JP2662792B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a light-emitting diode (LED), a semiconductor laser (LD), etc. composed of a GaInP-based mixed crystal which is a direct transition type III-V-based mixed crystal. A semiconductor light emitting device.

[Related Art 1] [Al _y Ga _1-y ] _x In which is a quaternary compound semiconductor material
FIG. 4 shows the dependence of the band gap and lattice constant of _1- xP on x and y. This system has the largest direct transition band gap in III-V compound semiconductor mixed crystals excluding nitrides, and is the most advantageous material for shortening the wavelength from green to orange as well as red wavelength. Used as a material for red LEDs and LDs. These LEDs and LDs are composed of GaInP and AlGaInP mixed crystal layers having the same lattice constant as GaAs which is a high-quality substrate crystal.

That is, without providing the composition gradient layer on the substrate,
AlGaInP cladding layer and GaInP or AlGaInP on As substrate
It is produced by directly growing an active layer. In this system, [Al _y Ga _1-y ] _x In _1-x P (0 ≦ y <1, x = 0.51) is GaAs
And an active layer having a composition of, for example, y = 0 and y
A red light-emitting device having a heterostructure with a cladding layer having a composition of = 0.5 can be obtained. A yellow light-emitting element is also obtained by appropriately selecting the value of y in the active layer. In addition, a light emitting element having an emission wavelength of 550 nm is theoretically possible. Referring to FIG. 4, on the GaAs substrate, [Al
_y Ga _1-y ] _0.51 In _0.49 P (0 <y <1) for the cladding layer,
It has been developed as a red light emitting device with a double hetero structure using Ga _0.51 In _0.49 P as the active layer. By increasing the Al mixed crystal ratio of the active layer on this line, a light emitting device with a shorter wavelength can be obtained. is there.

[Problem 1 to be Solved by the Invention] By the way, when a binary compound GaAs is used as a substrate crystal, GaAs has a band gap of 1.42 eV and has a large light absorption coefficient for light having a wavelength shorter than 870 nm. Have. Therefore, in the case of a visible light emitting element, there is no problem in the so-called edge emission type which emits light in parallel with the active layer. The absorption of light into the GaAs substrate becomes a problem. In other words, it is impossible to extract light from the GaAs substrate side due to good thermal radiation junction-down, and even if mounting is done with the substrate side down, it is possible to prevent high brightness due to the absorption effect of the substrate. Because it becomes. In other words, there is a limitation in the direction in which light of the LED or LD which is the final element is extracted, and there is a problem that there is a great restriction in the design of the element.

It is also desirable that the substrate be a large-area and high-quality crystal and have the same crystal structure as the mixed crystal epitaxial thin film. Therefore, III-V group compound AlGaInP
For mixed crystal epitaxial growth, GaP which is the same III-V binary compound is selected as the substrate crystal. GaP
Has a wide band gap of 2.26 eV, unlike GaAs,
In an element that is transparent to light having a wavelength longer than 0 nm and uses GaP as a substrate, light emission can be extracted from the substrate side, and a junction down advantageous for heat dissipation can be achieved. Further, since GaP is transparent even when the substrate side is down, light emitted to the substrate side can also be extracted to the upper side. As described above, light can be emitted in an arbitrary direction, and a great degree of freedom can be obtained for the design of the light emitting element, and heat generated in the active layer can be efficiently dissipated.

Despite such great advantages, a light-emitting device composed of an AlGaInP-based mixed crystal using a GaP substrate has not been developed so far because of a mismatch between the lattice constants of GaP and AlGaInP. This is because it was considered impossible to epitaxially grow the transition type AlGaInP directly on the GaP substrate due to (mismatch). As described above, in order to obtain a high-quality epitaxial thin film of a mixed crystal, a substrate matching the lattice constant of the mixed crystal is required. Unless lattice matching is achieved, a mixed crystal thin film having a desired composition is obtained. It cannot be formed.

Further, in the AlGaInP-based light emitting device, 630 to 550 nm
In order to shorten the wavelength to the region of
l It is necessary to increase the content. However, because Al is easily oxidized, the progress of element deterioration is accelerated when the Al content increases,
Since the device lacks stability and reliability, it is generally preferable that the active layer contains as little Al as possible, that is, GaInP.

Accordingly, it is an object of the present invention to provide a semiconductor light emitting device having a single hetero structure or a double hetero structure using a GaP substrate and using AlGaInP containing Al or GaInP not containing Al as an active layer on a GaP substrate. It is in.

[Problem 2 to be Solved by the Invention] As described in the problem 1, the AlGaInP active layer containing Al has a high performance as an element from the viewpoint of easy oxidation of Al, thermal conductivity, mobility and the like. Performance and reliability.
It is preferable that the Al concentration of the GaInP active layer be as low as possible.

In addition, a light emitting device provided with a GaInP active layer on a GaAs substrate,
Its emission wavelength is red at 650-700nm, other wavelengths,
For example, in a light emitting element of 550 to 630 nm (green to orange), it is inevitable that Al is contained in a light emitting region, and it is difficult to avoid the above-mentioned problems. However, if a substrate having a lattice constant between the lattice constant of GaAs and the lattice constant of GaP can be prepared, a mixed crystal having a bandgap equivalent to 550 to 630 nm can be obtained with a composition having a small mixed crystal ratio of AlP. Although this is clear from FIG. 4, a mixed crystal having this region composition has not been used because a substrate of such a high quality having a lattice constant cannot be supplied until now.

Accordingly, an object of the present invention is to provide an AlGaInP or G substrate grown on a substrate having a lattice constant smaller than that of GaAs and larger than that of GaP.
An object of the present invention is to provide a semiconductor light emitting device having an aInP active layer, in particular, a semiconductor light emitting device that emits light of a short wavelength of green to orange of 550 to 630 nm.

[Prior art 2] As described in [Prior art 1], AlGa on a GaAs substrate is used.
Red LDs with grown InP active layers are well known,
AlGaInP mixed crystal epitaxially grown on aAs substrate is GaAs
Are lattice matched with each other, and the lattice constants of both are completely matched. In other words, when AlGaInP is epitaxially grown on a GaAs substrate, [Al _y Ga _1-y ] _x In _1-x
Only x = 0.51 for P, that is, a mixed crystal on the lattice matching line with GaAs can be obtained. The problems associated with shortening the wavelength from green to orange are as described above.

As a solution to this problem, the lattice constant
It has been described that by preparing a substrate smaller than GaAs and larger than GaP, a light emitting region with a low AlP mixed crystal ratio and a wide band gap can be formed. As a conventional technique for obtaining a substrate having the desired lattice constant, there is a GaAs substrate. Ga _x I
The lattice constants and band gaps of n _1-x P and GaP _y As _1-y are as follows: a (X) = 5.4512X + 5.8688 (1-X) [Å] (1) E _g (X) = 1.351 + 0.643X + 0 .768X ² [eV at300K]
(2) is given by a (Y) = 5.4512Y + 5.6533 (1-Y) [Å] _{(3) E g (Y)} = 1.424 + 1.15Y + 0.176Y 2 [eV At300K] (4). For example, Ga _x In _1-x P is 570nm (2.175e
V) To obtain a substantial active region composition, from (2)
X = 0.694 and Y = 0.368 from (1) = (3). That is, sequentially changing the composition of the GaP _y As _1-y on GaP or GaAs substrates grown, finally GaP _0.368 As _0.632
If a GaPAs substrate having the following composition is prepared, Ga _0.694 In _0.306 P
Growth is possible. An example is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-11 / 1987.
No. 9984.

[Problem 3 to be Solved by the Invention] In the above example, E _g = 1.871 eV from (4), and G
It is understood that the aPAs composition gradient layer absorbs light of 570 nm.
That is, in GaPAs, the substrate having a lattice constant between GaAs and GaP becomes smaller than the band gap of the lattice-matched GaInP system,
There is exactly the same problem as problem 1.

Accordingly, an object of the present invention is to provide a semiconductor light emitting device having a material composition in which the band gap of a composition gradient layer formed on a GaP substrate and changed in composition to a target lattice constant is equal to or larger than the band gap of an active layer. Is to provide.

[Problem 4 to be Solved by the Invention] The above-mentioned GaPAs substrate is usually produced by vapor phase growth,
It becomes a surface morphology of a unique cross hatch pattern,
Even if a multilayer film is formed thereon, the surface morphology is hardly improved, and a flat interface cannot be obtained. In addition, there are many misfit dislocations, which significantly reduce the performance and reliability of edge-emitting LEDs and LDs.

Accordingly, an object of the present invention is to provide a semiconductor light emitting device having an AlGaInP-based multilayer film having good surface morphology and few dislocations even on a GaP substrate even if the lattice constant is different from that of GaP. .

[Means for Solving Problems 1 to 4] In order to achieve the objects for the above problems 1 to 4, in the semiconductor light emitting device of the present invention, the band gap between the GaP substrate and the light emitting region provided on the GaP substrate is not less than A strained superlattice made of a material having a band gap of, and a multilayer provided on the strained superlattice, wherein the multilayer has an AlGaInP active layer containing Al or a GaInP active layer not containing Al and an AlGaInP cladding layer. Things.

In the semiconductor light emitting device for the objects 1 to 4 of the present invention, 55
By providing a strained superlattice made of a material having a band gap equal to or greater than the band gap of the light emitting region on a GaP substrate that is transparent to light having a wavelength longer than 0 nm, lattice matching with GaAs has conventionally been achieved on a GaAs substrate. Only the mixed crystal of the condition grows and GaP
AlGaInP-based mixed crystals, which could not be grown on a substrate, can now be epitaxially grown on a GaP substrate, realizing a high-brightness LED. In other words, not only a composition mixed crystal under lattice matching conditions with respect to a GaAs substrate crystal but also a composition mixed crystal out of the matching conditions is epitaxially grown and can be used as a material for a semiconductor light emitting device.
In addition, when this method is applied to a GaAs substrate, there is no problem with an edge-emitting device, and as described above, it is possible to obtain a mixed crystal with a low AlP mixed crystal ratio and a short wavelength (550 to 630 nm) light emitting device. Needless to say.

Thus, strained superlattices have several types of
It has a structure in which five or more layers of 000 ° epitaxially grown thin films are alternately grown, and a strain field due to a difference in lattice constant exists at the hetero interface. At present, much research on this strained superlattice has been made in GaAs growth on a Si substrate. That is, it is an effective means for epitaxially growing crystals having different lattice constants of the substrate. This is based on the fact that when the epitaxially grown thin film is very thin, misfit dislocations are unlikely to enter, and that the strain field at the interface has the effect of stopping the propagation of dislocations.

In the present invention, it is possible to grow a target GaInP mixed crystal on GaP by using a strained superlattice at least including an AlInP / GaP structure on a GaP substrate. In other words, a substrate having a lattice constant smaller than that of GaAs and larger than that of GaP could be manufactured. At this time, the target GaIn
It is important to set the strained superlattice with a material having a band gap equal to or larger than the band gap of P mixed crystal. Therefore, Zn
II-VI materials such as Se may be used.

A semiconductor light emitting device using a GaP substrate has multiple layers,
This multilayer comprises an AlGaInP cladding layer, a GaInP active layer and an AlGaInP
It has a double hetero structure composed of a P clad layer or a single hetero structure composed of a GaInP active layer and an AlGaInP clad layer.

The material used for the semiconductor light emitting device of the present invention is most suitable for an LED or LD, and any structure of a double hetero junction or a single hetero junction is suitable as an LED or LD material. A pn junction may be formed at the hetero junction to form a surface emitting device, or a normal LD shape.
Alternatively, a multi-layered dopant of different conductivity type may be selectively diffused, and a light emitting region may be formed by the diffusion region and the GaInP active layer to form an LED or LD. It is convenient because the current injection efficiency can be improved, the emission luminance can be increased, and high-speed modulation can be obtained. The diffusion dopant depends on the conductivity type of the GaInP active layer, such as S, Si, Te, Se for the donor, and Ge, Cd, or the like for the acceptor.
Examples include Mg, Be, and Zn.

〔Example〕

Hereinafter, a semiconductor light emitting device of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a basic structure of a double hetero structure using a GaP substrate 1. This structure has a multilayer structure in which a strained superlattice layer 2 is formed on a GaP substrate 1 and a double hetero junction is formed on the strained superlattice layer 2. That is, the AlGaInP cladding layer 3 and the Al-free GaI
The nP active layer 4 and the AlGaInP cladding layer 5 are sequentially grown epitaxially.

This structure is characterized in that the GaInP active layer 4 is grown on the GaP substrate 1, but as described above,
Is provided with a strained superlattice layer 2 made of a material having a band gap equal to or larger than the band gap of the light emitting region.
The GaInP active layer 4 can be formed on the P substrate 1,
It is also possible to use AlGaInP containing Al as the active layer. In particular, since the GaInP active layer 4 does not contain Al, the stability and reliability of the device are greatly improved. GaP substrate 1
In addition, the strained superlattice layer 2 made of a material having a band gap equal to or larger than the band gap of the light emitting region is transparent to the light emitted from the GaInP active layer 4, and the GaP substrate 1 has high heat conductivity and heat dissipation. Since it is excellent, there is no limitation on the direction in which light is emitted when the device is used. In addition, the design for device formation is free, and heat generated in the GaInP active layer 4 is efficiently dissipated. When used as a surface-emitting LED, the external quantum efficiency was greatly improved.

In the case of manufacturing a green LED, for example, in the light emitting device using the GaP substrate, as shown in FIG. 2, a structure similar to a normal double heterostructure high-brightness LED may be used.
The band gap of the aInP active layer 4 may be set to 2.23 eV, and the band gap of the AlGaInP cladding layers 3 and 5 may be set to 2.4 eV. As shown in FIG. 3, a dopant of a conductivity type different from that of the constituent multilayers (that is, a donor of the GaInP active layer 4 is a donor of a p-type and an acceptor of an n-type of the n-type is diffused) to diffuse the diffusion regions DR and GaInP. The light emitting region AR may be formed by the active layer 4 and the p-side electrode material and the n-side electrode materials E1 and E2 may be provided by means such as vacuum evaporation. Light may be extracted from the end face or from the plane. In order to manufacture an LD having a short wavelength, a stripe-shaped active region may be formed into a resonator structure by further cleaving both ends of the material. In the light-emitting device having the structure shown in FIG. 2, the light is not absorbed by the GaP substrate 1 so that a reflection plate made of SiO ₂ is provided, and the light is taken out in any direction by preventing the light from being reflected. Since the device can emit light, there is a great degree of freedom in element design. In addition, Ga containing no Al
Since InP can be used as the active layer, the reliability of the light emitting element is high. Further, since the GaP substrate 1 is excellent in heat radiation, heat is radiated from the GaInP active layer 4 well. Even in a light emitting device having the structure shown in FIG. 3, since GaInP containing no Al is used as an active layer, high stability and high reliability can be guaranteed especially in the case of an LD, and it can be applied to a wide variety of applications.

An LD having a structure as shown in FIG. 3 is made of GaInP (or AlGaI).
In order to take advantage of the property that nP) has the largest direct transition bandgap and is most advantageous for shortening the wavelength, a short wavelength in the visible region from green to orange is obtained, and the density of high-disk memory and video disks is increased. This is a useful tool that holds the key to high performance of an optical information processing system such as high speed of a laser printer. In addition, green to orange visible light LDs have a potential for new applications not found in conventional LDs that oscillate in the infrared region as small, lightweight light sources that emit visible coherent light.

Next, GaP, which has obtained many advantages as described above,
An example of a method for forming the strained superlattice layer 2 on the substrate 1 will be described below.

First, p-type GaP is grown to 1 μm on a (100) p-type GaP substrate, which is 2 ° off in the <011> direction, by a normal reduced pressure MOVPE technique, and then 0.1 μm of p-type Al _0.73 In _0.27 P and p-type GaP is alternately grown by 10 layers, and then P-type [Al _0.7 Ga _0.3 ] _0.73
In _0.27 P was grown at 1 μm. This is a mixed crystal ratio when a green light-emitting element is aimed at. Needless to say, the mixed crystal ratio is selected at a desired emission wavelength.

After the formation of the strained superlattice layer 2 on the GaP substrate 1 as described above, metal organic chemical vapor deposition (MOVPE), molecular beam epitaxy (MBE), or liquid phase epitaxy (L
If the AlGaInP cladding layer 3, the GaInP active layer 4 and the AlGaInP cladding layer 5 constituting a multilayer by PE) or the like are epitaxially grown on the strained superlattice layer 2 in order, the semiconductor light emitting device having the structure shown in FIG. 1 is manufactured. . More preferably, a method of growing a multilayer including an active region continuously from the strained superlattice by MOVPE is preferable.

〔The invention's effect〕

Since the semiconductor light emitting device of the present invention is configured as described above, the following advantages can be obtained.

By providing a strained superlattice made of a material having a band gap equal to or larger than the band gap of the light emitting region on a GaP substrate, 1.
Al containing Al with a band gap of 55 eV to 2.25 eV
Since an active layer of GaInP mixed crystal, preferably an active layer of GaInp mixed crystal containing no Al can be grown, if the GaInP active layer is formed, the light emitting element has excellent reliability, and furthermore, a GaP substrate is used. There is no restriction on the direction in which light emission is taken out, the degree of freedom for light emitting element design is large, and heat radiation is excellent.

In a semiconductor light emitting device using a GaP substrate, pn is controlled by dopant control during crystal growth or by diffusion.
By forming a junction and providing a p-side electrode and an n-side electrode, an LED having a green to orange short wavelength band can be easily obtained.
In addition, for example, by forming a resonator by cleaving a constituent material as shown in FIG. 3 or the like, a visible light LD particularly in a short wavelength band can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a basic structure of a semiconductor light emitting device of the present invention, FIG. 2 is a sectional view of an example of a light emitting element using the structure of FIG. 1, and FIG. 3 uses the structure of FIG. FIG. 4 is a cross-sectional view of another example of the light-emitting element, showing the composition dependence of the band gap and the lattice constant. 1: GaP substrate 2: Strained superlattice layer 3,5: AlGaInP cladding layer 4: GaInP active layer DR: Diffusion area AR: Emission area E1, E2: Electrode

Claims (3)

(57) [Claims] 1. A strained superlattice comprising a GaP substrate, a strained superlattice made of a material having a bandgap equal to or larger than a bandgap of a light emitting region provided on the GaP substrate, and a multilayer provided on the strained superlattice, wherein the multilayer is made of Al. Containing AlGaInP or not containing GaI
A semiconductor light emitting device comprising an nP active layer and an AlGaInP cladding layer. 2. An AlGaInP structure in which a plurality of layers are sequentially formed on a strained superlattice.
Al with cladding layer and band gap smaller than cladding layer
2. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device has at least a double hetero structure including a GaInP or GaInP active layer and an AlGaInP cladding layer. 3. The semiconductor device according to claim 1, wherein the multilayer has at least a single heterostructure composed of an AlGaInP or GaInP active layer and an AlGaInP cladding layer in which a band gap formed on the strained superlattice is smaller than the cladding layer. Semiconductor light emitting device.