JPH06103759B2 - Semiconductor light emitting device - Google Patents

Description

The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device using an InGaAlP-based semiconductor material.

(Prior Art) InGaAlP-based materials have the largest direct transition type energy gap in III-V group compound semiconductor mixed crystals excluding nitrides,
It is attracting attention as a light emitting device material in the 0.5 to 0.6 μm band.
In particular, a pn junction type light emitting diode (Light Emitti
ng Diode: LED) is capable of emitting red to green light with high brightness as compared with a conventional material using an indirect transition type material such as GaP or GaAsP. In order to form a high-brightness LED, in addition to improving the luminous efficiency, it is possible to achieve effective light extraction to the outside by light absorption inside the element and the relative positional relationship between the light emitting part and the electrode. is important.

FIG. 3 shows a sectional view of a conventional LED having an InGaAlP light emitting part.

As shown in FIG. 3, n-InGaAl is formed on one main surface of the n-GaAs substrate 31.
P clad layer 32, n-InGaAlP active layer 33, p-InGaAlP clad layer 34, p-InGaP intermediate energy gap layer 35, p-GaAs
A contact layer 36 is sequentially laminated, and a p-side electrode 37 is formed on the p-GaAs contact layer 36, and an n-side electrode 38 is formed on the other main surface of the n-GaAs substrate 31. It is configured. The current distribution 39 in this element is shown by arrows, and the light emitting section 30 is shown by dots.

The Al composition of each layer is set so as to obtain high light emission efficiency, and the active layer serving as a light emitting layer has a double hetero junction in which the energy gap is smaller than the two clad layers. Note that the LED having such a double heterojunction structure will be described below.However, in consideration of the light extraction efficiency, which is a problem below, the layer structure of the active layer is not essential, but a single heterojunction structure or a homojunction structure. The structure can be changed as well.

In the structure shown in FIG. 3, the p-InGaAlP cladding layer 3
Since the resistivity of 4 is higher than that of the n-InGaAlP clad layer 32, there is almost no current spreading in the clad layer 34, and the light emitting portion is only directly below the intermediate energy gap layer 35, the contact layer 36 and the electrode 37, and the upper surface The light extraction efficiency in the direction was very low.

FIG. 4 is a structural cross-sectional view showing another LED having an InGaAlP light emitting part, and 41 to 48 in the figure correspond to 31 to 38 in FIG. 3 only in that the relationship of pn is reversed. The intermediate energy gap layer 45 is arranged not on the contact layer 46 side but on the substrate 41 side. The structure shown in this figure has a high resistivity.
By arranging the p-InGaAlP cladding layer 42 on the substrate 41 side, the current spread in the n-InGaAlP cladding layer 44 (current distribution 4
9) is slightly larger than the conventional example shown in FIG. However, most of the light emitting portion 40 is still directly below the contact layer 46 and the electrode 47, and no significant improvement in light extraction efficiency was observed.

(Problems to be solved by the invention) In the conventional semiconductor light emitting device having a light emitting portion made of InGaAlP, a large light extraction efficiency cannot be obtained from the state of the current distribution in the light emitting portion, and high brightness is realized. Was extremely difficult.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a semiconductor light emitting device capable of improving the current distribution in a light emitting section made of InGaAlP and improving the light extraction efficiency and the brightness. To do.

[Structure of Invention]

(Means for Solving the Problem) A semiconductor light emitting device of the present invention has a first conductivity type compound semiconductor substrate, and a light emitting section made of an InGaAlP layer on the compound semiconductor substrate, and a side opposite to the compound semiconductor substrate. In a semiconductor light-emitting device that extracts light from a surface other than an electrode formed on a part of the surface of the InGaAlP layer of the light-emitting portion,
The band gap is larger than that of the layer and the InGa of the light emitting portion is
It is characterized by comprising a second conductivity type GaAlAs layer having a larger layer thickness than the AlP layer.

(Operation) In the semiconductor light emitting device of the present invention, since the second conductivity type GaAlAs layer having a lower resistivity than the InGaAlP layer formed as the light emitting portion is present below the electrode on the light extraction side, the current injected from the electrode is Injected into the GaAlAs layer through the GaAs contact layer,
It will spread over a wide area. Therefore, the light emitting region can be expanded to a region other than directly under the electrode. In addition, Ga ₁ -pAlpAs should be made transparent so that the light emitting part is transparent to the wavelength of the emitted light.
By selecting the Al composition layer of the layer, it is possible to improve the light extraction efficiency.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing the outline of the structure of a semiconductor light emitting device according to an embodiment of the present invention. As shown in Fig. 1, n-GaAs
N-In _0.5 (Ga _1-x Al _x ) _0.5 P clad layer 1 on the main surface of substrate 11
2, In _0.5 (Ga _1-y Al _y ) _0.5 P Active layer 13, p-In _0.5 (Ga _1-z Al _z )
_{A 0.5} P clad layer 14, a p-Ga _1-p Al _p As layer 15, and a p-GaAs contact layer 16 are sequentially stacked, and Au-Zn is deposited on this contact layer 16.
On the other main surface of the n-GaAs substrate 11.
Each n-side electrode 18 made of -Ge is formed. The p-GaAlAs layer 15 is formed sufficiently thicker than the p-InGaAlP layer 14.

FIG. 2 shows the current distribution in the element of the device shown in FIG. 1 and the light emitting portion. In the same figure, the current distribution 29 in the device is shown by the broken line arrows, and the light emitting portion 20 is shown by the imprinting points. InGaAl
The Al compositions X, Y, and Z of each P layer satisfy Y ≦ X and Y ≦ Z so that high luminous efficiency can be obtained. That is, the energy gap of the active layer 13 which becomes the light emitting layer is two cladding layers of p and n.
Double heterojunctions smaller than 12 and 14 are formed.
Further, the Al composition layer of the p-GaAlAs layer is transparent to the emission wavelength of the active layer 13, is transparent to the emission wavelength of the active layer 13, the band gap than the active layer 13, Largely selected. Note that the LED having such a double heterojunction structure will be described below, but in consideration of the light extraction efficiency, the layer structure of the active layer is not essential, and the single heterojunction structure or the homojunction structure is the same. Can be thought of.

In the structure shown in FIGS. 1 and 2, the thickness of each layer,
The carrier index is set as shown in parentheses below. n-GaAs substrate 11 (80 μm, 3 × 10 ¹⁸ cm ^-3 ), n-InGaAl
P clad layer 12 (1 μm, 5 × 10 ¹⁷ cm ⁻³ ), InGaAlP active layer 13 (0.5 μm, undoped), p-InGaAlP layer 14 (0.2 μm
m, 4 × 10 ¹⁷ cm ^-3 ), p-GaAlAs layer 15 (3 μm, 3 × 10 ¹⁸
cm ⁻³ ) and p-GaAs layer 16 (0.1 μm, 3 × 10 ¹⁸ cm ⁻³ ).

The above-mentioned structure is different from the conventional structure in that a p-GaAlAs layer 15 having a thickness sufficiently thicker than that is formed on the p-InGaAlP cladding layer 12, and the superiority of this structure will be described below.

In the conventional structure as shown in FIG. 3, the current spread in the p-InGaAlP cladding layer 34 is small due to the high resistivity. It is possible to increase the current spread by increasing the film thickness, but in this InGaAlP material system, the thermal quality is poor and the crystal quality deteriorates by using a thick film, and the adverse effect on the upper layer also appears. Not preferable. The growth rate of the InGaAlP-based semiconductor material is limited due to its crystal quality, and the growth time must be extended when a thick film is grown. This means that when a highly diffusible impurity is used as the clad layer, the impurity diffuses into the active layer, resulting in deterioration of the device characteristics. Therefore, it is difficult to grow the InGaAlP layer as a thick film. On the other hand, a p-GaAlAs layer 15 that is lattice-matched with GaAs and has a low resistivity and a high growth rate can be formed with p-InGaAlP.
By forming it on the clad layer 14, the current injected from the electrode can be spread by the p-GaAlAs layer 15, and light can be emitted in a wide area other than immediately below the electrode. Used in this example
p-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P Cladding layer 14 and p- (Ga _0.2 A
l _0.8 ) As layer 15 has a resistivity of 1 Ωcm at p-cladding layer 14 and p- (Ga _0.2 Al _0.8 ) As layer 15 respectively.
Is 0.05 Ωcm. Since the difference in resistivity is large as described above, the current injected from the electrode is broadly spread in the p-GaAlAs layer 15 before reaching the p-clad layer 14.

In the above laminated structure, In _0.5 (Ga _1-y Al _y ) _0.5 P
When a device was constructed using 0.3 for the composition Y and a voltage was applied in the forward direction and a current was applied, the current distribution shown in Fig. 2 was obtained.
610 mm from the wide area of the device surface excluding 17 parts of p-side electrode (Au-Zn)
Light emission having a peak wavelength was obtained.

The present invention is not limited to the above embodiment. In the embodiment, the composition of the active layer is In _0.5 (Ga _0.7 A
Although l _0.3 ) _0.5 P was used, light emission in the visible light range from red to green can be obtained by changing the Al composition. Further, the composition of the cladding layer is In
_0.5 (Ga _0.3 Al _0.7 ) _0.5 P was used, but it is not limited to this composition as long as there is a sufficient band gap difference from the active layer for confining carriers. In the example, InGaAl
Between the P active layer 13 and the p-GaAlAs layer 15, the p-InGaAlP clad layer 14
However, the p-GaAlAs layer 15 was formed directly on the InGaAlP active layer 13.
The same effect can be obtained even if the structure is formed. However, in the case of this structure, the band gap difference with the active layer 13 is smaller than that in the case of forming the p-InGaAlP clad layer 14, and therefore carrier overflow is more likely to occur than in the above-mentioned example structure, and the device characteristics are slightly inferior. I will end up. However, due to the current spread in the p-GaAlAs layer,
It is highly significant to adopt a structure that can obtain much higher light extraction efficiency than the conventional structure. In addition to the structure described above, G is formed on the light emitting part made of InGaAlP with different Al composition.
It goes without saying that the same effect can be obtained even when the structure is such that the aAlAs layer is formed or the light emitting portion is formed by the InGaAlP layer and the GaAlAs layer.

The Al composition layer of the Ga _1-p Al _p As layer used 0.8 in the example, but it is sufficient if it has a band gap sufficient to be transparent to the emission wavelength from the light emitting portion, and the composition is limited to this composition. Not a thing. In addition, various modifications can be made without departing from the scope of the present invention.

〔The invention's effect〕

As described above, according to the present invention, in a semiconductor light emitting device using In _1-y (Ga _1-x Al _x ) _y P-based material (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1), p-InGaAlP By forming a p-GaAlAs layer with a low resistivity on the clad layer, which is sufficiently thicker than the clad layer, the current injected from the electrode part is p-InGaAl
Before reaching the P-clad layer, the p-GaAlAs layer spreads over a wide area except directly under the electrode. Therefore, the light emitting region can be expanded to a wide area other than directly under the electrode, and thereby the light extraction efficiency can be improved, and a high-luminance semiconductor light emitting device can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic structure of a semiconductor light emitting device according to one embodiment of the present invention, FIG. 2 is a sectional view showing a current distribution and a light emitting portion in the element of the above embodiment, and FIG. FIG. 4 is a sectional view showing a schematic structure of a conventional semiconductor light emitting device, and FIG. 4 is a sectional view showing a current distribution and a light emitting portion in an element of a conventional example. 11 ... n-GaAs substrate 12 ... n-InGaAlP clad layer 13 ... InGaAlP active layer 14 ... p-InGaAlP clad layer 15 ... p-GaAlAs layer 16 ... p-GaAs contact layer 17 ... p-side electrode, 18 ... n-side electrode 10 ... Light emitting part

Claims (1)

[Claims] 1. A first-conductivity-type compound semiconductor substrate, and a light-emitting portion composed of an InGaAlP layer on the compound semiconductor substrate,
In a semiconductor light emitting device that extracts light from a surface other than an electrode formed on a part of the surface opposite to the compound semiconductor substrate, the InGaAlP layer of the light emitting portion has a larger band gap than the InGaAlP layer and A semiconductor light emitting device comprising a second conductivity type GaAlAs layer having a larger layer thickness than the InGaAlP layer of the light emitting portion.