JP2000143398A - Gallium phosphide single crystal base plate, its production and method of producing gallium phosphide light-emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the GaP epitaxial growth layer with an extremely reduced dislocation density and a large luminous efficiency in high yield by lowering the dislocation density of the GaP single crystal at its surface less than a specific value and reducing the density of the dislocation loops lower than a specific value. SOLUTION: The dislocation density is kept at <=500 cm-2 and the density of the dislocation loops is lowered to <=500 cm-2. The layer having this specific value is formed on the surface of the substrate plate in a thickness of <=5 μm, the number of atoms in the dislocation loops is >=106 cm-3 per the unit volume, and Ld is >=65 μm from the surface of the substrate plate and Ld<=Ls is maintained simultaneously, when the thickness of the layer is represented by Ld and the thickness of the layer that has the above-stated number of atoms in the dislocation loops is defined as Ls. Such substrate plate is prepared by treating the substrate plate having the GaP crystal layer of <=500 cm-2 dislocation density prepared by the vertical Bridgeman method with heat at 850-1,200 deg.C in an atmosphere of phosphorus vapor lower than the Peq (the equilibrium vapor pressure of phosphorus in GaP).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaP single crystal substrate and a method for manufacturing the same, and further to a technical field related to a method for manufacturing a low-cost and high-performance GaP visible light emitting diode (LED).

[0002]

2. Description of the Related Art Hitherto, a blue LED (visible light emitting diode) using a SiC material has not been able to obtain high luminance, and thus its use has been limited. Recently, GaN-based blue LEDs with a brightness of 2 cd [cd: candela (unit of luminous intensity)] or more
Has been developed, and three primary colors of light can be obtained in addition to the existing red and green LEDs, making it possible to apply it to large high-brightness full-color displays. However, when comparing the luminance of these red, green, and blue LEDs, in the production of outdoor full-color displays, GaAlA
While the ultra-high brightness of 5 cd has already been achieved by the s-system double heterostructure, the problem that the brightness of the green LED is relatively insufficient has become apparent.

As a material for a green LED, GaP has been widely used in the past. Recently, a GaInN-based LED having an ultra-high brightness of about 5 cd has been developed next to a blue LED. On the other hand, the GaP-LED has a maximum luminance of about 0.2 cd, and is much inferior in luminance to GaInN-LED and InGaAlP-LED. However, for GaInN-LED and InGaAlP-LED,
In each case, expensive organic metal is used as a raw material for vapor phase epitaxial growth, and since single crystal sapphire is used for the substrate, the manufacturing cost is high.
In this case, there is an advantage that a liquid phase epitaxial growth method having a low production cost can be used, and an inexpensive LED can be supplied because the substrate is also inexpensive. Therefore, in order to provide a large-scale display using a large number of LED lamps at a commercially viable price, it is extremely important to increase the brightness of the low-cost GaP green LED.

In the first place, the emission mechanism of green GaP-LEDs is predominantly based on the mechanism of light emission due to recombination of free excitons. Therefore, the light emission efficiency depends on the structural defects such as dislocations and the impurity concentration in the epitaxially grown crystal serving as the active layer of the device. Greatly affected. That is, excitons are scattered by dislocations and impurity atoms, and the life thereof is shortened. Literature (Tatsuro Beppu, Applied Physics
Vol. 47, No. 1 (1978), P64-72) describes the dislocation density (in the range of 8 × 10 ⁴ to 2 × 10 ⁶ cm ^-2 ) and the light emission in the epitaxially grown layer (hereinafter referred to as epi layer) in GaP green LED. The relationship with efficiency has been reported. However, the luminous efficiency tends to be saturated near the lower limit of the dislocation density (8 × 10 ⁴ cm ⁻² ), and the effect when the dislocation density is further reduced has not been known.

Generally, an epi layer (epitaxially grown layer)
It is known that the dislocation density in the medium is determined by the dislocation density of the substrate single crystal, which is an important factor.
This is because when the epitaxial layer grows, the disorder of the atomic arrangement on the substrate surface due to the dislocation of the substrate single crystal is directly attracted. Therefore, in order to improve the crystallinity of the GaP epi layer, it is essential to reduce the dislocation density of the GaP single crystal of the substrate.

[0006] Recently, the present inventors have proposed that the vertical Bridgman method (hereinafter referred to as the VB method) has a dislocation density of 500 cm ^-2 or less.
We succeeded in fabricating a GaP single crystal substrate, and clarified the effect of improving luminous efficiency in the low dislocation density region, which was not known before (Japanese Patent Application No. 09-288584).

[0007] The dislocation density of a GaP single crystal substrate is usually determined by a so-called RC etching solution (HF: H ₂ O: HNO ₃ : AgNO ₃ = 4 ml: 8 ml: 6 m
(l: 10mg) is evaluated by the etch pit density of the surface etched. According to the previous literature, the etch pits include a D-pit caused by dislocation, a shallow dish-shaped S pit, and a cone-shaped CS pit.
JP-28800 describes that the dislocation density in the epi layer depends on the density of CS pits together with the D pits in the GaP substrate, and that the sum of the two corresponds to the dislocation density in the epi layer. The sum of 10 ⁴ cm ^-2 is required. For example, the D pit density obtained by chance is 10 ² cm ^-2
May dislocation density of the epitaxial layer even when using the platform of the wafer as a substrate becomes ^-2 10 ⁶ cm, its causes are not reduced the CS pit density, 10 ⁶ cm ^-2 It is caused by that. The origin of the D pit is known to be dislocation, but the origin of the S pit and CS pit has not been clarified. At present, the method is different.

[0008] The dislocation density of 500 produced by the aforementioned VB method
Even for GaP single crystal substrates of cm ^-2 or less, S pits, CS
It is often observed that pits are present at a high density of 10 ⁵ to 10 ⁶ cm ^-2 , and when such a substrate is used for epitaxial growth, that is, growth of an epi layer (hereinafter referred to as epi growth), an epitaxial growth crystal layer, It has been found that the dislocation density in the epi layer is as high as 10 ⁴ cm ^-2, which lowers the luminous efficiency.

On the other hand, since GaP originally has an indirect transition band structure, it cannot be denied that the luminance is relatively low as compared with GaAlAs-based high-brightness red LEDs and recent ultra-high-brightness InGaN-based green LEDs. It is considered difficult to surpass these in principle. Therefore, in GaP-LEDs, improvement of the performance and realization of the manufacturing process at lower cost are important technical development issues.

The current GaP-based LED does not use a GaP substrate itself as an active layer, but forms a junction structure such as pn or pin on several epi-grown layers formed on the substrate, and forms a bonding structure such as a luminescent layer ( (Active layer). Furthermore,
Even if we take only n layers, it is a multi-layer of several layers,
The manufacturing cost increases as the number of epi growth layers increases.

The current LED has a structure in which the epi layer is used as the active layer as described above because the crystallinity and purity of the substrate crystal are poor, and when a structure in which this is used as the active layer is adopted, There is no other choice since almost no emission luminance can be obtained. Furthermore, when the n-layer on the substrate is multi-layered and grown thick, similarly, when the epi-layer on the substrate is thin, the epi-layer is strongly affected by the substrate crystal and the crystallinity and purity are inferior. The thickness of the epi-grown layer is increased until this is alleviated.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a GaP epitaxial layer having a low dislocation density and a high luminous efficiency can be obtained with a good yield. An object of the present invention is to provide a GaP single crystal substrate suitable as a substrate for epitaxial growth of GaP, such as a substrate for LED production, and a method for producing the same.

Further, in the GaP-LED manufacturing process, a GaP-LED is manufactured by a process that does not require an epi-growth process with inferior productivity or a process in which the number of epi-growth processes is reduced as compared with the conventional process.
Accordingly, it is an object of the present invention to provide a method of manufacturing a GaP-LED capable of obtaining a GaP-LED having performance equal to or higher than the conventional one while reducing the manufacturing cost of the GaP-LED.

[0014]

In order to achieve the above object, a GaP single crystal substrate according to the present invention, a method for manufacturing the same, and a method for manufacturing a GaP-LED are described in claim 1. The method of manufacturing a GaP single crystal substrate according to claims 5 to 7 and the method of manufacturing a GaP-LED according to claims 8 to 11 are configured as follows.

That is, the GaP single crystal substrate according to claim 1 is
Dislocation density is not more 500 cm ^-2 or less, and the density of dislocation loops and having a surface is 500 cm ^-2 or less
It is a GaP single crystal substrate (first invention).

The GaP single crystal substrate according to the second aspect has a dislocation density of 500 cm ⁻² or less and a dislocation loop density of 50 cm ⁻² or less.
A GaP single crystal substrate characterized in that a layer having a thickness of 0 cm ^-2 or less is formed with a thickness of 5 μm or more from the substrate surface (second invention).

The GaP single crystal substrate according to claim 3 has a dislocation density of 500 cm ⁻² or less and a dislocation loop density of 50 cm ⁻² or less.
0 cm ^-2 or less layer is formed on the substrate surface, below which the number of atoms in the dislocation loop in the layer is 10 ⁶ cm per unit volume
GaP characterized in that a layer of ^-3 or more is formed
It is a single crystal substrate (third invention).

The GaP single crystal substrate according to claim 4, wherein the dislocation density is 500 cm ^-2 or less, and the dislocation loop density is 500 cm ^-2 or less. Assuming that the thickness of the layer in which the number of atoms is 10 ⁶ cm ^-3 or more per unit volume is Ls, Ld is 65 μm or more from the substrate surface, and the relationship between Ld and Ls is Ld ≦ Ls. 4. A GaP single crystal substrate according to claim 3, wherein the substrate is a GaP single crystal substrate.

A method of manufacturing a GaP single crystal substrate according to claim 5, wherein the GaP single crystal substrate having a dislocation density of 500 cm ^-2 or less on the substrate surface is heat-treated at 850 to 1200 ° C. (Fifth invention).

According to a sixth aspect of the present invention, in the method of manufacturing a GaP single crystal substrate, when the equilibrium phosphorus vapor pressure of GaP at the heat treatment temperature is P ^eq , the heat treatment is performed in a phosphorus vapor pressure atmosphere of P ^eq or less. (6th invention). The method of manufacturing a GaP single crystal substrate according to claim 7, wherein the dislocation density of the substrate surface is 500 cm ^-2 or less.
7. The method for manufacturing a GaP single crystal substrate according to claim 5, wherein the single crystal substrate is manufactured by a vertical Bridgman method (a seventh invention).

According to a eighth aspect of the present invention, there is provided a method of manufacturing a GaP-LED.
5. The method as claimed in claim 3, wherein the p-type or p-type dopant is doped.
A method for manufacturing a GaP light-emitting diode, characterized in that a pn junction is formed by diffusing an acceptor or donor element on the surface of the GaP single crystal substrate described above (an eighth invention). That is, in the method of manufacturing a GaP-LED according to claim 8, a pn junction is formed by diffusing an acceptor element onto the surface of the GaP single crystal substrate doped with an n-type dopant according to claim 3 or 4. 5. A pn junction is formed by subjecting a surface of the GaP single crystal substrate according to claim 3 or 4 doped with a p-type dopant to a diffusion treatment with a donor element. Is what you do. A GaP-LED according to claim 9
The method of manufacturing a GaP light-emitting diode according to claim 8, wherein the diffusion treatment is performed in an NH ₃ atmosphere (ninth invention).

The method for manufacturing a GaP-LED according to claim 10 is characterized in that:
5. The method as claimed in claim 3, wherein the p-type or p-type dopant is doped.
A method for manufacturing a GaP light-emitting diode, comprising forming a pn junction on the surface of the GaP single crystal substrate described above by epitaxial growth (a tenth invention). Further, in the method of manufacturing a GaP-LED according to claim 11, the epitaxial growth is performed by NH.
11. The method for producing a GaP light-emitting diode according to claim 10, which is performed in _three atmospheres (an eleventh invention).

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is embodied in the following manner, for example. A GaP single crystal substrate with a dislocation density of 500 cm ^-2 or less obtained by the VB method was
Heat treatment in a phosphorus vapor pressure atmosphere of ^eq (equilibrium phosphorus vapor pressure of GaP at heat treatment temperature) or less. Then, a GaP single crystal substrate according to the present invention is obtained.

Hereinafter, the function and effect of the present invention will be mainly described.

The present invention has been completed based on new findings obtained as a result of intensive studies on the formation phenomena and the origin of S and CS pits in VB-GaP crystals (GaP single crystals obtained by the VB method). It has been done.
The details will be described below.

The present inventors have developed a transmission electron microscope (TEM).
Single crystal grown by VB method (VB-GaP crystal)
Observing various defects in the crystal, the origin of the S pit defect was the so-called “super saturation” of Ga vacancies (points where Ga atoms escaped from the original lattice points) formed in a single crystal solidified from the melt. It was found to be an intrinsic type stacking fault. The reason that such vacancies are present at a high concentration in the first place is that a deviation from the stoichiometric composition of the melt (Ga amount <P
Amount). In other words, the vacancy defects generated by solidification become supersaturated as the temperature of the crystal decreases, and gather and precipitate on the {111} plane with defects in the crystal such as impurity atoms as nuclei. It is considered that a certain stacking fault is formed.

The size of the S pit defect is as small as about 0.05 μm in the seed-side crystal corresponding to the portion grown first from the melt, and is as large as about several μm in the tail-side crystal corresponding to the portion grown last from the melt. I understand. This is considered to be due to the fact that the deviation of the melt composition from the stoichiometric composition is further promoted with the crystal growth, or due to the difference in the thermal history after the crystal growth. In the tail-side crystal, two adjacent paired pits having a centered etch pit are observed, which confirms that the S pit is caused by a flank dislocation loop surrounding a stacking fault.

From the above, what has been conventionally called an S pit or a CS pit, the difference in appearance or absence of a core at the time of etching (S pit: no core, CS pit: It is understood that the same origin, that is, a stacking fault, has actually occurred. That is, the present inventors first revealed for the first time that a small-sized one is called an S pit and a large-sized one is called a CS pit.

Further, as described above, a flank-type dislocation loop is formed around the stacking fault. According to TEM observation, it has been found that a large number of fine precipitates of P exist here. From this, Ga vacancies (V _Ga ) were present in excess during crystallization from the melt, and V _Ga + P _P ( _{P at the} lattice position) = V _Ga -V _P (Intrinsic via reaction of the corresponding to stacking faults) + I _P (interstitial P atoms), and generates an I _P (interstitial P atom), those I _P is set as P fine precipitates dislocations, precipitated.

The background of the formation of stacking faults, which are macroscopic structural defects at a high density, due to such intrinsic point defects as vacancies, is based on the conventional LEC crystal [LEC method (liquid sealing pulling method). In the GaP single crystal obtained by), these point defects had a mechanism in which the dislocations acted as sinks and disappeared, whereas in the VB crystal, the dislocation density was low and the point defects remained in the crystal. This is considered to be due to the fact that it is easy to perform. That is, such an S pit defect is expected to be a more important defect in a VB crystal having achieved a low dislocation density.

As described above, the origin of the S pit defect has been clarified. Based on this finding, several methods for removing the S pit defect can be considered. Control of the melt composition during crystal growth is one of the methods. In the present invention, a method in which stacking faults are decomposed into vacancies again by heat-treating the single-crystal substrate and then diffused outward to the crystal surface to be eliminated is adopted as an S-pit defect removing method (fifth invention). Related matters).

According to the findings of the present inventors, in order to obtain a GaP epitaxial layer having an extremely low dislocation density, which is unprecedented, at a high yield, and to achieve a significant increase in luminance and a high yield of a GaP pure green LED, it is necessary to use GaP. The single crystal substrate needs to have a dislocation density of 500 cm ^-2 or less.

It is necessary to keep the density of dislocation loops at 500 cm ^-2 or less. The reason will be described below.

In the present invention, the dislocation density and the dislocation loop density can be measured by counting the pits formed by etching in the following manner. That is, the pit caused by the dislocation is usually called a D pit, and has a pit having a core such as A in FIG.
The dislocation is a line defect and is formed at a deep portion at an angle with respect to the substrate surface, so that it always has a pit having a core near the center regardless of the etching depth. on the other hand,
A pit caused by a dislocation loop has two types of pit shapes depending on its size and angle. A pit caused by a dislocation loop having a relatively small loop diameter has a centerless circular pit as shown in FIG. 5B (referred to as an S pit). In a dislocation loop having a relatively large loop diameter and a loop formed at an angle with respect to the substrate surface, as shown in FIG. 4C, a pit having a core such that two dislocations are close to each other. Appear in pairs (called CS pits). The distinction between the CS pit and the D pit can be made based on the point that the CS pits are overlapped to form a pair and the size thereof. Therefore, pits (D pits) caused by dislocations and pits (S pits and CS pits) caused by dislocation loops can be distinguished and counted, whereby the dislocation density and the dislocation loop density can be obtained.

A more specific example of how to determine the dislocation density and the dislocation loop density will be described below. RC etching solution for substrate surface (HF: H ₂ O: HNO ₃ : AgNO ₃ = 4ml: 8ml: 6ml: 10mg, 65 ℃)
And observed for 3 minutes using a differential interference microscope. The number of pits without core (S pits) having a pit diameter of 0.5 μm or more is counted, and the number per unit area: A is calculated. Pits having a pit diameter of less than 0.5 μm are considered to be caused by dislocation loops having a loop diameter of about 0.05 μm, and have almost no effect on the performance of the substrate. Pits (CS pits) that have a core and are found in pairs with overlapping pits are counted as one pair and counted.
Is calculated. This B is added to the above A, and the pit density (hereinafter, referred to as S pit density) due to the dislocation loop is obtained. Even when the dislocation loop is not exposed on the surface (in the case where the dislocation loop is just below the surface or in the case where it has already been removed by etching), it is measured as a pit. Is assumed to be の of the S pit density, and １ ／ of the S pit density is defined as the dislocation loop density.

On the other hand, the number of pits (D pits) that are core pits and are not paired is counted, and the number per unit area is calculated, which is defined as the dislocation density.

As a result of various experiments on the relationship between the epi growth and the surface of the GaP single crystal substrate, a GaP epi layer having an extremely low dislocation density, which has never been obtained before, was obtained at a high yield, and the high luminance and high yield of the GaP pure green LED were obtained. In order to achieve this, it is necessary for the GaP single crystal substrate not only to have a dislocation density of 500 cm ^-2 or less, but also to suppress the dislocation loop density, which actually affects epi growth, to 500 cm ^-2 or less. It turned out to be. This is a measured S-pit density of 1000
This is equivalent to the need to keep it below cm ^-2 .

Based on the above findings, the GaP single crystal substrate according to the present invention has, as described above, a surface having a dislocation density of 500 cm ⁻² or less and a dislocation loop density of 500 cm ⁻² or less. It is characterized by the following. Therefore, according to the GaP single crystal substrate according to the present invention, it is possible to obtain a GaP epilayer having a very low dislocation density and a high luminous efficiency, which has not been achieved in the past, with a good yield. The yield is improved (first invention).

In the case of epitaxial growth, a low dislocation loop layer, that is, a layer having a dislocation loop density of 500 cm ^-2 or less only needs to be present only on the outermost surface of the epitaxial growth. Etching to remove the substrate surface layer, which is a substrate pretreatment before epi growth,
Even if the melt back of the substrate in the early stage of the liquid phase epitaxy is taken into consideration, if a portion having a thickness of 5 μm from the substrate surface is formed as a layer having a dislocation loop density of 500 cm ⁻² or less (hereinafter referred to as a low defect layer). Is sufficient to obtain a GaP epilayer having a low dislocation density as described above. Therefore, if the low-defect layer is formed with a thickness of 5 μm or more from the substrate surface, a GaP epi-layer with extremely low dislocation density and high luminous efficiency, which has never existed in the past, can be obtained with good yield. Significantly higher brightness and higher yield of LEDs will be achieved (Part 2
invention).

Further, the formation of S-pit defects generated inside the substrate, that is, planar stacking faults surrounded by dislocation loops,
The impurity element in the low defect layer near the substrate surface, which has reduced the point defect concentration due to the outward diffusion, is also captured in the stress field by the dislocation loop, resulting in a decrease in the vacancy concentration in the substrate and the purity in the low defect layer. Has the effect of significantly improving In other words, dislocation loops are formed at a high density below the low defect layer, and the dislocation loops are formed and left, so that the crystallinity and purity near the substrate surface can be improved.

A substrate having such a low-defect layer with improved crystallinity and purity (hereinafter referred to as a high-purity low-defect layer or a high-quality layer) can form a light-emitting layer directly on the substrate surface. An object of the present invention is to provide a material having a higher function than the substrates according to the first and second aspects of the present invention and an application method thereof, and to manufacture an LED in which the substrate surface itself is used as an active layer (light emitting layer).

In this case, the thickness of the high-purity low-defect layer required on the substrate surface is appropriately selected depending on the LED structure formed here, but the low-defect layer is used directly as a part of the active layer. In an LED having such a structure, if the thickness is too small, the injected minority carriers generally diffuse to the lower layer and disappear in a non-luminous manner, so that the luminous efficiency of the LED decreases. From this point, it can be said that GaP requires a low defect layer thickness of about 50 μm or more. However, when the low defect layer is too thick, the proportion of the lower layer, that is, the portion where high-density dislocation loops are formed becomes small in the limited substrate thickness, so that the impurity trapping effect becomes insufficient, and the above-described effect (substrate surface) is obtained. The effect of improving the purity of the nearby low defect layer is not obtained.

The ratio of the lower layer necessary to obtain the above-mentioned effect is considered to depend on the impurity concentration in the substrate and the size (radius r) and density (D) of the dislocation loop for trapping the impurities. It is thought that it is necessary that the total length (2πrD) of the dislocation loop is sufficiently long to capture impurities having a predetermined concentration.

However, these relationships differ depending on the type of the impurity element, and are generally difficult to quantify. Therefore, it is necessary to actually determine them by experiments. Thus, as a result of an experiment, the following was found.

It is necessary that a layer in which the number of atoms in the dislocation loop in the layer is 10 ⁶ cm ^-3 or more per unit volume is formed below the low defect layer (third invention). Further, there is a relationship of Ls ≧ Ld between the thickness of the low-defect layer on one side of the substrate: Ld and the thickness of the lower layer: Ls in which the number of atoms in the dislocation loop is 10 ⁶ cm ⁻³ or more per unit volume. If so, good results can be obtained (fourth invention). At this time, Ld is 65 μm or more in consideration of suppression of non-luminous annihilation due to diffusion into the lower layer of the carrier and melting back of the substrate in the initial stage of the substrate pretreatment such as etching and liquid phase epitaxy. (Fourth invention).

For example, as-sliced GaP having a thickness of 300 μm
When an LED is manufactured using a single crystal substrate by liquid phase epi-growth as in the examples described later, the etching thickness + meltback thickness of the substrate surface on the device forming side needs to be about 15 μm. On the other hand, the thickness of the high-purity low-defect layer in the device is desirably 50 μm or more in view of the requirement of the carrier diffusion length (in terms of suppressing non-luminous annihilation due to diffusion into the lower layer of the carrier). Therefore, it is desirable that the thickness Ld of the low defect layer is 15 μm + 50 μm or more = 65 μm or more. It is desirable that Ld ≦ Ls (the thickness of the lower layer). Therefore, it is desirable that Ld be 65 μm to Ls (for example, 100 μm).

The size of the S pit caused by the dislocation loop is as small as about 0.05 μm in the seed-side crystal corresponding to the portion grown first from the melt, and about several μm in the tail-side crystal corresponding to the portion grown last from the melt. It becomes big. It can be considered that the reason for this is that the deviation of the melt composition from the stoichiometric composition is further promoted with the crystal growth, or that it is caused by the difference in the thermal history after the crystal growth. For example, due to the temperature gradient existing in the longitudinal direction of the crystal at the stage of cooling the crystal, the vacancies that have become supersaturated as the temperature at the lower part of the crystal lowers diffuse to the upper part (high temperature part) of the crystal with a lower degree of supersaturation, Void concentration is high on the tail side, and stacking faults (= S pit defects) caused by vacancy aggregates
It can be considered that the size has increased. Further, as described above, a flank-type dislocation loop is formed around the stacking fault. Observation by a transmission electron microscope revealed that a large number of fine precipitates of P existed here. From this, it is considered that the dislocation loop interacts with an excessive constituent element (P) or an impurity element to have an effect of trapping the P or the impurity element.

[0048] The low-defect layer such as with dislocation density of 500 cm ^-2 or less: GaP single crystal substrate according to the present invention having a (dislocation loop density 500 cm ^-2 or less layers) is the dislocation density: 500 cm ^- It can be manufactured by heat-treating a GaP single crystal substrate of ² or less at 850 to 1200 ° C. That is, a GaP single crystal substrate having a dislocation density of 500 cm ^-2 or less is heated to 850 to 1200 ° C.
The stacking fault, which is the origin of the S pit defect (generated by the aggregation of supersaturated Ga vacancies in the single crystal solidified from the melt), is again decomposed into Ga vacancies,
The vacancies can be diffused outward to the single crystal surface and eliminated, so that the number of stacking faults can be reduced and a low defect layer can be formed (fifth invention).

The temperature during the heat treatment (heat treatment temperature) is 850 to
The reason why the temperature is set to 1200 ° C. will be described below.

In order to form the low defect layer as described above within a practical time (within several tens of hours), the heat treatment temperature is set at an appropriate speed required for Ga vacancies to diffuse from the stacking faults to the single crystal surface. It is practical to use a speed that is sufficient for a heat treatment within several tens of hours. From this point, it is necessary to set the temperature to 850 ° C. or higher in a heat treatment for several tens of hours. If the temperature is lower than 850 ° C., the diffusion rate of Ga vacancies to the single crystal surface is low, so that a low defect layer cannot be formed even by heat treatment for several tens of hours. From this point, the lower limit of the heat treatment temperature was set to 850 ° C.

FIG. 1 shows the relationship between the heat treatment temperature and the thickness of the low defect layer. The thickness of a low defect layer formed when a GaP single crystal substrate having a dislocation density: 500 cm ^-2 or less was heat-treated at various temperatures for 20 hours was obtained by an experiment. At this time, the P vapor pressure of the atmosphere was set to be substantially equal to the equilibrium phosphorus vapor pressure (P ^eq ) of GaP at each temperature.

As the heat treatment temperature is higher, the diffusion rate of Ga vacancies to the surface of the single crystal is higher, and a low defect layer is formed on the surface of the single crystal in a short time, and is formed on the surface of the single crystal as shown in FIG. The thickness of the low defect layer increases, but at the same time, surface roughness due to thermal decomposition of GaP occurs. The decomposition pressure of GaP at 1200 ° C. is about 3 atm. For example, a suitable amount of P is added and sealed together with a GaP single crystal substrate in a quartz glass tube, and the inside of this sealed tube is filled.
If a P pressure of 3 atm, which is the same as the decomposition pressure of GaP, is generated, thermal decomposition of GaP is suppressed. When the temperature exceeds 1200 ° C, for example, 1250 ° C, the deformation due to the softening of the quartz glass tube is accelerated,
Since the decomposition pressure of GaP also becomes as high as 5 atm or more, heat treatment becomes difficult in a quartz glass sealed tube system. From this point, the upper limit of the heat treatment temperature is set to 1200 ° C.

For the above reasons, the heat treatment temperature is set to 850.
The temperature was set to 〜1200 ° C., and more preferably 900 to 1150 ° C. That is, when the temperature is 900 ° C. or higher, a low-defect layer having a thickness of 5 μm is formed by heat treatment for about 20 hours (a portion having a thickness of 5 μm or more from the substrate surface is formed in the low-defect layer). As a result, it is possible to surely obtain a GaP epitaxial layer having an extremely low dislocation density and a high luminous efficiency, which has not existed conventionally, as described above. When the temperature is lower than 900 ° C., a portion having a thickness of less than 5 μm from the substrate surface is formed in the low defect layer.
From this point, it is desirable that the temperature be 900 ° C. or higher. On the other hand, considering the heat resistance of the material used in the heat treatment system (for example, a quartz glass tube), heat treatment at 1150 ° C. or lower is industrially preferable.

The heat treatment conditions required for purifying the low-defect layer on the surface (forming a high-purity low-defect layer) will be described below.

The harmful point defects that cause a reduction in the brightness of the LED include impurities such as transition metal elements and oxygen that form deep levels in the GaP semiconductor, as well as vacancies and interstitial of Ga and P as constituent elements. An atom, an anti-site defect, and a compound defect of these and an impurity element can be considered. The diffusion rate in these GaPs is not always determined accurately, but the one with the lowest diffusion rate is considered to be Ga vacancy defects, and other transition metal elements, oxygen, etc. It is presumed to have a large diffusion rate at the above heat treatment temperature. Further, the composite defect is decomposed into impurities and point defects at the heat treatment temperature, and the behavior can be handled by considering the respective diffusion rates.

In the first place, the formation of the low defect layer is caused by the decomposition of stacking faults as vacancy aggregates during the heat treatment and outward diffusion of Ga vacancies and P vacancies into the substrate surface. This Ga
Since the diffusion rate of vacancies is the lowest as described above, at the stage where the low defect layer is formed on the substrate surface layer, the impurity elements and point defects have already moved sufficiently and are captured on dislocation loops inside the substrate. You can think that it is.

However, the behavior of the trapping of an impurity element into the dislocation loop differs depending on the interaction energy between the element and the dislocation, and the trapping rate differs depending on the temperature and the impurity element concentration. In general, the temperature at which the diffusion rate slows down and effectively freezes the movement of atoms and point defects (approximately 700
Above ° C), the higher the interaction energy, the lower the temperature, and the higher the impurity concentration, the higher the trapping rate.

Therefore, it is not necessary to perform a heat treatment longer than the heat treatment time for forming the low defect layer, especially for trapping impurities.
It is recommended that the temperature be reduced to about 100 ° C / h to around 0 ° C.
This is effective for trapping impurities. That is, by this cooling, impurity elements and the like not captured at the heat treatment temperature for forming the low defect layer can be further captured in the dislocation loop, and the capture rate of the impurity elements and the like can be extremely increased.

The atmosphere for the heat treatment is preferably a phosphorus vapor pressure atmosphere of GaP equilibrium phosphorus vapor pressure ^Peq or less at the heat treatment temperature, and the heat treatment is desirably performed in such an atmosphere (the sixth invention). That is, in order to suppress the thermal decomposition of GaP,
P may be added and sealed in the atmosphere to generate a P partial pressure (P vapor pressure). At this time, if the P partial pressure (P vapor pressure) is high, the Ga vacancy concentration near the surface of the single crystal becomes high, although it is good in terms of suppressing the thermal decomposition of GaP.
Outward diffusion of Ga vacancies is inhibited. If a P vapor pressure higher than the decomposition pressure of GaP at a certain heat treatment temperature (= equilibrium P vapor pressure P ^eq ) is applied, the thermal decomposition of GaP is completely suppressed, but the outward diffusion of Ga vacancies is suppressed. It was found that the formation of the low defect layer near the surface was remarkably inhibited, and the formation of the low defect layer near the surface was significantly slowed down. Therefore, the atmosphere during the heat treatment for forming the low defect layer is P
It is preferable to use an atmosphere having a low vapor pressure. However, if the P vapor pressure is low at a high temperature, thermal decomposition of GaP is promoted. In consideration of this point, it is preferable to set the decomposition pressure of GaP (= equilibrium P vapor pressure P ^eq ) as the upper limit and set the P vapor pressure lower than that. In other words, the atmosphere for the heat treatment is G at the heat treatment temperature.
It is desirable that the phosphorus vapor pressure atmosphere of less equilibrium phosphorus vapor pressure P ^eq of aP. However, when the heat treatment temperature is relatively high and the phosphorus vapor pressure is low, the formation rate of the low defect layer is high, but Ga
Since the thermal decomposition of P proceeds rapidly, it is necessary to take measures such as limiting the heat treatment time to a short time.

In the above heat treatment, in addition to the above-described method of heat treatment in a closed tube system such as a sealed tube of quartz glass, heat treatment in an open tube system while flowing an inert gas such as argon or hydrogen gas to prevent oxidation. Can be adopted. For heat treatment method of the latter open pipe system, or flowing P gas from the heated P source, such as by adding (inflow) a phosphorus compound gas such as PH _3, P-partial pressure of the heat treatment atmosphere in the system Can be controlled.

Prior to the liquid phase epitaxy, a GaP single crystal substrate may be subjected to a heat treatment in a hydrogen atmosphere in an epitaxy furnace to form a low defect layer on the substrate surface. In this case, there is an advantage that epi growth can be performed in the epi growth furnace following the heat treatment without removing the substrate from the furnace.

In order to obtain a GaP single crystal substrate according to the present invention having a dislocation density of 500 cm ⁻² or less and having a low defect layer, a GaP single crystal substrate having a dislocation density of 500 cm ⁻² or less subjected to a heat treatment is: It can be obtained by a method for producing a compound semiconductor single crystal having a low dislocation density described in Japanese Patent Application No. 09-288584. An example of the method described in Japanese Patent Application No. 09-288584 is as follows.

That is, this method provides a compound semiconductor having a low dislocation density by a vertical Bridgman method or a vertical temperature gradient method in which a temperature gradient is applied to a raw material melt and a crystal is solidified from below to above to obtain a single crystal. A method for producing a single crystal,
The temperature gradient applied to the melt is an upper region having a small temperature gradient of 7 ° C./cm or less,
A method for producing a compound semiconductor single crystal having a low dislocation density, comprising: a lower region having a large temperature gradient formed by a quadruple temperature gradient, and having a boundary between the two regions in a range where the crystal grows. It is. According to this method, a compound semiconductor single crystal having a dislocation density of 500 cm ^-2 or less can be obtained.
Therefore, when the compound semiconductor single crystal manufactured by this method is set as a GaP single crystal substrate, a GaP single crystal substrate having a dislocation density of 500 cm ⁻² or less can be obtained.

[0064]

(Example 1) 50 mm in diameter, plane orientation {111},
Six VB-GaP single-crystal substrates with a dislocation density of 200 cm ^-2 (GaP single-crystal substrates obtained by the VB method) were vacuum-enclosed in a quartz glass tube with an inner diameter of 70 mm while standing on a quartz glass substrate holder. . At this time, the equilibrium P of GaP at each heat treatment temperature is placed in the quartz glass tube together with the GaP single crystal substrate.
An amount of red phosphorus that generates a partial pressure (equilibrium P vapor pressure P ^eq ), that is, an amount of red phosphorus that makes the P vapor pressure of the atmosphere during the heat treatment equal to P ^eq was added. The amount of red phosphorus added is
It was determined on the assumption that phosphorus exists as a P ₄ molecule at each heat treatment temperature and behaves as an ideal gas.

The S of the VB-GaP single crystal substrate before vacuum encapsulation
The pit density was about 2.3 million cm ^-2 and was high density. The S pit density of this substrate was measured by using an RC etching solution (HF: H ₂ O: HNO ₃ : AgNO ₃ = 4 ml: 8 ml: 6 ml: 10 mg,
After etching at 65 ° C.) for 3 minutes, the etched surface was observed by an optical microscope (differential interference microscope), and the number was determined by counting the number of shallow dish-shaped etch pits without a core formed on the surface.

The GaP single crystal substrate and the quartz glass tube enclosing red phosphorus were set in a heat treatment furnace, and 850, 900,
After heat treatment at 1000, 1150, and 1200 ° C. for 20 hours, it was taken out of the furnace and rapidly cooled.

The GaP single crystal substrate after the heat treatment was replaced with # 11
After cleaving at 0 ° plane, AB etchant (H ₂ O: AgN
O ₃ : CrO ₃ : HF = 20 ml: 80 mg: 10 g: 10 ml, 50 ° C) and 4
Etching was performed for 0 minutes, followed by observation with a differential interference microscope to measure the S pit density. From the measurement result of the S pit density, the low defect layer (S pit density: 1000
The thickness of a layer having a size of cm ⁻² or less, that is, a layer having a dislocation loop density of 500 cm ⁻² or less, was obtained. FIG. 1 shows the relationship between the heat treatment temperature of the GaP single crystal substrate and the low defect layer thickness after the heat treatment.

In the vicinity of the surface of the GaP single crystal substrate after the heat treatment, a low defect layer (a layer having an S pit density of 1000 cm ^-2 or less, ie, a dislocation loop density of 500 cm ^-2 or less) was formed. The thickness of the low defect layer is 3 μm at a heat treatment temperature of 850 ° C.
m, heat treatment temperature: 110 μm at 1200 ° C., and increased sharply with heat treatment temperature rise.

Heat treatment temperature: The GaP single crystal substrate obtained by heat treatment at 1150 ° C. was used for epi growth after lapping both surfaces by about 10 μm to remove the outermost surface. That is, the GaP single crystal substrate after lapping is etched with aqua regia for 5 minutes, and then (1) by a usual liquid phase epi growth apparatus.
11) An undoped GaP layer (GaP epi layer) on the P
m grown.

After the GaP epi layer grown in this manner was etched with an RC etchant for 3 minutes, the etched surface was observed with a differential interference microscope and the number of dislocations was counted to determine the dislocation density on the epi growth surface. Measured. As a result, the dislocation density in the epi layer is 300 ~ 450cm ^-2
And it was confirmed that it was low.

(Comparative Example 1) The dislocation density and the S pit density of the GaP single crystal substrate taken from the position adjacent to the GaP single crystal substrate in Example 1 with a single crystal ingot were measured. The dislocation density was 210 cm ^-2 and the S pit density was 2.8 million cm ^-2 , which were the same as in the case of the GaP single crystal substrate before heat treatment in Example 1 within an error range.

The GaP single crystal substrate was used for epi growth without heat treatment, and a GaP epi layer was grown by 20 μm.
At this time, the substrate was placed on the epi-growth slide board at the same time as the epi-growth substrate of Example 1, so that both were grown under the same conditions.

The dislocation density was measured for the GaP epitaxial layer grown as described above. The dislocation density in the epi layer is 120
00 cm ^-2 . This is because the S pit density in the GaP single crystal substrate for epi growth is high, and the high density S pits have introduced high density dislocations into the epi layer.

(Example 2) A diameter of 50 mm and a plane orientation of # 11
1 V, VB-GaP single crystal substrate 6 with a dislocation density of 200 to 500 cm ^-2
With the pieces standing on the quartz glass substrate holder,
It was vacuum-sealed in a quartz glass tube of mm. At this time, red phosphorus was added into the quartz glass tube together with the GaP single crystal substrate. The amount of red phosphorus added was varied. That is, the added amount of red phosphorus is an amount determined under the assumption that phosphorus exists as a P ₄ molecule at each heat treatment temperature and behaves as an ideal gas.
The vapor pressure was changed to 4 atm, 5 atm, 1.6 atm, 0.32 atm, and 0.16 atm.
In this inside, 1.6Atm corresponds to GaP equilibrium P vapor pressure P ^eq at 1150 ° C..

The VB-GaP single crystal substrate before vacuum sealing
The pit density was approximately 2 million to 4.1 million cm ^-2 , indicating high density.

The GaP single crystal substrate and the quartz glass tube enclosing red phosphorus were set in a heat treatment furnace, heat-treated at 1150 ° C. for 20 hours, taken out of the furnace, and rapidly cooled.
With respect to the GaP single crystal substrate after the heat treatment, the thickness of the low defect layer was determined in the same manner as in Example 1. The results are shown in FIG. 2 as a relationship between the P vapor pressure during the heat treatment of the GaP single crystal substrate and the low defect layer thickness after the heat treatment.

The thickness of the low defect layer in the GaP single crystal substrate after the heat treatment was thicker as the P vapor pressure during the heat treatment was lower. When the P vapor pressure was 5 atm, the average was 32 μm, but the P vapor pressure was 0.16. In the case of atm, it was 180 μm. However, whereas the P vapor pressure weight change before and after the heat treatment in the case of more than GaP equilibrium P vapor pressure P ^eq (1.6atm) was observed almost 0.1%, and P vapor pressure 0.32Atm, 0.16at
m, the weight change before and after heat treatment was 4
% And 9.6%, and the surface roughness of the substrate was observed correspondingly.

However, the P vapor pressure of 0.16 at
In the case of m, a low defect layer was formed over the entire GaP single crystal substrate, and there was no S pit defect.

For the GaP single crystal substrate obtained by heat treatment at the above-mentioned P vapor pressure: 0.16 atm, the both surfaces were wrapped at 20 μm per side to remove the outermost surface. The GaP epi layer is formed in the same way as
The growth was 20 μm. And for this GaP epilayer,
When the dislocation density was measured, the dislocation density in the GaP epilayer was
450 cm ^-2 , confirming the effect of heat treatment.

The GaP epilayer (GaP epilayer according to Example 2) was irradiated with 488 nm light of an argon laser, and the 555 nm pure green photoluminescence intensity at room temperature was measured.
On the other hand, for the GaP epi layer according to Comparative Example 1, pure green photoluminescence intensity at 555 nm was measured in the same manner as described above. As a result, in the case of the GaP epilayer according to Example 2, the pure green photoluminescence intensity was about 2.5 times that of the GaP epilayer according to Comparative Example 1, and the luminous efficiency was remarkable in the epilayer having a low dislocation density. It was confirmed that it was increasing.

(Embodiment 3) Diameter 50 mm, plane orientation # 11
A single VB method-GaP single crystal substrate having a dislocation density of 500 cm ^-2 is placed on a quartz glass substrate holder and placed in a quartz glass reaction tube having an inner diameter of 80 mm. Heat treatment was performed at 1100 ° C. for 5 hours in a hydrogen gas stream. Then, the thickness of the low defect layer of the GaP single crystal substrate after the heat treatment was determined in the same manner as in Example 1. As a result,
It was found that a portion having a thickness of 15 μm from the substrate surface was a low defect layer.

(Comparative Example 2) Diameter 50 mm, plane orientation # 11
1 V, a single crystal substrate of VB-GaP single crystal with a dislocation density of 400 cm ^-2 is placed on a quartz glass substrate holder and placed in a quartz glass reaction tube with an inner diameter of 80 mm. Medium heat treatment was performed at 1250 ° C. for 5 hours. The GaP single crystal substrate after the heat treatment was a low defect layer over the entire thickness of the substrate. However, the heat treatment reduced the weight by 35% and made the substrate thickness significantly non-uniform, so that the above heat treatment conditions were inappropriate.

(Embodiment 4) Diameter 50 mm, plane orientation # 11
1 V, a single VB-GaP single crystal substrate with a dislocation density of 500 cm ^-2 is placed on a quartz glass substrate holder and placed in a quartz glass reaction tube with an inner diameter of 80 mm. Medium heat treatment was performed at 1200 ° C. for 5 hours. GaP after this heat treatment
As for the single crystal substrate, a portion having a thickness of 35 μm from the substrate surface was formed in the low defect layer. The weight loss rate by heat treatment was 8%, and the surface was somewhat roughened.
A flat surface was obtained by lμm lapping.

(Example 5) A diameter of 50 mm and a plane orientation of # 11
1 V, a single VB-GaP single crystal substrate with a dislocation density of 500 cm ^-2 is placed on a quartz glass substrate holder and placed in a quartz glass reaction tube with an inner diameter of 80 mm, and a nitrogen gas flow of 1 L / min. Heat treatment was performed at 850 ° C. for 60 hours. As for the GaP single crystal substrate after the heat treatment, a portion having a thickness of 5 μm from the substrate surface was formed in the low defect layer. The rate of weight loss by the heat treatment was 0.05%, and almost no surface roughness was observed.

After the heat-treated GaP single crystal substrate was etched with aqua regia for 5 minutes without lapping,
In the same manner as in Example 1, the GaP epi layer was
Grew. When the dislocation density of this GaP epilayer was measured, the dislocation density in the GaP epilayer was 450 cm ^-2 on average in the plane, which was good.

Example 6 A VB-GaP single crystal having a diameter of 52 mm, a thickness of 300 μm, a plane orientation of {111}, an average dislocation density of 200 cm ⁻² , and a Te-doped carrier concentration of 8 × 10 ¹⁷ cm ⁻³ was used. Six crystal substrates were vacuum-enclosed in a quartz glass tube having an inner diameter of 70 mm in a state of standing on a quartz glass substrate holder. At this time, red phosphorus was added to the quartz glass tube together with the GaP single crystal substrate in such an amount as to generate an equilibrium P partial pressure of GaP at the heat treatment temperature. The amount of red phosphorus added is such that phosphorus
_It was determined on the assumption that it exists as _four molecules and behaves as an ideal gas. In this example, the heat treatment temperature was 1100 ° C., the internal volume of the quartz glass tube was 500 ml, and 0.676 g of red phosphorus was added.

After the above quartz tube filling was heat-treated at 1100 ° C. for 20 hours, it was cooled down to 700 ° C. at 100 ° C./h, the furnace power was turned off, and it was allowed to cool.

The heat-treated GaP single crystal substrate was cleaved, etched with an AB etchant, and observed. As a result, a high-purity low-defect layer having a thickness of 65 μm was formed near the surface of the GaP single crystal substrate. . As a result of RC etching observation of the (111) plane, S pits due to dislocation loops having a diameter of about 2 μm or less were observed inside the substrate at a high density of about 1.2 million / cm ⁻² .

The density D of atoms on the dislocation loop surface forming the S-pit defect of the substrate per unit volume is D (cm ⁻³ ).
= Π × r ² × {S / (t + 2r)} × 7.8 × 10 ¹⁴ Here, r (cm) is determined by selecting ten dislocation loops having a loop diameter of 0.05 μm or more by transmission electron microscope observation and averaging the radiuses of these loops. S (cm ⁻² ) is the S pit density,
Determined by the method described above (method based on RC etching observation).
t (cm) is the etching depth. Also, 7.8 × 10 ¹⁴ (
atoms · cm ⁻² ) is the atomic density of the (111) plane in GaP. In this embodiment, it was calculated to be ^{D = 1 × 10 17 cm -3} .

Using the above substrate, the red L
ED was prepared. After removing the surface layer of one substrate by aqua regia about 15 μm, the substrate and ZnP ₂ : 0.2 g were again sealed in a quartz tube together with a 10 Torr oxygen atmosphere, and Zn diffusion treatment was performed at 800 ° C. for 90 minutes. The substrate after this diffusion treatment has a Ga (111)
It was polished and removed by 0 μm, and a Zn diffusion profile was measured on the P (111) surface side by a semiconductor profile analyzer. As a result, a Zn diffusion layer of 5 μm was formed, and the surface layer was p-type. The hole concentration near the pn junction interface is 2 × 10 ¹⁷
cm ^-3 .

An ohmic electrode for LED was formed on the substrate after the above-mentioned Zn diffusion treatment by a usual lithography method. Au-Zn alloy was deposited on the p-GaP side and Au-Ge alloy was deposited on the n-GaP side as an electrode material, and ohmic contact was obtained through heat treatment. Then, each chip was separated by dicing, and the light emission luminance was measured on a prober.

The emission wavelength is 700 nm red, and commercially available L
Zn, O fabricated by epitaxial growth on EC substrate
The brightness was about 25% higher than the brightness of an LED chip with a diffused p-GaP / n-GaP / n-GaP substrate structure.

(Example 7) A pure green LED was manufactured as follows using a GaP single crystal substrate on which a high-purity low-defect layer was formed by the same heat treatment method as in Example 6. After removing about 15 μm of the surface layer of the substrate with aqua regia, the substrate and 0.2 g of ZnP ₂ were vacuum-sealed to 5 × 10 ⁻⁶ Torr in a quartz tube, and then heated at 780 ° C.
The Zn diffusion treatment was performed for 120 minutes. Using the substrate after the Zn diffusion treatment, an LED chip was manufactured in the same manner as in Example 6.

The emission luminance of the LED chip was measured. The LED chip according to this example is a p-GaP / n-GaP / i-Ga fabricated on a commercially available LEC substrate by an epitaxial growth process.
Compared to pure green LED chip with P / n-GaP substrate structure,
The emission luminance at 555 nm under the current of mA was almost the same.

Example 8 A VB-GaP single crystal having a diameter of 52 mm, a thickness of 300 μm, a plane orientation of {111}, an average dislocation density of 200 cm ⁻² , and a Te-doped carrier concentration of 5 × 10 ¹⁷ cm ⁻³ was used. Six crystal substrates were vacuum-enclosed in a quartz glass tube having an inner diameter of 70 mm in a state of standing on a quartz glass substrate holder. At this time, red phosphorus was added to the quartz glass tube together with the GaP single crystal substrate in such an amount as to generate an equilibrium P partial pressure of GaP at the heat treatment temperature. The amount of red phosphorus added is such that phosphorus
_It was determined on the assumption that it exists as _four molecules and behaves as an ideal gas. In this example, the heat treatment temperature was 1200 ° C., the inner volume of the quartz glass tube was 500 ml, and 1.10 g of red phosphorus was added.

After the above quartz tube filling was heat-treated at 1200 ° C. for 15 hours, it was cooled down to 700 ° C. at 100 ° C./h, the furnace power was turned off, and allowed to cool.

AB etching of the cleaved surface of the GaP single crystal substrate after the heat treatment was observed. As a result, a high-purity low-defect layer having a thickness of 100 μm was formed near the surface of the GaP single crystal substrate. Also, as a result of RC etching observation of (111) plane,
Inside the substrate, S pits caused by dislocation loops having a diameter of about 5 μm or less were observed at a high density of about 500,000 / cm ⁻² . In this case, the density D per unit volume of atoms on the dislocation loop surface forming the S pit defect is 2.7 × 10 ¹⁸ cm ⁻³ .

Using the above substrate, a pure green LED using the substrate as an n-layer was manufactured by a liquid phase epitaxy method as follows. After the surface layer of the substrate was removed by etching with aqua regia about 15 μm, the i-GaP layer was removed to a thickness of 5 μm and then p-
A GaP layer was grown to 30 μm. From the epi-substrate thus obtained, the same method as in Example 6
A chip was prepared.

The emission luminance of the LED chip was measured. The LED chip according to this example is a nitrogen-doped p-Ga produced by an epitaxial growth process on a commercially available LEC substrate.
Compared to pure green LED chip with P / n-GaP / i-GaP / n-GaP substrate structure, 555nm emission luminance is 20% under 20mA current
it was high.

Example 9 An epitaxy was performed in an NH ₃ atmosphere by flowing NH ₃ gas into a liquid phase epitaxy furnace. Except for this point, a pure green LED chip was manufactured in the same manner as in Example 8. Then, the emission luminance of the LED chip was measured. This LED chip is a p-GaP / n-GaP / i-
Compared to a pure green LED chip with a GaP / n-GaP substrate structure (N-doped), the emission luminance at 565 nm was 25% higher under a current of 20 mA.

(Example 10) The dislocation density on the substrate surface was 10c.
m ^-2 , S pit density is 800cm ^-2 (dislocation loop density: 400cm
^-2 ), below which the density D per unit volume of atoms on the dislocation loop surface forming S-pit defects is 1 × 10 ¹⁶ cm.
^-3 high S pit defect layer (high dislocation loop density layer)
Using a 300 μm thick GaP substrate formed with a thickness of 0 μm, a pure green LED chip was manufactured in the same manner as in Example 9. Then, the emission luminance of the LED chip was measured. This LED chip is a p-GaP / n-GaP / i-
Compared with a green LED chip having a GaP / n-GaP substrate structure (N-doped), the emission luminance at 565 nm was almost equal under a current of 20 mA.

(Comparative Example 3) The heat treatment time in the heat treatment conditions in Example 8 was set to 20 hours.
Perform the same heat treatment as in
A GaP substrate on which a high-purity low-defect layer having a thickness was formed was obtained. Using this GaP substrate, a pure green LED chip was manufactured in the same manner as in Example 7. Then, the emission luminance of the LED chip was measured. This LED chip is used in Example 7
As compared with the case of the LED chip according to the above, only a brightness of about 45% was obtained.

Comparative Example 4 The heat treatment temperature in the heat treatment conditions in Example 6 was set to 1000 ° C., except for this point.
The same heat treatment as in the case was performed to obtain a GaP substrate having a high-purity low-defect layer having a thickness of 18 μm formed near the substrate surface. this
Using a GaP substrate, a pure green LED chip was manufactured in the same manner as in Example 7. Then, the emission luminance of the LED chip was measured. This LED chip is used in Example 7
Only about 40% of the brightness was obtained as compared with the case of the LED chip according to the above.

(Comparative Example 5) The heat treatment temperature in the heat treatment conditions in Example 6 was set to 1080 ° C.
The same heat treatment as in the case was performed to obtain a GaP substrate having a high-purity low-defect layer having a thickness of 60 μm formed near the substrate surface. this
Using a GaP substrate, a pure green LED chip was manufactured in the same manner as in Example 7. Then, the emission luminance of the LED chip was measured. This LED chip is used in Example 7
As compared with the case of the LED chip according to the above, only a luminance of about 65% was obtained.

(Comparative Example 6) The dislocation density on the substrate surface was 10c
m ^-2 , S pit density is 800cm ^-2 (dislocation loop density: 400cm
^-2 ), below which the density D per unit volume of the atoms of the dislocation loop surface forming the S pit defect is 0.5 × 10 ¹⁶
cm ^-3 high S pit defect layer (high dislocation loop density layer)
Using a 300 μm thick GaP substrate formed with a thickness of 120 μm, an LED chip was fabricated in the same manner as in Example 9. Then, the emission luminance of the LED chip was measured. This LED chip and p-GaP / n-GaP / i-GaP / n-
20mA with GaP substrate structure (N-doped) green LED chip
Comparing the emission luminance at 565 nm under the current of the above, the LED chip according to Comparative Example 6 obtained only about 70% of the luminance of the latter LED chip.

[0106]

The GaP single crystal substrate according to the present invention has an extremely low dislocation density and a surface (low defect layer) having an extremely low dislocation loop density. A GaP epilayer (epitaxially grown layer) having a low and high luminous efficiency can be obtained with good yield.
P Pure green LED (visible light emitting diode) has the effect of greatly increasing the brightness and yield.

Further, a layer having a high dislocation loop density can be formed below the low defect layer. In this case, the low defect layer can be a high purity low defect layer having extremely excellent purity and crystallinity. The high-purity low-defect layer is used as an active layer (light-emitting layer).
When an active layer is formed by providing an epi-growth layer on the high-purity low-defect layer, the effect of reducing the thickness of the epi layer can be obtained.

The method of manufacturing a GaP single crystal substrate according to the present invention provides the G
There is an effect that an aP single crystal substrate can be obtained by a simple method of heat treatment.

Since the method of manufacturing a GaP-LED according to the present invention uses a substrate having a high-purity low-defect layer as described above, this high-purity low-defect layer can be used as an active layer. When an epi growth layer is provided on the low defect layer to form an active layer, the epi layer can be made thinner.
The GaP-LED manufacturing process can manufacture a GaP-LED by a process that does not require an epi-growth process with inferior productivity or a process that reduces the number of epi-growth processes compared to the conventional process.
A GaP-LE with the same or better performance as before, while reducing manufacturing costs.
It has the effect of being able to obtain D.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a heat treatment temperature and a low defect layer thickness of a GaP single crystal substrate according to an example of the present invention.

FIG. 2 is a diagram showing a relationship between P _P4 (P vapor pressure) and a low defect layer thickness during heat treatment of a GaP single crystal substrate according to an example of the present invention.

FIG. 3 is a drawing substitute photograph showing a micrograph of an etched surface of a GaP single crystal substrate.

FIG. 4 is a drawing substitute photograph showing a micrograph of an etched surface of a GaP single crystal substrate.

FIG. 5 is a drawing substitute photograph showing a micrograph of an etched surface of a GaP single crystal substrate.

Continued on the front page (72) Inventor Seiichiro Omoto 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo F-term in Kobe Steel, Ltd. Kobe Research Institute (reference) 4G077 AA03 BE43 CD10 FC04 FC05 FE02 5F041 AA03 AA40 CA23 CA37 CA63 CA73 CA74

Claims (11)

[Claims] Claims: 1. A dislocation density of 500 cm ^-2 or less, and
A GaP single crystal substrate having a surface having a dislocation loop density of 500 cm ^-2 or less. 2. A dislocation density of 500 cm ^-2 or less, and
A GaP single crystal substrate, wherein a layer having a dislocation loop density of 500 cm ^-2 or less is formed with a thickness of 5 µm or more from the substrate surface. 3. A dislocation density of 500 cm ^-2 or less, and
Layer density of dislocation loops is 500 cm ^-2 or less is formed on the substrate surface, the layer number is the unit volume per 10 ⁶ cm ^-3 or more atoms in the dislocation loops of intra-layer thereunder is formed A GaP single crystal substrate. 4. A layer having a dislocation density of 500 cm ^-2 or less and a dislocation loop density of 500 cm ^-2 or less.
Ld, the number of atoms in the dislocation loop is 10 ⁶ per unit volume
4. The GaP single cell according to claim 3, wherein, when the thickness of the layer that is not less than cm ^-3 is Ls, Ld is not less than 65 μm from the substrate surface, and the relationship between Ld and Ls is Ld ≦ Ls. Crystal substrate. 5. A method for manufacturing a GaP single crystal substrate by heat-treating a GaP single crystal substrate having a dislocation density of 500 cm ⁻² or less on a substrate surface at 850 to 1200 ° C. 6. The method of manufacturing a GaP single-crystal substrate according to claim 5, wherein the heat treatment is performed in an atmosphere of phosphorus vapor pressure equal to or lower than P ^eq when an equilibrium phosphorus vapor pressure of GaP at the heat treatment temperature is P ^eq . 7. The method of manufacturing a GaP single crystal substrate according to claim 5, wherein the GaP single crystal substrate having a dislocation density of 500 cm ⁻² or less on the substrate surface is manufactured by a vertical Bridgman method. 8. A pn junction is formed by subjecting a surface of the GaP single crystal substrate according to claim 3 or 4 doped with an n-type or p-type dopant to an acceptor or donor element by diffusion treatment. A method of manufacturing a GaP light emitting diode. 9. The method according to claim 8, wherein the diffusion process is performed in an NH ₃ atmosphere. 10. A method of manufacturing a GaP light-emitting diode according to claim 3, wherein a pn junction is formed by epitaxial growth on the surface of the GaP single crystal substrate doped with an n-type or p-type dopant. 11. The method according to claim 10, wherein the epitaxial growth is performed in an NH ₃ atmosphere.