JP2001015798A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a InGaAlP system semiconductor light emitting device, which has characteristics which could not be obtained by using a conventional GaAs substrate, and further is improved in the aspect of environmental protection. SOLUTION: By using a germanium substrate 1 instead of a GaAs substrate, the difference in thermal expansion coefficient between the substrate 1 and InGaAlP system semiconductor can be reduced, and further, thermal stability at a high temperature can be improved significantly. As a result, the light emitting characteristics and reliability of a semiconductor light emitting device can be improved, in comparison with those of a conventional light emitting device. Furthermore, if a p-type substrate is used, a resistance can be made lower than the resistance of the conventional light emitting device, and flexibility of design of a light emitting device can be expanded significantly. It is also advantageous a point in comparison with the conventional light emitting device in that the content of arsenic (As) can be reduced dramatically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor light emitting device. More specifically, the present invention relates to germanium (G
e) LED using InGaAlP formed on substrate
(Light emitting diode) and LD (la
The present invention relates to a light emitting device such as a ser diode (semiconductor laser), which relates to a semiconductor light emitting device that emits light of red, light, yellow, yellow-green, green, or the like having various characteristics that cannot be obtained by a device formed on a conventional GaAs substrate.

[0002]

2. Description of the Related Art Semiconductor light-emitting elements have many advantages such as compactness, low power consumption, and excellent reliability. In recent years, indoor and outdoor display boards and railway / traffic which require high light emission luminance are required. It is also being widely applied to traffic lights and vehicle lighting. Further, it is being widely used as a light source for various types of optical communication using an optical fiber or the like as a medium. In particular, a light emitting layer using an InGaAlP-based material, which is a quaternary compound semiconductor, can emit light in a wide wavelength band from red to green by adjusting the composition.

[0003] In this specification, "InGaAlP"
"System" means the composition formula ln_xGa_yAl _1-xyIn P
The composition ratios x and y are 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, provided that
Semiconductor of any composition changed within the range of (x + y) ≦ 1
Shall include the body. That is, InGaP, InAl
Mixed crystal system such as P, InGaAlP, GaP, GaAlP
Are also included in the “InGaAlP system”. Further
Contains arsenic (As) in addition to phosphorus (P) as a group V element.
It also includes the mixed crystal that it has.

Conventionally, a substrate of an InGaAlP-based light emitting diode (LED) has a silicon (Si) impurity.
It has been common to use an n-type GaAs substrate using.

FIG. 9 is a schematic sectional view showing a conventional InGaAlP-based semiconductor light emitting device.

That is, the light emitting device 100 shown in FIG.
Are formed on an n-type GaAs substrate 104, an n-type GaAs buffer layer 115, an n-type InAlP clad layer 106,
GaAlP active layer 105, p-type InAlP cladding layer 1
03, a current block layer 107 and a p-type GaAlAs current diffusion layer 118 are sequentially stacked.
And an n-side electrode 110 are formed. Each semiconductor layer 1
04 to 118 are, for example, metal organic chemical vapor deposition (M
It is epitaxially grown by the OCVD method.

[0007]

However, since the conventional semiconductor light emitting device as illustrated in FIG. 9 uses a GaAs substrate, it is necessary to design the device in accordance with the physical properties of the GaAs substrate. The degree of freedom was not always sufficient. At the same time, the characteristics of the light emitting element are also determined by the physical properties of the GaAs substrate, so that it cannot be said that various requirements can be sufficiently satisfied.

Further, in recent years, environmental problems on the earth have become more serious, and accompanying this, there has been a rapid rise in awareness of environmental problems around us, especially the problem of garbage. One solution to this problem is "recycling", but not many products can do this. Recycling of semiconductor light emitting devices is not easy and, if possible, has a limited life. The InGaAlP compound constituting a main part of the light emitting element has no particular toxicity.
On the other hand, gallium arsenide (GaAs) used for the substrate
Is not as harmful as arsenic (As) oxide, but it is desirable to reduce its usage in view of its impact on the environment.

As described above, the conventional semiconductor light emitting device uses a GaAs substrate, so that the degree of freedom in device design is not sufficient, the device characteristics are limited, and further improvements are also made in terms of environmental measures. It was desirable.

The present invention has been made based on the recognition of these various problems. That is, the present invention provides a semiconductor light-emitting device having various characteristics that have not been obtained conventionally and using improved germanium (Ge) substrates in place of the conventional GaAs substrate and improved in environmental measures. It is intended to do so.

[0011]

In order to achieve the above object, a semiconductor light emitting device of the present invention comprises a germanium substrate,
And a light-emitting layer made of an InGaAlP-based semiconductor, whereby better light-emitting characteristics and reliability can be obtained than when a conventional GaAs substrate is used.

Alternatively, the semiconductor light emitting device of the present invention has a first
A germanium substrate of a conductivity type, a first cladding layer made of an InGaAlP-based semiconductor of a first conductivity type provided on the germanium substrate, and an InGaAlP-based semiconductor provided on the first cladding layer A light emitting layer, and a second conductivity type InGa provided on the light emitting layer.
And a second clad layer made of an AlP-based semiconductor, whereby better light emitting characteristics and reliability can be obtained as compared with a conventional double hetero light emitting element using a GaAs substrate. .

[0013] Here, a light-transmitting electrode layer provided on the second clad layer is further provided.
A surface-emitting light-emitting element can be obtained.

[0014] Further, a buffer layer provided between the germanium substrate and the first cladding layer and having a bandgap larger than the germanium substrate and smaller than the first cladding layer is further provided. The operation voltage of the device can be reduced by alleviating the discontinuity, and the crystal quality of the epitaxial growth layer can be improved.

Here, as a material of the buffer layer,
It is desirable to use InGaP.

[0016] Further, an intermediate gap layer provided between the germanium substrate and the buffer layer and having a band gap larger than the germanium substrate and smaller than the buffer layer is further provided to further reduce band discontinuity. As a result, the operating voltage of the device can be further reduced, and the crystal quality of the epitaxial growth layer can be further improved.

Here, it is desirable to use GaAs as a material of the intermediate gap layer.

Further, when the first conductivity type is an n-type and the second conductivity type is a p-type, a light-emitting element having good characteristics of an n-down type can be obtained.

On the other hand, the first conductivity type is a p-type and the second conductivity type is an n-type, so that a low-resistance p-down type element which cannot be obtained by a conventional light emitting element using a GaAs substrate. Can be realized.

Further, the germanium substrate has a main surface having a plane orientation inclined from (100) in the range of 2 ° to 16 °, thereby suppressing the generation of anti-phase domains and the Al composition. The emission wavelength can be shortened without positively increasing the emission wavelength. That is, it is possible to achieve both emission luminance and a shorter wavelength.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a conceptual diagram showing a sectional structure of a semiconductor light emitting device according to a first embodiment of the present invention. The light emitting element 10A shown in FIG.
e-substrate (thickness: 250 μm) 1 on a p-type InGaP
Buffer layer (layer thickness: 0.05 μm) 2, p-type InAlP
A structure in which a cladding layer (layer thickness: 0.6 μm) 3, an InGaAlP active layer (layer thickness: 0.6 μm) 5, an n-type InAlP cladding layer (layer thickness: 0.6 μm) 6, and a current block layer 7 are sequentially stacked. Having. Also, on the n side of the element, ITO
A transparent electrode 8 made of (indium tin oxide) is formed, and an n-side electrode 9 is provided at a portion corresponding to the current block layer 7. On the other hand, on the back surface of the Ge substrate 1, a p-side electrode 10 is provided.

Light emitted from the active layer 5 can pass through the transparent electrode 8 and be extracted upward in the figure. The current blocking layer 7 is made of, for example, p-type InAlP, and has a role of preventing current from being injected below the light-shielding metal electrode 9. By providing such a current blocking layer, it is possible to suppress light emission at the lower portion of the metal electrode 9 and improve the efficiency of external emission of light emission from the active layer 5.

The composition of the active layer 5 can be appropriately determined so that the emission wavelength becomes a predetermined color such as red, yellow, yellowish green, or green.

The present embodiment has one feature in that the above-described laminated structure of the light emitting element is formed on the Ge substrate 1. A semiconductor substrate required when forming a light-emitting element using an InGaAlP-based semiconductor includes:
Not everything is good. The conditions include, for example, the following.

(1) The lattice constant is the same as that of the InGaAlP-based semiconductor.

(2) The thermal expansion coefficient is close to that of the InGaAlP-based semiconductor.

(3) No deterioration or alteration at the crystal growth temperature (about 700 ° C.) of the InGaAlP-based semiconductor.

(4) Good conductivity.

The most important conditions among these are the above (1)
"Lattice constant". Compared with a conventionally used gallium arsenide (GaAs) substrate, the lattice constant of gallium arsenide is 0.5653 nm, while the lattice constant of germanium is 0.5657 nm, and both have extremely close values ( Both values are at 300K). Incidentally, the lattice constant of silicon (Si) is 0.1.
5431 nm.

In terms of the crystal structure, gallium arsenide is a zinc blende type while germanium is a diamond type, and both have very similar crystal structures.

On the other hand, comparing the thermal expansion coefficients,
_0.5 Ga _0.5 P 5.24 - whereas a ^{(10 6 K -1),} gallium arsenide 6.40, germanium is 5.7, for the InGaAlP-based semiconductor,
It can be seen that germanium has a coefficient of thermal expansion closer to that of gallium arsenide. Therefore, it is possible to reduce the distortion caused by the difference in the coefficient of thermal expansion during the temperature lowering process after the crystal growth, and to obtain a crystal having better quality than before.

Further, in view of thermal stability, in the case of gallium arsenide, arsenic (As) is easily desorbed from the crystal surface at a temperature of about 300 ° C. or more and becomes unstable. It is necessary to form a controlled atmosphere. On the other hand, germanium is extremely stable even at a high temperature of 700 ° C. or more, and can stably grow a crystal of an InGaAlP-based semiconductor.

As described above, by employing a Ge substrate, it is possible to grow a crystal of higher quality than a conventional light emitting device using a GaAs substrate, thereby improving the light emitting characteristics and reliability of the light emitting device. can do.

Specifically, the LED having the structure shown in FIG.
(Invention) and an LED (Comparative Example) in which the same laminated structure was formed on a GaAs substrate were prototyped, and the characteristics of both were compared. As a result, the emission luminance of the LED of Comparative Example was 8 cd. On the other hand, the emission luminance of the LED of the present invention was 10 cd, and a 25% improvement was obtained.

On the other hand, germanium also has high conductivity. In particular, looking at the drift mobility of holes, the mobility of gallium arsenide is 400 (cm ² / (V · s)), whereas the mobility of holes is 1900 in the case of germanium. high. In other words, in the case of germanium,
A low-resistance p-type substrate can be realized, and the degree of freedom in designing a light-emitting element is greatly increased.

The light emitting device 10A illustrated in FIG. 1 also has a conductivity type opposite to that of the conventional light emitting device illustrated in FIG. 9 and a low resistance by adopting the p-type Ge substrate 1 as the substrate. Element can be easily obtained. That is, by using the p-type substrate, the polarity of the electrode can be inverted, and a new use can be developed.

FIG. 2 is a conceptual diagram showing a schematic configuration of a light emitting device capable of selectively emitting light from a semiconductor light emitting element formed on an n-type substrate and a semiconductor light emitting element formed on a p-type substrate. That is, in the light emitting device 30,
Semiconductor light emitting element A and semiconductor light emitting element B on mounting substrate S
And have been implemented. Here, the semiconductor light emitting element A is an element formed using an n-type substrate, and the semiconductor light emitting element B is an InGaAlP-based light emitting element formed on a p-type Ge substrate as illustrated in FIG. .

The light emitting element A and the light emitting element B are connected in parallel to the power supply V.

In such a light emitting device 30, either the light emitting element A or the light emitting element B can be driven according to the polarity of the current output from the power supply. That is, when a forward current is supplied to the light emitting element A, the light emitting element B
In the opposite direction and does not emit light. Conversely, light emitting element B
When a forward current is supplied to the light emitting element A, the light is emitted in the reverse direction and does not emit light. If the light emitting colors of the light emitting element A and the light emitting element B are changed, two-color light emission becomes possible. As described above, it is possible to selectively drive two types of light emitting elements with a simple configuration.

Here, in the case of a conventional light emitting device using a gallium arsenide substrate, the resistance of the light emitting device tends to be higher when the substrate is p-type than when it is an n-type substrate. As a result, also in the light emitting device 30 as illustrated in FIG. 2, the light emitting elements A and B have different resistance values, and the light emission intensity cannot be balanced only by simply reversing the polarity of the power supply. There was a problem.

On the other hand, according to the present invention, p-type Ge
A light emitting element formed on a substrate has substantially the same resistance as a light emitting element formed on an n-type substrate. As a result, even when the light emitting device 30 as illustrated in FIG. 2 is configured, the two types of light emitting elements can emit light with almost the same light emission intensity simply by inverting the polarity of the power supply. Become.

On the other hand, according to the present invention, by forming a light emitting element on a Ge substrate, an effect that integration with other optical elements and electronic elements can be easily obtained is also obtained. For example,
Monolithically forming a light receiving element such as a photodiode or an avalanche photodiode on a Ge substrate and an InGaAlP-based light emitting element achieves functions such as transmitting and receiving light or monitoring output light with a single integrated element can do.

Further, a driving circuit and a control circuit for a light emitting element such as an InGaAlP LED or LD can be integrated on the same Ge substrate. As a result,
It is possible to realize a high-performance optical functional element which is smaller and lighter than the conventional one.

Further, the semiconductor light emitting device of the present invention is advantageous in that the content of arsenic (As) can be dramatically reduced as compared with a conventional light emitting device using a gallium arsenide substrate. FIG. 3 is a conceptual diagram comparing the structure of the light emitting device of the present invention with that of a conventional light emitting device. In the InGaAlP-based light emitting device, the thickness of the substrate is usually 250 μm or more in many cases. This thickness is determined in terms of ease of wafer handling in the manufacturing process. On the other hand, the total thickness of the laminated portion of the light emitting element is
It is at most about 5 μm. That is, in the InGaAlP-based semiconductor light emitting device, the substrate occupies 98% or more of the whole.

As shown in FIG. 3, in the case of a conventional device using a gallium arsenide substrate, half of the device is occupied by arsenic. That is, the ratio of arsenic is close to 49% of the entire light emitting element.

On the other hand, in the case of the light emitting device of the present invention using a germanium substrate, both the substrate and the laminated portion
Arsenic is not contained at all. That is, it is possible to dramatically reduce the amount of arsenic used, which is advantageous from an environmental point of view.

Next, a method for manufacturing the light emitting device 10A of the present embodiment will be briefly described. In the light emitting element 10A, each of the semiconductor layers 2 to 7 is formed by MOCVD (metal-organic ch
emical vapor deposition (organic metal chemical vapor deposition) method. The temperature for crystal growth by MOCVD is typically about 700 ° C. In the present invention, since a germanium substrate is used, there is no problem of arsenic desorption as in the case of a gallium arsenide substrate. Before the growth of the germanium substrate, it is desirable to raise the temperature to about 1000 ° C. to remove the natural oxide film on the surface.

As a raw material used in the MOCVD method for growing the InGaAlP-based semiconductor layer, for example,
Organic metals such as trimethylgallium (TMG), trimethylaluminum (TMA) and trimethylindium (TMI), arsine (AsH ₃ ), phosphine (PH
₃ ) and the like.

The n-type cladding layer 6 is doped with silicon (Si) as an n-type impurity, and the buffer layer 2 and the p-type cladding layer 3 are zinc (Zn), magnesium (Mg) or carbon (C) as p-type impurities. Doping). As a raw material of each impurity such as silicon, zinc, and carbon, for example, silane (SiH ₄ ), dimethyl zinc (DMZ), and carbon tetrabromide (CBr ₄ ) can be used.

On the other hand, the ITO transparent electrode 8 can be formed by, for example, a sputtering method. Finally, the electrodes 9 and 10 are formed and divided into chip shapes to complete the light emitting device.

(Second Embodiment) FIG. 4 is a conceptual diagram showing a cross-sectional structure of a semiconductor light emitting device according to a second embodiment of the present invention. In this figure, the same parts as those described above with reference to FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Also in the present embodiment, p-type Ge is used as the substrate.
By using the substrate 1, the various functions and effects described above with respect to the first embodiment can be similarly obtained.

Further, in this embodiment, a p-type GaAs intermediate gap layer (layer thickness: 0.05 μm) 11 is inserted between the Ge substrate 1 and the InGaP buffer layer 2.

FIG. 5 is a conceptual diagram showing a band structure near a substrate of a light emitting element for main light emission. The band gap of germanium as a substrate is 0.80 eV (a value at 300 K), whereas the band gap of the InGaP buffer layer 2 is considerably large at 1.91 eV. As a result, there is a relatively large band discontinuity between the Ge substrate and the InGaP buffer layer. That is, as shown in FIG. 5, the valence band energy Ev of the p-type Ge substrate 1 and the p-type InGaP buffer layer 2 has a “shift” of about 0.8 eV. If both are joined as they are, a high barrier due to discontinuity of the valence band is formed at the interface,
When a forward voltage is applied, the inflow of holes tends to be blocked. As a result, the element resistance may increase and the operating voltage may increase.

In order to deal with this problem in the structure of the first embodiment illustrated in FIG. 1, the carrier concentration of the p-type InGaP buffer layer 2 is increased to about 1 × 10 ¹⁸ cm ⁻³ , May be made relatively large to reduce the element resistance.

On the other hand, in the second embodiment, an intermediate gap layer 11 having a band gap approximately between the Ge substrate 1 and the InGaP buffer layer 2 is provided between the Ge substrate 1 and the InGaP buffer layer 2. By doing so, the discontinuity of the valence band is alleviated, the flow of holes is promoted, and the element resistance against forward bias can be reduced.

Specifically, when the buffer layer 2 is made of InGaP, the intermediate gap layer 11
It can be formed of As. The layer thickness is
For example, it can be about 0.05 μm. In this specific example, the amount of band discontinuity of the valence band formed at the interface between the Ge substrate 1 and the intermediate gap layer 11 is about 0.5 e.
V, the valence band discontinuity formed at the interface between the intermediate gap layer 11 and the InGaP buffer layer 2 is reduced to about 0.3
It is possible to reduce the resistance to about eV, thereby preventing the pile-up of holes and reducing the element resistance.

The material of the intermediate gap layer is G
Even if a material containing arsenic (As) such as aAs is adopted,
The thickness of the layer is as thin as about 0.05 μm, and the absolute amount of arsenic contained in the light-emitting element is extremely small.

Also, such an intermediate gap layer 11
Also serves as a buffer layer. That is, by inserting this layer, the crystallinity of each of the semiconductor layers 2 to 7 to be epitaxially grown thereon is further improved,
The light emission characteristics and reliability of D and LD can also be improved.

(Third Embodiment) FIG. 6 is a conceptual diagram showing a sectional structure of a semiconductor light emitting device according to a third embodiment of the present invention. The semiconductor light emitting device 10C of the present embodiment includes:
On an n-type Ge substrate 12 (thickness: 250 μm), an n-type
aAs intermediate gap layer 13 (layer thickness: 0.05 μm), n
Type InGaP buffer layer 14 (layer thickness: 0.05 μm),
The light reflection layer 15, the n-type InAlP cladding layer 6 (layer thickness:
0.6 μm), InGaAlP active layer 5 (layer thickness: 0.6
μm), p-type InAlP cladding layer 3 (layer thickness: 0.6 μm)
m), p-type GaAlAs intermediate gap layer 16 (layer thickness:
0.05 μm), ap + -type GaAs contact layer 17 (layer thickness: 0.05 μm), and a current block layer 7 are sequentially stacked. Further, an ITO transparent electrode 8 and a front surface electrode 9 are formed on the p-side of the element, and a back surface electrode 10 is formed on the back surface of the substrate 1.

In this embodiment, an n-type Ge substrate is used unlike the first and second embodiments. Then, the n-type InGaP buffer layer 14 and the n-type InAlP
By inserting the light reflection layer 15 between the clad layer 6 and the clad layer 6, the light emission luminance can be approximately doubled. Further, by providing an n-type GaAs intermediate gap layer 13 having an intermediate band gap between the Ge substrate 12 and the InGaP buffer layer 14, as described above with respect to the second embodiment, the discontinuity of the band is achieved. And the operating voltage of the element can be reduced.

Here, the conductivity type and the polarity of the light emitting device of this embodiment are opposite to those of the devices of the first and second embodiments. Therefore, the ITO transparent electrode 8 is made of p-type InAlP
Even if it is formed in direct contact with the cladding layer 3, good ohmic contact cannot be obtained, and the operating voltage of the device may increase. In order to avoid this, in the present embodiment, the p-type GaAlAs intermediate gap layer 16 is provided between the p-type InAlP cladding layer 3 and the ITO transparent electrode 8.
And ap ⁺ -type GaAs contact layer 17 are provided.

The p ⁺ -type GaAs contact layer 17 is made of an IT
This is a layer for obtaining a low-resistance ohmic contact with the O transparent electrode 8. In order to sufficiently lower the contact resistance, the carrier concentration of the contact layer 17 is preferably set to 1 × 10 ¹⁹ cm ⁻³ or more, and more preferably 1 × 10 ²⁰ cm ⁻³ or more.

The p-type GaAlAs intermediate gap layer 16 is
It has the effect of reducing the band discontinuity between the GaAs contact layer 17 and the InAlP cladding layer 3 and lowering the operating voltage. Therefore, it is desirable that the composition of the intermediate gap layer 16 be determined so as to have an intermediate band gap between the contact layer 17 and the cladding layer 3.

Although the GaAs contact layer 17 and the GaAlAs intermediate gap layer 16 contain arsenic (As), their thickness may be as small as about 0.05 μm. The impact on the environment is negligible.

The intermediate gap layer 16 also functions as a buffer layer. That is, by inserting this layer, the crystallinity of each semiconductor layer epitaxially grown thereon can be further improved, and the light emitting characteristics and reliability of the LED and LD can be improved.

(Fourth Embodiment) FIG. 7 is a conceptual diagram illustrating the cross-sectional structure of a semiconductor light emitting device according to a fourth embodiment of the present invention. That is, also in the present embodiment,
A predetermined element structure D is formed on the Ge substrate 21. The conductivity type of the Ge substrate 21 may be p-type or n-type.
The element structure D includes first to third elements depending on the conductivity type of the substrate 21.
Any of the structures as illustrated with respect to the embodiments can be used. Further, an electrode or the like (not shown) can be appropriately provided as needed.

The Ge substrate 21 in this embodiment has a so-called “off angle”. That is, the main surface of the substrate has a plane orientation inclined from the (100) plane in the [011] direction by 2 to 16 °. InGaAlP or GaAs on Ge substrate
When growing a compound semiconductor such as s, there is a tendency that the group III element and the group V element are not always arranged regularly and alternately. That is, the group III element and the group V element are G
It tends to be fixed randomly to the atomic sites on the surface of the e-substrate, and discontinuous boundaries are formed in the periodic arrangement of the group III element and the group V element. The area surrounded by such discontinuous boundaries is called an "anti-phase domain".

On the other hand, in the present embodiment, G
By giving the “off-angle” to the e-substrate, the formation of “anti-phase domains” can be suppressed. As a result of the study by the present inventors, when the “off angle” of the Ge substrate is set to a plane orientation inclined by 2 ° or more from the (100) plane to the [011] direction as described above, the formation of the “anti-phase domain” is suppressed, It was found that good crystals were obtained.

The InGaP or InGaAlP grown on the inclined substrate having the “off angle” as described above,
The emission wavelength tended to be shorter than that grown on the (100) plane. That is, the same aluminum (A
l) Even when grown under the conditions of the composition, light is emitted at a shorter wavelength,
Further, it was found that the light emission luminance of the element was increased. It is well known that the reason for this is that a regular arrangement of group III atoms occurs. That is, for example, when InGaP is grown, the group III atoms In and Ga are not randomly present in the crystal but the InIn is oriented in a certain plane orientation.
.., GaGaGa... May be alternately and regularly arranged. When such a regular arrangement is generated, the band gap becomes smaller than in the case of random arrangement, and the emission wavelength becomes longer. However, when growing on a substrate having a certain "off angle", a regular arrangement is unlikely to occur,
An emission wavelength relatively shorter than that on the (100) plane is obtained.

Specifically, for example, the active layer is made of InGaAs.
When the light emitting element formed on a Ge substrate having no “off angle” is compared with a light emitting element formed on a Ge substrate having an inclination of 15 ° as an “off angle”, the emission wavelength is about 10 nm shorter. It was found that the wavelength was increased and the emission luminance was about twice as high. However, it was also found that when the “off angle” of the substrate was increased, the effect of shortening the wavelength gradually became saturated, and even when the “off angle” was 16 ° or more, no further reduction in the wavelength occurred.

When the active layer is formed on a just substrate, it is necessary to increase the Al composition of the active layer in order to shorten the emission wavelength. However, when the Al composition of the active layer is increased, the emission luminance tends to decrease. This is considered to be because Al is easily oxidized, and when the Al composition is increased, a small amount of oxygen present in the atmosphere during the crystal growth is taken into the crystal and acts as a non-radiative recombination center.

On the other hand, in the present embodiment,
By using a Ge substrate having an "off angle", A
The emission wavelength can be shortened without positively increasing the l-composition. That is, it is possible to achieve both emission luminance and a shorter wavelength.

As described above, by inclining the plane orientation of the Ge substrate from the (100) plane in the range of 2 to 16 ° in the [011] direction, the generation of anti-phase domains is suppressed, and at the same time, the light emitting device And the wavelength can be shortened.

(Fifth Embodiment) FIG. 8 is a conceptual diagram illustrating the cross-sectional structure of a semiconductor light emitting device according to a fifth embodiment of the present invention. The light emitting device shown in FIG. 1 is a semiconductor laser, and has an n-type GaAs intermediate gap layer 13 (layer thickness: 0.0 μm) on an n-type Ge substrate 12 (thickness: 250 μm).
5 μm), n-type InGaP buffer layer 14 (layer thickness: 0.
05 μm), n-type InAlP cladding layer 6 (layer thickness: 0.
6 μm), InGaAlP active layer 5 (layer thickness: 0.6 μm)
m), p-type InAlP cladding layer 3 (layer thickness: 0.6 μm)
m), current block layer 7, p-type GaAs contact layer 1
9 (layer thickness: 3 μm) are sequentially laminated. Further, electrodes 9 and 10 are formed on the p side and the n side of the element, respectively.

The current blocking layer 7 is made of, for example, n-type InA
1P, and is formed to have a stripe-shaped opening so that current can be efficiently injected into the active layer 5.

Also in this embodiment, by using the Ge substrate 12 as the substrate, the various functions and effects described above with respect to the first embodiment can be similarly obtained.

Further, by providing the intermediate gap layer 13, the band discontinuity can be reduced and the operating voltage can be reduced, as in the third embodiment described above. If a p-type substrate is used as the Ge substrate, the conductivity type of the device can be reversed as described above with respect to the first embodiment, thereby greatly increasing the degree of freedom in device design.
On the other hand, if the “off angle” is provided on the Ge substrate, as described above with reference to the fourth embodiment, it is possible to suppress the generation of the anti-phase domain, improve the light emission luminance, and simultaneously shorten the wavelength.

The embodiment of the invention has been described with reference to examples. However, the present invention is not limited to these specific examples. For example, the structure of the semiconductor light emitting device described above is merely an example. In addition, the present invention is similarly applied to semiconductor light emitting devices having various structures using an InGaAlP-based semiconductor for a light emitting layer (active layer). The effect can be obtained. Further, the material and composition of each layer constituting the semiconductor light emitting element can be appropriately selected from known materials and used similarly.

For example, the active layer may have a so-called multiple quantum well (MQW) type structure, and an optical guide layer having an intermediate refractive index between the active layer and the cladding layer may be provided between the active layer and the cladding layer. A so-called graded structure in which the composition of the cladding layer is gradually changed may be used.

[0081]

The present invention is embodied in the form described above, and has the following effects.

First, according to the present invention, for an InGaAlP-based light emitting device, a crystal having a quality equal to or higher than that of a conventional one can be grown by using a germanium substrate instead of a GaAs substrate. Specifically, by using a germanium substrate, the substrate and InGaAl
The difference in the thermal expansion coefficient of the P-based semiconductor can be reduced, and the thermal stability at a high temperature can be significantly improved.
As a result, the light emitting characteristics and reliability of the semiconductor light emitting device can be improved as compared with the conventional case.

Further, when the substrate is of a p-type, the resistance can be made lower than in the conventional case, and the degree of freedom in the design of the light emitting element is greatly expanded.

The present invention is also advantageous in that the arsenic (As) content can be dramatically reduced as compared with a conventional light emitting device using a GaAs substrate.

Further, according to the present invention, the Ge substrate and the In substrate
By providing an intermediate gap layer having a band gap approximately between the two, between the GaP buffer layer and the GaP buffer layer, the discontinuity of the valence band is reduced, the inflow of holes is promoted, and the element resistance against forward bias is reduced. Can be reduced. The intermediate gap layer also serves as a buffer layer, further improving the crystallinity of each semiconductor layer epitaxially grown thereon, and improving the light emitting characteristics and reliability of LEDs and LDs.

Further, according to the present invention, by using a Ge substrate having an “off angle”, generation of an antiphase domain is suppressed, and the emission wavelength is shortened without positively increasing the Al composition. be able to. That is,
It is possible to achieve both emission luminance and shorter wavelength.

As described above, according to the present invention, it is possible to provide an lnGaAlP-based light-emitting device such as an LED or an LD, which has excellent light-emitting characteristics and life characteristics and has a significantly reduced influence on the environment. As a result, the industrial benefits are enormous.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a cross-sectional structure of a semiconductor light emitting device according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating a schematic configuration of a light emitting device capable of selectively emitting light from a semiconductor light emitting element formed on an n-type substrate and a semiconductor light emitting element formed on a p-type substrate.

FIG. 3 is a conceptual diagram comparing the configuration of a light emitting device of the present invention with that of a conventional light emitting device.

FIG. 4 is a conceptual diagram illustrating a cross-sectional structure of a semiconductor light emitting device according to a second embodiment of the present invention.

FIG. 5 is a conceptual diagram illustrating a band structure near a substrate of a light emitting element for main light emission.

FIG. 6 is a conceptual diagram illustrating a cross-sectional structure of a semiconductor light emitting device according to a third embodiment of the present invention.

FIG. 7 is a conceptual diagram illustrating a cross-sectional structure of a semiconductor light emitting device according to a fourth embodiment of the present invention.

FIG. 8 is a conceptual diagram illustrating a cross-sectional structure of a semiconductor light emitting device according to a fifth embodiment of the present invention.

FIG. 9 is a schematic sectional view showing a conventional InGaAlP-based semiconductor light emitting device.

[Explanation of symbols]

 Reference Signs List 10A to 10E Semiconductor light emitting device 1, 12, 21 Ge substrate 2, 14 InGaP buffer layer 3 n-type InAlP cladding layer 5 InGaAlP active layer 6 p-type InAlP cladding layer 7 current blocking layer 8 ITO transparent electrode 9, 10 electrode 11, 13 , 16 Intermediate band gap layer 15 Light reflection layer 17 p-type GaAs contact layer 19 p-type contact layer

Claims (10)

[Claims] 1. A semiconductor light emitting device comprising: a germanium substrate; and a light emitting layer made of an InGaAlP-based semiconductor. 2. A germanium substrate of a first conductivity type, and a first conductivity type of I provided on the germanium substrate.
a first cladding layer made of an nGaAlP-based semiconductor; and an InGaAlP provided on the first cladding layer.
A light emitting layer made of a system semiconductor, and a second conductivity type InGaAl provided on the light emitting layer
And a second cladding layer made of a P-based semiconductor. 3. The device according to claim 2, further comprising a light-transmitting electrode layer provided on said second clad layer.
The semiconductor light-emitting device according to claim 1. 4. A buffer layer provided between said germanium substrate and said first cladding layer, said buffer layer having a band gap larger than said germanium substrate and smaller than said first cladding layer. The semiconductor light emitting device according to claim 2, wherein: 5. The semiconductor light emitting device according to claim 4, wherein said buffer layer is made of InGaP. 6. An intermediate gap layer provided between said germanium substrate and said buffer layer, said intermediate gap layer having a band gap larger than said germanium substrate and smaller than said buffer layer. 6. The semiconductor light emitting device according to 5. 7. The semiconductor light emitting device according to claim 6, wherein said intermediate gap layer is made of GaAs. 8. The semiconductor light emitting device according to claim 2, wherein said first conductivity type is n-type and said second conductivity type is p-type. 9. The semiconductor light emitting device according to claim 2, wherein said first conductivity type is p-type, and said second conductivity type is n-type. 10. The germanium substrate according to claim 1, wherein a main surface of the germanium substrate has a plane orientation inclined from (100) in a range of 2 ° to 16 °. Semiconductor light emitting device.