JP2680762B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device such as a visible light emitting diode and a semiconductor laser.

[0002]

2. Description of the Related Art As the visible light emitting diode described above,
Conventionally, the one shown in FIG. 4 is known. This light emitting diode is formed by n-In _1-y (G
a _1-X Al _X ) _y P cladding layer 2, p-In _1-y (Ga _1-X
Al _x ) _y P active layer 3, p-In _1-y (Ga _1-x Al _x ) _y P
A clad layer 4 and a p-Ga _1-x Al _x As current diffusion layer 5 are laminated in this order, an n-type electrode 6 is formed on the entire lower surface of this laminate, and a p-type electrode 7 is formed on a part of the upper surface. ing.

That is, this light emitting diode has a double hetero structure in which both sides of the active layer 3 are sandwiched between the cladding layers 2 and 4 having a high band gap in order to effectively confine injected carriers in the active layer 3. Further, the mixed crystal ratios x and y of the cladding layer 2 are adjusted so as to be lattice-matched with the GaAs substrate 1.

In the light emitting diode having such a structure, the emission wavelength is 590 nm (bandgap Eg = 2.1 eV) when the Al mixed crystal ratio x of the active layer 3 is, for example, 0.3.
become. Further, the Al mixed crystal ratio x of the cladding layers 2 and 4 is set to 0.7 (Eg = 2.
When set to 3 eV), a light emitting diode (LED) with high efficiency and high brightness can be obtained.

FIG. 2 is a diagram showing the relationship between the band gap (vertical axis) and the lattice constant (horizontal axis). In the figure, points A, B and C indicate the lattice constant and the band gap in AlP, GaP and InP, respectively. The polygonal line connecting AC is a line showing the relationship between the band gap and the lattice constant when the mixed crystal ratio x of In _{1 -X} Al _X P, which is a ternary mixed crystal semiconductor, is changed, and
Polygonal line connecting -C are ternary mixed crystal semiconductor Ga _y an In
It is a line showing the relation between the band gap and the lattice constant when the mixed crystal ratio y of _1- yP is changed. The part encircled by a line A-B-C, a four-component mixed crystal semiconductor _{In 1-y (Ga 1-} X A
The relationship between the band gap and the lattice constant when the Al mixed crystal ratio and the Ga mixed crystal ratio of l _x ) _y are changed is shown. In the figure, the part surrounded by a broken line indicates that the quaternary mixed crystal semiconductor is an indirect transition region, and the shaded part surrounded by a solid line indicates that the quaternary mixed crystal semiconductor is a direct transition region. ing.

The band gap and lattice constant of each layer in the conventional light emitting diode shown in FIG. 4 will be described below with reference to FIG. The clad layer 2 provided on the GaAs substrate 1 at the point D has a bandgap of 2.3 eV and an In _1-y (Ga _1-X Al _X on the F point having the same lattice constant as the D point of the GaAs substrate 1). ) _Y P (x = 0.1
5, y = 0.51) is generally selected. In addition, the active layer 3 has the same lattice constant as that of the F point and a band gap of In _1-y (Ga _{1 -X} A on the E point lower by 0.2 eV than the F point).
l _X ) _y P (X = 0.07, y = 0.51) is generally selected. The band gap and lattice constant of this active layer 3 are
In order to achieve high brightness and high efficiency, the values that can directly enter the transition region are taken into consideration.

In the conventional light emitting diode having such a structure, since the active layer 3 is a direct transition type semiconductor, the light emitting efficiency and the internal quantum efficiency can be increased. But G
The absorption edge of the aAs substrate 1 is 1.42 eV (wavelength is 0.87
μm), the light emitted to the substrate side out of the light emitted from the active layer 3 is absorbed by the GaAs substrate 1,
There is a problem that the external quantum efficiency drops by about half.

As a conventional light emitting diode, the one shown in FIG. 5 is known. In this light emitting diode, the laminated body portion is formed on a n-GaP substrate 8 made of a GaP (absorption edge is 2.26 eV; wavelength is 0.55 μm) crystal.
After growing the lattice relaxation layer 9 in which the mixed crystal ratio y of In _1-y Ga _y P is changed stepwise so as to be lattice-matched, the n-InGaP layer 10 and the p-InGaP layer 11 each having a fixed lattice constant are grown.
Are formed in this order to have a light emitting layer of a pn junction. Therefore, in the light-emitting diode having this structure, the InGaP pn junction is provided, and the n-GaP substrate 8 is transparent at an emission wavelength of 565 nm to 650 nm, so that the external quantum efficiency can be increased.

However, in order to obtain a higher external quantum efficiency, when forming the above-mentioned InGaP-based double heterostructure on the GaP substrate 8, if the In mixed crystal ratio is increased, as understood from FIG. , The position of the corresponding point is B
Since the band gap is lowered by moving in the direction of B → C on the −C line and the lattice constant is increased, a pn junction having good crystallinity cannot be obtained. Also, 550 to 570
The active layer that emits light in the short wavelength band of nm (2.25 to 2.18 eV) has a drawback in that there is no means for forming a clad layer that sufficiently blocks carriers.

[0010]

As described above, in the conventional visible light emitting diode, if the GaAs substrate is used, the light emitted from the active layer is absorbed by the substrate, and the external quantum efficiency is deteriorated. In a light emitting diode in which an In _1-y Ga _y P lattice relaxation layer is grown on a GaP substrate that is transparent at a wavelength of 0.55 μm or more, and a pn junction of InGaP is formed, the absorption edge of the substrate is 2. Since it is relatively high at 26 eV, there is almost no light absorption by the substrate, but homo pn
Since it is a junction, there is a problem that the injected carrier density does not increase, the absorption loss of emitted light increases, and the internal quantum efficiency does not increase.

The present invention has been made to solve the above problems, and the emitted light is not absorbed by the substrate,
Moreover, it is an object of the present invention to provide a semiconductor light emitting device capable of increasing carrier density by a heterojunction to reduce absorption loss of light and thereby generating light of high brightness and short wavelength.

[0012]

A semiconductor light emitting device of the present invention comprises a GaP substrate and In _{1- x} in steps on the GaP substrate.
A lattice relaxation layer formed by changing the mixed crystal ratio x of Al _x P;
A plurality of layers formed on the lattice relaxation layer, the plurality of layers being in a state in which the lowermost layer is lattice-matched with the uppermost portion of the lattice relaxation layer, and the In _1-X Al _X P layer and the In _1-y (Ga _1-X A
Since it contains the l _x ) _y P layer, the above-mentioned object can be achieved thereby.

[0013] The plurality of layers, the In _1-X Al X P layer to the top and lattice matching of the lattice relaxation layer, the In _1-x Al x bandgap than P layer less In _1-y (Ga _{1- X} Al _X ) _y P
It is also possible to have a double heterostructure consisting of a layer and an In _1-x Al _x P layer.

[0014]

In the present invention, since the GaP substrate is used, light absorption can be suppressed. In _1-X A on the GaP substrate
Since the l _x P layer is used as the lattice relaxation layer, as shown in FIG. 2, In _{1 -y} (Ga _{1 -x} Al) which is a direct transition region is formed.
_It is possible to form an active layer in ( _X ) _y P (hatched area in FIG. 2) and to form a double hetero structure or a single hetero structure capable of emitting light with high efficiency and high brightness.

[0015]

1 is a cross-sectional view showing a light emitting diode to which the present invention is applied. The light-emitting diode, on the n-GaP substrate 8, lattice relaxation layer 1 made of _{n-In 1-y Al y} P
_{2, n-In 1-y} Al y lower clad layer 13 made of P,
An active layer 14 made of p-In _1-y (Ga _1-x Al _x ) _y P and an upper clad layer 15 made of p-In _1-y Al _y P are formed in this order, and the entire lower surface of this laminated body is formed. An n-type electrode 6 is formed on the upper part of the upper surface, and a p-type electrode 7 is formed on part of the upper surface.

Next, a method of manufacturing such a light emitting diode will be described. The growth method is MOCVD (Metal Organ).
ic Vapor Deposition) method was used.

[0017] First, on n-GaP substrate 8 as shown in FIG. 1, to grow the _{n-In 1-y Al y} P lattice relaxation layer 12.
At this time, the substrate 8 is a substrate having a plane orientation of (100), or 0 to 10 ° off in which doping is easy.
It is preferable to use a substrate (<011> direction). Also,
The mixed crystal ratio y of Al is 1.0, for example, immediately after the start of growth.
And gradually decrease as the growth of the lattice relaxation layer 12 progresses. How to reduce it is shown in Figure 3.
As shown in FIG. 3A, the ratio of AlP to InP is continuously decreased, or as shown in FIG. 3B, the ratio is decreased discontinuously. The thickness of the lattice relaxation layer 12 is, eg, 1-20 μm. In addition, the lattice relaxation layer 12
The uppermost Al mixed crystal ratio y is, for example, 0.78 to 0.75.
Choose

Next, the same Al mixed crystal ratio y = 0.78-0.
75 2 The n-In _1-y Al y lower clad layer 13 of P in
Grow 5 μm. The lower clad layer 13 has a lattice constant of 5.55 angstroms, and the lattice constant difference is 0.1 angstrom with respect to the lattice constant 5.45 angstroms of the GaP substrate 8. It is relaxed by the relaxation layer 12.

Then, on the lower clad layer 13, p-
In _1-y (Ga _1-x Al _x ) _y P (x = 0.02, y = 0.
The active layer 14 of 70) is grown.

Next, on the active layer 14, p-In having the same mixed crystal ratio y = 0.78 to 0.75 as that of the lower cladding layer 13 is formed.
5~15μm upper clad layer 15 made of _1-y Al y P
Let it grow. At this time, InAlP having a high Al mixed crystal ratio y
P-type heavy doping of the layer is very difficult, so p
The growth is made as thick as possible so that the injection current from the side electrode 7 is easily diffused. For _{example, p-In 1-y Al} y P (y
= 0.75), the dopant concentration of the cladding layer is 5
When the ^density is × 10 ¹⁷ cm ^-3, the film thickness is set to 15 to 20 μm in order to sufficiently diffuse holes in the active layer 14.

Therefore, in the light emitting diode of the present invention having such a configuration, In is formed on the GaP substrate 8.
_{By using the 1-X} Al _X P layer as the lattice relaxation layer 12, In, which is the direct transition region of the hatched portion in FIG.
_The active layer 14 can be formed of _1-y (Ga _1-x Al _x ) _y P. That is, in the lattice relaxation layer 12, as shown in FIG. 2, the lower / upper clad layer 1 extends from the point A along the line A-C in the direction C.
Move to point G at points 3 and 15. The active layer 14 has the same lattice constant and is located on the H point where the band cap is lower than the G point, and the H point exists in the direct transition region of the hatched portion.
Further, since a double hetero structure capable of emitting light with high efficiency and high brightness can be formed, it is possible to increase the carrier density and reduce the absorption loss of light, thereby generating light with high brightness and a short wavelength. .

In the present invention, a similar effect can be obtained even if the p-GaP substrate is used instead of the n-GaP substrate 8 and the doping of each layer in the embodiment of FIG. 1 is reversed. Nor. In this case, the upper clad layer 15 is nI
It becomes an nAlP layer and can be easily doped at a high concentration. Moreover, since the diffusion length of electrons is longer than the diffusion length of holes, the thickness of the upper cladding layer 15 may be thin. For example, when the dopant concentration is 1 × 10 ¹⁸ cm ⁻³ , there is no problem even if the thickness of the upper cladding layer 15 is 5 to 6 μm.

Although the present invention is applied to the light emitting diode having the double hetero structure in the above-mentioned embodiments, the present invention is not limited to this, and can be applied to the light emitting diode having the single hetero structure. In that case, a lattice relaxation layer in which the mixed crystal ratio is gradually changed is formed on the GaP substrate, and the ternary mixed semiconductor is formed on the lattice relaxation layer in a lattice match with the uppermost portion of the lattice relaxation layer. A certain In _1-X Al _X P crystal layer is formed, and In _1-y (Ga _{1 -X),} which is a quaternary mixed crystal semiconductor, is formed thereon.
An Al _x ) _yP crystal layer may be formed. In the case of this configuration, since a GaP substrate that can shorten the emission wavelength is used as the substrate, there is an advantage that higher-luminance light emission can be performed as compared with the conventional example shown in FIG.

Although MOCVD is used as the epitaxial growth method in this embodiment, other methods such as molecular beam epitaxy (MBE), ALE (atomic layer epitaxy) or CBE (actinic ray epitaxy) may be used. You can also

Regarding the light-emitting diode manufactured according to the present invention, when the emission wavelength is 560 nm and the external quantum efficiency is 6% or more, when the resin is molded to a diameter of 5 mmφ, the driving current is 10 mA as the brightness at 20 mA.
We were able to achieve a high brightness of candela.

Although the above description applies to a light emitting diode, it goes without saying that the present invention can be similarly applied to a semiconductor laser or the like.

[0027]

According to the present invention, since the GaP substrate is used, the absorption of light can be suppressed. In addition, I on the GaP substrate
Since the n _1-X Al _X P layer is used as the lattice relaxation layer,
It is possible to form an active layer of In _1-y (Ga _1-x Al _x ) _y P which is a direct transition region, and to form a double hetero structure or a single hetero structure capable of emitting light with high efficiency and high brightness. This makes it possible to provide a semiconductor light emitting device having a high brightness and a short wavelength.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a light emitting diode which is an embodiment of the present invention.

FIG. 2 is a diagram showing a band cap, a lattice constant, and an emission wavelength.

FIG. 3 is a diagram showing a method for forming a lattice relaxation layer.

FIG. 4 is a sectional view showing a conventional light emitting diode.

FIG. 5 is a cross-sectional view showing another conventional light emitting diode.

[Explanation of symbols]

 6 Lower Electrode 7 Upper Electrode 8 n-GaP Substrate 12 Lattice Relaxation Layer 13 Lower Clad Layer 14 Active Layer 15 Upper Clad Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Matsumoto 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Tadashi Takeoka 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Sharp Corporation (72) Inventor Masaki Kondo 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Prefecture Sharp Corporation (72) Inventor Osamu Yamamoto 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (72) Inventor Saburo Yamamoto 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture (56) References JP-A-1-296677 (JP, A) JP-A-1-243482 (JP, A) JP-A-49-5585 (JP, A) JP 61-102786 (JP, A) JP 3-283675 (JP, A)

Claims (2)

(57) [Claims] 1. A GaP substrate, a lattice relaxation layer formed on the GaP substrate by gradually changing a mixed crystal ratio x of In _1-x Al _x P, and a lattice relaxation layer formed on the lattice relaxation layer. Consists of multiple layers,
The plurality of layers are in a state in which the lowermost layer is lattice-matched with the uppermost portion of the lattice relaxation layer, and the In _1-X Al _X P layer and the In layer are formed.
A semiconductor light emitting device including a _1-y (Ga _{1 -X} Al _X ) _y P layer. Wherein said plurality of layers, the In _1-X Al _X P layer to the top and lattice matching of the lattice relaxation layer, the In _1-x Al _x bandgap than P layer less In _1-y (Ga _1-X Al _X ) _y P
The semiconductor light emitting device according to claim 1, which has a double hetero structure including a layer and an In _1-x Al _x P layer.