JPH0477713B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to liquid phase crystal growth of GaAlAs, in particular, by providing a certain temperature difference in a melt containing a solute,
This paper relates to the liquid phase crystal growth of GaAlAs using the temperature difference method, in which solute is continuously transported from a high temperature section to a low temperature section, and crystals are sequentially grown on a large number of substrates in the low temperature section.

[Prior art] Ga _1-x Al _x As is the composition in the crystal (proportion of AlAs) x
It is a mixed crystal semiconductor whose bandgap energy can be changed from 1.43eV to 2.16eV by changing the . Therefore, Ga _1-x Al _x As is widely used as a material for light emitting diodes (LEDs) that emit light from infrared to visible light. For example, the wavelength
To obtain a 660nm red light LED, the p-
For Ga _1-x Al _x As, x should be about 0.35, x should be about 0.15 to obtain an LED with a wavelength of 780 nm, and x should be about 0.01 to obtain an infrared light LED with a wavelength of 850 nm. Therefore,
In a GaAlAs LED, x in p-Ga _1-x Al _x As is determined depending on the target emission wavelength. n
-Ga _{1-X Al} x of p-Ga _1-x Al _x As is n-Ga _1- x x of Al _x As is p-Ga _1-x
A value is selected that is necessary to confine electrons and holes in the Al _x As light-emitting layer, or to effectively guide light emitted from p-Ga _1-x Al _x As to the outside of the crystal without absorbing it. For example, if x in p-Ga _1-x Al _x As is 0.35, x in n-Ga _1-x Al _x As is chosen to be 0.6-0.85.

The active region of an LED is usually produced by epitaxial growth on a substrate crystal. As the substrate crystal, it is desirable to obtain one that is not expensive, has a large diameter, and has good crystallinity. The Ga _1-x Al _x As mixed crystal has little lattice mismatch with the GaAs crystal over the entire range of composition x. Therefore, a high-quality Ga _1-x Al _x As can be grown epitaxially. For these reasons, GaAlAs is currently widely used as a high-brightness, high-output light emitting diode that emits light ranging from infrared light to red light.

Liquid phase crystal growth is widely used as a crystal growth technique, especially for compound semiconductors. A slow cooling method, a temperature difference method, and the like are known as liquid phase crystal growth methods.

The slow cooling method is, for example, a method in which a crystalline material is heated and melted in a crucible, and then gradually cooled and crystallized. It is divided into the Stockburger method, Bridgeman method, etc. depending on the cooling method, crucible shape, etc.

The temperature difference method is a method in which a high-temperature zone and a low-temperature zone are formed with a certain temperature difference (or temperature gradient), and raw materials are supplied from the high-temperature zone and crystals are precipitated in the low-temperature zone. However, in a narrow sense, it refers to a method in which a temperature difference is provided within a solution (melt), and the solute is dissolved (supplied) in the high temperature part, and the solute is precipitated from the supersaturated solution in the low temperature part. That is,
In the temperature difference method liquid phase crystal growth method, the growth material (solute)
This method creates a temperature difference in a solution (melt) in which the solute is dissolved, transports the solute toward the substrate by temperature gradient and diffusion, and grows crystals on the substrate. Because it can grow at a constant temperature, it can achieve a uniform impurity concentration and composition. This method allows a large number of crystals with good crystallinity to be obtained in succession. For example, in the case of a GaAlAs-based crystal, a melt made of a Ga solution is placed in a melt bath made of graphite, and crystal growth is performed at 800°C-1000°C with a temperature difference of 10°C-200°C. Using this method, light emitting diodes, lasers, etc. with excellent characteristics are manufactured.

FIG. 15 schematically shows an example of a temperature difference method liquid phase growth apparatus. A slider 53 carrying a semiconductor substrate is housed in the entrance side preliminary chamber 51, and is successively pushed up through the gate valve 62 by the slider pressing mechanism 55. Preferably, the inlet side preliminary chamber 51 is preheated in a preliminary heating furnace 59. The pushed-up slider is sent into the growth chamber 57 through the gate valve 63 by the slider drive mechanism 61.
A melt tank 64 is provided in the growth chamber 57, and the main heater 67 heats the melt tank 64. The substrate 69 on the slider 53 contacts the melt at the bottom of the melt layer 64 to cause crystal growth. The slider carrying the substrate on which crystal growth has been completed is sent to the outside of the growth chamber 57 via the gate valve 73, and is sent to the slider receiving mechanism 7.
7 and is stored in the outlet side preliminary chamber 79 via the gate valve 74.

FIG. 16 is an enlarged explanatory view of an example of the melt tank 64 portion. Solute Al in the solvent Ga,
GaAs is melted and stored in a p-melt tank 65 and an n-melt tank 66. In addition, p as an impurity
Zn is dissolved in the melt tank 65, and Te is dissolved in the n melt tank. The amount of Al in the n-melt tank 66 is preferably greater than the amount of Al in the p-melt tank 65 in order to make the bandgap of the n-type region that will grow later larger than that of the p-type region. For example, to obtain a red-emitting Ga _1-x Al _x As light-emitting diode, the AlAs composition ratio x should be approximately 0.35 in the p-type region,
The amounts of Al and GaAs are determined to be about 0.6-0.85 in the n-type region. A vertical temperature difference is set in both melt tanks 65 and 66 as shown on the right side of the figure. For example, at a temperature of 800℃−1000℃, the temperature difference is 10℃−200℃.
℃ set. To continuously supply the solute, the solute is floated above the melt, which is a high-temperature part, or a solute storage part is created and brought into contact with the melt. The solute dissolves to saturation solubility in the high temperature section and is transported to the low temperature section by diffusion. Since the solubility usually increases with temperature, it becomes a supersaturated solution in a low temperature region and is in a state where it can precipitate. The substrates are sequentially brought into contact with such melt low temperature parts. For example, a growth time of about 60 minutes yields a growth layer of 55-60 μm.

FIG. 17 shows the relationship between temperature and time. As can be seen from the figure, the temperature distribution remains constant. Initially, the first substrate contacts the bottom of the p-melt and grows a p-type layer. Next, move the slider so that the first substrate is in contact with the bottom of the n-melt, and the second substrate is in contact with the bottom of the p-melt. Therefore, respective growth layers are formed. Now on the first board there is a p
An n-type layer is grown on the type layer to form a diode. In this way, epitaxial growth is performed on a large number of substrates.

Next, electrodes are attached to the p-side and n-side, respectively, and separated and cut to obtain a high-brightness GaAlAs light-emitting diode. High brightness Ga1−xAlxAs made in this way
As shown in FIG. 18, a light emitting diode is usually
A p-type Ga _1-x Al _x As layer 82 and an n-type Ga _1-x Al _x As layer 83 are epitaxially grown on a p-type GaAs substrate 81 , and an anode electrode 85 is formed on the p-type GaAs substrate 81 .
It has a structure in which a cathode electrode 84 is formed on an n-type Ga _1-x Al _x As layer 83.

According to Japanese Patent Application Laid-Open No. 61-39514, etc., high brightness
The following requirements are listed for obtaining a Ga _1-x Al _x As light emitting diode: (a) p-Ga 1-x Al x As with high luminous efficiency, and p-Ga _1-x Al _x As with high luminous efficiency;
Ga _1-x Al _x The proportion x of AlAs is larger than that of As (that is, the band gap energy is large and p
Ga _1-x Al _x Emission from As is not absorbed)n-
(b) Forming a heterostructure p-n junction with Ga _1-x Al _x As as shown in Figure 19; (b) As shown in the band model of Figure 20, p-
In order to efficiently inject electrons into the Ga _1-x Al _x As light-emitting layer, the heterojunction and the pn-junction must be aligned. (c) As shown in Figure 21, the p-Ga _1- The carrier concentration (acceptor concentration) Na of the x Al _x As luminescent layer and the donor concentration Nd of the n-Ga _{1- x Al} (d) Optimize the growth thickness of each p and n layer optically and electrically; (e) Use high quality crystals with few crystal defects.

[Problems to be solved by the invention] As described above, in a high-brightness Ga _1-x Al _x As light-emitting diode, the brightness of the light-emitting diode is related to the thickness of the p-type layer and the n-type layer. However, it was unclear exactly what kind of relationship was governing, and it was difficult to determine the manufacturing conditions.

The present invention provides maximum brightness as a light emitting diode when an n-type Ga _1-x Al _x As layer is formed on a Zn-doped p-type Ga _1-x Al _x As layer by temperature difference liquid phase growth. The purpose of this study is to find out what conditions are desirable to obtain this.

[Study conducted to solve the problem] First, we investigated what relationship the thickness dn of the n-Ga _1-x Al _x As layer had with the brightness of the light-emitting diode.

FIG. 9 shows measurement data of light emitting diode (LED) brightness versus n-layer thickness _do . The brightness initially increases almost linearly with the n-layer thickness _do and then saturates. The brightness of this LED n-Ga _1-x Al _x
The As layer thickness dependence can be understood as follows.

(a) Light generated near the pn-junction of an LED is extracted not only from the surface parallel to the pn-junction plane but also from the perpendicular sides. Also, the refractive index of the LED crystal is greater than the refractive index of the external surroundings (air, sealing material), resulting in a critical angle (Θc). When the angle of incidence exceeds the critical angle, total internal reflection occurs and no light can be extracted from that surface. That is,
The only light that can be emitted from one point on the crystal surface is the light that travels toward the apex from a direction included in a conical shape with that point as the apex inside the crystal and the critical angle as the half-apex angle.

FIG. 10 is a diagram showing light emitted from one point and emitted from a plane parallel to the pn-junction. The shaded area is a cone within the critical angle (Θc). Assume that the solid angle of this cone is ω, and that all the light within the cone can be extracted to the outside. If the light emission is uniform over the entire solid angle, the proportion of light that can be extracted to the outside is ω/
4π, which can be expressed as ω/4π=2π(1−cosΘ _c ). That is, it will be constant regardless of the thickness d _o of the n-layer.

Next, light emitted from a surface (side surface) perpendicular to the pn-junction will be explained with reference to FIGS. 11A and 11B.

FIG. 11A shows the case where the n-layer 83 is thin.
Even if the light is within the critical angle Θ _c toward the side,
Since the n-layer is thin, much of the light impinges on the surface parallel to the pn-junction, and only a portion of the light can be extracted directly from the side surfaces. As shown in FIG. 11B, as the n-layer 83 becomes thicker, the amount of light that can be extracted directly from the side increases. by the way,
The brightness of an LED is determined by the sum of the light emitted from the surface and the light emitted from the sides. That is, the total light emitted from the front and side surfaces of the LED increases as the n-layer thickness d _o increases up to a certain value of d _o . However, above that value, almost all of the light directed toward the sides within the critical angle will be extracted to the outside. (However, p-Ga _1-x Al _x
Since As has a larger absorption coefficient than n-Ga _1-x Al _x As, only the influence of the thickness of the n-Ga _1-x Al _x As layer was considered. ) (b) Generally, as shown in Figure 12, an LED has an electrode of a finite size at the center of its front surface, and an electrode covering almost the entire surface is formed on the opposing back surface. Due to this shape arrangement of the electrodes and the finite electrical resistance of the n-Ga _1-x Al _x As layer with which the surface electrodes are in ohmic contact, the current flowing through the LED is distributed from the center to the periphery as shown in Figure 12. The current density at the p-n junction surface is
It is high just below the surface electrode and becomes smaller towards the periphery. This tendency becomes more severe as the thickness of the n-Ga _1-x Al _x As layer becomes smaller.
Since the amount of light generated per unit area of the pn-junction surface is proportional to the current density, the current density distribution can be considered to be the light emission distribution at the pn junction surface. That is, as the thickness _do of the n-layer decreases, the proportion of light emitted from the pn-junction directly under the surface electrode increases. However, pn− directly below the surface electrode
Since the light emitted from the bonded surface cannot be extracted outside the crystal due to the surface electrode, as the d _o becomes smaller, the amount of light extracted from the surface also decreases. Therefore, the brightness of the LED is n
As long as the thickness of the layer is below a certain level, the thickness of the n layer will also increase. When the n-layer becomes thicker than a certain level, the proportion of light that is blocked by the electrodes on the n-layer decreases, and the amount of light that can be taken out to the outside becomes n
It probably has nothing to do with the thickness of the layer.

From (a) and (b) above, the brightness of the LED is n-Ga _1-x
It depends on the thickness d _o of the Al _x As layer, and the brightness increases up to a certain value of d _o . However, if d _o is sufficiently thick, the influence of both (a) and (b) will be reduced, and the brightness of the LED will no longer depend on the thickness of the n-layer. That is, as shown in FIG. 9, as the thickness of the n-layer increases, the brightness of the LED will gradually become saturated.

By the way, in the temperature difference method, solutes are transported and grown by concentration diffusion caused by a concentration gradient in the melt subjected to a temperature difference (ΔT). Crystals grow at a constant growth rate under certain conditions. Therefore, the crystal layer (n layer)
The thickness of the film is determined by the temperature difference during growth and the growth time. The growth rate is proportional to the temperature difference (ΔT). That is, as shown in FIG. 13, the thickness d _o of the growth layer in the temperature difference method increases in proportion to the growth time t ₁ ,
Its slope (growth rate) will be determined by the temperature difference (ΔT). Therefore, if other conditions are constant, the brightness of the LED in Figure 9 is n-Ga _1-x Al _x As
Layer thickness dependence and n-Ga _1-x Al _x As in Figure 13
From the relationship between the growth layer thickness d _o and the growth time t ₁ , the brightness of the LED will be expressed as shown in Figure 14 for the growth time t ₁ of the n-Ga _1-x Al _x As layer. . In other words, according to Fig. 14, the brightness of the LED is hardly affected by the time beyond that if the necessary and sufficient thickness of the n-Ga _1-x Al _x As layer is obtained; It should also not depend on the composition x of _{the 1-x} Al _x As layer.

However, in reality, if the growth time _t1 of the n-layer is taken too long, the brightness of the LED decreases. 1st
If you use the growth apparatus shown in Figure 5-17 and follow the simplest manufacturing process, the growth time of the p- layer and the n-
The crystal is kept at a high temperature for the same time as the n-layer growth time or an integral multiple thereof after the n-layer growth. Therefore, the growth time of the n layer is t ₁
The relationship between the total time t, which is the subsequent time t ₂ of holding at a high temperature in the same growth atmosphere, and the brightness of the LED was investigated. The measurement results are shown in Figure 2. moreover,
When trying to obtain a Ga _1-x Al _x As light-emitting diode by temperature difference liquid phase growth, the crystal growth conditions are
It is highly conceivable that this is closely related to the proportion x of AlAs in the Ga _1-x Al _x As crystal. By the way, composition x
If the growth temperature is constant, Al dissolved in the melt
It was found that it is determined by the weight ratio of [Al]/[GaAs]=y. Therefore, the data was organized using y as a parameter. As is clear from Figure 2, for each value of y, the brightness of the LED changes over the total time t
increases as the number increases, and then decreases. The saturated region varies depending on y, and as y increases, the region becomes saturated in a smaller region of total time t. By rearranging this relationship, we can calculate the optimal total time t ₀ and Al in Ga solution.
The weight ratio [Al]/[GaAs] between Al and GaAs is shown in Figure 1.

[Means for solving the problem] n in temperature difference liquid phase epitaxial growth method
- The sum of the layer growth time t ₁ and the subsequent exposure time t ₂ to high temperature in the same growth atmosphere is determined by the weight ratio of Al and GaAs dissolved in the melt [Al]/[GaAs] = y Make it.

In more detail, a Zn-doped p-type Ga _1-x Al _x As layer is followed by an n-type Ga _1-x Al _x As layer by temperature difference liquid phase epitaxial growth.
When growing a Ga _1-x Al _x As layer to obtain a heterojunction light emitting diode, the growth time t ₁ of the n-Ga _1-x Al _x As layer after the growth of the p-Ga _1-x Al _x As layer is , n-Ga _1-x
The total time t (minutes) including the time t ₂ during which the Al _x As layer is kept at high temperature in the same growth atmosphere after growth is the ratio of Al and GaAs dissolved in the melt [Al]/[GaAs] =
Let the time be determined from y and t=α・exp(−β・y)±33% (1) α=193, β=3.6.

[Operation] By selecting the total time t of the n-layer growth time t ₁ and the subsequent time t ₂ held at high temperature in the same growth atmosphere as described above, the grown Ga _1-x Al _x As crystal is At composition x, the highest optical output can be obtained with good yield and good reproducibility. The reason for this is thought to be as follows.

In the temperature difference liquid phase epitaxial growth method, a certain temperature difference is applied to the melt and the temperature is maintained at a constant temperature. 1000℃). And during this growth and during the total time t held at the high temperature after the growth, p-Ga _1-x
Zn, which is an acceptor impurity in Al _x As and has a large diffusion coefficient, diffuses into the n-Ga _1-x Al _x As layer, and
It compensates for the donor in the Ga _1-x Al _x As layer, effectively lowering the donor impurity density and eventually causing an inversion to p-type. This phenomenon occurs more strongly in areas adjacent to the p-type region, and becomes less severe as the distance from the p-n junction increases.

When the portion of the n-type region adjacent to the pn junction is inverted to p-type, the p-type region becomes wider and the position of the pn junction moves. On the other hand, Ga and Al, which are the constituent elements of the crystal,
The diffusion rate of these elements is slower than that of impurity elements, and the position of the heterojunction hardly moves.

This change will be explained with reference to FIGS. 3A and 3B. In FIG. 3A, the vertical axis represents the impurity density N, and the horizontal axis represents the distance in the depth direction of the substrate. FIG. 3B shows a band model, where the vertical axis represents energy and the horizontal axis represents distance in the depth direction. In FIGS. 3A and 3B, the positions of the horizontal axes correspond.

First, a p-type layer is formed, and an n-type layer begins to be formed thereon. This is shown by the dashed line. As the impurity changes from p-type to n-type and a heterojunction is formed, the band gap also widens, forming a heteropn junction. As the formation of the n-type layer continues, Zn diffuses from the p-type layer into the n-type layer. This Zn concentration distribution is shown by the dashed line in FIG. 3A. Due to compensation between p-type impurity and n-type impurity, Zn
The portion where the impurity concentration becomes higher than the n-type impurity concentration is reversed to p-type. Even in areas where the n-type impurity concentration is higher than the diffused Zn concentration, the effective donor concentration decreases. The resulting effective impurity concentration is shown by the solid line in Figure 3A. The pn junction moves to the part that was the n-type layer. By the way, this p-Ga _1-x Al _x As region p2, which has newly become p-type, is a semiconductor region with a relatively wide band gap. That is, as shown in FIG. 3B, a heterojunction is created in the p-type region and a homopn junction is created in the relatively wide bandgap region.

When the width of this p-Ga _1-x Al _x As expansion region p2 increases, some of the electrons injected from the n-Ga _1-x Al _x As layer are transferred to the p-Ga _1-x Al _x As layer, which is the light emitting layer. A new region p created by Zn diffusion before reaching the As layer
It recombines with the hole of 2 and disappears, p-Ga _1-x Al _x As
Does not contribute to light emission in the layer. Namely, the requirements for obtaining the high brightness Ga _1-x Al _x As light emitting diode mentioned above
(a) and (b) will no longer be satisfied. Figure 4 shows experimental data on the relationship between the moving distance of this pn junction and the brightness of the light emitting diode.

In FIG. 4, the vertical axis represents the relative light emitting output of the light emitting diode, and the horizontal axis represents the moving distance of the pn junction from the heterojunction. Although there is some variation in the data,
It is clear that the luminous output decreases almost linearly as the p-n junction moves.

That is, when the n-Ga _1-x Al _x As layer is thickened,
Up to a certain thickness, it has the effect of increasing the brightness of the light emitting diode, as shown in FIG. At the same time n-Ga _1-x
As the total time t between the growth time of the Al _x As layer and the subsequent time held at high temperature in the growth atmosphere increases, the p-n junction moves due to impurity compensation,
This has the effect of reducing the light emission output as shown in FIG.
When both effects are combined, an optimal range exists for the total time t, as shown in FIG.

The diffusion rate of the fast-diffusing impurity Zn is
It is thought that it changes depending on the composition x of the base material, that is, Ga _1-x Al _x As. If the growth temperature is constant, the composition x in the crystal is determined by the weight ratio [Al]/[GaAs] of the solute in the melt. So the composition x
The diffusion coefficient of Zn with respect to the change in was measured at 900℃. The results are shown in Figure 5. For increasing composition x
The diffusion coefficient of Zn increases almost exponentially.

Therefore, the weight ratio of n-melt [Al]/[GaAs]
As =y increases, the composition x of the Ga _1-x Al _x As crystal increases, Zn diffusion progresses more, and the pn junction moves more quickly to the n-GaAlAs layer. The moving distance of the p-n junction (thickness of the p-GaAlAs region p2 in Figure 3B) changes as time passes after the start of the n-GaAlAs layer growth using the weight ratio [Al]/[GaAs] = y as shown in Figure 6. It changes like this. Therefore, if only the influence of Zn diffusion is taken into consideration, the relationship between the luminescence output and the growth time will be the same as that shown in FIG. 7, which is a combination of FIGS. 4 and 6. The maximum value of the total time t for which the brightest LED is obtained is n-
As the melt weight ratio [Al]/[GaAs]=y increases, the length becomes shorter.

In an actual light emitting diode, the relationship shown in Figure 9 depends on the thickness of the n layer, and the relationship between the n
Total time t of layer growth time and subsequent high temperature holding time
As shown in Figure 7, there are relationships between the two. When both are combined, characteristics as shown in FIG. 8 are expected. That is, the brightness of the light emitting diode shown on the vertical axis increases at first, saturates, and then decreases as the total time t increases, shown on the horizontal axis. In this way, it can be explained that the total time t is in the optimum range. Also, if the diffusion coefficient is the composition x or the weight ratio y in the melt,
It is understood that the optimum time changes depending on the weight ratio of n melts [Al]/[GaAs]=y. The influence of the weight ratio [Al]/[GaAs]=y of this n melt is experimentally determined in FIG. 1, and expressed quantitatively by equation (1). Therefore, by using the time t determined according to equation (1), even if the weight ratio [Al]/[GaAs] = y in the n melt is changed, growth can be achieved under the best conditions, and the n melt can be grown under the best conditions. Weight ratio [Al]/
When [GaAs]=y, a light emitting diode with the highest optical output or brightness can be obtained with high yield and high reproducibility.

EXAMPLE A heterojunction GaAlAs light emitting diode with an n-Ga _1-x Al _x As layer having a desired composition x is manufactured.

A growth apparatus as shown in FIG. 15 is used. A Ga solution (p-melt) in which Al and GaAs as growth materials and Zn as a p-type impurity are dissolved, Te as an n-type impurity, Al and as a growth material
A Ga solution in which GaAs is dissolved (n-melt) is placed in a container made of graphite, maintained at 800°C to 1000°C, and with a temperature difference of 10°C to 200°C. In order to obtain a heterostructure, the solute weight ratio [Al]/[GaAs]=y of the n-melt is selected to be larger than the solute weight ratio y of the p-melt.

The slider on which the board is mounted is the slider drive mechanism 5.
5, 61, 77, etc., individually and collectively. These controls can be performed manually or by using the control device 5.
It can also be done automatically by setting 0.

First, a substrate crystal is brought into contact with the low temperature side of the p-melt and held for a certain period of time (growth time). The substrate is held by a slider made of graphite. By maintaining the p-melt, a p-GaAlAs layer with Zn as an acceptor grows. The growth rate is about 60 minutes and the growth layer thickness is 30-60 μm.

Next, bring the substrate crystal into contact with the low temperature side of the n-melt,
Holding the growth time t1, Te becomes the donor n-
Grow GaAlAs layer. This allows a heteropn junction to be formed. Further, the growth atmosphere is kept in a high temperature region for a time t2. Similarly, GaAlAs heteropn layers are grown on multiple substrates.

Note that the high temperature region is the growth temperature +10°C to -30°C.
It is an area in the temperature range of ℃.

Here, the total time t=t1+t2 is Weight ratio [Al]/[GaAs] in n melt = y t=α・exp(−β・y)±33% (1) α=193, β=3.6 choose to satisfy.

Also, when y is input using the control device 50, (1)
t may be automatically set according to the formula.

Next, electrodes are attached to the p-side and n-side, respectively, and separated and cut to obtain a high-brightness GaAlAs light emitting diode (LEP).

[Effect of the invention] As described above, the n-
The total time t of the growth time of the GaAlAs layer and the time held at high temperature in the growth atmosphere after the growth of the n-GaAlAs layer is defined as the weight ratio of Al-group GaAs dissolved in the n-melt [Al]/[GaAs] = y. By setting the time within the time determined by Equation (1), (1) A high-brightness, high-efficiency LED can be obtained by a simple process of adjusting the time.

(2) Because the process is simple, high-brightness, high-efficiency LEDs can be obtained efficiently and with good reproducibility.

(3) High-brightness, high-efficiency LEDs can be obtained immediately after the completion of the crystal growth process.

[Brief explanation of the drawing]

Figure 1 shows the optimum time for the total time t of n-layer growth and subsequent high-temperature process to obtain the maximum optical output according to an embodiment of the present invention.The weight ratio of Al and GaAs in Ga melt [Al]/[GaAs] = graph shown as a function of y, Figure 2 is a data plot showing changes in brightness versus total time t with y as a parameter, Figures 3A and 3B are lines showing changes in impurity distribution and band structure. Figure 4 is a data plot showing the change in optical output with respect to the moving distance of the pn junction, Figure 5 is a data plot showing the measurement results of the diffusion coefficient of Zn, and Figures 6, 7, and 8. is a conceptual diagram for analyzing the phenomenon, Figure 9 is a data plot showing changes in optical output with respect to the thickness of the n-layer, Figures 10 and 11 are
Figure A, Figure 11B, Figure 12, Figure 13, Figure 14
The figure is a conceptual diagram for analyzing the phenomenon, Figure 15 is a schematic diagram of the liquid phase crystal growth apparatus, Figure 16 is a partially enlarged view of Figure 15, and Figure 17 is a graph of temperature versus time to explain the growth operation. , FIG. 18 is a schematic sectional view illustrating an LED, FIGS. 19 and 20 are band structure diagrams showing the energy gap distribution, and FIG. 21 is a line diagram showing the impurity concentration distribution. Explanation of symbols, 64, 65, 66...melt tank,
53...Slider, 1P...p-type layer on the first substrate, 1N...n-type layer on the first substrate, 2P...2
p-type layer on the second substrate, 2N...n on the second substrate
mold layer, 81...substrate, 82...p layer, 83...n
Layer, 84... anode electrode, 85... cathode electrode.

Claims (1)

[Claims] 1. Zn as a p-type impurity and as a growth material
P-melt containing Al and GaAs, metal as n-type impurity, and Al and GaAs as growth materials
A temperature difference is created between the n-melt and the n-melt in which the p-Ga _1-x Al _x As layer and the n-
In the crystal growth method using the temperature difference method for growing Ga _1-x Al _x As, the growth time of the n-Ga _1-x Al _x As layer after the growth of the p-Ga _1-x Al _x As layer and the n-Ga _1-x Al _x After the growth of the As layer, the total time t (minutes) including the time held at high temperature in the same growth atmosphere is n Weight ratio of Al and GaAs dissolved in the melt [Al]/[GaAs]y and t=α·exp(−β·y)±33% α=193 and β=3.6. A Ga _1-x Al _x As crystal growth method.