JPH0346280A - Light emitting diode - Google Patents

Abstract

PURPOSE:To enable a light emitting diode to emit light rays of different wavelengths at the same time from the same light projection position and to prevent problems such as a coupling loss and an image-forming position by a method wherein the light emitting diode is provided with a laminar structure composed of two or more p-type semiconductor layers, two p-type semiconductor layers adjacent to each other form a heterojunction, and the p-type semiconductor layers are specified in forbidden bandwidth. CONSTITUTION:A light emitting diode is provided with a p-type semiconductor 1, an n-type semiconductor 2, and a single p-n heterojunction 3, where the p-type semiconductor 1 is composed of p-type semiconductor layers P1 and P2 which form a heterojunction 4. Provided that the forbidden bandwidths of the p-type semiconductor P1 and P2 and the n-type semiconductor 2 are represented by Ep1, Ep2, and En respectively, they are so set as to satisfy a formula, En>Ep1>Ep2. The thickness of the p-type semiconductor layer P1 is smaller than the diffusion length of minor carriers which are injected from the n-type semiconductor 2 into the p-type semiconductor 1. By this setup, light rays of different wavelengths can be obtained from the same projection position at the same time, and for instance, problems such that light rays of different wavelengths are not equal in coupling loss and have not the same image-forming position can be eliminated.

Description

Detailed Description of the Invention (Industrial Application Field) This invention can emit multiple lights of different wavelengths at the same time, and can be used as a light source for an obstacle detection sensor or a remote controller, for example, to provide operating light. The present invention relates to a light emitting diode that can simultaneously obtain light for displaying operation and operation, and can be used as a light source for facsimile machines and optical printers to automatically correct differences in sensitivity characteristics when replacing photoreceptors.

(Prior art) Light emitting diodes, which utilize the phenomenon of light emission when a forward current is passed through a pn heterojunction (heterojunction between a p-type semiconductor and an n-type semiconductor), are well known and have been used for various purposes. Many are offered.

Incidentally, in recent years, it has been proposed to use such light emitting diodes to simultaneously obtain a plurality of lights of different wavelengths. For example, the invention in JP-A-62-34467, the invention in JP-A-63-20129, the invention in JP-A-50-57592, the invention in JP-A-56-69880, the invention in JP-A-64-5
For this purpose, the invention No. 0493 arranges a plurality of light emitting diodes with different emission wavelengths close to each other or on top of each other, or arranges a plurality of light emitting diodes with different emission wavelengths on the same semiconductor substrate. It also forms a pn heterojunction. That is, each of these has one p
Since a device with an n-heterojunction can only obtain light of one type of wavelength, a device with multiple pn-heterojunctions can obtain multiple lights with different wavelengths corresponding to each pn-heterojunction. This is how it was done. However, in such a so-called composite light emitting diode, the emitting position for each wavelength of light is different, so for example, when the emitted light is input into an optical fiber, the coupling loss is not the same for each wavelength of light. When used in a precision optical system, the image formation position for each wavelength of light may not be the same.

(Problem to be solved by the invention) The purpose of the invention is to simultaneously transmit multiple lights of different wavelengths.
Moreover, it can be obtained from the same emission position, and the above-mentioned
An object of the present invention is to provide a light emitting diode that can solve problems regarding coupling loss and imaging position.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides only one
A light emitting diode having a heterojunction of a p-type semiconductor and an n-type semiconductor, in which light emitted by the p-type semiconductor passes through the n-type semiconductor and is emitted from the surface of the n-type semiconductor, The type semiconductor has a layered structure of a plurality of p-type semiconductor layers, and two phase-adjacent p-type semiconductor layers form a heterojunction, and the forbidden band width of each p-type semiconductor layer is equal to the above n The total thickness of the p-type semiconductor layers excluding the p-type semiconductor layer located farthest from the n-type semiconductor is injected from the n-type semiconductor into the p-type semiconductor. To provide a light emitting diode characterized by being thinner than the diffusion length of minority carriers.

The light emitting diode of this invention simultaneously emits multiple lights of different wavelengths, but it has only one pn heterojunction between a p-type semiconductor and an n-type semiconductor, and unlike the above-mentioned conventional one, the light emitting diode There is no such thing as more than one.

Now, a p-type semiconductor is made up of a plurality of p-type semiconductor layers that are connected to each other in a heterojunction. The number of p-type semiconductor layers is equal to the number of lights of different wavelengths emitted by the p-type semiconductor.

In a light emitting diode with a pn heterojunction, p
Light emitted by the n-type semiconductor passes through the n-type semiconductor and exits from the surface of the n-type semiconductor. Therefore, the forbidden band width of the p-type semiconductor and the n-type semiconductor is the same as that of the p-type semiconductor.
, , If that of an n-type semiconductor is E, then E, ,>E.

The relationship has become similar. This point is the same in this invention, and the forbidden band width of each p-type semiconductor layer of the p-type semiconductor is n
In order from the one closest to the type semiconductor, El, E
2,...E, (m is the number of p-type semiconductor layers), E,,〉El〉E2〉...〉EI? l-1〉E
, , l holds true. That is, the forbidden band width of the p-type semiconductor layer becomes larger as the layer is located closer to the n-type semiconductor. Note that the forbidden band width is also called an energy band width or a forbidden band width.

The emission wavelength in each p-type semiconductor layer is determined by the magnitude of the forbidden band width. Further, the ratio of the intensity of light emitted by each p-type semiconductor layer depends on the thickness of the p-type semiconductor layer and the concentration of impurities.

In order for all p-type semiconductor layers to emit light, the minority carriers (electrons) injected from the n-type semiconductor to the p-type semiconductor must reach each p-type semiconductor layer, and the majority carriers (positive hole). Therefore,
The total thickness of the p-type semiconductor layers excluding the p-type semiconductor layer located farthest from the n-type semiconductor is thinner than the diffusion length of minority carriers injected from the n-type semiconductor to the p-type semiconductor.

(Function) Minority carriers injected from the n-type semiconductor into each p-type semiconductor layer of the p-type semiconductor combine with majority carriers in each p-type semiconductor layer, and each p-type semiconductor layer has its own forbidden band width. It emits light of the appropriate wavelength. All of the generated light passes through the n-type semiconductor and exits from the same position on the surface of the n-type semiconductor.

(Embodiment) In FIG. 1, a light emitting diode includes an n-type semiconductor 1,
It has only one pn heterojunction 3 with an n-type semiconductor 2. Further, the n-type semiconductor 1 forms a heterojunction 4,
It consists of two p-type semiconductor layers P1 and P2. The p-type semiconductor layer P2 also serves as an n-type semiconductor substrate. Then, the forbidden band width E is the forbidden band width of the p-type semiconductor layer P1.
, that of the p-type semiconductor layer P2 is EP2, and that of the n-type semiconductor layer 2 is E. As shown in the figure, the relationship is Eゎ>E pl >E P2. Moreover, a p-type semiconductor layer P.

is thinner than the diffusion length of minority carriers injected from the n-type semiconductor 2 to the n-type semiconductor 1. moreover,
A p-type surface electrode 5 is provided on the p-type semiconductor layer P2, and a p-type surface electrode 5 is provided on the p-type semiconductor layer P2.
An n-type point electrode 6 is formed on each side. According to this light emitting diode, the p-type semiconductor layer P
Light λ1 due to □ and light λ2 due to the p-type semiconductor layer P2, which has a different wavelength, are obtained simultaneously and from the same position on the surface of the n-type semiconductor 2.

To explain in more detail, GaAs is used as the p-type semiconductor layer P2 which also serves as the n-type semiconductor substrate, and p-type AI, Gax-, and As (x=0.4) are grown on it by liquid phase epitaxial growth. A p-type semiconductor layer P1 is formed, and on top of that, similarly n-type A IX Ga1-x A
s (x=0.7) by liquid phase epitaxial growth and n
A type semiconductor 2 is formed.

At this time, the thickness of the p-type semiconductor layer P1 is made thinner than the diffusion length of minority carriers injected from the n-type semiconductor 2. Further, a surface electrode 5 made of an Au-Zn alloy is formed on the surface of the p-type semiconductor layer P2 opposite to the surface of the heterojunction 4, and
A point electrode 6 made of an Au-Ge alloy is formed on the surface of the type semiconductor 2 opposite to the surface of the pn heterojunction 3.

In the light emitting diode configured in this way, light with a wavelength of 890 nm is emitted by the p-type semiconductor layer P2, and p-type semiconductor layer P2
Light having a wavelength of 670 nn is generated by the type semiconductor layer P1.

FIG. 3 shows the emission spectrum of the light emitting diode as described above, and by controlling the thickness of the p-type semiconductor layer P1, each wavelength can be adjusted as shown in (a), (b), and (C). can change the ratio of light intensities. That is, if the thickness of the p-type semiconductor layer P1 is increased, the light from the p-type semiconductor layer P1 becomes dominant as shown in (a). Conversely, if the thickness of the p-type semiconductor layer P1 is reduced, the light from the p-type semiconductor layer P2 becomes dominant, as shown in (C). In addition, the third
In the figure, λ on the horizontal axis is wavelength (nm), and I on the vertical axis
is the relative light intensity.

In the light emitting diode of the embodiment shown in FIG. 1, the p-type semiconductor layer P2 also serves as the p-type substrate, but as shown in FIG. The two can also be separated by liquid phase epitaxial growth.

At this time, the n-type semiconductor substrate 7 and the p-type semiconductor layer P2 are
A homozygous 8 is formed. In this way, the crystal quality of the p-type semiconductor layer P2 is improved, and the output is improved.

In the above, we have explained the case where the n-type semiconductor consists of two n-type semiconductor layers, but it is also possible to similarly provide three or more n-type semiconductor layers to obtain three or more types of light with different wavelengths. Needless to say, it can be done.

In addition, although the above description has been made of a light emitting diode having a pn heterojunction made of Ga, Al, and As, other semiconductors that can change the forbidden band width without significantly changing the lattice constant, such as In and A semiconductor made of Ga, As, and P can also be used.

In addition, in this invention, the n-type semiconductor is used for light emission. This is because, in general, in compound semiconductor light emitting diodes, defects that become non-light emitting centers occur in the n-type semiconductor less than in the n-type semiconductor, and the luminous efficiency of the n-type semiconductor is higher than that of the n-type semiconductor. It is. Further, since the diffusion length of minority carriers in an n-type semiconductor is longer than that in an n-type semiconductor, it is easier to control the intensity ratio of each emission wavelength. That is, even if a p-type semiconductor and an n-type semiconductor are configured in the opposite manner to that of the present invention, it is possible to emit light of multiple wavelengths simultaneously, but this invention is not effective in terms of luminous efficiency, controllability of intensity ratio, etc. It is more practical to use this configuration.

(Effects of the Invention) The light emitting diode of the present invention has a layered structure of a plurality of p-type semiconductor layers including a p-type semiconductor forming a pn heterojunction with an n-type semiconductor, and the forbidden band width of each p-type semiconductor layer is n. The total thickness of the p-type semiconductor layer excluding the p-type semiconductor layer located farthest from the n-type semiconductor is calculated as the total thickness of the minority carriers injected from the n-type semiconductor to the p-type semiconductor. Because it is thinner than the diffusion length, multiple lights with different wavelengths can be obtained at the same time and from the same emission position, even though there is only one pn heterojunction. This can prevent inconveniences such as the coupling loss not being the same for each wavelength of light when entering an optical fiber, and the imaging position not being the same for each wavelength when used in a precision optical system. It becomes like this.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing the layer structure and forbidden band width of light emitting diodes of different embodiments of the present invention, and FIG. 3 is a schematic diagram showing the light emitting diode shown in FIGS. 1 and 2. It is a graph showing an emission spectrum by a diode. 1: p-type semiconductor p, : p-type semiconductor layer P2: p-type semiconductor layer 2: n-type semiconductor 3: heterojunction of p-type semiconductor and n-type semiconductor 4: heterojunction of p-type semiconductor 5: surface electrode 6: Point electrode 7: p-type semiconductor substrate 8: p-type semiconductor homojunction E; forbidden band width E;: forbidden band width E9 of n-type semiconductor: forbidden band width Ep2 of p-type semiconductor layer P1: p-type semiconductor layer P2 and the forbidden band width λ of the p-type semiconductor substrate 7 : ■ : Wavelength λ1 : Wavelength λ2 : Wavelength relative light intensity

Claims (1)

[Claims] A light-emitting diode that has a single heterojunction of a p-type semiconductor and an n-type semiconductor, so that light emitted by the p-type semiconductor passes through the n-type semiconductor and is emitted from the surface of the n-type semiconductor. The p-type semiconductor has a layered structure of a plurality of p-type semiconductor layers, two adjacent p-type semiconductor layers form a heterojunction, and the forbidden band width of each p-type semiconductor layer is is larger as it is located closer to the n-type semiconductor side, and
The total thickness of the p-type semiconductor layers excluding the p-type semiconductor layer located farthest from the n-type semiconductor is thinner than the diffusion length of minority carriers injected from the n-type semiconductor to the p-type semiconductor. A light emitting diode featuring