JP3020542B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) 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 band gap in III-V compound semiconductor mixed crystals excluding nitrides, and have a band gap of 0.1.
It is attracting attention as a light emitting element material in the 5-0.6 μm band. In particular, pn-junction light-emitting diodes (LEDs) that use GaAs as a substrate and have a light-emitting portion made of InGaAlP lattice-matched to the GaAs substrate have a red-to-green color, compared to conventional indirect transition materials such as GaP and GaAsP. High-luminance light emission is possible. In order to form a high-brightness LED, it is necessary not only to increase the luminous efficiency, but also to realize effective light extraction to the outside due to light absorption inside the device and the relative positional relationship between the light-emitting part and the electrodes. is important.

FIG. 6 shows a cross-sectional view of a conventional LED having an InGaAlP light emitting portion.

As shown in FIG. 6, n-GaAs substrate 61 has n-
InGaAlP cladding layer 62, n-InGaAlP active layer 63, p-InGaAl
P cladding layer 64, p-InGaP intermediate band gap layer 65, p-Ga
As contact layers 66 are sequentially laminated, and a p-side electrode 67 is formed on the p-GaAs contact layer 66, and an n-side electrode 68 is formed on the other main surface of the n-GaAs substrate 61 to form a light emitting element. Have been. The light emitting portion in this element is indicated by 69, and the current distribution is indicated by an arrow.

The Al composition of each layer is set so as to obtain high luminous efficiency, and the band gap of the active layer 63 serving as a light emitting portion is formed as a double hetero junction smaller than the two cladding layers 62 and 64. In the following, an LED having such a double heterojunction structure will be described. However, considering the light extraction efficiency to be discussed below, the layer structure of the active layer is not essential, and a single heterojunction structure or a homojunction structure is not considered. The same can be considered for the structure.

In the structure shown in FIG. 6, when an attempt is made to obtain orange luminescence having a wavelength of about 600 nm, the In _0.5 (Ga _{1 -X}
Al _x ) _0.5 The Al composition of the P layer is x = 0.3. In this case, in order to sufficiently confine carriers in the active layer 63 and obtain high luminous efficiency, the Al composition x of the cladding layers 62 and 64 is set to 0.7 or more. ,
It is necessary to increase the band gap difference from the active layer 63. On the other hand, it has been found that the resistivity in the p-type InGaAlP layer largely depends on the Al composition. FIG. 5 shows the dependence of the carrier concentration and the resistivity of the p-type InGaAlP layer on the Al composition when Zn is used as the doping material.
The supply amount of the Zn doping material during the growth of InGaAlP is constant. As the Al composition increases, the carrier concentration decreases. In particular, when x = 0.4 or more, the carrier concentration sharply decreases, and the resistivity increases accordingly.

That is, in the structure as shown in FIG. 6, p-InGaAl
Since the resistivity of the P cladding layer 64 is larger than that of the n-InGaAlP cladding layer 62, there is almost no current spreading in the cladding layer 64, and the light emitting portion is composed of the intermediate band gap layer 65 and the contact layer 6.
6 and only below the electrode 67, the light extraction efficiency in the upper surface direction was extremely low.

FIG. 7 is a structural cross-sectional view showing another LED having an InGaAlP light emitting portion. In FIG. 7, 71 to 78 correspond to 61 to 68 in FIG. 6 except that the relationship of the pn junction is reversed. . The intermediate band gap layer 75 is arranged not on the contact layer 76 side but on the substrate 71 side. In the structure as shown in this drawing, the current spreading (arrow in the drawing) in the n-InGaAlP cladding layer 74 is shown in FIG. 6 by disposing the p-InGaAlP cladding layer 72 having high resistivity on the substrate 71 side. It is slightly larger than the example shown. However, most of the light emitting portion 79 was directly below the contact layer 76 and the electrode 77, and no improvement in the light extraction efficiency was observed.

(Problems to be Solved by the Invention) As described above, conventionally, in a semiconductor light emitting device having a light emitting portion made of InGaAlP, a large light extraction efficiency cannot be obtained from a current distribution state in the light emitting portion, and high luminance is realized. It was difficult to do.

The present invention has been made in view of the above circumstances, and an object thereof is to improve a current distribution in a light emitting portion made of InGaAlP, and to improve a light extraction efficiency and a luminance. It is to provide an element.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is that the cladding layer provided between the light emitting portion made of InGaAlP and the electrode is two layers, and the cladding layer on the electrode side with respect to the active layer side is formed. The object is to make the resistivity smaller.

That is, the present invention provides an InGaAlP on a first conductivity type semiconductor substrate.
In a semiconductor light emitting device in which a light emitting layer made of is laminated and light is extracted from a surface other than an electrode provided on a part of the surface opposite to the substrate with respect to the light emitting layer, the light emitting layer is A first second conductivity type cladding layer made of InGaAlP having a large band gap, and having a band gap larger than that of the light emitting layer and a resistivity higher than that of the cladding layer on the first second conductivity type cladding layer. A second clad layer of the second conductivity type made of small InGaAlP is provided.

The present invention also provides a method for changing the resistivity of the first second conductivity type cladding layer (first cladding layer) and the second second conductivity type cladding layer (second cladding layer) by adding impurities to the first cladding layer. Doping Zn as a material, doping the second cladding layer with Mg as an impurity, or changing the Al composition of the second cladding layer to
The first cladding layer is made smaller than the Al composition.

(Operation) According to the present invention, the resistivity of the second cladding layer is lower than that of the first cladding layer due to the selection of impurities or the difference in Al composition. That is, the second cladding layer on the light extraction electrode side has a lower resistivity than the first cladding layer on the light emitting section side. Therefore, the current injected from the electrode is injected into the second cladding layer and spreads over a wide range. Therefore, the light-emitting region can be expanded to a region other than immediately below the electrode, and light extraction efficiency and luminance can be improved.

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

FIG. 1 is a sectional view showing a schematic structure of a semiconductor light emitting device according to a first embodiment of the present invention. As shown in FIG. 1, an n-In _0.5 (Ga _{1 -X} Al _X ) _0.5 P cladding layer 12, In _0.5 (Ga
_1-Y Al _Y ) _0.5 P active layer 13, p-In _0.5 (Ga _{1 -Z} Al _Z ) _0.5 P cladding layer 14 (Zn-doped), p-In _0.5 (Ga _{1 -Z} Al _Z ) _0.5 P cladding layer 15 (Mg-doped), a p-Ga _{1 -P} Al _P As intermediate band gap layer 16 and a p-GaAs contact layer 17 are sequentially laminated, and a p-type electrode 18 made of Au-Zn GaAs
An n-type electrode 19 made of Au-Ge is formed on the other main surface of the substrate 11. The Mg-doped cladding layer 15 (first
Is formed thicker than the Zn-doped cladding layer 14 (second cladding layer of the second conductivity type).

FIG. 2 is a schematic diagram showing a current distribution and a light emitting region in the light emitting device shown in FIG. In the figure, the current distribution 22 in the device is indicated by a broken arrow, and the light emitting region 21 is indicated by a node. The Al composition x, y, z of each layer of InGaAlP satisfies y ≦ x, y ≦ z so as to obtain high luminous efficiency. For example,
Let x = z = 0.7 and y = 0.3. That is, the active layer that becomes the light emitting section
A double hetero junction is formed in which the band gap of 13 is smaller than the two cladding layers 12 and 14 adjacent to each other with p and n. The Al composition p in the intermediate band gap layer 16 may be smaller than the Al composition x, z of the cladding layers 12, 14, and p = 0 may be set.

In the structure shown in FIGS. 1 and 2, the thickness of each layer and the carrier concentration are set as shown in parentheses below. n-GaAs substrate 11 (80 μm, 3 × 10 ¹⁸ cm ⁻³ ), n
-InGaAlP cladding layer 12 (1 μm, 5 × 10 ¹⁷ cm ⁻³ ), InG
aAlP active layer 13 (0.5 μm, undoped), Zn-doped p-I
nGaAlP cladding 14 (0.2 μm, 4 × 10 ¹⁷ cm ⁻³ ), Mg-doped p-InGaAlP cladding layer 15 (1 μm, 1 × 10 ¹⁸ c
m ^-3 ), p-InGaP intermediate band gap layer 16 (0.05 μm,
1 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 17 (0.1 μm,
3 × 10 ¹⁸ cm ⁻³ ).

The difference between the structure of the present embodiment and the conventional structure is that p-InGaAl
The p-InGaAlP Mg-doped cladding layer 15 having a larger thickness and a lower resistivity can be formed on the Zn-doped cladding layer 14 of P. The superiority of this structure will be described below. I do.

In the conventional structure as shown in FIG. 6, p-In
The current spread in the GaAlP cladding layer 64 is small because the resistivity of the cladding layer 64 is high. It is conceivable to increase the spread of current by increasing the film thickness.
In the case of the P material type, it is not preferable because the thermal conductivity is poor and the crystal quality is deteriorated by forming a thick film, and an adverse effect on the upper layer appears. In addition, the growth rate of the InGaAlP-based semiconductor material is limited from the viewpoint of crystal quality, and when growing a thick film, the growth time must be extended. This means that when an impurity having a high diffusivity is used as the impurity of the cladding layer, the impurity is diffused into the active layer, thereby deteriorating the device characteristics. For this reason, it is difficult to grow the InGaAlP layer into a thick film.

In addition, when Zn is doped in this InGaAlP-based material, it is difficult to obtain a high carrier concentration due to its low activity rate.In addition, Zn is an impurity having a high diffusibility and is doped into the active layer by high concentration doping. Diffusion occurs, which also causes deterioration of device characteristics. It is desirable to increase the band gap difference between the cladding layer and the active layer to confine the current in the active layer. For this purpose, the Al composition must be increased. But Zn is Al
The disadvantages described above become more pronounced as the composition increases.

On the other hand, Mg can be doped at a high concentration even with a high Al composition, and a low-resistance p-InGaAlP layer can be formed. For this reason, when a Mg-doped layer 15 of low resistance p-InGaAlP is laminated on a Zn-doped layer 14 of p-InGaAlP having high resistivity to form a p-cladding layer, the current injected from the electrode is reduced by p-InGaAlP. Can be spread with Mg-doped layer 15,
Light emission is possible in a region other than immediately below the electrode.

P-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P Zn-doped cladding layer used in this embodiment
14 and Mg-doped cladding layer of p-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P
At 15 the resistivity at the carrier concentration is 1 Ωcm for the cladding layer 14 and 0.3 Ωcm for the cladding layer 15. Due to such a difference in resistivity, the current injected from the electrode 18 reaches the cladding layer 15 before reaching the cladding layer 14.
It can be spread over a wide area.

In _0.5 (Ga _1-Y Al _Y ) _0.5 P active layer with the above-mentioned laminated structure
A device was formed by using 0.3 as the Al composition y of 13 and a current was applied by applying a voltage in the forward direction. As a result, the current distribution became as shown in FIG. 2, and 610 nm from the device surface wide area excluding the p-side electrode 17.
A light emission having a peak wavelength was obtained. Note that InGaAlP
A similar effect can be obtained by providing the carrier concentration distribution in the growth direction in the Mg-doped p-cladding layer on the light emitting portion composed of But InGaAlP
The doping of Mg in the base material is as shown in FIG.
It is clear from experiments by the present inventors that it is difficult to control the low carrier concentration. Therefore, it is difficult to provide the carrier concentration distribution in the growth direction in the Mg-doped p-cladding layer on the light emitting portion.

As described above, according to the present embodiment, the active layer 13 serving as the light emitting portion
The Zn-doped cladding layer 14 and the Mg-doped cladding layer 15 on top
, The current injected from the electrode 18 can be spread over a wide range by the cladding layer 15, and the light emitting region can be expanded to a region other than immediately below the electrode. Therefore, it is possible to improve the efficiency of extracting light from the periphery of the electrode, and thereby to achieve higher luminance.

FIG. 4 is a sectional view showing a schematic structure of a semiconductor light emitting device according to a second embodiment of the present invention. An n-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P cladding layer 42, In
_0.5 (Ga _0.7 Al _0.3 ) _0.5 P active layer 43, p-In _0.5 (Ga _0.3 Al
_0.7 ) _0.5 P cladding layer (first second conductivity type cladding layer)
44, p-In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P current spreading layer (second second conductivity type cladding layer) 45 and p-GaAs contact layer 47 are sequentially laminated, and on this contact layer 47, Au-Zn The p-side electrode 48 made of Au-Ge is formed on the other main surface of the n-GaAs substrate 41.
Side electrodes 49 are formed respectively.

In the structure shown in FIG. 4, the thickness of each layer and the carrier concentration are set as shown in parentheses below. n-
GaAs substrate 41 (80 μm, 3 × 10 ¹⁸ cm ⁻³ ), n-InGaAlP cladding layer 42 (1 μm, 5 × 10 ¹⁷ cm ⁻³ ), InGaAlP active layer 4
3 (0.5 μm, undoped), p-InGaAlP cladding layer 44
(1 μm, 4 × 10 ¹⁷ cm ⁻³ ), p-InGaAlP current spreading layer 4
5 (3 μm, 1 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 47
(0.1 μm, 3 × 10 ¹⁸ cm ⁻³ ).

The difference between the structure of the present embodiment and the conventional structure is that p-InGaAl
On the P cladding layer 44, p-InGaA having a lower Al composition is formed.
This is because the lP current spreading layer 45 is formed, and the superiority of this structure will be described below.

In the conventional structure as shown in FIG. 6, the current spread in the p-InGaAlP cladding layer 34 is small because the resistivity of the cladding layer 34 is as high as 1 Ωcm or more as described above. As shown in FIG. 5, in an InGaAlP layer having a high Al composition of x = 0.7 or more, such as used for the cladding layer, the activation rate of Zn is low and the saturation carrier concentration is low.
Obtaining a low resistance layer is very difficult.

On the other hand, as in the present embodiment, a p-InGaAlP current spreading layer 45 having a lower Al composition than the p-InGaAlP cladding layer 44 and capable of obtaining a higher carrier concentration and a lower resistivity is provided on the cladding layer 44. By forming, the current injected from the electrode 48 can be expanded, and light emission can be performed in a wide area other than immediately below the electrode.

The p-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P cladding layer 44 and the p-In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P current spreading layer 45 used in this embodiment have a resistivity of 1 Ωcm at the above carrier concentration. And 0.1
Ωcm. As described above, the current injected from the electrode due to the large difference in resistivity is spread over a wide area by the current spreading layer 45 before reaching the cladding layer 44. Accordingly, the current distribution becomes similar to that of the previous embodiment, and light emission can be obtained from a wide area of the element surface excluding the p-type electrode 48. In addition, from the device formed with the laminated structure of this embodiment, light emission having a peak wavelength at 610 nm was obtained as in the previous embodiment.

Note that the present invention is not limited to the above-described embodiments. In the first embodiment, In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P was used as the composition of the active layer. However, by changing the Al composition, light emission can be obtained in the visible light range from red to green. . Furthermore, the Al composition of the cladding layer only needs to have a band gap difference with the active layer sufficient to confine carriers, and is not limited to 0.7 but can be changed as appropriate.

In the second embodiment, the composition of the p-InGaAlP current spreading layer is set to In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P. However, the Al composition is lower than that of the p-cladding layer, the resistance can be reduced, and the light emitting layer can be formed. The composition is not limited to this composition as long as the composition has a band gap larger than the band gap energy. Also, the p-InGaAlP current spreading layer is
Although the structure having the layers is shown, if the InGaAlP layer has a smaller Al composition than the cladding layer and is larger than the band gap of the light emitting layer, the same effect can be obtained even in a structure in which two or more layers having different compositions are stacked. Further, a composition gradient layer in which the Al composition is gradually reduced from the cladding layer may be formed.

In any of the embodiments, p and n may be reversed. Further, the layer structure of the light emitting section including the active layer is not limited to the double hetero structure, but may be a single hetero junction structure or a homo junction structure.
In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, the cladding layer provided between the light emitting portion made of InGaAlP and the electrode is made into two layers,
Since the resistivity of the cladding layer on the electrode side is made smaller than that of the active layer side, the current injected in the cladding layer on the electrode side can be expanded. Therefore, the light-emitting area in the light-emitting portion can be made larger than immediately below the electrodes, thereby improving the light extraction efficiency and the luminance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a schematic structure of a semiconductor light emitting device according to a first embodiment of the present invention, FIG. 2 is a schematic diagram showing current spreading in the device, and FIG. FIG. 4 is a characteristic diagram showing the relationship between the carrier concentration and the carrier concentration, FIG. 4 is a sectional view showing a schematic structure of a second embodiment of the present invention,
Characteristic diagram showing the relationship between the composition and carrier concentration and resistivity,
6 and 7 are cross-sectional views each showing a conventional element structure. 11,41 n-GaAs substrate (first conductivity type semiconductor substrate), 12,42 n-InGaAlP cladding layer, 13,43 InGaAlP active layer, 14,44 p-InGaAlP cladding layer 1, second conductive type cladding layer), 15,45... P-InGaAlP cladding layer (second second conductive type cladding layer), 16... P-InGaP intermediate band gap layer, 17,47. GaAs contact layer, 18,19,48,49 ... electrode, 21 ... light emitting area, 22 ... current distribution.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Itaya 1 Tokoba, Komukai Toshiba-cho, Saisaki-ku, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-61-232686 (JP, A) JP-A-50-19382 (JP, A) JP-A-63-164384 (JP, A) JP-A-62-172782 (JP, A) JP-A-2-151085 (JP, A) JP-A-58-165385 (JP, A) JP-A-62-264680 (JP, A) JP-A-3-171679 (JP, A) JP-A-3-129892 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H01L 33/00

Claims (2)

(57) [Claims] An InGa film formed on a first conductivity type semiconductor substrate.
A light emitting layer made of AlP, a first second conductive type clad layer made of InGaAlP formed on the light emitting layer and having a band gap larger than that of the light emitting layer, and a layer formed on the first second conductive type clad layer Formed with a larger band gap than the light emitting layer and a smaller resistivity than the cladding layer.
A second second-conductivity-type clad layer made of InGaAlP; and an electrode provided on a part of the second second-conductivity-type clad layer. A semiconductor light-emitting device, wherein the light is diffused in the lateral direction by the cladding layer of the second conductivity type, and light is extracted from the surface of the cladding layer of the second conductivity type excluding the electrode forming portion. 2. The first cladding layer of the second conductivity type is doped with Zn as an impurity, and the cladding layer of the second second conductivity type is doped with Mg as an impurity. 2. The semiconductor light emitting device according to claim 1, wherein the Al composition of the second conductivity type cladding layer is smaller than the Al composition of the first second conductivity type cladding layer.