JP3848409B2 - ZnSe epitaxial substrate and manufacturing method thereof - Google Patents

Description

【図面の簡単な説明】
【図１】本発明の実施例に用いられた液相成長用カーボン製スライドボートの横断面図である。
【図２】本発明の比較例３に用いられた熱処理用石英アンプルの横断面図である。
【符号の説明】
１ スライドボート
２ メルトバック用溶液ホルダ
３ 成長用溶液ホルダ
４ 熱処理用溶液ホルダ
５ スライダー
６ キャビティ
７ 成長用単結晶基板
８ 液体封止剤
９ メルトバック溶液
１０ 成長用溶液
１１ 熱処理用溶液
１２ 炉心管
１３ 炉
１４ 石英アンプル
１５ ＺｎＳｅエピタキシャル基板
１６ 石英製仕切り板
１７ 熱処理用Ｚｎ融液[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high carrier density ZnSe single crystal thin film used as a blue light emitting device and a method for producing the same.
[0002]
[Prior art]
In a liquid phase growth method of a ternary or quaternary mixed crystal semiconductor thin film mainly composed of a II-VI group compound semiconductor such as ZnSe, Se, Te, TeSe, Ga, In, or the like has been studied as a growth solvent. Among these, a thin film or bulk crystal can be obtained using Se, Te or TeSe solvent, and therefore, practical research on blue light emitting elements or element substrates has been conducted. However, the conventional technology has the following problems.
[0003]
In the growth method using Se, since the vapor pressure is high and the loss due to evaporation is significant, it is common to use a quartz glass container with a sealed tube treatment in order to lower the growth temperature and also to suppress the evaporation of Se. Since the vapor pressure of Se must be equal to or lower than the withstand pressure, the growth conditions are restricted. For this reason, the growth temperature is controlled to about 850 ° C., but this growth vessel is not practical because P and N layers cannot be continuously grown.
[0004]
For the production of a practical device, a carrier density of 10 ¹⁷ cm ⁻³ or more, desirably 10 ¹⁸ cm ⁻³ or more is required. Even in growth using ZnCl ₂ as a solvent or growth in an open tube system using Ga or In (for example, a slide boat method), the carrier density of the produced crystal is about 10 ¹³ to 10 ¹⁴ cm ^−3. It was. Even when grown with an alloy of Ga, In and Zn, the carrier density was about 3 × 10 ¹⁶ cm ⁻³ .
[0005]
In order to obtain a crystal having such a carrier density, a technique has been conventionally performed in which a crystal once grown is heat-treated in a Zn melt to increase the carrier density.
[0006]
On the other hand, it is preferable that p-type and n-type impurities can be arbitrarily added to constitute an electronic device such as an LED. However, II-VI group compound semiconductors are not only difficult to be p-type, but low resistance n-type substrates are not easily produced.
A conventional method for producing a low resistivity n-type crystal of an II-VI intermetallic compound semiconductor is to form a ZnSe crystal that has not been doped or effectively doped into a wafer shape and sealed in a vacuum ampule. For example, it is immersed in a Zn solution or a Zn solution to which a group III element (Ga, In) is added, and heat treatment is performed to activate the group III element in the crystal or to diffuse the group III element from the crystal surface.
[0007]
Japanese Patent Laid-Open No. 6-293600 discloses a step of liquid-phase growth of ZnSe crystals from a solution containing a group III to group VII element of 0.5 mol% or less as an impurity, and the grown crystals are immersed in a Zn solution, at 600 ° C. or higher. There is a description of a process for activating impurities by performing a heat treatment at a temperature of. Here, a technique is disclosed in which a grown crystal is once taken out and washed, and then vacuum-sealed in a quartz ampoule together with Zn, and the crystal is heat-treated in a Zn solution.
[0008]
In such a conventional technique, since a method in which a grown crystal is once taken out and vacuum-sealed in a quartz tube is used, there are the following defects.
(1) Since the grown crystal is taken out once, the number of processes increases and the product throughput decreases.
(2) Since the quartz tube is vacuum-sealed, the process becomes complicated. Also, once used, the quartz tube cannot be reused, increasing the manufacturing cost.
(3) There is a risk of contaminating the crystal when the grown crystal is taken out, and the contaminant becomes a dopant in the subsequent heat treatment step, making it difficult to control the electrical characteristics of the crystal and reducing the production yield.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to improve the above-described defects, and is produced by continuously performing a crystal growth step and a heat treatment step without taking out a single crystal thin film grown by a liquid phase growth method. The object is to establish a high-quality and high carrier density n-type ZnSe single crystal thin film and a method for manufacturing the same.
[0010]
[Means for Solving the Problems]
The present inventors have intensively studied to solve such problems, and found that it is possible to perform Zn melt heat treatment of a ZnSe single crystal thin film by a slide boat method, and a low resistance n-type capable of forming an element. A ZnSe epitaxial substrate could be obtained. In other words, the present invention performs crystal growth by performing Zn melt heat treatment on an n-type ZnSe single crystal thin film grown on a high resistance ZnSe single crystal substrate from a group III solvent using a slide boat method by a slide boat method. The present invention relates to a low resistance n-type ZnSe epitaxial substrate capable of forming an element obtained by continuously performing heat treatment and heat treatment on the same slide boat, and a method for manufacturing the same.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Zn has a high vapor pressure of 0.3 to 0.9 at a heat treatment temperature of 800 ° C. to 900 ° C., and it is very difficult to handle because it evaporates when heat-treated in an open tube system of a normal slide boat method. .
However, as described in Japanese Patent Application No. 7-171513, when the opening portion of the solution holder of the slide boat is sealed with a liquid sealant such as B ₂ O ₃ , the evaporation rate is reduced. Can be heat-treated. Since this heat treatment can be performed in the same configuration as the normal liquid phase growth except that the opening of the solution holder is sealed, the heat treatment can be performed by the same slide boat for growth.
Therefore, the heat treatment can be performed immediately after the thin film is grown in the liquid phase, and the steps of the heat treatment from the growth can be performed continuously. In the present invention, since a thin film is obtained by liquid phase growth, a relatively thick thin film having a thickness of about 10 to 100 μm can be obtained.
Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
[0012]
[Example 1]
FIG. 1 is a cross-sectional view of a liquid-phase growth carbon slide boat used in the present embodiment, which will be described with reference to this figure.
As a material for the slide boat, DFP-3-2 manufactured by POCO was used. For Zn, 6N zinc manufactured by Dowa Mining Co., Ltd. was used, and for the liquid sealing B ₂ O ₃ , BOROGLASS-20 manufactured by Toyama Pharmaceutical Co., Ltd. was used.
[0013]
First, 20 g of 6N (99.9999%) In as a growth solvent and about 0.85 g of ZnSe as a solute are placed in the crystal growth solution holder 3, and a liquid sealant (B _{2 is formed} so as to cover the upper part thereof. About 5 g of O ₃ ) 8 was supplied.
Next, in a meltback solution holder 2 for performing meltback, which is substrate surface treatment performed immediately before the growth, 10 g of Zn having a purity of 6N is put as the meltback solution 9, and a liquid sealant (B ₂ O is applied so as to cover the upper part thereof. ₃ ) 8 was supplied.
Next, 20 g of 6N purity Zn and about 3.3 mg of ZnSe for substrate dissolution prevention are placed in the heat treatment solution holder 4 as the heat treatment solution 11, and a liquid sealant (B ₂ O ₃ ) 8 is formed so as to cover the top. Supplied.
[0014]
On the other hand, the single crystal substrate for growth 7 was set by subjecting a cavity (facing part) 6 provided in the slider 5 to surface treatment in advance.
In this case, the pretreatment of the substrate was performed according to the following procedure. First, a ZnSe single crystal grown by a high pressure melting method was cut into a plane orientation (100) to prepare a substrate having a predetermined dimension (5 mm × 5 mm × thickness 1 mm). Next, after rough polishing with Al ₂ O _{3 having a} particle size of 5 μm, mirror polishing was performed with diamond having a particle size of 1 μm. Next, in order to remove the contamination layer and the work-affected layer, etching is performed for 5 minutes with a 1% bromomethanol solution, and in order to remove residual bromine (bromine) from the substrate surface, boiling is performed in acetone and drying is performed. A substrate dried in a nitrogen atmosphere was used as a substrate for thin film growth.
[0015]
The slide boat 1 having completed the growth preparation as described above was inserted into the core tube 12 in the horizontal electric furnace 13, and the inside of the core tube was replaced with a nitrogen atmosphere and pressurized to 3 atm. Thereafter, the temperature is raised to 905 ° C. at a rate of temperature rise of 15 ° C./min, and then kept isothermally at 905 ° C. for 30 minutes (hereinafter referred to as soak), so that the solute concentration is about 3 in the crystal growth solution holder 3. A ZnSe / In solution of .3% was obtained.
After the soak, the temperature was lowered to 900 ° C. at 1 ° C./min, and then the slider 6 was moved to move the cavity 6 to the bottom of the meltback solution holder 2 and bring the substrate 7 into contact with the meltback solution 9. In this state, the substrate 7 was melt-backed by holding at 900 ° C. for 5 minutes.
[0016]
Thereafter, the cavity 6 is moved by the slider 5 and transferred to the bottom of the growth solution holder 3, and the furnace temperature is set to 0.2 ° C./min from 900 ° C. to 850 ° C. with the substrate 7 in contact with the growth solution 10. A single crystal thin film of ZnSe was grown on the substrate while lowering the temperature.
When the growth of the thin film is completed, the slider 5 is moved, the cavity 6 is moved to the bottom of the heat treatment solution holder 4, the growth thin film on the substrate 7 is brought into contact with the heat treatment solution 11 and held at 850 ° C. for 30 hours. Then, the grown thin film was heat-treated in the Zn melt.
[0017]
When the heat treatment was completed, the slider 5 was moved to retract the cavity 6 from each solution holder, and then the furnace temperature was lowered to room temperature at about 4 ° C./min.
Thereafter, the slide boat 1 is taken out of the core tube 12, and an alloy of Ga and In is used to remove the heat treatment solution (Zn) remaining on the surface of the obtained substrate with a ZnSe single crystal thin film (hereinafter referred to as an epitaxial substrate). (Alloy composition: Ga _0.83 In _0.17 ) It was immersed in the melt at 300 ° C. for 30 minutes. The epitaxial substrate from which the solution was removed from the surface in this way was further etched for 1 minute with a 0.5% bromomethanol solution, then boiled in acetone and dried in a dry nitrogen atmosphere.
When the thin film on the epitaxial substrate thus obtained was subjected to hole measurement at room temperature, its carrier density and hole mobility were about 2 × 10 ¹⁷ cm ⁻³ and 260 cm ² V ⁻¹ S ⁻¹ , respectively. there were. The film thickness of the thin film was about 73 μm.
[0018]
[Example 2]
In a crystal growth holder 3, 18 g of 6N pure as a growth solvent and 1.1 g of 6N pure Zn (solvent composition: In _0.9 Zn _0.1 ) and about 0.22 g of ZnSe as a solute are covered. Thus, about 5 g of liquid sealing agent (B ₂ O ₃ ) 8 was supplied.
Next, a melt-back solution holder 2 was prepared in the same manner as in Example 1. Next, a solution holder 4 for heat treatment was prepared in the same manner as in Example 1. Next, a growth single crystal substrate 7 was prepared in the same manner as in Example 1. The pretreatment of the substrate was performed in the same procedure as in Example 1.
[0019]
The slide boat 1 that has been prepared for growth is set in a furnace and soaked in the same manner as in Example 1 to obtain a ZnSe / In solution having a solute concentration of about 0.85% in the crystal growth solution holder 3. It was.
After the soak, the substrate 7 was melted back in the same manner as in Example 1. Thereafter, a single crystal thin film of ZnSe was grown on the substrate in the same manner as in Example 1.
When the growth of the thin film was completed, the grown thin film was heat-treated in the Zn melt as in Example 1.
[0020]
When the heat treatment was completed, the furnace temperature was lowered to room temperature in the same manner as in Example 1. Thereafter, the obtained epitaxial substrate was subjected to a surface treatment in the same manner as in Example 1.
When the thin film on the obtained epitaxial substrate was subjected to hole measurement at room temperature, its carrier density and hole mobility were about 2 × 10 ¹⁸ cm ⁻³ and 290 cm ² V ⁻¹ S ⁻¹ , respectively. The film thickness of the thin film was about 66 μm.
[0021]
[Comparative Example 1]
A solution holder 3 for crystal growth was prepared in the same manner as in Example 1. Next, a melt-back solution holder 2 was prepared in the same manner as in Example 1. Next, a growth single crystal substrate 7 was prepared in the same manner as in Example 1. The pretreatment of the substrate was performed in the same procedure as in Example 1.
The slide boat 1 for which growth preparation was completed was set in a furnace in the same manner as in Example 1 and soaked.
After the soak, the substrate 7 was melted back in the same manner as in Example 1. Thereafter, a single crystal thin film of ZnSe on the substrate was grown in the same manner as in Example 1.
When the growth of the thin film was completed, the slider 5 was moved to retract the cavity 6 from each solution holder, and then the furnace temperature was lowered to room temperature at about 4 ° C./min. That is, the Zn melt heat treatment was not performed on the grown thin film.
Thereafter, the obtained epitaxial substrate was subjected to a surface treatment in the same manner as in Example 1.
When the thin film on the obtained epitaxial substrate was subjected to hole measurement at room temperature, its carrier density and hole mobility were about 5 × 10 ¹⁵ cm ⁻³ and 100 cm ² V ⁻¹ S ⁻¹ , respectively. The film thickness of the thin film was about 78 μm.
[0022]
[Comparative Example 2]
A crystal growth solution holder 3 was prepared in the same manner as in Example 2. Next, a melt-back solution holder 2 was prepared in the same manner as in Example 2. Next, a growth single crystal substrate 7 was prepared in the same manner as in Example 2. The pretreatment of the substrate was performed in the same procedure as in Example 2.
The slide boat 1 for which growth preparation was completed was set in a furnace in the same manner as in Example 2 and soaked.
After the soak, the substrate 7 was melted back in the same manner as in Example 2. Thereafter, a single crystal thin film of ZnSe was grown on the substrate in the same manner as in Example 2.
When the growth of the thin film was completed, the slider 5 was moved to retract the cavity 6 from each solution holder, and then the furnace temperature was lowered to room temperature at about 4 ° C./min. That is, the Zn melt heat treatment was not performed on the grown thin film.
Thereafter, the obtained epitaxial substrate was subjected to a surface treatment in the same manner as in Example 2.
When the thin film on the obtained epitaxial substrate was subjected to hole measurement at room temperature, the carrier density and hole mobility were about 1 × 10 ¹⁶ cm ⁻³ and 250 cm ² V ⁻¹ S ⁻¹ , respectively. The film thickness of the thin film was about 70 μm.
[0023]
[Comparative Example 3]
FIG. 2 is a transverse cross-sectional view of the heat treatment quartz ampoule used in this comparative example, and will be described with reference to this figure.
A ZnSe epitaxial substrate was prepared by the method of Comparative Example 2. The epitaxial substrate 15 was enclosed in a quartz ampule 14 having an inner diameter of 8.5 mm and a length of 8 cm together with 10 g of Zn having a purity of 6N and about 1.6 mg of ZnSe for preventing dissolution of the substrate at a vacuum degree of 10 ⁻⁶ Torr.
[0024]
Prior to vacuum sealing, the inner wall of the quartz ampule 14 was cleaned by the following procedure. First, ultrasonic cleaning was performed for 10 minutes with a neutral detergent, and then ultrasonic cleaning was performed for 10 minutes with pure water. Then, it boiled in acetone, degreased, and immersed in aqua regia for 12 hours, the metal component which remained on the quartz substrate was removed. Finally, the quartz surface was etched with 50% hydrofluoric acid for 5 minutes.
As shown in FIG. 2A, the quartz ampule 14 having been vacuum-sealed was placed in a furnace as shown in FIG. 2A and held at 850 ° C. for 30 hours to perform heat treatment in the Zn melt of the grown thin film. In addition, a quartz partition plate 16 that is cleaned in the same manner as the quartz ampule 14 is attached inside the quartz ampule 14 so that the epitaxial substrate 15 does not float on the Zn melt 17 during the heat treatment. Has been.
[0025]
After completion of the heat treatment, the quartz ampule 14 was rotated 180 degrees together with the furnace, and the Zn melt 17 was separated from the epitaxial substrate 15 as shown in FIG.
Thereafter, the furnace temperature was decreased to room temperature at about 4 ° C./min to obtain an epitaxial substrate subjected to the Zn melt heat treatment.
The obtained epitaxial substrate was immersed in an alloy of Ga and In (alloy composition: Ga _0.83 In _0.17 ) at 300 ° C. for 30 minutes in order to remove the heat treatment solution (Zn) remaining on the surface. The epitaxial substrate from which the solvent was removed from the surface in this way was further etched with a 0.5% bromomethanol solution for 1 minute, then boiled in acetone and dried in a dry nitrogen atmosphere.
When the thin film on the epitaxial substrate thus obtained was subjected to hole measurement at room temperature, its carrier density and hole mobility were about 2 × 10 ¹⁸ cm ⁻³ and 280 cm ² V ⁻¹ S ⁻¹ , respectively. there were. The film thickness of the thin film was about 62 μm.
[0026]
【The invention's effect】
The carrier density of the thin film obtained as a result of Example 1 is 2 × 10 ¹⁷ cm ^−3, which is about two orders of magnitude higher than the carrier density of the thin film obtained as a result of Comparative Example 1 of 4 × 10 ¹⁵ cm ^−3. It is a value. In addition, the carrier density of the thin film obtained as a result of Example 2 is 2 × 10 ¹⁸ cm ^−3, which is also approximately compared with the carrier density of the thin film obtained as a result of Comparative Example 2 of 1 × 10 ¹⁶ cm ^−3. The value is two digits higher. The thin films obtained with the high carrier density (10 ¹⁷ to 10 ¹⁸ cm ⁻³ ) of Examples 1 and 2 have a low resistivity of about 10 ⁻² Ω / cm, and they can be used to form practical elements. It seems possible. On the other hand, the carrier density of the obtained thin film was 2 × 10 ¹⁸ cm ⁻³ even in Comparative Example 3 in which the Zn melt heat treatment was performed on the thin film of Comparative Example 2, but as shown in Table 1. Compared to the case of Example 2, the number of processes increased, and it took time to finally obtain a thin film having a high carrier density. Therefore, according to the manufacturing method of the present invention, an epitaxial substrate having a high carrier density can be provided with a small number of steps, and the economic effect is great.
[0027]
[Table 1]

[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a carbon slide boat for liquid phase growth used in an example of the present invention.
FIG. 2 is a cross-sectional view of a heat treatment quartz ampoule used in Comparative Example 3 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Slide boat 2 Solution holder for melt back 3 Solution holder for growth 4 Solution holder for heat treatment 5 Slider 6 Cavity 7 Single crystal substrate for growth 8 Liquid sealant 9 Melt back solution 10 Solution for growth 11 Solution for heat treatment 12 Core tube 13 Furnace 14 Quartz ampule 15 ZnSe epitaxial substrate 16 Quartz partition plate 17 Zn melt for heat treatment

Claims (5)

In a method for producing a ZnSe epitaxial substrate, comprising a step of liquid-phase growth of a thin film on a single crystal substrate and a step of heat-treating the thin film in a Zn melt to increase the carrier density of the thin film. A method of manufacturing a ZnSe epitaxial substrate, wherein the heat treatment step is continuously performed in the same crystal growth apparatus. In a method for producing a ZnSe epitaxial substrate, comprising a step of liquid-phase growth of a thin film on a single crystal substrate and a step of heat-treating the thin film in a heat treatment solution comprising Zn and ZnSe in order to increase the carrier density of the thin film. A method for producing a ZnSe epitaxial substrate, wherein the heat treatment step is continuously performed in the same crystal growth apparatus following the liquid phase growth step. The method for producing a ZnSe epitaxial substrate according to claim 1 or 2, wherein the thin film is a ZnSe single crystal thin film having a carrier density of 10 ¹⁷ cm ^-3 or more and doped with In. The method for producing a ZnSe epitaxial substrate according to any one of claims 1 to 3, wherein the liquid phase growth step is a step of liquid phase growth of a ZnSe single crystal thin film on a single crystal substrate using a group III solvent. The method for manufacturing a ZnSe epitaxial substrate according to any one of claims 1 to 4, wherein the crystal growth apparatus is a slide boat type crystal growth apparatus including at least a single crystal thin film growth chamber and a Zn melt heat treatment chamber.

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