JP2002047095A - PRODUCTION METHOD FOR Ga-DOPED SILICON SINGLE CRYSTAL, THE Ga-DOPED SILICON SINGLE CRYSTAL, AND SILICON SINGLE CRYSTAL SOLAR CELL MADE OF THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for a Ga-doped silicon single crystal capable of suppressing the occurrence of OSF(oxidation-induced stacking fault) due to a heavy metal in the subject crystal useful as the material for a solar cell, and also provide the Ga-doped silicon single crystal for the solar cell having no optical degradation and a high photoelectric conversion efficiency and a silicon single crystal solar cell made of the same. SOLUTION: This method comprises doping gallium in a silicon single crystal, adding the smaller amount of aluminum than that of gallium and growing the single crystal by a CZ method to produce the Ga-doped silicon single crystal. The obtained silicon single crystal is added with gallium as a dopant, the concentration of gallium contained in the crystal is 5×1017-3×1015 atoms/cm3, and aluminum is added in the lower concentration than that of gallium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a Ga-doped silicon single crystal by the Czochralski method (hereinafter sometimes referred to as CZ method) useful as a material for a solar cell, and a Ga-doped silicon single crystal. Further, the present invention relates to a silicon single crystal solar cell manufactured therefrom.

[0002]

2. Description of the Related Art With the development of semiconductor device technology, quality requirements for a CZ silicon single crystal using the Czochralski (hereinafter referred to as CZ) method have been diversified.
In addition, the demand for low cost is becoming severe. In particular, when a silicon single crystal is used as a material for a solar cell, it is a major issue to improve the conversion efficiency and reduce the manufacturing cost.

[0003] The technical background of using a silicon single crystal as a material for a solar cell will be described below. When solar cells are classified based on their substrate materials, they can be broadly classified into three types: "silicon crystalline solar cells", "amorphous (amorphous) silicon solar cells", and "compound semiconductor solar cells". Crystalline solar cells include “single-crystal solar cells” and “polycrystalline solar cells”. Among these, a solar cell having a high conversion efficiency, which is the most important characteristic as a solar cell, is a "compound semiconductor-based solar cell", and its conversion efficiency reaches nearly 25%. However, it is very difficult to make a compound semiconductor as a material for the compound semiconductor-based solar cell, and there is a problem that the solar cell substrate is widely used in terms of manufacturing cost, and its use is limited. I have.

[0004] Here, the "conversion efficiency" is a value indicating the "ratio of energy that can be converted into electric energy by the solar cell and taken out by the solar cell with respect to the energy of light incident on the solar cell". It refers to a value expressed as a percentage (%) (also called photoelectric conversion efficiency).

As a solar cell having the second highest conversion efficiency after a compound semiconductor solar cell, a silicon single crystal solar cell follows, and its power generation efficiency is about 20%, which is close to that of a compound semiconductor solar cell. Substrates can be procured relatively easily, and thus have become the mainstay of commonly used solar cells. Furthermore, although the conversion efficiency is about 5 to 15%, which is inferior to the above-mentioned two solar cells, the production cost of the solar cell substrate material is low. Batteries and the like have also been put to practical use.

Next, a method of manufacturing a general silicon single crystal solar cell will be briefly described. First, in order to obtain a silicon wafer serving as a substrate of a solar cell, a Czochralski method or a floating zone melting method (hereinafter, FZ method, floating method) is used.
A columnar silicon single crystal ingot is produced by the Zone method). Further, the ingot is sliced and processed into a thin wafer having a thickness of, for example, about 300 μm, and the wafer surface is etched with a chemical solution to remove processing distortion on the surface, thereby obtaining a wafer (substrate) to be a solar cell. This wafer is subjected to an impurity (dopant) diffusion treatment to form p on one side of the wafer.
After forming the n-junction surface, electrodes are attached to both surfaces, and finally, an antireflection film for reducing loss of light energy due to reflection of light is provided on the surface on the incident side of sunlight to complete the solar cell.

In recent years, demand for solar cells has been expanding as one of clean energy due to environmental problems.
The high energy cost compared to general commercial power is an obstacle to its widespread use. In order to reduce the cost of the silicon crystal solar cell, it is necessary to further increase the conversion efficiency while reducing the manufacturing cost of the substrate. For this reason, the substrate of a single crystal solar cell is not suitable for electronics for manufacturing a so-called semiconductor element, or a cone or tail that is not a product in a single crystal rod is used as a raw material. Lowering the cost of substrate materials has been attempted. However, the procurement of such raw materials is unstable and the amount is limited. Considering the growing demand for silicon single crystal solar cells in the future, such a method can stabilize the required amount of solar cell substrates. It is difficult to produce.

On the other hand, a silicon wafer used as a substrate material of a single crystal type solar cell has a substrate lifetime (hereinafter, sometimes referred to as Lifetime, LT) which is one of its characteristics having a value of 10 μs. Otherwise, it cannot be used as a solar cell substrate, and further, to obtain a solar cell with high conversion efficiency, the substrate lifetime is required to be preferably 200 μs or more.

However, when a single crystal made by the CZ method, which is the mainstream of the current single crystal rod manufacturing method, is irradiated with intense light when the solar cell is processed into a solar cell, the lifetime of the solar cell substrate is reduced. As a result, sufficient conversion efficiency cannot be obtained to cause light degradation, and there is a need for improvement in the performance of solar cells.

When a solar cell is manufactured using the CZ method silicon single crystal, when strong light is applied to the solar cell, the life time is reduced and light degradation occurs due to boron and oxygen existing in the single crystal substrate. Is known to be the effect of At present, a p-type wafer is mainly used as a conduction type of a wafer used as a solar cell, and boron is usually added to the p-type wafer as a dopant. And
The single crystal rod used as the material of this wafer is manufactured by the CZ method (MCZ method).
Method, or the FZ method, but the FZ method or the MCZ method (magnetic field pulling method, Magn method)
In the etic field applied CZ method, the production cost of a single crystal rod is higher than that of a normal CZ method. I have.

However, a high concentration of oxygen is present in a crystal manufactured by the CZ method. Therefore, if boron and oxygen in a p-type CZ silicon single crystal affect the lifetime characteristic and cause photodegradation. There is a problem to say.

In order to solve such a problem, the present applicant has disclosed in the earlier application (Japanese Patent Application No. 11-264549) that Ga (Ga) is used instead of B (boron) as a p-type dopant.
It was proposed to use (gallium). This allows
Light degradation hardly occurs, and a silicon single crystal having high conversion efficiency can be obtained.

However, the fact that the CZ crystal is pulled by adding Ga does not mean that the manufacturing cost required for pulling the crystal can be reduced as compared with the conventional B-doping, and the problem of reducing the manufacturing cost still remains. ing. On the other hand, the suppression of light degradation does not mean that all the problems relating to conversion efficiency have been solved.

On the other hand, in the case of a CZ single crystal, oxidation-induced stacking faults (Oxidation-induced stacking faults) are considered.
ng Fault (hereinafter sometimes referred to as OSF) in some cases. In the silicon single crystal in which the OSF has been generated, the lifetime is reduced, and the light is deteriorated.
It has been found that there is a problem that the conversion efficiency is reduced. In a silicon single crystal used for a semiconductor device such as an integrated circuit, the generation of OSF is caused by the purification of polycrystalline silicon as a raw material, the purification of quartz glass crucibles and members in a furnace,
Decreased due to improvements in lifting conditions.

[0015]

However, since silicon for solar cells is required to be inexpensive, polycrystalline silicon and quartz glass crucibles used as raw materials must be expensive and have high purity. Not necessarily. Therefore, a raw material having a high heavy metal level may be used, and there is a concern that OSF nuclei due to the heavy metal may be present, which may reduce the minority carrier lifetime and consequently reduce the photoelectric conversion efficiency of the solar cell. .

The present invention has been made in view of the above problems, and therefore, a method of manufacturing a Ga-doped silicon single crystal capable of suppressing generation of OSF due to heavy metals in a Ga-doped silicon single crystal useful as a material for a solar cell. The main object of the present invention is to provide a Ga-doped silicon single crystal for a solar cell having high photoelectric conversion efficiency without causing light degradation and a silicon single crystal solar cell using the same.

[0017]

According to the present invention, there is provided a method for producing a Ga-doped silicon single crystal according to the present invention, comprising the steps of: producing a Ga (gallium) -doped silicon single crystal by the Czochralski method; A method for producing a Ga-doped silicon single crystal, characterized in that a single crystal is grown by adding Al (aluminum) in an amount smaller than that of Ga (claim 1).

As described above, by adding a smaller amount of Al than Ga during the growth of a Ga-doped silicon single crystal, heavy metal impurities, particularly Cu (copper), introduced from the melt during the growth of the single crystal can cause the crystal to grow. It is possible to prevent diffusion and aggregation to form a core of OSF.

In this case, the concentration of Ga in the silicon single crystal is 5 × 10 ¹⁷ atoms / cm ^{3 to} 3 × 10 ¹⁵ at.
Preferably, the single crystal is grown so as to be oms / cm ³ (claim 2), and the Al concentration in the silicon single crystal is 1 × 10 ¹³ atoms / cm ^{3 to} 5 × 10 ¹⁵ a.
It is preferable that the single crystal is grown so as to have a density of toms / cm ³ (claim 3).

By adding such concentrations of Ga and Al, it is possible to surely prevent light degradation such as B doping and to suppress the generation of OSF due to heavy metals to prevent a reduction in lifetime. it can.

The addition of Al may be performed by growing a silicon crystal to which a high concentration of Al has been added in advance and using a doping agent formed by crushing the high concentration Al-doped silicon crystal (claim 4) or quartz glass. It may be performed by eluting Al into the silicon melt from the inner surface of the crucible (claim 5).

By doping Al with such a method, G
Al can be easily and reliably added to the a-doped silicon single crystal at a predetermined concentration with high accuracy.

The Ga-doped silicon single crystal of the present invention is manufactured by the above manufacturing method. Since the Ga-doped silicon single crystal manufactured by the method of the present invention is doped with desired concentrations of Ga and Al, it becomes a silicon single crystal suitable for solar cells.

Further, the Ga-doped silicon single crystal of the present invention can be used as a dopant produced by the Czochralski method.
Is a silicon single crystal to which the concentration of Ga contained in the crystal is 5 × 10 ¹⁷ atoms / cm ^{3 to} 3 × 1
It is a Ga-doped silicon single crystal characterized by having an atomic density of 0 ¹⁵ atoms / cm ³ and a lower concentration of Al than Ga.

In this case, the concentration of Al contained in the single crystal
Is 1 × 10¹³atoms / cm ³~ 5 × 10^Fifteena
toms / cm³(Claim 8).

As described above, when the concentration of Ga is 5 × 10 ¹⁷ a
If it is toms / cm ^{3 to} 3 × 10 ¹⁵ atoms / cm ³ , the resistivity will be in the range of 0.1 Ω · cm to 5 Ω · cm, and the substrate lifetime will be 10 μs or more. It becomes possible. If Al is added to this, even if heavy metal impurities are present in the raw material and the like are introduced into the single crystal, the heavy metal impurities are diffused and agglomerated in the single crystal by Al in the single crystal to cause nuclei of OSF. The formation is prevented, and a reduction in lifetime due to heavy metal impurities is also prevented. Therefore, when a solar cell is manufactured using such a single crystal, a solar cell having a low internal resistance and a high substrate lifetime is used, and thus a high photoelectric conversion efficiency can be obtained. The concentration of Ga is 1.5 × 10 ¹⁷ atoms / cm ^{3 to} 5 × 1
0 ¹⁵ atoms / cm ³ and a resistivity of 0.2Ω ·
cm to 2.0 Ω · cm is more preferable.

[0027] The silicon single crystal solar cell manufactured from the Ga-doped silicon single crystal of the present invention (claim 9) is a high-efficiency solar cell that is inexpensive and free from light deterioration because the life time is not reduced. .

Hereinafter, the present invention will be described in detail. The inventor of the present invention uses a Ga-doped silicon single crystal for a solar cell and, despite preventing photodegradation of the lifetime due to the influence of B (boron) and oxygen, a reduction in the lifetime may occur. As a result of investigating the cause, it was found that heavy metal impurities, particularly Cu contained in raw materials and quartz crucibles, in particular, diffused and aggregated in the single crystal to generate OSF nuclei, which caused a reduction in lifetime. . Therefore, the present inventor has proposed that, in order to prevent the diffusion and aggregation of Cu,
Has been confirmed to be effective, thereby completing the present invention.

The addition of Al to the N-type silicon single crystal doped with P (phosphorus) is effective for the time-dependent change of the OSF when stored at room temperature in an ingot state specifically observed in the N-type silicon single crystal. Is disclosed in JP-A-8-73293. As disclosed in the publication, O
In order to suppress the temporal change of SF, it is essential that the content of Cu contained in the raw material and the quartz crucible be reduced to a low level.

However, in the case of a Ga-doped silicon single crystal, the conductivity type is P-type, and the OS due to the diffusion and aggregation of heavy metal impurities, particularly Cu, in the single crystal.
It was believed that the formation of F nuclei would not occur. However, for silicon single crystals for solar cells, polycrystalline silicon and quartz glass crucibles used as raw materials to reduce the cost of crystallization are not necessarily of high purity, and raw materials with high levels of heavy metals must be used. There is. In such a case, although the OSF does not change over time, it has been confirmed by the present inventors that the OSF is generated and the lifetime is reduced which is presumed to be caused by heavy metal impurities. Among heavy metals, Fe (iron) can be cited as an element that greatly contributes to a reduction in the lifetime. However, even if the concentration of iron is low, a reduction in the lifetime is observed, and Cu may be considered as the cause. Was.

Using a high-purity raw material (polycrystalline silicon) used for a semiconductor device such as an integrated circuit or a quartz crucible, a Ga-doped silicon single crystal having a resistivity of 0.2 Ω · cm to 2.0 Ω · cm is pulled up. When the wafer is processed into a wafer and subjected to an OSF test at 1100 ° C. for 60 minutes in a wet oxygen atmosphere after processing, no OSF is generated.
When inexpensive polycrystalline silicon or quartz crucibles with a high u content were used, generation of OSF was observed in Ga-doped silicon single crystals having the same resistivity range. In addition, when the lifetime was measured using a wafer cut from the vicinity of the tail of the single crystal (a portion having a resistivity of about 0.2 Ω · cm), it was 14 μs when using a high-purity raw material, 3μ for crystals using raw materials with high Cu content
s and lifetime were significantly reduced.

Therefore, using an inexpensive polycrystalline silicon or quartz crucible having a high Cu content, the Al concentration in the single crystal is set to 1 × in the vicinity of the tail of the single crystal (the portion having a resistivity of 0.2 Ω · cm). It is added so as to be 10 ¹⁵ atoms / cm ³ ,
A Ga-doped silicon single crystal having a resistivity of 0.2 Ω · cm to 2.0 Ω · cm was pulled. In this crystal, no OSF was generated in the OSF test, and the crystal was found near the tail (having a resistivity of 0.2
(A portion of Ω · cm) was 13 μm, and almost no decrease was observed.

As described above, in the Ga-doped silicon single crystal of the present invention, the life time is not reduced even if the raw material is slightly contaminated with heavy metals such as Cu. Therefore, a silicon single crystal solar cell manufactured using this crystal is used. In this case, the photoelectric conversion efficiency is as high as 20% or more even in a large area such as 100 cm ² . In addition, deterioration after light irradiation is high performance of 0.5% or less. Such high-performance and high-efficiency solar cells can be manufactured at low cost.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, an example of the configuration of a single crystal pulling apparatus using the CZ method used in the present invention will be described with reference to FIG.

The single crystal pulling apparatus 100 comprises a bottom chamber 101 for accommodating a crucible 102 for melting a raw material, and a top chamber 11 for accommodating and taking out the pulled single crystal.
0. And the top chamber 110
A wire take-up mechanism 109 for pulling up a single crystal is provided at the upper portion of the wire, and performs operations such as winding down and winding up the wire 1 in accordance with the growth of the single crystal. At the tip of the wire 1, a seed crystal S is attached to a seed holder 22 for pulling up a silicon single crystal.

On the other hand, the crucible 102 in the bottom chamber 101 is composed of quartz 103 on the inside and graphite 104 on the outside. A heater for melting the polycrystalline silicon raw material charged in the crucible is provided around the crucible 102. 105
Are disposed, and the heater is surrounded by a heat insulating material 106. The crucible is filled with a melt L of silicon dissolved by heating with a heater. The crucible is supported by a support shaft 107 that can rotate and move up and down, and a driving device 108 for that purpose is attached to the bottom of the bottom chamber. Alternatively, a rectifying cylinder 2 for rectifying the inert gas introduced into the furnace may be used.

Next, a method for manufacturing a silicon single crystal using the above apparatus will be described. First, a polycrystalline silicon raw material and Ga and Al dopants were mixed with a quartz crucible 1.
03 and heated by the heater 105 to melt the raw material. In this embodiment, Ga and Al are put into the crucible together with the polycrystalline raw material before melting, but may be put into the crucible during or after melting the polycrystalline raw material. In addition, since mass concentration of single crystals requires fine concentration adjustment, high-concentration Ga-doped silicon crystals and Al-doped silicon crystals are prepared in advance, and finely crushed to prepare a doping agent. It is preferable to adjust the polycrystalline silicon so as to have a desired concentration and then feed the polycrystalline silicon.

The addition of Al can also be performed by eluting Al into the silicon melt from the inner surface of the quartz glass crucible. In this case, as disclosed in JP-A-8-73293, the average Al concentration in the depth direction from the inner surface of the quartz glass crucible is set to, for example, more than 30 μm and 1 mm in the range of 30 μm from the inner surface. It is possible to use quartz glass crucibles that are higher than the average concentration up to. A near the inner surface of a quartz glass crucible
The l-concentration is determined by the A concentration in the product Ga-doped silicon single crystal.
What is necessary is just to determine so that 1 density | concentration may become a desired value.

Next, when all the polycrystalline silicon raw materials are melted, a seed crystal S for growing a single crystal rod is attached to the tip of the wire 1 of the pulling mechanism, and the wire 1 is gently rolled down to melt the tip of the seed crystal. Contact with liquid L. At this time, the crucible 102 and the seed crystal S are rotating in directions opposite to each other, and the inside of the pulling machine is in a depressurized state and is filled with an inert gas such as argon, which flows from the upper part of the furnace. .

When the temperature around the seed crystal is stabilized, the seed crystal S
Then, while rotating the crucible 102 in the opposite directions, the wire 1 is gently wound up and the pulling of the seed crystal is started. Then, necking for eliminating the slip dislocations generated in the seed crystal is performed. When necking is performed to a thickness and length at which the slip dislocation disappears, the diameter is gradually increased to produce a single crystal cone portion, and the diameter is increased to a desired diameter. When the cone diameter has expanded to a predetermined diameter, the process shifts to production of a constant diameter portion (straight body portion) of a single crystal rod. At this time, the concentration of oxygen contained in the single crystal to be grown can be appropriately adjusted by controlling the rotation speed of the crucible, the pulling speed, the pressure of the inert gas in the chamber, the flow rate, and the like. Also,
The crystal diameter is controlled by adjusting the temperature and the pull rate.

After the straight body portion of the single crystal is pulled up by a predetermined length, the diameter of the crystal is reduced to form a tail portion. Then, the tip of the tail is separated from the silicon melt surface, and the grown silicon single crystal C is placed in a top chamber. Roll up to 110 and wait for the crystals to cool. When the single crystal rod is cooled to a temperature at which it can be removed, it is removed from the pulling machine.

The Ga-doped silicon single crystal of the present invention is a silicon single crystal to which Ga is added as a dopant manufactured by the Czochralski method, and the concentration of Ga contained in the crystal is 5 × 10 ¹⁷ atoms / cm. ^{3 to} 3 × 10 ¹⁵
atoms / cm ³ , and Al at a lower concentration than Ga is added.

When the concentration of Ga is 5 × 10 ¹⁷ atoms / c
When m ³ greater than, causes decreased photoelectric conversion efficiency of the solar cell lifetime reduction of minority carriers due to Auger recombination in the substrate for the resistivity of the substrate is extremely lowered occurs, Ga concentration of 3 × 10 ¹⁵ a
When the value is smaller than toms / cm ³ , the resistivity of the wafer becomes higher than necessary, and when a solar cell is used, power is consumed by the internal resistance of the solar cell, and the photoelectric conversion efficiency is reduced.

The concentration of Al contained in the single crystal is 1 × 1
0 ¹³ atoms / cm ^{3 to} 5 × 10 ¹⁵ atoms /
cm ³ is preferable because the effect of preventing the diffusion and aggregation of heavy metals, particularly Cu, is low when the Al concentration is less than 1 × 10 ¹³ atoms / cm ^3. If it is larger than 10 ¹⁵ atoms / cm ³ , there is a possibility that the influence of Al on the reduction of the lifetime may occur.

That is, the resistivity of the single crystal of the present invention should be dominantly determined by Ga as a dopant. When the concentration of Al exceeds Ga, the influence of Al on the resistivity increases, and Lifetime is greatly reduced. Therefore, in a crystal having a relatively low Ga concentration, the Al concentration may be as low as about one order of magnitude of the Ga concentration. However, in a crystal having a relatively high Ga concentration, the Al concentration must be at least two orders of magnitude lower than the Ga concentration. Is preferred.

The solar cell manufactured using the single crystal of the present invention has a simple structure in which a pn junction is formed by diffusing a dopant such as P (phosphorus) on the back side, and Al electrodes are formed on the front and back sides. Although a structure may be used, a structure in which a known device is performed for higher efficiency is preferable. As such, for example, RP-PERC (Random Pyramid-
Passivated Emitter and Re
ar Cell) type structure.

[0047]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto. (Example 1) 55 kg of high-purity polycrystalline silicon in which Cu is not detected by surface and bulk atomic absorption analysis is placed in a quartz crucible having an inner diameter of 18 inches (about 450 mm).
Ga was added so that the single crystal had a resistivity of 0.8 Ω · cm. Ga was produced by growing a silicon crystal to which high concentration Ga was added in advance, crushing the silicon crystal, and adding an appropriate amount as a dopant. At this time, the Al concentration was 5 × 10 ¹⁴ atoms / c at the portion where the solidification rate of the single crystal was 0.8.
It was added to the quartz crucible as a dopant of Al 53mg such that m ^3. To eliminate the influence of impurities dissolved from the crucible, the Al concentration near the inner surface of the quartz crucible is 1
A synthetic quartz crucible having less than ppm was used. In addition to these raw materials, 10 ppbw of Cu as a contaminant was added to the weight of polycrystalline silicon. After containing these in a quartz crucible, a Ga-doped silicon single crystal was grown.

A wafer was cut out from the obtained Ga-doped silicon single crystal, and the processing strain on the surface was removed by etching. After that, a heat treatment was performed at 1100 ° C. for 60 minutes in a wet oxygen atmosphere, and the surface was selectively etched to form an OSF. The outbreak was investigated. As a result, no OSF was observed despite the intentional Cu contamination. When the lifetime was measured using another wafer,
The value was as high as μs.

The lifetime was measured by treating the sliced wafer with a mixed acid of HF: HNO ₃ = 5%: 95%, etching away the slice damaged layers on both sides, and then cleaning the wafer. Air Mass)
After irradiating with steady light for 30 hours under the conditions of 1.5, HF
Removes the natural oxide film on the surface. Followed by iodine,
A chemical passivation (CP) treatment using an ethanol mixed solution was performed to reduce carrier recombination on the crystal surface, and the lifetime was measured using a microwave-PCD method (photoconductivity decay method).

(Example 2) As a quartz glass crucible, the average concentration of Al from the inner surface to a depth of 30 μm was 500 pp.
A Ga-doped silicon single crystal that was intentionally contaminated with Cu was grown in the same manner as in Example 1 except for using mw as a dopant and not adding Al as a dopant. G obtained
After cutting a wafer from an a-doped silicon single crystal and removing the processing strain on the surface by etching, 1100 ° C.
Then, heat treatment was performed in a wet oxygen atmosphere for 60 minutes, and the surface was selectively etched to investigate the generation of OSF. As a result, no OSF was observed. When the lifetime was measured using another wafer, it was 550 μs
It was a high value.

(Comparative Example 1) A Ga-doped silicon single crystal was grown in the same manner as in Example 1 except that Al was not added. A wafer is cut out of the obtained Ga-doped silicon single crystal, and the processing strain on the surface is removed by etching. After that, a heat treatment is performed at 1100 ° C. for 60 minutes in a wet oxygen atmosphere, and the surface is selectively etched to investigate the generation of OSF. did. As a result, OSF was observed at a high density of 500 pieces / cm ² . Further, when the lifetime was measured using another wafer, it was found to be 100 μs, which was much lower than that of the wafer of Example 1.

(Example 3, Comparative Example 2) A wafer was cut out from the Ga-doped silicon single crystal (resistivity about 0.8 Ω · cm) of Example 1, Example 2, and Comparative Example 1, and HF: HN
The processing strain at the time of slicing was removed with a mixed acid of O ₃ = 5%: 95% to obtain a wafer having a thickness of 380 μm. Using this wafer, an RP-PERC solar cell of 10 cm × 10 cm was produced, and the photoelectric conversion efficiency and deterioration due to light irradiation were evaluated.

The photoelectric conversion efficiency of the solar cell was measured by placing a solar cell on a measuring table whose temperature was adjusted to 25 ° C. and generating a steady light under a condition of AM (air mass) 1.5 with a solar simulator using a halogen lamp as a light source. The cell was irradiated, and the voltage and current that could be taken out of the cell were measured to calculate the photoelectric conversion efficiency of the solar cell. Here, the photoelectric conversion efficiency refers to a value defined by the following equation. [Photoelectric conversion efficiency] = [power extracted from cell unit area] / [light energy irradiated per cell unit area] × 100 (%)

Further, under the condition of AM1.5, 30
The photovoltaic conversion efficiency of the solar cell after irradiation for more than an hour was also measured, and the photodegradation was evaluated in comparison with the photovoltaic conversion efficiency before light irradiation.

As a result, the photoelectric conversion efficiency of the solar cell manufactured from the Ga-doped silicon single crystal of Example 1 was as high as 20.4% before and after light irradiation, and no light deterioration was observed. The photoelectric conversion efficiency of the solar cell manufactured from the Ga-doped silicon single crystal of Example 2 was 20.2 before and after light irradiation.
%, And no light deterioration was observed. On the other hand, Comparative Example 1
Although the photoelectric conversion efficiency of the solar cell manufactured from the Ga-doped silicon single crystal was 18.9% before and after light irradiation, no light deterioration was observed, but the efficiency did not reach 20%.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, the Czochralski method referred to in the present invention includes a so-called MCZ method (magnetic field application pulling method) for growing a single crystal while applying a magnetic field to a melt in a crucible. This includes an application method, a horizontal magnetic field application method, a vertical magnetic field application method, and the like. That is, the method for producing a single crystal according to the present invention is naturally applicable to the MCZ method and exerts its effect.

[0058]

As described above, according to the present invention,
An OSF nucleus is not formed even if there is contamination of a heavy metal, particularly Cu, so that a Ga-doped silicon single crystal which does not cause a reduction in life time is obtained. Therefore, the single crystal of the present invention is particularly useful for a solar cell, which can improve the photoelectric conversion efficiency of the solar cell, and also contributes to cost reduction because it is not always necessary to use a high-purity raw material.

That is, in the Ga-doped silicon single crystal of the present invention, the life time does not decrease even if the raw material is slightly contaminated with heavy metals such as Cu. Therefore, in a silicon single crystal solar cell manufactured using this crystal, Even in a large area such as 100 cm ^{2, the} photoelectric conversion efficiency can be as high as 20% or more. In addition, since deterioration after light irradiation is as high as 0.5% or less, there is an advantage that a high-performance and high-efficiency solar cell can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a structural example of a single crystal pulling apparatus by a CZ method used in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wire, 2 ... Rectifier cylinder, 22 ... Type holder, 10
0: single crystal pulling device, 101: bottom chamber,
102: crucible, 103: quartz crucible, 104: graphite crucible, 105: heater, 106: heat insulating material, 10
7 ... support shaft, 108 ... drive device, 109 ... wire winding mechanism, 110 ... top chamber. C: growing crystal, L: silicon melt, S: seed crystal.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G077 AA02 BA04 CF10 EB01 HA12 HA20 PB01 PB05 PB09 5F051 AA02 AA16 CB03 CB18 5F053 AA13 AA14 DD01 FF04 GG01 HH04 JJ01 KK10 LL05 RR03

Claims (9)

[Claims] 1. A method for producing a silicon single crystal doped with Ga (gallium) by the Czochralski method, wherein a single crystal is grown by adding a smaller amount of Al (aluminum) than Ga. Of producing a Ga-doped silicon single crystal. 2. The method according to claim 1, wherein the concentration of Ga in the silicon single crystal is 5 or more.
× 10 ¹⁷ atoms / cm ^{3 to} 3 × 10 ¹⁵ atoms
The method for producing a Ga-doped silicon single crystal according to claim 1, wherein the single crystal is grown so as to have a s / cm ³ . 3. An Al concentration in the silicon single crystal is 1 ×
10 ¹³ atoms / cm ^{3 to} 5 × 10 ¹⁵ atoms
^{3. The} method for producing a Ga-doped silicon single crystal according to claim 1, wherein the single crystal is grown so as to have a density of / cm ³ . 4. The method according to claim 1, wherein said adding Al grows a silicon crystal to which a high concentration of Al has been added in advance.
The method for producing a Ga-doped silicon single crystal according to any one of claims 1 to 3, wherein a doping agent produced by crushing the doped silicon crystal is used. 5. The method according to claim 1, wherein the addition of Al is performed by eluting Al into the silicon melt from the inner surface of the quartz glass crucible.
3. The method for producing a Ga-doped silicon single crystal according to item 1. 6. A Ga-doped silicon single crystal manufactured by the manufacturing method according to claim 1. Description: 7. A silicon single crystal to which Ga is added as a dopant produced by the Czochralski method, wherein the concentration of Ga contained in the crystal is 5 × 10 ¹⁷ atoms / cm.
^{3 to} 3 × 10 ¹⁵ atoms / cm ³ , wherein Ga is added at a lower concentration than Ga.
Doped silicon single crystal. 8. The method according to claim 1, wherein the concentration of Al contained in the crystal is 1 ×.
10 ¹³ atoms / cm ^{3 to} 5 × 10 ¹⁵ atoms
/ Cm ³ / Ga 3.
Doped silicon single crystal. 9. A silicon single crystal solar cell produced from the Ga-doped silicon single crystal according to claim 6. Description: