JPH1154774A - Solar cell and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a III-V mixed crystal compound semiconductor used for a high-efficiency solar cell to be restrained in transition of lattice mismatching so as to obtain a solar cell of high efficiency. SOLUTION: As to a solar cell structure where ternary or more III-V mixed crystal compound semiconductor is used, a growth condition observation measurement structure 2 which is formed of III-V compound semiconductor layer which contains, at, least, either of III and V element that form the mixed crystal semiconductor, is formed of the mixed crystal semiconductor of them, and used for precisely determining the mixed crystal composition condition of the above mixed crystal semiconductor is provided between a semiconductor substrate 3 and a solar cell structure 1. The growth condition observation measurement structure 2 is observed through a method such as a spectral ellipsometry or the like, whereby data such as growth speed and other can be obtained, and a solar cell which is formed of mixed crystal semiconductor of required composition and high in efficiency can be obtained taking the above data into consideration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell and a method for manufacturing the same.

[0002]

2. Description of the Related Art In order to spread solar cells widely in the world, it is necessary to greatly reduce the power generation cost. A solar cell having high photoelectric conversion efficiency can provide a large output in a small area, and is considered to be one solution to cost reduction of the solar cell.

A solar cell using a group III-V compound semiconductor material, which is known as a representative example of a solar cell having high photoelectric conversion efficiency, has the following disadvantages. (1) Forbidden band suitable for efficiently absorbing sunlight. (2) The lattice constant and the forbidden band width can be controlled by the mixed crystal of a plurality of semiconductors, and it is suitable for manufacturing a tandem solar cell. It is a promising solar cell.

[0004] Specific examples thereof are described in the literature, "Technical Digest of Ninth International Photovoltaic Science and Engineering Conference" (Technical Digest).
of 9th International Photo
ovoltaic Science and Engi
As described on page 525 (1996), a two-terminal tandem type solar cell using gallium indium phosphide (GaInP) for the upper solar cell and gallium arsenide (GaAs) for the lower solar cell. In fact, a high photoelectric conversion efficiency exceeding 30% is realized.

[0005]

SUMMARY OF THE INVENTION GaInP used as a material for the upper cell of the above-mentioned tandem solar cell
Is lattice matched with GaAs used for the substrate and the lower cell when the composition ratio of Ga to In is about 52%. Since the thickness of the pn junction layer, which is the active layer in the solar cell, needs to be about several μm, the control range of the composition ratio of Ga for suppressing the occurrence of lattice mismatch dislocation is about ± 2%.

If the composition ratio of Ga deviates from the range of 50 to 54%, lattice mismatch dislocations are generated in the film during crystal growth, and the crystallinity is greatly reduced. cause.

Therefore, it is indispensable to precisely control the composition ratio of Ga in manufacturing a high-efficiency solar cell using GaInP for the pn junction layer. The same is true for GaIn
The same can be said for a solar cell structure in which a ternary or more III-V mixed crystal compound semiconductor other than P is used.

[0008] As a method for fabricating this type of solar cell, a molecular beam epitaxy (MBE) method or a metal organic chemical vapor deposition (MOCVD) method is mainly used. Changes over time in growth conditions due to changes in the raw materials and the state in the growth chamber have become a significant problem.
Therefore, in order to improve the yield of the manufactured element, it is necessary to adjust the growth conditions as needed.

In order to overcome this problem, a method conventionally used is to directly determine the composition ratio of each layer by in-situ observation during the crystal growth of each layer of the solar cell structure, and to feed back the result to the growth conditions. This is a method for realizing an appropriate composition on the spot and continuing the crystal growth. In practice, spectroscopic ellipsometry and other techniques have been used for in-situ observation.However, accurate measurement requires a certain thickness, and the most important active layer in a solar cell has an inappropriate composition. May need to be stacked.

Accordingly, an object of the present invention is to provide a solar cell capable of precisely controlling the composition of three or more ternary group III-V mixed crystal compound semiconductors used for the solar cell.

[0011]

In order to achieve the above object, a fundamental feature of the structure of the solar cell of the present invention is that a mixed crystal composition of the solar cell structure is provided between a semiconductor substrate and the solar cell structure. In order to indirectly determine the growth condition, the structure is provided with a growth condition observation measurement structure including a plurality of layers.

It is desirable that the composition of each layer of the growth condition observation / measurement structure contains an element of the same family as the mixed crystal composition of the solar cell structure. For example, a GaInP solar cell, which is a typical mixed crystal composition solar cell, is generally MB
A film is grown and formed by the E method or the MOCVD method. The film growth process proceeds by the group III element reaching and bonding to the growth substrate surface covered with the group V element having a high vapor pressure. Therefore, the growth rate is determined by the supply amount of the group III element. For example, when the supply amount of Ga is the same,
Growth rates of GaAs and GaP [GaAs] and [GaP]
Can be considered almost the same.

[GaAs] ≒ [GaP] (Equation 1) Therefore, the above-mentioned growth condition observation measurement structure is represented by AlAs
Layer, a GaAs layer, and a GaInP layer, the pn junction of the solar cell may include Ga containing Ga.
Observation measurement of two layers, an As layer and a GaInP layer, showed that Ga
As and GaInP growth rates [GaAs] and [GaInP
P] can be obtained. The observation measurement can be performed, for example, by interrupting the film growth after the completion of the growth condition observation measurement structure and measuring the film thickness of each layer by a spectroscopic ellipsometry measurement method.

The two growth rates [GaAs] and [Ga
InP], the growth rate [Ga
From the ratio of [As] and [GaInP], it is possible to obtain the mixed crystal composition ratio X of Ga in Ga _X In _{1 -X} P and, as shown in Equation 3, the InP growth rate [InP] from the difference. it can.

X = [GaP] / ([GaP] + [InP]) ≒ [GaAs] / [GaInP] (Equation 2) [InP] = [GaInP] − [GaP] ≒ [GaInP] − [GaAs] ( (Equation 3) In consideration of this result, the growth conditions may be optimized so that the desired composition ratio X (0.50 ≦ X ≦ 0.54) and growth rate of GaInP can be obtained.

Further, regarding the window layer, the growth rate [AlAs] of AlAs can be obtained by measuring the AlAs layer, so that it can be considered together with the growth rate [InP] of InP obtained as described above. A desired composition ratio and growth rate of AlInP for forming the window layer can be easily obtained.

As described above, the conditions of the element structure as designed can be obtained with respect to the mixed crystal composition ratio and the film thickness during the crystal growth of the solar cell structure.

The basic features of the manufacturing process of the solar cell according to the present invention include a process of forming a growth condition observation / measurement structure on a semiconductor substrate, and observation of the growth condition observation / measurement structure. And a step of forming a solar cell structure according to the determined growth conditions.

More specifically, in order to achieve the above object, the present invention provides a pn junction layer of a semiconductor, a window layer having a forbidden band width made of a material wider than that of the pn junction layer, and forming the same. In a solar cell in which a ternary or more III-V mixed crystal compound semiconductor is used for all or a part of a solar cell having a semiconductor substrate as a main component, a mixed crystal of the mixed crystal semiconductor having the above solar cell structure is used. III-V compound containing at least one of the group III and group V elements constituting the mixed crystal semiconductor of the solar cell structure between the semiconductor substrate and the solar cell structure in order to determine the growth condition of the composition It is intended to provide a solar cell structure characterized by stacking a plurality of semiconductor layers and a mixed crystal semiconductor layer thereof.

[0020]

1 and 2 show a solar cell having the structure of the present invention and a manufacturing process thereof. As shown in FIG. 1, the solar cell of the present invention has a solar cell structure 1 according to the present invention, and a growth condition observation and measurement structure for indirectly determining a growth condition of a mixed crystal composition of the solar cell structure 1. 2, the structure is formed on the semiconductor substrate 3. Then, as shown in FIG.
To form a growth condition observation measurement structure 2 on the semiconductor substrate 1,
In step S22, the growth condition observation measurement structure 2 is observed.
The growth condition of the solar cell structure is determined based on the result, and the solar cell structure 1 is formed in step S23.

[0021]

【Example】

Embodiment 1 FIG. 3 shows a first embodiment of the solar cell according to the present invention.

In this embodiment, a pn junction layer 11 is formed on a GaAs semiconductor substrate 3 as a solar cell structure (layer group) 1.
This is a single-junction solar cell structure using three mixed crystal semiconductor layers, namely, a GaInP layer 12 and an AlInP layer as the window layer 13. Growth condition observation / measurement structure (group of layers) used as an observation measurement layer that determines the composition control condition of the mixed crystal semiconductor of solar cell structure 1
2 from an GaAs semiconductor substrate 3 (including a buffer layer) side, an AlAs (aluminum arsenide) layer 21, G
It was formed by laminating an aAs layer 22 and a GaInP layer 23 in this order. The thickness of each of these layers 21, 22, 23 is
It is preferably about 0.1 μm. The reason is that the Ga composition range in which the critical film thickness is 0.1 μm or less in GaInP is about 10%. Even if GaInP having an improper composition is laminated, if the composition of the film is within the range, the lattice composition becomes larger. This is because generation of mismatch dislocations can be suppressed.

Next, after the growth of the growth condition observation / measurement structure layer 2 is completed, the film thickness of each of the laminated layers is measured by spectroscopic ellipsometry, and the growth rate is determined thereby.
FIGS. 4, 5 and 6 show the GaAs layer and A, respectively.
The results of comparing the film thickness of each of the lAs layer and the GaInP layer obtained by spectroscopic ellipsometry measurement with the film thickness actually obtained by observing the cross section by a scanning electron microscope (SEM) are shown. The straight lines in FIG. 4, FIG. 5 and FIG. As is clear from these figures, a very good agreement is obtained, and it can be seen that even in the case of the laminated structure, the film thickness measurement accuracy of the spectral ellipsometry is very high. Also, even if the film thickness to be laminated is 0.1 μm,
It can also be seen that sufficient film thickness measurement accuracy can be obtained.

The procedure for determining the optimum growth condition from the growth rate thus obtained is as described above, but will be described again below.

In general, the film growth process of the MBE method or the MOCVD method proceeds when the group III element reaches and bonds to the growth substrate surface covered with the group V element having a high vapor pressure. Therefore, the growth rate is determined by the supply amount of the group III element. For example, when the supply amount of Ga is the same, GaAs
And the growth rate of GaP can be considered to be the same.

Therefore, in the embodiment of FIG. 3, the GaAs layer 22 and the GaInP layer 23 of the growth condition observation / measurement structure 2 are used.
From the ratio of the growth rates of GaAs and GaInP obtained by the measurement, the composition ratio of Ga mixed crystal, and the growth rate of InP can be obtained from the difference between them. In consideration of this result, the growth conditions may be optimized so that desired conditions of the composition ratio of GaInP and the growth rate are obtained.

The growth rate of AlAs can also be obtained by measuring the AlAs layer 21. Therefore, considering the growth rate of InP obtained as described above, a desired AlIn
The conditions of the composition ratio of P and the growth rate can be obtained.

As described above, at the time of actual crystal growth of the solar cell structure, it is possible to manufacture an element structure as designed with respect to the mixed crystal composition ratio and the film thickness.

Next, a method of manufacturing the solar cell having the structure shown in FIG. 3 will be described. The growth method is gas source MBE (GS-M
BE) method, and the manufacturing apparatus shown in FIG. 9 is used.

In the present embodiment, a metal is used as a group III raw material, and a gas raw material is used as a group V element supply source. That is, in FIG. 9, a metal material source, gallium (Ga), indium (In), and aluminum (Al) housed in containers each having a shutter are selectively used by controlling the opening and closing of the corresponding shutter.

Arsenic (As) is used as a source of the group V element.
As for, arsine (AsH3) and phosphine (PH3) for phosphorus (P) are thermally cracked and used as gaseous materials.

Beryllium (Be) is used as a p-type doping material, and silicon (Si) is used as an n-type doping material. The semiconductor substrate to be manufactured is p-type GaAs
s (100 faces) semiconductor substrate.

In the As atmosphere under the supply of AsH3, G
After the oxide film on the surface of the aAs substrate 31 is removed by thermal cleaning for 10 minutes, the buffer layer 32 is formed on the substrate 31.
As the p-type GaAs layer 32 (dope concentration 7 × 10 ¹⁸ / c
m ³ ) is grown by 0.5 μm.

Thereafter, as a growth condition observation measurement structure 2,
p-type AlAs layer 21 (dope concentration 3 × 10 ¹⁸ / c
m ³ ), p-type GaAs layer 22 (doping concentration 3 × 10 ¹⁸ /
cm ³ ), p-type GaInP layer 23 (dope concentration 3 × 10
¹⁸ / cm ³ ) is grown by 0.1 μm each.

After completion, the growth is interrupted, and spectroscopic ellipsometry is performed to measure the thickness of each layer. From the obtained growth rate, the Ga composition ratio of GaInP was 52%, and the
In InP, growth conditions are set so that an Al composition ratio of 53% can be obtained.

Subsequently, under the appropriate growth conditions after the change, the crystal growth of the solar cell structure is started. First, p-type G
aInP base layer 11 (Dope concentration 2 × 10 ¹⁷ / c
m ³ ). Then, close the Be shutter.
At the same time, the Si shutter is opened to reduce the n-type GaInP emitter layer 12 (dope concentration 2 × 10 ¹⁸ / cm ³ ) to 0.0.
Grow 5 μm.

Further, an n-type AlInP layer 13 is used as a window layer.
(Dop concentration 4 × 10 ¹⁸ / cm ³ ) is grown to 0.03 μm. Finally, an n-type GaAs cap layer having a doping concentration of 4 × 10 ¹⁸ / cm ³ is grown to a thickness of 0.5 μm for good electrical contact with the electrode material.

After the film thus manufactured has undergone an electrode manufacturing process, the cap layer is removed by etching, and an antireflection film is formed on the surface to complete the device. The efficiency of this solar cell was 19%.

[Embodiment 2] FIG. 7 shows, as a second embodiment, GaInP in the upper cell 120 and G in the lower cell 110.
An example of a tandem solar cell using aAs will be described. In this embodiment, AlInP layer 21, AlAs layer 22, Ga
Three layers of As23 are used.

As described above, the AlInP layer 21 and the Al
The growth rate of InP is determined from the growth rate with the As layer 22, and by considering the growth rate of GaAs together with the growth rate of GaP, GaInP having a desired composition ratio can be obtained.
Further, when the layers are stacked in this order from the substrate side in the order of the forbidden band width, the effect of repelling minority carriers equivalent to that of the back surface field layer can be obtained, and the recombination loss of carriers in solar cell characteristics can be reduced.

In the upper cell 120 shown in FIG.
P, the growth method of each layer of the tandem thick battery using GaAs for the lower cell 110 is the same as in the first embodiment described above.
A gas source MBE (GS-MB
It can be performed by the method E).

Using a semiconductor substrate 3 of p-type GaAs (100 surfaces), an oxide film on the substrate surface is removed by thermal cleaning for 10 minutes in an As atmosphere under the supply of AsH 3, and then a buffer is formed on the substrate 31. As a layer, a p-type GaAs layer 32 (dope concentration: 7 × 10 ¹⁸ / cm ³ ) is grown to a thickness of 0.5 μm.

Thereafter, the p-type AlInP layer 21 (dope concentration 3 × 10 ¹⁸ / cm ³ ), p-type AlAs
Layer 22 (dope concentration 3 × 10 ¹⁸ / cm ³ ), p-type GaAs
The s layer 23 (dop concentration: 3 × 10 ¹⁸ / cm ³ )
grow by μm.

After completion, the growth is interrupted, and spectroscopic ellipsometry is performed to measure the thickness of each layer. From the obtained growth rate, using a relational expression between each raw material cell temperature and the growth rate,
The raw material cell temperature was changed to obtain a Ga composition ratio of 52% for GaInP and an Al composition ratio of 53% for AlInP.

Subsequently, crystal growth of the solar cell structure was started under the proper growth conditions determined as described above. First,
p-type GaAs base layer 111 (dope concentration 2 × 10 ¹⁷ /
cm ³ ) is grown to 3.0 μm. Thereafter, the Be shutter is closed, and at the same time, the Si shutter is opened and the n-type Ga
As emitter layer 112 (dope concentration 4 × 10 ¹⁸ / cm
³ ) is grown by 0.1 μm to produce a bottom cell 110.

Subsequently, the bottom cell 110 and the top cell 1
In order to form a tunnel junction 100 between the two, the temperature of the Si is raised and the n-type GaAs layer 101 (doping concentration 4 × 1
0 ¹⁸ / cm ³ ) is grown 0.05 μm. Subsequently, switching between Si and Be is performed, and after growing the p-type GaAs layer 102 (doping concentration 5 × 10 ¹⁹ / cm ³ ) to 0.05 μm,
The shutters other than As are closed.

Next, a 0.5 μm p-type GaInP base layer 121 (dope concentration: 2 × 10 ¹⁷ / cm ³ ) is grown.
Thereafter, the Be and Si shutters are switched, and the n-type GaI
nP emitter layer 122 (doping concentration 4 × 10 ¹⁸ / cm
³ ) is grown by 0.1 μm to form a top cell 120.

Next, an n-type AlInP layer 13 is used as a window layer.
(Dop concentration 4 × 10 ¹⁸ / cm ³ ) is grown to 0.03 μm. Finally, for good electrical contact with the electrode material, an n-type GaAs cap layer having a dopant concentration of 4 × 10 ¹⁸ / cm ³ is grown to a thickness of 0.5 μm and finished.

As described above, a three-layer tandem solar cell having good crystallinity and electrically connected by tunnel junction from the top cell 120 to the bottom cell 110 is formed by a series of growth. After the produced film passes through the electrode production process step, the cap layer is removed by etching, and an antireflection film is formed on the surface to complete the device. This solar cell showed a very high efficiency of 31%.

[Embodiment 3] FIG. 8 shows an example of a GaInAs solar cell in which a GaInAs solar cell structure is formed on an InP substrate 31. In this case, the growth condition observation measurement structure 2
Uses a GaInAs 21 and an InP layer 22. As in the above-described example, from the consideration of the two growth rates, desired conditions of the composition ratio of GaInAs and the growth rate can be obtained, and the element structure can be manufactured as designed.

The method for growing the device of this embodiment is the MOCVD method. In this embodiment, trimethyl gallium (TMG), trimethyl indium (TM
A) Arsine (AsH) for arsenic (As) as a source of I), trimethylaluminum (TMA) and group V elements
3) Phosphine (PH3) is used for phosphorus (P). Further, diethyl zinc (DEZn) is used as a p-type doping material, and silane (Si
H4) is used. The semiconductor substrate to be manufactured is p-type InP
(100 faces) The substrate 31.

In a P atmosphere supplied with PH3, the substrate 3
After removing the oxide film on the surface of the substrate 1 by thermal cleaning for 10 minutes, a p-type In layer was formed on the substrate 31 as a buffer layer.
0.5 μm of P layer 32 (dope concentration 5 × 10 ¹⁸ / cm ³ )
grow m. Thereafter, as a mixed crystal composition control layer of the dummy solar potential structure 2, a p-type GaInAs layer 21 (doping concentration 2
× 10 ¹⁸ / cm ³ ), p-type InP layer 22 (doping concentration 2
× 10 ¹⁸ / cm ³ ) is grown by 0.1 μm each.

After completion, the growth is interrupted, and spectroscopic ellipsometry is performed to measure the thickness of each layer. From the obtained growth rate, G was calculated using the relationship between the flow rate of each raw material and the growth rate.
(a) The raw material cell temperature is set so that GaInAs having a composition ratio of 47% can be obtained.

Next, the process of growing the crystal of the solar cell structure under appropriate growth conditions will be described. First, the p-type GaInAs base layer 11 (dope concentration 4 × 10 ¹⁷ / c)
m ³ ). Next, the supply of DEZn is stopped,
At the same time, the supply of SiH4 is started to grow the n-type GaInAs emitter layer 12 (doping concentration 1 × 10 ¹⁸ / cm ³ ) to 0.4 μm. Further, an n-type InP layer 13 (dope concentration: 1 × 10 ¹⁸ / cm ³ ) was used as a window layer to a thickness of 0.05 μm.
grow up. Finally, n-type GaInA having a dopant concentration of 4 × 10 ¹⁸ / cm ³ for good electrical contact with the electrode material.
The s cap layer is grown to 0.5 μm.

After the film thus manufactured has undergone an electrode manufacturing process, the cap layer is removed by etching, and an antireflection film is formed on the surface to complete the device. The efficiency of this solar cell was 12%.

[0056]

According to the present invention, in a solar cell structure using a ternary or more III-V mixed crystal compound semiconductor, a condition for growing a mixed crystal composition of the mixed crystal semiconductor is determined. As a layer, between a semiconductor substrate and a solar cell structure, a group III-V compound semiconductor layer containing at least one of Group III and Group V elements constituting the mixed crystal semiconductor, and a mixed crystal semiconductor layer thereof. By providing a growth condition observation measurement structure, information such as a growth rate can be obtained from the composition control layer before the actual solar cell structure is formed. A mixed crystal semiconductor having the following mixed crystal composition can be realized, and a solar cell having high photoelectric conversion efficiency can be manufactured with high yield.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a solar cell according to the present invention.

FIG. 2 is a manufacturing process diagram of a solar cell according to the present invention.

FIG. 3 shows a GaI formed on a GaAs substrate according to the present invention.
FIG. 3 is an element structure diagram of an nP solar cell.

FIG. 4 is a diagram comparing a film thickness obtained by spectroscopic ellipsometry and observation with a cross-sectional scanning electron microscope (SEM).

FIG. 5 is a diagram comparing a film thickness obtained by spectroscopic ellipsometry and observation with a cross-sectional scanning electron microscope (SEM).

FIG. 6 is a diagram comparing the film thickness obtained by spectroscopic ellipsometry and observation with a cross-sectional scanning electron microscope (SEM).

FIG. 7 shows a GaI formed on a GaAs substrate according to the present invention.
FIG. 3 is an element structure diagram of an nP / GaAs two-layer tandem solar cell.

FIG. 8 shows a GaIn formed on an InP substrate according to the present invention.
The element structure figure of As solar cell.

FIG. 9 is a structural diagram of an apparatus for manufacturing a solar cell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solar cell structure 2, ... Growth condition observation measurement structure 3, Semiconductor substrate 4, Antireflection film, 5 ... Metal electrode

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Katsura Tamura 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (7)

[Claims] 1. A method for observing and measuring growth conditions comprising a plurality of layers, each containing an element of the same family as the mixed crystal composition of the solar cell structure, between the semiconductor substrate and the solar cell structure. Features solar cells. 2. A semiconductor substrate comprising: a semiconductor substrate; and a solar cell structure formed on the semiconductor substrate.
A semiconductor pn junction layer and a window layer made of a material having a wider forbidden band width are provided.
In a solar cell using a III-V or higher mixed crystal compound semiconductor, the mixed crystal semiconductor having the solar cell structure is provided between the semiconductor substrate and the solar cell structure.
III containing at least one of Group I and V elements
A solar cell having a growth condition observation measurement structure in which a plurality of group V compound semiconductor layers and a mixed crystal semiconductor layer thereof are stacked. 3. The solar cell according to claim 2, wherein the window layer is aluminum indium phosphide, the pn junction layer is gallium indium phosphide, and the semiconductor substrate is gallium arsenide. Is a material selected from the group consisting of gallium arsenide, aluminum arsenide, gallium indium phosphide, aluminum indium phosphide and a mixed crystal material thereof. 4. The solar cell according to claim 2, wherein pn
In a solar cell structure in which the bonding layer is gallium indium arsenide and the window layer and the semiconductor substrate are indium phosphide,
A solar cell, wherein the mixed crystal composition control layer is made of a material selected from indium phosphide, gallium indium arsenide, aluminum indium arsenide, or a mixed crystal material thereof. 5. The solar cell according to claim 2, wherein the plurality of semiconductor layers forming the growth condition observation / measurement structure have a forbidden band from the semiconductor substrate side to the solar cell structure side. A solar cell characterized by being stacked in order of increasing width. 6. A tandem solar cell according to claim 2, wherein a plurality of solar cell structures are stacked in tandem. 7. A step of forming a growth condition observation measurement structure on a semiconductor substrate, and observing the growth condition observation measurement structure.
A method for manufacturing a solar cell, comprising: determining a growth condition of a solar cell structure based on the result; and forming a solar cell structure according to the determined growth condition.