JPH01164792A - Method for growing liquid phase crystal by temperature difference - Google Patents

Abstract

PURPOSE:To suppress the evaporation of a component having high vapor pressure the generation of a flaw by bringing a grown layer into contact with melt used for post-treatment which has same composition as melt used for growth and is in such a state that the crystal is not grown for a constant time after growing crystal. CONSTITUTION:A P-melt tank 13 for holding P-melt 33 incorporating P-type impurity, an N-melt tank 15 for holding N-melt 35 incorporating N-type impurity and a melt tank 17 for post-treatment for holding melt 37 used for post- treatment which has same composition as N-melt 35 and is in such a state that grow of crystal is not caused are successively arranged in a reaction pipe 11. Temp. distribution of the vertical direction wherein the upper part is high temp. and temp. is lowered according to proceeding toward the lower part is preset in the P-melt 33 and the N-melt 35 and a substrate 25 is successively brought into contact with the P-melt 33 and the N-melt 35 and held for a constant time and a crystal layer is grown on the substrate 25. Then this grown layer is brought into contact with the melt 37 used for post-treatment and held for a constant time to perform post-treatment.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to liquid phase crystal growth, and in particular, to a process in which a certain temperature difference is created in a melt in which a solute is dissolved, and the solute is continuously transported from a high temperature area to a low temperature area. This paper relates to liquid-phase crystal growth using a temperature difference method in which crystals are grown in a low-temperature region.

[Prior Art] 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. Depending on the cooling method, crucible shape, etc., it is divided into the Stock-Barker method, Bridgman method, 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 created in a solution (melt), the solute is dissolved (supplied) in the high temperature part, and the solute is precipitated from a supersaturated solution in the low temperature part, that is, temperature difference method liquid phase crystallization. Growth method uses growth material (solute)
This is a method in which a temperature difference is applied to a solution (melt) in which the solute is dissolved, and the solute is transported toward the substrate by diffusion to grow crystals on the substrate. Because the crystal can be grown at a constant temperature, it has a uniform impurity concentration and composition. For example, 1 is a method in which a large number of crystals with good quality can be obtained in succession.

In the case of GaAlAs-based crystals, a melt made of Ga solution is placed in a melt bath made of graphite, and heated at 800°C-10
By this method, crystal growth is performed by setting a temperature difference of 10°C to 200'C at 00°C.
~, lasers, etc. are being manufactured.

FIG. 3 schematically shows an example of a conventional temperature difference method liquid phase growth apparatus. A slider 53 on which a semiconductor substrate is placed is housed in an entrance side preliminary chamber 51, and a slider pushing mechanism 5
5 in turn is pushed up through the gate valve 62. Preferably, the entrance side preliminary chamber 51 is preheated in a preliminary heating furnace 59. The pushed-up slider is sent into the growth chamber 57 through a gate valve 63 by a slider drive mechanism 61. A melt tank 64 is provided in the growth chamber 57, and a main heater 67 heats the melt 1a64. The substrate 69 on the slider 53 is melted W! The slider carrying the substrate on which crystal growth has been carried out is brought into contact with the melt at the lower part of the chamber 64 and sent out of the growth chamber 57 via the gate valve 73, and then sent via the gate valve 74 by the slider receiver 877. It is stored in the exit side preliminary chamber 79.

FIG. 4 is an enlarged explanatory view of one example of the melt tank 64 portion.

Solutes AI and GaAs are dissolved in Ga, which is a solvent, and stored in a P melt tank 65 and an N melt tank 66. Further, as impurities, Zn is dissolved in the P melt tank 65, and Te is dissolved in the N melt tank. In order to make the bandgap of the N-type region that grows later larger than the bandgap of the P-type head region, the amount of AI in the N-melt tank 66 is preferably larger than the amount of A1 in the P-melt tank 65, for example,
In order to obtain a red-emitting Ga AI As light-emitting diode No. xx-, the composition ratio X of AlAs should be approximately 0.35. Determine the amount of AI and GaAs so that it is approximately 0.6-0.85 in the n-type region 1-car melt tank 6'5.66
A temperature difference in the vertical direction as shown by the cloth in the figure is set within the area. For example, a temperature difference of 10°C to 200°C is provided at a temperature of 800°C to 1000°C. To continuously supply 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, the substrates are successively brought into contact with such low-temperature parts of the melt, where the melt becomes a supersaturated solution and can be precipitated.

For example, a growth layer of 50-60 μm can be obtained with a growth time of about 60 minutes.

As can be seen from FIG. 5, which shows the relationship between temperature and time, the temperature distribution is kept constant. Initially, the first substrate is in contact with the bottom of the P melt, and the P type layer is grown.First, the slider is moved 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. do it like this. Therefore, respective growth layers are formed. Now, on the first substrate, a P-type layer is grown on the bottom and an N-type layer is grown on top, forming a diode. In this way, epitaxial growth is performed on a large number of substrates.

[Problem to be solved by the invention] Journal of Crystal Growth
31, 215 (1975), GaAs
Among its components, GaP etc. have high vapor pressure components (
As and P) evaporate during crystal growth at high temperatures, causing lattice defects V.
In light-emitting diodes (LEDs), it has been shown that it is easy to create crystal defects called acancies, reducing crystallinity, and that crystallinity can be improved by applying an optimal vapor pressure to the growth melt during crystal growth. The crystal defects form a deep level (Deep LeVel), and the deep level formed in one light emitting region acts as a trap center that captures injected electrons and holes, and becomes a non-radiative recombination center. That is, deep levels have a great negative effect on the luminous efficiency of the LED. In order to obtain a high-brightness LED, it is most important to grow a crystal with few single crystal defects.

For example, Joiurnal of Crystal Gr.
According to the method presented in owth 31, 215 (1975).

Since vapor pressure is applied to the growing melt during crystal growth, the generation of defects is minimized during growth. However, after the pn junction is formed by crystal growth, H2
, Ar, etc., and heat treatment is applied more than necessary.

The surface of the growth layer is exposed to high temperature H2 gas, etc.

As and the like evaporate and defects occur. Unless the generation of defects after growth is suppressed, the highest crystallinity cannot be achieved.

The requirements for high brightness cannot be fully satisfied.

"Means for Solving the Problems" According to the present invention, there is provided a method for temperature difference liquid phase crystal growth in which a growth layer is brought into contact with a melt having the same composition as the growth melt after crystal growth.

If a melt with the same composition as the growth melt is brought into contact with the substrate under exactly the same conditions as the growth melt, new growth will begin, so the amount of post-treatment melt that is brought into contact with the growth layer after growth is the same as that of the growth melt. Although it contains impurity metals and growth materials, the following methods are used to prevent growth.

For example, in the production of a GaAIS light emitting diode, after growing a p-GaAlAs layer and an n-GaAlAs layer, that is, following the growth of an n-melt for growing the n-GaAlAs layer, a solute with the same composition as the n-melt is grown. The growth layer is kept in contact with the melt, which dissolves and does not grow, for a certain period of time.

Here, the state in which the same type of solute as n-melt is dissolved and not grown is typically 1 (a) From the saturation solubility determined by the growth temperature.

By melting the growth material of 5 times or more, a large amount of microcrystals are precipitated in the melt, and even if the substrate or the GaAlAs growth layer comes into contact with the melt, crystals are precipitated mainly using these microcrystals as nuclei, and the substrate Or G a A I A s
State where no growth is made on the growth layer; (b) The amount of the impurity metal to be dissolved, for example (Te) and the growth material is n GaAIA
, is the same as the n-melt used to grow the s-layer, but a temperature difference is applied only to this melt using a local heating heater that has a calorific value that partially cancels out the temperature difference created for growth. (C) The amounts of the impurity metal to be dissolved, such as (Te), and the growth material are the same, but at least while the growth layer is in contact with the melt, the melt is heated locally using a heater. There are three conditions in which the temperature is maintained at least 10 times higher than the growth temperature:

[Effect] A melt with the same structure as the growth melt will apply the optimum vapor pressure to the growth layer to prevent defects.

The occurrence of defects can be effectively prevented.

[Example] The present invention will be described in detail with reference to FIGS. 1 and 2.

The structure shown in FIG. 1 corresponds to the melt tank 64 of the overall structure shown in FIG. 3, and is compared with the structure shown in FIG. 2 according to the prior art.

A P melt tank 13 is placed inside the quartz reaction tube 11. N melt tank 15
．． Post-processing non-growth melt tanks 17 are arranged, each with P
Melt 33. N Melt 35. Non-growth melt for post-processing 37
It accommodates. Each melt tank requires an opening at the bottom, and a slider 21 that slides inside the kite closes the opening. A recess 23 for storing a substrate is provided in the upper surface of the slider 21, and a substrate 25 is placed in the recess 23.

P melt 33 contains Ga as a solvent, AI as a growth material,
GaAs and P-type impurity Zn are dissolved. N melt 35 contains Ga as a solvent, AI as a growth material, and Ga as a growth material.
As and N-type impurity Te are dissolved. Like the N melt 35, the non-growth melt 37 for post-treatment also uses G, which is a solvent.
a to A1. GaAs and Te are dissolved as solutes.

P Melt 33. Inside the N melt 35, a vertical temperature distribution is set, as shown by the cloth portion in the figure, where the temperature is high at the top and gradually decreases toward the bottom. As a result, the solute with a difference in saturation solubility is transported from the upper high-temperature part to the lower low-temperature part, and crystal growth occurs on the substrate crystal as a seed.

A solute equivalent to that in the N-melt 35 is dissolved in the non-growth melt 37 for post-treatment. The non-growth melt 37 is also N
It is set at almost the same temperature as Melt 35. Therefore,
The vapor pressure of each component is applied from the non-growth melt 37 to the growth layer 27 placed below, thereby preventing components with high vapor pressure from coming out of the growth layer 27. This prevents defects from occurring. In order to make the non-growth melt 37 not cause crystal growth, it is necessary to break the mechanism of crystal growth. Possible methods include a method of precipitating the gas at a temperature of 100 nm, or a method of cutting off the transport by eliminating the temperature gradient somewhere.

To carry out the first method, for example, a large amount of microcrystals are precipitated by melting the growth material at a high temperature, which greatly exceeds the saturation solubility at the growth temperature, and then raising the temperature to the growth temperature. This can also be achieved by making it preferentially occur in microcrystals.

For example, the growth material is dissolved at five times or more the saturation solubility at the growth temperature.

To prevent solute transport, all or part of the temperature gradient that is the driving force for transport can be removed. If only the negative part of the temperature distribution is removed, it is done on the substrate side.

In other words, it is best to avoid creating a temperature distribution in which the temperature drops from top to bottom at least in the melted part directly above the substrate. This can be achieved by providing a heating heater.

Further, such a change in temperature distribution may not be carried out regularly, but may be carried out only when the substrate is in contact with the melt.

In this case, precipitation can be prevented even without eliminating the temperature gradient by lowering the degree of supersaturation of the supersaturation solution by increasing the temperature. For example, the composition of the post-treatment melt 37 may be changed to N
Precipitation can be prevented by keeping the composition of the melt 35 the same and maintaining the growth temperature while the substrate is not in contact with it, and increasing the temperature of the post-treatment melt by 10 degrees or more when the substrate comes into contact with the post-treatment melt. can.

The substrate on the slider 21 is first grown with a P-type epitaxial layer under the P-melt 33, and then transferred under the N-melt 35 to grow an N-type epitaxial layer thereon. This creates a light emitting diode structure with a PN junction. This is the process indicated by IP-IN for the first substrate in the graph of FIG. Conventionally, after this, H
I was exposed to high temperature atmospheric gas such as 2Ar, but 1
In this embodiment, it is further placed under a non-growth melt 37 for post-treatment. This prevents the component elements from escaping.

Furthermore, this melt contains the same type of growth material as the growth melt, but it is in a state where it is not allowed to grow.
There is no need to obtain an unnecessary growth thickness that is more than necessary, and there is no need for extra processes such as scraping the surface in subsequent processes.

In addition, this method does not require a separate process after the growth is completed, but rather utilizes the time that is unavoidable in continuous growth, so it does not require any separate equipment and does not impair mass productivity.

Note that this method can be applied to other than GaAIAs LED.

It can be applied to crystals using temperature difference method liquid phase epitaxial growth such as GaP and GaAs.

[Effect of the invention] According to the method of the invention, even after crystal growth, the crystal has A
Because it is covered with melt with sufficient high vapor pressure such as s,
Evaporation of As from the crystal is suppressed, and the occurrence of defects is suppressed to a minimum. Therefore, non-radiative recombination centers can be reduced and the performance of the LED can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main part of an apparatus for carrying out a crystal growth method according to an embodiment of the present invention, FIG. 2 is a graph of temperature versus time for explaining the crystal acid lengthening step, and FIG. 3 is a graph of temperature versus time. FIG. 4 is a sectional view of the whole and main parts of a conventional crystal growth apparatus, and FIG. 5 is a graph of temperature versus time for explaining the crystal growth process. Explanation of symbols 13.15, 17 Melt tank 21 Slider 25 Substrate 33.35 Growth melt 37 Non-growth melt

Claims (4)

[Claims] (1) A temperature difference method solution in which a temperature difference is applied to a growth melt in which impurity metals and growth materials are dissolved, and a substrate is brought into contact with the low temperature side of these solutions and held in contact for a certain period of time to grow a crystal layer on the substrate. In the phase crystal growth method, after crystal growth, the growth layer is brought into contact for a certain period of time with a post-treatment melt that dissolves the same type of impurity metal and growth material as those dissolved in the growth melt and does not cause crystal growth. A method characterized by holding. (2) The method according to claim 1, wherein the post-treatment melt is a melt prepared by melting a growth material in an amount that is five times or more the saturation solubility determined by the growth temperature. (3) The method according to claim 1, wherein the post-treatment melt melts the same amount of impurity metals and growth materials as the growth melt, but is kept in a state where no temperature difference is created. (4) The post-processing melt melts the same amount of impurity metals and growth materials as the growth melt, but the temperature of the melt is at least 10 degrees higher than the growth temperature while the growth layer is in contact with this melt. The method according to claim 1, wherein the method of claim 1 is maintained at a higher level.