band by devising the constituent material and structure of the semiconductor multilayer film reflection film, and at the same time, the direction parallel to the bonding plane. The aim is to improve the light extraction efficiency by creating a Bragg reflector that becomes a loss for the light guided to.

That is, the present invention comprises a semiconductor substrate, a semiconductor multilayer reflective film formed of a semiconductor thin film formed on the semiconductor substrate, and a semiconductor laminated structure portion including a light emitting layer formed on the semiconductor multilayer reflective film. Then, in the semiconductor light emitting device that extracts light from the surface opposite to the semiconductor substrate, the semiconductor multi-layer reflective film has the first Bragg reflector having wide reflection band characteristics and the second Bragg-type reflector having high reflectance characteristics. It is characterized by being configured by.

Here, the following are preferred embodiments of the present invention. (1) In the semiconductor laminated structure part, the light emitting layer has a first conductivity type and a second conductivity type.
It has a double hetero structure sandwiched by conductive clad layers. (2) The substrate is GaAs and the double hetero structure is InG
It must be an aAlP-based material. (3) The semiconductor multilayer reflection film is composed of two types of Bragg-type reflecting mirrors, the first Bragg-type reflecting mirror on the substrate side has wide reflection band characteristics, and the second Bragg-type reflecting mirror on the semiconductor laminated structure side. Has high reflectance characteristics. Use InAlP / InGaAlP as a highly reflective and transparent Bragg reflector, and InAlP / GaAs as a Bragg reflector having wide reflection band characteristics and absorption loss. (4) The semiconductor multilayer reflection film is composed of three or more kinds of semiconductor layers having different materials, compositions or film thicknesses, and one of them is a semiconductor layer having a loss with respect to the emission wavelength. (5) The semiconductor multilayer reflective film is made of In _0.5 (Ga _1-x Al) having an optical film thickness of λ / 4 with respect to the emission center wavelength λ.
_{x) 0.5} P and _{Ga 1-y Al y As (} 0 ≦ x ≦ 1,0 ≦ y
<1) At least three types of semiconductor layers having different compositions. (6) The semiconductor multilayer reflector has an optical thickness of In _0.5 (Ga) greater than λ / 4 with respect to the emission center wavelength λ.
_1-x Al _x ) _0.5 P and Ga _1-y Al _y A thinner than λ / 4
s (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) has a pair of optical film thicknesses of λ
/ 2 and consists of at least two or more alternating layers of different compositions.

[0015]

According to the present invention, by combining two or more types of Bragg-type reflecting mirrors to form a semiconductor multilayer reflecting film, a reflecting film having the characteristics of each reflecting mirror is obtained. With this structure, the high reflectance required as an LED,
It is possible to easily prepare a reflective film having a wide reflection band characteristic and effectively reducing the end face light. This allows
The light extraction efficiency can be improved, and a high-luminance semiconductor light emitting device can be realized. In addition, it is necessary to set the two Bragg reflectors in the above-mentioned positional relationship,
Excellent characteristics were obtained as compared with the case where these positional relationships were reversed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an LED according to a first embodiment of the present invention.
3 is a cross-sectional view showing the element structure of FIG. In the figure, 101 is n-Ga
It is an As substrate, and n-I is formed on one main surface of the substrate 101.
n _0.5 Al _0.5 P / GaAs 10 pairs of first reflective film (Bragg type reflecting mirror) 102, n-In _0.5 Al _0.5
P / In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P 2nd reflecting film (Bragg type reflecting mirror) 103, n-In consisting of 10 pairs
_0.5 (Ga _1-l Al ₁ ) _0.5 P cladding layer 104, In
_0.5 (Ga _1-m Al _m ) _0.5 P active layer 105, p-In
_0.5 (Ga _1-n Al _n ) _0.5 P cladding layer 106, n-
In _0.5 (Ga _1-p Al _p ) _0.5 P current blocking layer 107,
p-Ga _1-q Al _q As current diffusion layer 108, p-GaA
The s contact layer 109 is laminated in the above order, and the contact layer 109 is processed into a circular shape. Then, the p-side electrode 110 made of AuZn / Au is formed on the contact layer 109, and AuGe / Au is formed on the other main surface of the substrate 101.
Is formed on the n-side electrode 111.

Here, I which constitutes the double hetero structure portion
The Al composition l, m, n of each nGaAlP layer is set so that m ≦ l, m ≦ n is satisfied so that high luminous efficiency can be obtained. That is, the energy gap of the active layer 105 serving as a light emitting layer is two p-n cladding layers 104,
A double heterostructure smaller than 106 is formed. The Al composition p of the current blocking layer 107 is set to m ≦ p. Note that these InGaAlP layers are lattice-matched with GaAs which is the substrate 101.

The p-GaAlAs current diffusion layer 108 is also used.
The Al composition q is selected to have a larger bandgap than that of the active layer 105 so that the Al composition q is transparent to the emission wavelength of the active layer 105. Although an LED having such a double hetero structure will be described below, the layer structure of the active layer portion is not essential in view of the light extraction efficiency, and a single hetero junction structure, a homo junction structure, or a quantum junction structure is used. A well structure can be similarly considered.

In the structure shown in FIG. 1, the thickness and carrier concentration of each layer are set as shown in parentheses below. n-clad layer 104 (0.6 μm, 5 × 10 ¹⁷ c
m ⁻³ ) Active layer 105 (0.3 μm, undoped) p-clad layer 106 (0.6 μm, 4 × 10 ¹⁷ c
m ⁻³ ) n-current blocking layer 107 (0.15 μm, 2 × 10 ¹⁸ cm
^-3 ) p-current diffusion layer 108 (5 μm, 3 × 10 ¹⁸ cm ⁻³ ) p-contact layer 109 (0.1 μm, 3 × 10 ¹⁸ cm)
^-3 ) Further, the first and second reflective films 102 and 103 that form the semiconductor multilayer reflective film are as follows. That is, the thickness of each constituent layer, the light emitting wavelength lambda ₀ from the active layer 105, and an optical thickness of λ _0/4. The carrier concentration of each constituent layer is 5 × 10 ¹⁷ c
It was set to be m ^-3 or more.

The difference between the above structure and the conventional structure is that In
Light emitting part (double heterostructure) 10 made of GaAlP
No. 1 between the 4, 105, 106 and the GaAs substrate 101
The reflective film 102 and the second reflective film 103 are formed, and the superiority of this structure will be described below.

InGa in the second reflective film 103 of FIG.
The AlP layer is a high-refractive index layer constituting a reflecting mirror as described later, and at the same time plays a role of pulling out the light of the active layer guided by the double hetero structure to the reflecting mirror side. In order to obtain a sufficient leakage effect, it is necessary to insert at least one layer with a film thickness equivalent to λ / 4 thickness. The light exuded to the reflecting mirror side is the first reflecting film 102.
It is absorbed by the GaAs layer at, which reduces stray light.

Next, a detailed description of the reflection characteristics will be given. FIG. 2 shows the relationship between the logarithm of the first reflective film 102 and the second reflective film 103 and the reflectance by the simulation. The parameters used here are shown in (Table 1) below (DEAspens, et al, JAP 60, 754 (1986),
H. Tanaka, et al, JAP 59,985 (1986)).

[0023]

[Table 1]

The first reflective film 102 is made of InG as a constituent layer.
Since GaAs, which has absorption loss for the light from the aAlP active layer 105, is used, the reflectance is saturated when the number of logarithms is large. Since the difference in the refractive index between InAlP and GaAs is large where the logarithm is small, the reflectance is higher than that of the second reflective film 103. Since the constituent layers of the second reflective film 103 are both transparent to the light from the active layer, a very high reflectance can be obtained in a place with a large number of logarithms.

FIG. 3 shows the relationship between the full width at half maximum (FWHM) of the reflection spectrum of the two reflection films 102.103 and the logarithm of the simulation. The first reflective film 102 saturates at a relatively wide value as the number of logarithms increases, and the second reflective film 103 becomes gradually narrower. That is, it is understood from these calculation results that the first reflective film 102 has a relatively low reflectance but a wide reflection band, and the second reflective film 103 has a relatively high reflectance but a narrow reflection band. It is understood that is due to the relationship between the refractive index of each constituent layer and the absorption coefficient.

In FIG. 4, a first reflective film 102 (10 pairs), a second reflective film 103 (20 pairs) and 10 pairs of each of these two reflective films are provided on the substrate side of the first reflective film 102, and then on the second reflective film 102. Reflective film 10
3 is a view showing a reflection spectrum of a hybrid type reflection film having No. 3 formed by simulation. The spectra of the first reflective film (10 pairs) and the second reflective film (20 pairs) have the relationship between the reflectance and the half width as described above. From the spectrum of the hybrid type reflection film, the peak value of the reflectance is about 90%, which is higher than that of the other reflection films, and the full width at half maximum shows the value of 50 nm. The value of this half width is the spectrum of emission from the LED active layer of InGaAlP 12 to 14 nm (H. Sugawara, et al, JJAP 3
1,2446 (1992)), which is sufficiently wide, and is considered to have a sufficiently large manufacturing tolerance.

From these calculation results, it is understood that the hybrid type reflection film is effective in improving the light extraction efficiency and has a sufficiently large manufacturing tolerance. Regarding the logarithmic setting,
The number of the second reflective films 103 is 20 pairs or less, preferably 15 pairs or less, because the band becomes narrower as the number of pairs increases. Since the resistance of the first reflecting mirror 102 increases as the number of pairs increases, the number of pairs is preferably 20 or less, and more preferably 15 or less. Considering the purpose of reducing stray light, the optimum condition is to set about 10 pairs each as described in the embodiment.

In practice, the p-side electrode 1 having the laminated structure shown in FIG.
The diameter of 10 is 200 μmφ and the diameter of the current blocking layer 107 is 240 μmφ, and each of them is formed in a concentric shape.
_0.5 (Ga _1-m Al _m ) _0.5 P An element was formed by setting the Al composition m of the P active layer 105 to 0.3, and when a voltage was applied in the forward direction and a current was applied, the p-side electrode 110 part was removed. It has a peak wavelength of 585 nm from a wide area on the device surface and has a luminous intensity of 3
Light emission exceeding cd was obtained. In addition, there was almost no stray light from the edge light, and it was possible to reduce the light to a level at which there was no practical problem. p-
The effect of light absorption by the Ga _1-q Al _q As current diffusion layer 108 can be reduced even for short wavelength light emission by setting the Al composition q high, and the Al composition q is 0.7 to 0.8. And an In _0.5 (Ga _1-m Al _m ) _0.5 P active layer 105 having an Al composition m of 0.5 and a peak wavelength of 555 n
Even in the green light emitting device of m, light emission exceeding 3 cd was obtained.

As described above, according to this embodiment, InGaA
Two reflection films having different reflection characteristics, the first reflection film 102 and the second reflection film, are provided between the 1P active layer 105 and the n-GaAs substrate 101.
Since the reflection 103 is provided, the light emitted to the substrate side from the active layer 105, which could not be extracted to the outside of the element in the conventional structure, is reflected by the reflection films 102 and 10.
At 3, the light can be effectively extracted by reflecting it toward the surface of the element.

In addition, in this embodiment, in the laminated reflective film, a reflective mirror (second reflective film 103) having a high reflectance characteristic that is transparent to the emission wavelength is provided nearer to the active layer 105, and the substrate 101 is formed. By providing a reflecting mirror (first reflecting film 102) having a wide reflection band nearer to, a hybrid type reflecting mirror having a high reflectance and a wide reflection band having two reflecting film characteristics is formed. And the second reflective film 103
The light in the active layer 105 can be exuded by, and the first reflecting mirror 102 can have a loss. As a result, the light extraction efficiency is improved and the LE with high brightness is
D can be realized, stray light can be reduced, and manufacturing tolerance such as mass productivity and reproducibility can be widened.

FIG. 5 shows an LE according to the second embodiment of the present invention.
It is sectional drawing which shows the element structure of D. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The difference between this embodiment and the first embodiment described above lies in the structure of the second reflecting film forming the Bragg reflector.

That is, in the present embodiment, the constituent materials of the second reflective film 503 are InAlP and GaA as in the first reflective film 102.
There are two types, s, and the thickness of each of the first reflection film 102 and the first reflection film 102 is changed to provide a reflection film having different reflection characteristics. Here, In forming the second reflective film 503
AlP / GaAs1 the optical thickness of pairs, the GaAs layer while maintaining the lambda _0/2 thinner than λ _0/4, InAlP
Thicker than the layer λ _0/4. The other conditions (thickness of each layer, carrier concentration) were the same as those in the first embodiment.

With such a structure, InGaAlP
The GaAs layer of the second reflective film 503, which has absorption loss for the light from the active layer 105, is the GaAs layer of the first reflective film 102.
Since it is thinner than the layer, it reduces absorption loss for light in the junction direction, and is effective for light guided in parallel with the junction direction because it is near the active layer 105. Can have a loss. In addition, the effective reflectance is high in terms of reflection characteristics. Therefore, by using the hybrid type reflection film by this combination, the same effect as the effect described in the first embodiment can be obtained.

FIG. 6 shows an LE according to the third embodiment of the present invention.
It is sectional drawing which shows the element structure of D. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.
In this embodiment, the reflection characteristics of the semiconductor multilayer reflection film are gradually and continuously changed without dividing the reflection characteristics into two unlike the first reflection film and the second reflection film.

[0035] This embodiment is different from the second embodiment, while maintaining the optical film thickness of the InAlP / GaAs1 pair of reflecting films 602 to lambda _0/2, GaAs layer closer to the active layer 105 the thinner than λ _0/4, InAlP
Thicker than the layer λ _0/4. Then, InAlP / GaAs closer to the GaAs substrate 101 in the reflective film 602
InAlP in pair, such that each optical thickness GaAs is lambda _0/4, gradually changes in the reflection film 602. The other conditions were the same as those in the first and second embodiments.

With such a structure, since the absorption loss for the light from the active layer 105 is different between the light emitting portion in the reflective film 602 and the substrate 101, the effective reflectance is different. The same effect as the effect shown in the second embodiment can be obtained.

Up to now, the surface emitting type double hetero structure In
In a GaAlP LED, light from the end of the active layer or from the lateral direction is emitted while being guided inside the active layer, so that the wavelength is longer than that of the light emitted from the surface of the element due to loss inside the active layer. However, this has been described as a problem that monochromaticity is impaired and two-color light emission occurs when the overall radiation from the device is viewed. In order to prevent this, the above embodiment has been shown, but in order to maximize the effect of the light absorption layer in the reflecting mirror, it is effective to reduce the thickness of the cladding layer.

For example, in the second and third embodiments, the GaAs forming the reflection film serves as a loss layer, and the thickness of the active layer is 0.3 μm in these embodiments, so the n-InGaAlP cladding is used. The thickness of the layer 104 is 0.3μ
It is effective to make it m or less. With this structure, it is possible to more effectively prevent the emitted light from the end face by compensating for the loss in the guided mode of light in the active layer 105.

The present invention is not limited to the above embodiments. In the embodiment, the reflective film has a structure of InGa.
Although AlP-based material and GaAlAs-based material were used, InG
The same effect can be obtained by using an aAsP-based material or a II-VI group material. Further, regardless of the material system, the same effect can be obtained when the reflective film is formed by a film having a superlattice film formed therein and having a refractive index changed. Further, in the embodiment, 0.3 or 0.5 is used as the Al composition of the active layer,
By changing the Al composition, light emission in the visible light range from red to green can be obtained. Further, the present invention can be applied not only to the light emitting diode but also to a surface emitting laser. In addition, various modifications can be made without departing from the scope of the present invention.

[0040]

As described above in detail, according to the present invention, I
By providing a hybrid type reflective film, which is a combination of a reflective film having a high reflectance and a reflective film having a wide reflective band, between the light emitting portion made of nGaAlP or the like and the substrate, a reflective film having a high reflectance and broadband reflection is formed. As a result, it is possible to realize a high-brightness semiconductor light emitting device capable of improving the light extraction efficiency and reducing stray light of a different color wavelength.

[Brief description of drawings]

FIG. 1 is a sectional view showing an element structure of an LED according to a first embodiment.

FIG. 2 is a characteristic diagram showing the relationship between the logarithm of the first and second reflective films and the reflectance.

FIG. 3 is a characteristic diagram showing a relationship between a half width and a logarithm of a reflection spectrum in the first and second reflection films.

FIG. 4 is a characteristic diagram showing a reflection spectrum of a hybrid type reflection film.

FIG. 5 is a sectional view showing an element structure of an LED according to a second embodiment.

FIG. 6 is a sectional view showing an element structure of an LED according to a third embodiment.

FIG. 7 is a cross-sectional view showing a device structure of a conventional LED having an InGaAlP light emitting portion.

[Explanation of symbols]

101 ... n-GaAs substrate 102 ... n-InAlP / GaAs first reflection film (Bragg type reflection mirror) 103 ... n-InAlP / InGaAlP second reflection film (Bragg type reflection mirror) 104 ... n-InGaAlP clad layer 105 ... InGaAlP Active layer 106 ... p-InGaAlP cladding layer 107 ... n-InGaAlP current blocking layer 108 ... p-GaAlAs current diffusion layer 109 ... p-GaAs contact layer 110 ... p-side electrode 111 made of AuZn / Au 111 ... n made of AuGe / Au Side electrode 503 ... InAlP / GaAs second reflection film (Bragg type reflection mirror) 602 ... InAlP / GaAs reflection film (Bragg type reflection mirror)

Claims (1)

[Claims] 1. A semiconductor substrate, a semiconductor multilayer reflective film formed of a semiconductor thin film formed on the semiconductor substrate, and a semiconductor laminated structure portion including a light emitting layer formed on the semiconductor multilayer reflective film, A semiconductor light emitting device that extracts light from a surface opposite to the semiconductor substrate, wherein the semiconductor multilayer reflective film has a wide reflection band characteristic.
And a second Bragg reflecting mirror having a high reflectance characteristic.