JP2766311B2 - 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 having a light emitting layer made of InGaAlP.

(Prior Art) InGaAlP-based materials have the largest direct transition type energy gap among III-V compound semiconductor mixed crystals excluding nitrides, and are attracting attention as light emitting device materials in the 0.5 to 0.6 μm band. InGaAlP with GaAs as substrate and lattice matching
Junction type light-emitting diode (Light Em
Itting Diodes (LEDs) can emit red to green light with higher luminance than conventional indirect transition materials such as GaP and GaAsP. In order to create a high-brightness LED, it is necessary not only to increase the luminous efficiency, but also to absorb light inside the device,
It is important to realize effective light extraction to the outside, depending on the relative positional relationship between the light emitting unit and the electrodes.

FIG. 5 is a sectional view showing a structure of a conventional LED having an InGaAlP light emitting portion. In FIG. 5, reference numeral 51 denotes an n-GaAs substrate, and 52 denotes n-InGaAlP.
Cladding layer, 53 an InGaAlP active layer, 54 a p-InGaAlP cladding layer, 55 a p-InGaP intermediate energy gap layer, 56
Is a p-GaAs contact layer, 57 is a p-side electrode, and 58 is an n-side electrode. The arrows in the figure indicate the current distribution in the device, and the hatched portions indicate the light emitting portions.

The Al composition of each layer is set so as to obtain high luminous efficiency, and the energy gap of the active layer serving as the luminescent layer has a double heterojunction smaller than the two cladding layers. In the following, an LED having such a double heterojunction structure will be described. However, in consideration of light extraction efficiency to be considered below, the layer structure of the active layer portion 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 as shown in FIG. 5, since the resistivity of the p-InGaAlP cladding layer 54 is higher than that of the n-InGaAlP cladding layer 52, there is almost no current spread in the cladding layer 54.
The light emitting part is the intermediate energy gap layer 55 and the contact layer 56
In addition, only light was directly below the electrode 57, and the light extraction efficiency in the upper surface direction was extremely low.

FIG. 6 is a structural cross-sectional view showing another LED having an InGaAlP light emitting portion. In FIG. 6, 61, to 68 correspond to 51 to 58 in FIG. 5 except that the relationship of pn is reversed. doing. The intermediate energy gap layer 65 is arranged not on the contact layer 66 side but on the substrate 61 side. In the structure as shown in this figure, by disposing the p-InGaAlP cladding layer 62 having a high resistivity on the substrate 61 side, the current spread in the n-InGaAlP cladding layer 64 is smaller than that of the conventional example shown in FIG. It is slightly larger than that.
However, most of the light emitting portion still has the contact layer 66.
And immediately below the electrode 67, no significant improvement in 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, large light extraction efficiency cannot be obtained from the current distribution state in the light emitting portion, and high luminance is realized. It was extremely 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 improve a light extraction efficiency and a luminance. It is to provide a device.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to improve the arrangement position and shape of the intermediate energy gap layer to improve the current distribution state in the light emitting section.

That is, the present invention provides a light emitting device formed by stacking a compound semiconductor substrate of the first conductivity type (for example, GaAs) and at least a first conductivity type InGaAlP layer and a second conductivity type InGaAlP layer forming a pn junction on the substrate. In a semiconductor light emitting device comprising a light emitting portion and an electrode for current confinement formed in a part of the light emitting portion, energy between the first conductivity type InGaAlP layer of the light emitting portion and the substrate is higher than that of the substrate. The gap is large and the first
An intermediate energy gap layer of the first conductivity type having an energy gap smaller than that of the conductivity type InGaAlP layer is selectively formed, and the first conductivity type InGaAlP is formed at least under a part of the electrode.
The P layer is brought into direct contact with the substrate.

(Operation) According to the present invention, the intermediate energy gap layer does not exist in at least a part immediately below the electrode on the light extraction side, and the intermediate energy gap layer exists in a region other than immediately below the electrode. The current flowing in the energy gap layer extends to a region other than immediately below the electrode.
In particular, by forming the intermediate energy gap layer in a pattern opposite to the electrode pattern, the current from the electrode can be extended to a peripheral region immediately below the electrode. Therefore, the light emitting region can be expanded to a region other than immediately below the electrode, thereby improving the light extraction efficiency.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

FIG. 1 is a perspective view showing a schematic configuration of a semiconductor light emitting device according to one embodiment of the present invention, with a part thereof being cut away. 11 in the figure is p
-GaAs substrate 12 is p-InGaP intermediate energy gap layer, 13 _{p-In 0.5 (Ga 1-} X Al X) 0.5 P cladding layer, 14
In _0.5 (Ga _{1 -Z} Al _Z ) _0.5 P active layer, 15 is n-In _0.5 (Ga _{1 -Y}
Al _Y ) P clad layer, 16 is an n-GaAs contact layer, 17 is an n-side electrode, and 18 is a p-side electrode. The intermediate energy gap layer 12 is formed in a pattern opposite to that of the electrode 17. That is,
The intermediate energy gap layer 12 does not exist immediately below the n-side electrode 17, and the p-InGaAlP cladding layer 13 directly contacts the exposed portion 11 a of the p-GaAs substrate 11 immediately below the electrode 17.

FIG. 2 is a cross-sectional view showing the element structure of the device shown in FIG. 1, and shows a current distribution in the element and a light emitting section.
An arrow 21 in the figure indicates a current distribution in the element, and a hatched portion 22 indicates a light emitting portion. The Al composition x, y, z of each layer satisfies z ≦ x, z ≦ y so that high luminous efficiency can be obtained. That is, the energy gap of the active layer 14 serving as the light emitting layer has two p, n , A double heterojunction smaller than 15 is formed. In the following, an LED with such a double heterojunction structure will be described.However, from the viewpoint of light extraction efficiency, the layer structure of the active layer is not essential. Can be.

In the structure shown in FIGS. 1 and 2, p-GaAs
The voltage drop at the interface between the substrate 11 and the p-InGaAlP cladding layer 13 is much larger than the voltage drop at each interface of the p-GaAs substrate 11, the p-InGaP intermediate energy gap layer 12, and the p-InGaAlP cladding layer 13. . For this reason, a current selectively flows in a portion where the p-InGaP intermediate energy gap layer 12 exists. At this time, the resistivity of the p-InGaAlP cladding layer 13 is larger than that of the n-InGaAlP cladding layer 15 and the current is n-InG
aThe AlP clad layer 15 spreads greatly. Therefore, in the InGaAlP active layer 14, a current flows in a peripheral portion immediately below the electrode 17.

As described above, according to the present embodiment, by arranging the intermediate energy gap layer 12 immediately below the electrode 17 so as not to exist, most of the light emission occurs in a portion where the electrode 17 is not provided. Therefore, the generated light is transmitted to the contact layer 16 and the electrode.
The light is extracted outside without being hindered by the light emitting device 17, and a high light extraction efficiency and, consequently, a high-luminance light emission become possible.

FIG. 3 is a perspective view showing a schematic configuration of another embodiment of the present invention, and FIG. 4 is a schematic view showing the positional relationship between the intermediate energy gap layer and the n-side electrode in the same embodiment as viewed from the element surface side. In the figure, 31 to 38 correspond to 11 to 18 in FIG. 1, and the material and composition ratio of each part are the same as those in FIG. This embodiment is different from the above-described embodiment in the pattern of the n-side electrode and the pattern of the intermediate energy gap layer. That is, a plurality of n-side electrodes 37 are arranged in a stripe shape, and a plurality of intermediate energy gap layers 32 are arranged in a stripe shape in a direction orthogonal to the n-side electrode 37.

Such an intermediate energy gap layer 32 and the n-side electrode 37
In this arrangement, the intermediate energy gap layer 32 is
Although it may be directly below the electrode 37, the current spreads to a portion not hidden by the electrode 37, and high light extraction is possible. In addition, the structure shown in FIG. 3 has an advantage that a complicated mask alignment is not required when the intermediate energy gap layer 32 and the n-side electrode 37 are formed.

Further, in this embodiment, by arranging the intermediate energy gap layer 32 in parallel with the n-side electrode 37, that is, in a pattern opposite to that of the electrode 37, the light extraction efficiency can be further improved. However, in this case, mask alignment between the intermediate energy gap layer 32 and the n-side electrode 37 is required.

Note that the present invention is not limited to the above-described embodiments. In the embodiment, the semiconductor light emitting device using p-InGaP as the intermediate energy gap layer has been described. However, the intermediate energy gap layer is generally an intermediate energy gap between the InGaAlP cladding layer and the GaAs substrate, for example, In InP.
It goes without saying that similar effects can be obtained with GaAlP or GaAlAs. The structure of the light emitting unit is not limited to the double hetero structure, but may be a single hetero structure or a homojunction structure. Further, the conductivity type of each part can be reversed. In this case, the positional relationship between the p and n cladding layers is upside down, and the spread of current in the active layer is smaller than that of the embodiment, but is much larger than that of the conventional structure shown in FIGS. 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, an intermediate energy gap layer is selectively formed between a substrate and a light emitting portion, and an intermediate energy gap layer is formed at least partially below an electrode on a light extraction side. Since there is no gap layer and the intermediate energy gap layer exists in a region other than immediately below the electrode, the current flowing from the electrode to the intermediate energy gap layer spreads to a region other than immediately below the electrode. Therefore, the light emitting region can be expanded to a region other than immediately below the electrode, whereby the light extraction efficiency can be improved, and a high-luminance semiconductor light emitting device can be realized.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a schematic structure of a semiconductor light emitting device according to an embodiment of the present invention, FIG. 2 is a sectional view showing an element structure of the above embodiment, and FIG. FIG. 4 is a perspective view showing a schematic configuration of another embodiment, FIG. 4 is a plan view schematically showing the positional relationship between the intermediate energy gap layer and the n-side electrode in the embodiment of FIG. 3, FIG. 5 and FIG. 1 is a sectional view showing a schematic structure of a conventional device. 11,31 p-GaAs substrate, 12,32 p-InGaP intermediate energy gap layer, 13,33 p-InGaAlP cladding layer,
14,34 ... InGaAlP active layer, 15,35 ... n-InGaAlP cladding layer, 16,36 ... n-GaAs contact layer, 17,37 ... n-side electrode, 18,38 ... p-side electrode, 21 ... current distribution, 22 ... light-emitting part.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideto Sugawara 1 Toshiba Research Institute, Komukai, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-61-35514 (JP, A) 1-296677 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 33/00

Claims (1)

(57) [Claims] 1. A light emitting portion formed by laminating a first conductivity type compound semiconductor substrate, at least a first conductivity type InGaAlP layer and a second conductivity type InGaAlP layer forming a pn junction on the substrate, A semiconductor light-emitting device comprising: a current confinement electrode formed in a part of the light-emitting portion; wherein the energy gap is larger than the substrate between the first conductivity type InGaAlP layer of the light-emitting portion and the substrate; and 1st conductivity type
An intermediate energy gap layer of a first conductivity type having an energy gap smaller than that of the InGaAlP layer is selectively formed, and the first conductivity type InGaAlP layer and the substrate are brought into direct contact with each other at least under the electrode. Characteristic semiconductor light emitting device.