JPH09106955A - Epitaxial wafer and semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve simultaneously the problem of a zigzag thyristor and the problem of unevenness of the surface of a wafer by a method wherein the surface of a GaAs single crystal substrate is slanted at a prescribed angle from the face (100) or the face equivalent to the face (100). SOLUTION: In the case where a substrate of the orientation not a slanted is used, there is not a directivity property in the form of the surface of an epitaxial wafer because the density of atomic layer steps is low and the steps exist randomly on the surface of the substrate, but in the case where the orientation of the substrate is slanted, the atomic layer steps exist at intervals proportioned to the reciprocal number of the tangent of the slanted angle of the orientation and the form of the surface of the wafer is formed so as to have a striped pattern in the directions to correspond to the steps existing with the intervals. Moreover, a natural reverse temperature in an epitaxial layer is different from that in the region of the steps and in the case where the orientation of the substrate is an orientation (100), the latter natural inversion temperature is low. As a result, an N-type part 2 is grown in the layer of a P-type part 3 and a zigzag thyristor 4 is easy to generate. By setting the slant of the orientation between 0.5 deg. and 5.0 deg., the formation of a thyristor and a junction having little surface unevenness are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial wafer and a semiconductor light emitting device, and more particularly to a GaAs or AlGaA doped with silicon on a GaAs single crystal substrate by a slow cooling liquid phase epitaxial growth method.
The present invention relates to an epitaxial wafer in which an epitaxial thin film made of s is grown and a pn junction is formed in the epitaxial thin film by utilizing the natural inversion of silicon, and a semiconductor light emitting device manufactured from the wafer.

[0002]

2. Description of the Related Art Silicon as a dopant in III-V group compound semiconductors is known as an amphoteric impurity. That is, since silicon is a group IV element, it becomes a donor by substituting the group III element of the semiconductor matrix and becomes an acceptor by substituting the group V element. As a result, the conductivity type and effective carrier concentration of the group III-V compound semiconductor to which silicon is added are determined by the magnitude relationship and the difference in concentration between the group III element-substituted silicon and the group V element-substituted silicon, respectively. .

A slow cooling method liquid phase epitaxial growth method is used to add GaAs or AlGaAs to which silicon is added.
It is generally known that when an epitaxial thin film made of is grown, the temperature dependence of the segregation coefficient of silicon as a donor and the segregation coefficient of an acceptor are different. Infrared light emitting diodes utilizing this phenomenon are widely manufactured.

That is, in manufacturing the above infrared light emitting diode, GaAs or AlG added with silicon is used.
When an epitaxial thin film made of aAs is grown using the slow cooling liquid phase epitaxial growth method, when the growth temperature is high, the segregation coefficient of silicon as a donor is larger than that of an acceptor.
The grown epitaxial thin film becomes n-type. However, in the process of cooling the system during growth, the size relationship between the segregation coefficient of silicon as a donor and the segregation coefficient of an acceptor is reversed at a certain temperature, so that the epitaxial thin film grown at low temperature becomes p-type. . As a result, a pn junction is formed in the epitaxial thin film. Such a phenomenon is generally called natural inversion of silicon, and the temperature at which the magnitude relationship of the segregation coefficient is inverted is called the natural inversion temperature.

The advantages of the method of manufacturing a light emitting diode by utilizing the natural inversion of silicon are as follows.
That is, in the production of a light emitting diode by the other commonly used liquid phase epitaxial growth method, two solutions must be prepared in order to grow a p-type thin film and an n-type thin film. On the other hand, if the above method is used, a pn junction can be formed with only a single solution. Therefore, since the number of solution baths required for one substrate is small, it is possible to grow a large number of substrates in the epitaxial growth furnace having the same volume, and mass production and cost reduction can be achieved.

[0006]

However, the pn junction interface in the epitaxial thin film formed by utilizing the natural inversion of silicon as described above has a wedge in the p layer as schematically shown in FIG. There was a case where a structure in which n layers were inserted into the mold appeared. When separating a light emitting device from an epitaxial wafer having such an interface shape, a dotted line 5 in FIG.
When the elements are separated so that this structure is included in one element as shown in FIG. 2, an element which should originally be a diode (pn structure) as shown in FIG. The thyristor (pnpn structure) as shown in FIG. 2 (b) is obtained, and even if a rated voltage is applied, a current may stop flowing. In the following, the structure in which the wedge-shaped n-layer enters the p-layer will be referred to as a lightning-type thyristor 4 in view of its shape and characteristics.

The cause of the lightning type thyristor may be various factors such as temperature fluctuation and non-uniformity of the silicon concentration in the solution, but no clear conclusion has been obtained so far. An object of the present invention is to reduce or eliminate the generation of an energetic thyristor, which is a problem peculiar to a pn junction formed by utilizing the natural inversion of silicon, and eliminate the generation of a thyristor structure generated in a light emitting element. . In addition, the object of the present invention is to solve the above-mentioned problem of unevenness on the surface of an epitaxial wafer, which is accompanied by a method described later found by the present inventors as a means for eliminating the above-mentioned lightning type thyristor. To provide.

[0008]

When an epitaxial thin film made of GaAs or AlGaAs doped with silicon is grown on a GaAs single crystal substrate by the slow cooling liquid phase epitaxial growth method, in the conventional technique, the GaAs single crystal is used. The substrate is generally a (100) plane or a plane equivalent thereto. As a result of repeated studies on the reduction of the lightning type thyristor,
The surface of the substrate used for epitaxial growth is (100)
It was found that tilting from the plane or a plane equivalent thereto affects the shape of the pn junction interface. That is, when the inclination of the surface of the substrate is within 0.2 degrees, the shape of the pn junction interface is the same as when there is no inclination in the substrate surface orientation, but when the inclination is 0.5 degrees or more, the epitaxial growth surface of the lightning type thyristor. It became clear that the length in the direction parallel to is 50 μm or less, and further, if the inclination is 1 degree or more, the lightning type thyristor is eliminated. The present inventor has arrived at the present invention based on the above findings.

That is, according to the present invention, an epitaxial thin film made of GaAs or AlGaAs to which silicon is added is grown on a GaAs single crystal substrate by the slow cooling liquid phase epitaxial growth method, and natural inversion of silicon is utilized in the epitaxial thin film. In an epitaxial wafer having a pn junction, the GaAs single crystal substrate is
The surface is 0.5 from the (100) plane or its equivalent plane.
It is characterized by being inclined more than one degree.

On the other hand, as the inclination of the substrate surface from the low index plane increases, the surface of the epitaxial wafer generally tends to have more irregularities. Since such unevenness on the surface causes various defects in the process of manufacturing the light emitting device, it is desirable that the unevenness on the surface of the epitaxial wafer is as small as possible. In carrying out the above-mentioned invention, the present inventor examined the upper limit of the tilt angle of the substrate that can be allowed in order to prevent the unevenness of the surface of the epitaxial wafer from causing various defects in the process of manufacturing the light emitting device. As a result, it has been found that if the inclination angle is 5 degrees or less, it is possible to prevent the above unevenness of the surface from causing various defects in the process of manufacturing the light emitting device by a method such as surface polishing. .

Therefore, according to the present invention, an epitaxial thin film made of GaAs or AlGaAs to which silicon is added is grown on a GaAs single crystal substrate by the slow cooling liquid phase epitaxial growth method, and natural inversion of silicon is utilized in the epitaxial thin film. In an epitaxial wafer having a pn junction formed thereon, the surface of the GaAs single crystal substrate is tilted from the (100) plane or a plane equivalent thereto by 0.5 to 5 degrees.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the surface of the GaAs single crystal substrate is inclined by 0.5 degrees or more from the (100) plane or a plane equivalent thereto. The reason why the present invention can solve the problem of the occurrence of the lightning type thyristor is considered to be as follows.

As is well known, the morphology of the surface of an epitaxial wafer depends on the inclination of the substrate surface orientation. This is because the density of atomic layer steps generated on the substrate surface by tilting the substrate surface orientation has an inclination of the surface orientation. It depends on the size. That is, when using a substrate in which the plane orientation of the substrate is not tilted, the density of this atomic layer step is low, and since it randomly exists on the surface, the morphology of the surface of the epitaxial wafer has no directionality, When the substrate plane orientation is tilted, the atomic layer steps on the substrate surface are present in the tilted direction of the plane orientation at intervals proportional to the reciprocal of the tangent of the tilted angle. It has a striped pattern in the direction corresponding to this.

Next, let us consider the shape of the pn junction interface. As a whole, the epitaxial layer grows perpendicularly to the substrate surface.
As shown in (4), it progresses in the direction 8 different from the growth direction.

Since the epitaxial layer and the atomic layer step have different growth rates and growth directions, the effective segregation coefficients of the impurities corresponding to the respective regions are different. In the case of GaAs to which silicon is added, the natural inversion temperature changes depending on the growth orientation, as described in Journal of Applied Physics, Volume 42, pages 4512-4513 (published in 1971). Therefore, the natural inversion temperature is different in the regions of the epitaxial layer and the atomic layer step, and when the substrate plane orientation is the (100) plane, the atomic layer step has a lower natural inversion temperature. Therefore, in the process of epitaxial growth, the atomic layer step does not naturally invert even when the temperature of the system reaches the natural inversion temperature of the epitaxial layer, and the trace of the progress of the atomic layer step until the system reaches the natural inversion temperature of the atomic layer step. Only becomes n-type. As a result, it is considered that the lightning type thyristor as shown in FIG. 1 is generated.

If the surface of the substrate is tilted, atomic layer steps are present on the surface, as described above. Since these atomic layer steps are fused with each other during the epitaxial growth, they have a macroscopic structure that can be visually confirmed after the epitaxial growth is completed. The timing when this fusion occurs is closer to the epitaxial growth start position as the atomic step density increases. From the experimental result, when the inclination of the plane orientation is 0.5 degree, this fusion occurs slightly on the lower temperature side than the natural inversion temperature of the epitaxial layer, that is, on the side where the epitaxial growth proceeds. Therefore, the length of the lightning type thyristor becomes shorter than that when the substrate surface orientation is not inclined. When the gradient is further increased, the atomic layer step density becomes higher, and the atomic layer steps are fused before the spontaneous inversion temperature of the epitaxial layer is reached. Therefore, it is considered that the lightning type thyristor will not occur.

According to the experiments conducted by the present inventor, it is clear that the minimum value of the inclination of the substrate when this atomic layer step is completely fused before the natural inversion temperature of the epitaxial layer is reached is 1 degree. It was Even if the substrate surface is tilted by 0.5 degrees, the atomic layer steps are fused immediately after the spontaneous growth of the epitaxial layer grown perpendicular to the (100) plane. Since it was sufficiently smaller than the element size, it became clear that there was no hindrance to the production of the light emitting element.

Since the present invention can solve the problem of the generation of the lightning type thyristor by the above-described action, the effect of the present invention does not depend on the orientation of tilting the substrate.
Therefore, in the present invention, the substrate may be tilted in any direction.

However, it is known that the natural inversion temperature depends on the plane orientation of the substrate in the growth of the GaAs or AlGaAs epitaxial thin film to which silicon is added. For this reason, the ratio of the layer thicknesses of the n layer and the p layer formed by epitaxial growth and the carrier concentration on the surface side (p side) of the epitaxial layer change depending on the orientation of the substrate surface orientation. Therefore, depending on the orientation of tilting the substrate surface orientation, the grown GaAs or AlGaAs epitaxial thin film has the following characteristic characteristics with respect to the ratio of the n-layer and p-layer thickness and the carrier concentration on the surface side (p-side) of the epitaxial layer. It should be noted that there are differences.

That is, in the first case, the direction in which the substrate plane is tilted is a direction in which a nonpolar plane appears with respect to the (100) plane [110], [1-10], [101] or [1].
0-1] direction, in this case, the respective epitaxial layer thicknesses and surface carrier concentrations of the p-layer and the n-layer are the same as in the case of using a substrate having no inclination in the plane orientation. Therefore, in this case, an epitaxial thin film having the same characteristics as in the case of using the non-tilted substrate can be obtained under the same epitaxial growth conditions as in the case of using the non-tilted substrate.

In the second case, the azimuth of inclining the substrate surface is [111] or [1-1-1] with respect to the (100) plane.
When the direction is the direction in which the (111) A plane appears, in this case, the p layer becomes thicker and the surface carrier concentration increases due to the same epitaxial growth conditions as in the case where a non-tilted substrate is used.

In the third case, the azimuth of inclining the substrate surface azimuth is [11-1] or [1-11] with respect to the (100) plane.
When the (111) B plane appears, the p layer becomes thin and the surface carrier concentration decreases under the same epitaxial growth conditions as in the case where a non-tilted substrate is used.

The fourth case is a case where the substrate is tilted in a direction that does not apply to any of the first to third cases. In this case, the p-layer and n-layer epitaxial layer thickness ratios and the natural inversion temperature are in a mixed state of the first to third cases. In any of these cases, there is no difference in the characteristics of the manufactured elements, so the substrate surface azimuth may be tilted in either direction if the above points are noted.

Since the lightning type thyristor is eliminated by such means, the thyristor of the light emitting device manufactured from such an epitaxial substrate is eliminated.

However, in carrying out the present invention, the unevenness of the surface of the epitaxial wafer caused by tilting the substrate changes in intensity depending on the thickness of the epitaxial thin film to be grown. Generally, the unevenness on the surface of the epitaxial wafer tends to become stronger as the thickness of the epitaxial thin film increases. Therefore, even if the upper limit of the angle of tilting the substrate is 5 degrees, if the thickness of the growing epitaxial thin film is too thick, the unevenness on the surface of the epitaxial wafer becomes too strong, which causes various defects in the process of manufacturing the light emitting device. The cause is likely to occur.

The inventor has found that the thickness of an epitaxial thin film in which a substrate is tilted by 0.5 to 5 degrees does not cause surface irregularities to the extent of causing various defects in the process of manufacturing a light emitting device. By investigating the upper limit of the thickness, it was found that the occurrence of various defects can be significantly reduced in the process of manufacturing the light emitting device by setting the thickness of the growing epitaxial thin film to 150 μm or less. Therefore, in the present invention, the thickness of the grown epitaxial thin film is preferably 150 μm or less. When the thickness of the grown epitaxial thin film is larger than 150 μm, the unevenness of the surface becomes too strong and various causes of defects are likely to occur in the process of manufacturing the light emitting device for the reason described above. Here, the thickness of the epitaxial thin film can be controlled by adjusting the temperature range for epitaxially growing the thin film and the thickness of the solution used for the growth.

In the above description, an epitaxial thin film made of GaAs is taken as an example, but the similar phenomenon is
Since this also occurs when an epitaxial thin film made of 1GaAs is laminated, the present invention grows an epitaxial thin film made of AlGaAs doped with silicon (Si) on a GaAs single crystal substrate by the slow cooling liquid phase epitaxial growth method. It can be similarly used in the case of an epitaxial wafer in which a pn junction is formed by utilizing the natural inversion of silicon. In carrying out the present invention, the epitaxial wafer according to the present invention is a GaAs or AlGaAs in which silicon (Si) is added and a pn junction is formed by utilizing natural inversion.
Even if the structure has an additional epitaxial thin film such as a window layer for improving the light extraction efficiency other than the epitaxial thin film made of, the effect is the same. In this case, the total thickness of all the epitaxial thin films to be laminated is preferably 150 μm or less.

[0028]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

As an example of the present invention, the surface of the substrate is [1-10] from the (100) plane in the crystallographic plane orientation.
An n-type GaAs substrate was prepared which was inclined in the directions of 0.5 degree, 1.0 degree, 2.0 degree, and 5.0 degree, respectively. For comparison, the surface of the substrate has a crystallographic plane orientation of 0. 0 from the (100) plane to the [1-10] direction.
An n-type GaAs substrate tilted at 2 degrees and 10.0 degrees was prepared. In order to fabricate an infrared light emitting diode structure on these substrates, GaA doped with silicon by a slow cooling liquid phase epitaxial growth method using a normal slide boat method.
An epitaxial thin film made of s was laminated.

As a solution for epitaxial growth, a mixture of Ga as a solvent, 145 g of GaAs polycrystal as a solute and 1 g of Ga as a solute, and 2 g of silicon as a dopant per 1 kg of Ga was used. Add this solution to the solution tank and
With the As substrate placed separately on the growth apparatus, the slide boat of the growth apparatus was placed in the growth furnace and the atmosphere was changed to 910 in a hydrogen atmosphere.
The temperature was raised to 0 ° C., and GaAs polycrystal and silicon were completely dissolved in the Ga solution. Subsequently, the temperature of this solution was lowered to 905 ° C., and then a slide boat was slid to guide the solution onto the substrate. At this time, the thickness of the Ga solution on the substrate is 10
The jig was designed to be mm. Then, the temperature was lowered at a cooling rate of 1 ° C./min to grow an epitaxial thin film on the GaAs substrate. After reaching 785 ° C., the atmosphere gas was changed to argon and the mixture was allowed to cool. Approximately 860 ℃ under these growth conditions
Corresponds to the above-mentioned natural inversion temperature of silicon, and a pn junction was formed in the epitaxial thin film by this step.

The thus obtained epitaxial wafer has a GaAs epitaxial thin film with a thickness of about 120.
μm, of which about 40 μm from the substrate side was an n-type conductive type, and about 80 μm above it was a p-type conductive type. The carrier concentration of the GaAs epitaxial thin film is about 5 × 10 ¹⁷ cm ^{−3 for} n-type near the interface with the substrate and about 2 × 10 ¹⁸ cm for p-type on the surface of the epitaxial thin film.
^{Was -3} . The morphology of the surface and the pn junction interface shape of the epitaxial wafer for infrared light emitting diode manufactured as described above will be described.

Table 1 shows the shape of the pn junction interface and the quality of the surface morphology of the epitaxial wafers manufactured using the substrates having different surface inclination angles. The pn junction interface shape was observed by a polarization microscope after cleaving the epitaxial substrate, etching with an etching solution having a composition of sulfuric acid: hydrogen peroxide: water = 8: 1: 1 for 3 minutes. Table 1
Regarding the junction interface shape, ○ indicates that there is no lightning type thyristor at all, and Δ indicates that the length of lightning type thyristor is less than 50 μm over the entire epitaxial substrate, and length of lightning type thyristor is 200 μm
If even one point of the above was observed, it was indicated as x. Regarding the surface morphology, if the normal ohmic electrode can be formed without polishing the surface of the epitaxial wafer in the element process, a circle is shown, and if a polishing process with a depth of 10 μm is added, a normal ohmic electrode can be formed. Some of these are indicated by Δ, and those by which ohmic electrode formation is impossible even by polishing to a depth of 10 μm are indicated by X.

[0033]

[Table 1]

From Table 1, the shape of the pn junction interface changes depending on the angle of inclination of the surface of the substrate, and is 2 when the angle of inclination is 0.2 degrees.
It can be seen that the lightning type thyristor having a thickness of 00 μm or more can be seen, but the lightning type thyristor cannot be seen at all when the inclination angle is 1.0 degree or more. Further, it can be seen that when the tilt angle is 0.5 degree, the length of the lightning type thyristor is 50 μm or less, although it is generated. Similarly, from Table 1, the morphology of the surface of the epitaxial wafer also changes depending on the angle of inclination of the surface of the substrate. When the angle of inclination is 2.0 degrees or less, normal ohmic contact is performed without polishing the surface of the epitaxial wafer in the element process. Although the surface is good enough to form an electrode, it can be seen that when the inclination angle is 10.0 degrees, the surface having strong irregularities is such that ohmic electrode formation is impossible even by polishing to a depth of 10 μm. Further, it can be seen that when the inclination angle is 5.0 degrees, a normal ohmic electrode can be formed by adding a polishing step with a depth of 10 μm, and the surface becomes uneven to some extent.

Further, light emitting devices were manufactured from epitaxial wafers manufactured by using substrates having different surface inclination angles, and the occurrence states of thyristors were compared. Here, the planar shape of the light emitting device was a substantially square of 250 μm square. Table 2 shows the results of the thyristor generation status. Here, the number of samples is about 100,000 for each tilt angle of the substrate. From this result, it is understood that the thyristor does not occur when a substrate having a substrate inclination angle of 0.5 degrees or more is used. From the results described above, the superiority of the present invention is clear.

[0036]

[Table 2]

[0037]

As described above, the present invention reduces or eliminates the generation of the lightning type thyristor, which is a problem peculiar to the pn junction formed by utilizing the natural inversion of silicon, and the thyristor structure generated in the light emitting element. Has the effect of eliminating the occurrence of. At the same time, the present invention has been found by the present inventor as means for solving the above-mentioned lightning type thyristor.
In addition to the method of inclining the surface of the aAs single crystal substrate from the (100) plane or a plane equivalent thereto by 0.5 degrees or more, the effect of simultaneously solving the problem of the newly generated unevenness of the surface of the epitaxial wafer is obtained. Have.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an inazuma type thyristor.

FIG. 2 is a schematic diagram illustrating (a) a light emitting device manufactured from a region including a normal pn junction and (b) a light emitting device manufactured from a region including a lightning type thyristor of an epitaxial substrate.

FIG. 3 is a schematic diagram for explaining the epitaxial growth direction and the atomic step growth direction.

[Explanation of symbols]

 1 n-type GaAs substrate 2 n-type epitaxial thin film 3 p-type epitaxial thin film 4 lightning-type thyristor 5 cutting line for device isolation 6 atomic layer step 7 epitaxial growth direction 8 atomic layer step progress direction

[Procedure amendment]

[Submission date] February 22, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

Therefore, according to the present invention, an epitaxial thin film made of GaAs or AlGaAs to which silicon is added is grown on a GaAs single crystal substrate by the slow cooling liquid phase epitaxial growth method, and natural inversion of silicon is utilized in the epitaxial thin film. In the epitaxial wafer having a pn junction formed thereon, the surface of the GaAs single crystal substrate is tilted within a range of 0.5 degrees or more and 5 degrees or less from a (100) plane or a plane equivalent thereto. It is a thing.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

The inventor of the present invention, in the epitaxial thin film in which the substrate is tilted within the range of 0.5 degrees or more and 5 degrees or less, has a surface irregularity that causes various defects in the process of manufacturing the light emitting device. By investigating the upper limit of the thickness of the epitaxial thin film that does not cause the occurrence of defects, it was found that various defects can be significantly reduced in the process of manufacturing the light emitting device by setting the thickness of the growing epitaxial thin film to 150 μm or less. It was Therefore, in the present invention, the thickness of the grown epitaxial thin film is preferably 150 μm or less. The thickness of the growing epitaxial thin film is 150μ
If it is larger than m, the unevenness of the surface becomes too strong and various causes of defects are likely to occur in the process of manufacturing the light emitting device for the reason described above. Here, the thickness of the epitaxial thin film can be controlled by adjusting the temperature range for epitaxially growing the thin film and the thickness of the solution used for the growth.

Claims (3)

[Claims] 1. A slow-cooling liquid phase epitaxial growth method is used to grow an epitaxial thin film of GaAs or AlGaAs doped with silicon (Si) on a GaAs single crystal substrate, and utilize the natural inversion of silicon in the epitaxial thin film. An epitaxial wafer having a pn junction, wherein the GaAs single crystal substrate has a surface inclined by 0.5 to 5 degrees from a (100) plane or a plane equivalent thereto. 2. The epitaxial wafer according to claim 1, wherein the total thickness of all the laminated epitaxial thin films is 150 μm or less. 3. A semiconductor light emitting device manufactured from the epitaxial wafer according to claim 1.