JP2512188B2 - Compound semiconductor photoelectric conversion device on Si substrate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a compound semiconductor photoelectric conversion device on a Si substrate, and more particularly to the structure of a photoelectric conversion device having a III-V group compound semiconductor layer on a Si substrate. .

[Conventional technology]

FIG. 4 shows, for example, a conventional compound semiconductor photoelectric conversion device on a Si substrate shown on page 196 of a collection of papers presented at the 3rd International Conference on Photovoltaics held in 1987. Here, a GaAs solar cell on a Si substrate will be described as an example of a compound semiconductor photoelectric conversion element on a Si substrate.

In FIG. 4, 1 is a Si substrate, 2 is n-type GaAs epitaxially grown on the first main surface of the Si substrate 1, and 3 is GaAs and AlGaAs (or InGaAs) further grown thereon.
Superlattice (hereinafter referred to as GaAs / AlGaAs superlattice), 2'is n-type GaAs as an active layer of a solar cell, and 4 is GaAs / AlGaAs.
P-type GaAs for forming a pn junction, which is formed on n-type GaAs2 'formed on superlattice 3 and absorbs light energy as an active layer of a solar cell to generate electricity, 5 is on p-type GaAs4 P-type AlGa, which is formed on the surface and acts as a window layer for solar cells
As and 6 are antireflection films (hereinafter, ARC: Anti Reflection Coat) for making as much light as possible enter the inside of the solar cell.
), 7 is formed by forming a hole in ARC6 and p-type AlGaAs5 and patterning so as to contact p-type GaAs4. The photocurrent generated by light irradiation is effectively collected and taken out to the outside. A p-type metal electrode 8 is an n-side metal electrode formed on the back surface side of the Si substrate 1.

 Next, the operation will be described.

Light is p-type GaAs4 and n-type through ARC6 and p-type AlGaAs5
When incident on GaAs2 ', the incident light is absorbed in this region and converted into carriers of electrons and holes, and the electrons generated in p-type GaAs4 pass through the pn junction to n-type GaAs2' and n-type GaAs2 '.
The holes generated in the above process diffuse into the p-type GaAs4 through the pn junction, and the positive charge is the p-side metal electrode 7 and the negative charge is the n-type.
It is collected in the side metal electrode 8, a voltage is generated between the terminals, and a current can be taken out from between the terminals.

[Problems to be Solved by the Invention]

Since the conventional GaAs solar cell on Si substrate is configured as described above, it seems that there is no problem in current extraction in principle, but when actually used as a solar cell, this p-electrode 7 and n-electrode are used. It is necessary to connect an interconnector on the 8 side for extracting current. For this connection, a parallel gap welding method, which has high reliability at the connection point, is generally used in GaAs solar cells and the like.
When applied to a GaAs solar cell on a Si substrate having a structure as shown in the figure, thermal damage causes thermal and mechanical damage to the GaAs layer under the welding of the p-electrode 7, which reduces the adhesive force of the interconnector at that location. Also, the problem of deterioration of solar cell characteristics due to pn junction breakdown occurs. In addition, GaAs and Si
The thermal expansion coefficient of Si is 2.4 × 10 ^-6 [K ^-1 ] and that of GaAs is 5.7 × 10 ^-6.
[K ^-1 ], the deformation of the element due to the difference between the two,
That is, in the solar cell of FIG. 4, when the n-electrode 8 is viewed upward, there is a deformation in which the n-electrode 8 has a convex shape. As shown in FIG. 2 (a), a connector is welded to the n-electrode side. At this time, as shown in FIG. 2 (a), mechanical and thermal stress is applied from the welding head 15 to this convex side, and cracks easily occur in the GaAs layer at the portion corresponding to the welding location. However, in severe cases, there was a problem that even the Si substrate was broken and could not be used as a solar cell.

The present invention has been made in order to solve the above problems, and it is possible to prevent cracks in the GaAs layer and cracks in the solar cell during welding of the external connector on the p electrode and n electrode of the solar cell. An object is to obtain a compound semiconductor photoelectric conversion device on a Si substrate that can be prevented.

[Means for solving the problem]

In the compound semiconductor photoelectric conversion device on the Si substrate according to the present invention, the second conductivity type electrode is connected to the second conductivity type III-V compound semiconductor layer formed on the first main surface of the Si substrate, and Part passes through the side surface of the Si substrate through the insulating film, is formed on the same surface as the second main surface of the Si substrate, and is continuously formed in a portion not on the second main surface. The one-conductivity type electrode is also formed on the second main surface of the Si substrate and a part of the electrode is continuously extended to a portion other than the second main surface.

Further, according to the present invention, a portion of the first conductivity type electrode (n electrode) and the second conductivity type electrode (p electrode) which is not on the second main surface of the Si substrate, that is, a portion protruding to the outside of the solar cell, It has a stress relief structure.

[Action]

Since the tip portions of the p-electrode and the n-electrode in the present invention are present in the region of the Si-substrate III-V compound semiconductor solar cell where Si and III-V compound semiconductor do not exist, the external connector is connected at this portion. As a result, the III-V compound semiconductor solar cell is not affected by mechanical and thermal stress, and problems such as deterioration of the characteristics and shape crack of the III-V compound semiconductor solar cell on the Si substrate occur. Without the need for a practical assembly.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional perspective view of a GaAs solar cell on a Si substrate which is a compound semiconductor photoelectric conversion device on a Si substrate according to an embodiment of the present invention. In the figure, 1 is an n-type Si substrate, 2 is this
N-type GaAs epitaxially grown on the Si substrate 1 and 3 are GaAs / AlGaAs (or InGaAs) further grown thereon.
Etc.) superlattice, 2'is n-type Ga as active layer of solar cell
As, 4 are formed on the GaAs / AlGaAs superlattice 3, p-type GaAs for forming a pn junction that absorbs light energy and generates electricity as an active layer of the solar cell, and 5 is formed on p-type GaAs4, P-type AlGaAs serving as a window layer of the solar cell, 6 is an antireflection film (ARC), 7 is a hole formed in ARC6 and p-type AlGaAs5, and is bonded to the p-type GaAs layer 4 and through the insulating film 9. The p-electrode is formed by wiring the side surface of the Si substrate and is continuously extended to the outside of the same plane as the second main surface. 7a is a grid electrode portion thereof, and 7b is a bus electrode welding portion. Reference numeral 8 is an n-electrode formed on the second main surface and the same main surface as the second main surface and extending continuously to the outside of the second main surface, of which 8a is an n-electrode formed on the second main surface, 8b is a bus electrode weld.
Reference numeral 9 is an insulating film for electrically insulating the p-electrode 7 from the n-type GaAs and n-type Si substrate, and 10 is an insulating film for preventing a short circuit between the p-electrode 7 and the n-electrode 8.

Since the operation of the solar cell itself of the GaAs solar cell on the Si substrate according to the present embodiment is the same as that of the conventional example, description thereof will be omitted, and the characteristic operation of the present embodiment will be described. P according to this invention
The electrode weld 7b and the n electrode weld 8b are on the Si substrate.
Since it exists outside the GaAs layer and the Si substrate of the GaAs solar cell,
When the external connector is welded to the GaAs layer, the thermal and mechanical stress associated with the welding does not reach the GaAs layer, so that not only the GaAs layer is not cracked, but also the Si substrate is not cracked by the stress. As described in the conventional example, when a GaAs layer is formed on a Si substrate, stress is relieved due to the movement of dislocations in the high temperature region during the slow cooling process after the epitaxial growth is usually performed at a high temperature of about 700 ° C. However, when it is cooled down to around 350 ° C, dislocations move and it becomes impossible to relieve the stress.
The stress generated by the difference in the coefficient of thermal expansion is formed inside. This inherent amount of stress is on the Si substrate
Sufficient to generate cracks in the GaAs layer (up to 1.5 × 10 ⁹
dyn / cm ² ) is accumulated. In a static state, it may barely withstand this stress, but when mechanical and thermal dynamic stress, such as welding of an external connector, is applied to this, this triggers the GaAs layer. A crack is generated, and this crack divides the GaAs layer and causes deterioration of the photovoltaic characteristics of the GaAs solar cell.

The solar cell is rarely used alone when actually used, and a plurality of solar cells are connected to each other using an external connector. As shown in FIG. 4, in the conventional GaAs solar cell on the Si substrate, the n-electrode is on the second main surface of the Si substrate, and when an external connector is connected to the n-electrode side, the n-electrode is shown in FIG. As shown in Figure 5, the solar cell bent in a convex shape is pressed locally by the welding head 15 until it comes into flat contact with the welding table 14 and heated, so that a bending moment is first applied to the entire solar cell, and further the pole part is further applied. Since the thermal stress is applied from the welding head, it corresponds to the part where the welding head is in contact.
A clutch was generated in the GaAs layer and the Si substrate was cracked.

On the other hand, in the above embodiment of the present invention, as shown in FIG. 1, since the n electrode 8 is formed on the first main surface of the Si substrate, the n electrode 8 is formed as shown in FIG. At the time of welding the external connector to the electrode 8b, the solar cell 11 has a concave shape, and even if the welding head 15 pressurizes the n-electrode 8b for welding, the other end of the solar cell floats and the Si substrate No mechanical stress is applied to the upper GaAs layer 11. Further, since the GaAs layer does not exist under the n-electrode, the GaAs layer is not adversely affected by the local heating from the welding head 15. Therefore, in this embodiment, it is possible to connect the external connector without deteriorating the characteristics of the solar cell or causing structural destruction, and the GaAs solar cell on the Si substrate can be put into practical use.

In the above embodiment, the p-bus electrode welded portion 7b has a flat plate shape, but the p-bus electrode welded portion 7b may have a stress relief structure, one example of which is shown in FIG. FIG. 3 shows a mesh type.
By making the bus electrode welded portion into a mesh type in this way, when welding the external connector to each electrode, the force applied to the cell when the welding head 15 presses on the n electrode 8b for welding is released. It is possible to obtain a more reliable cell connecting portion when modularized, and it is possible to improve the characteristics of the solar cell.

Of course, the shape of the stress relief is not limited to the mesh type, and of course, another structure may be used as long as the force applied to the cell is released.

Although the embodiment of the present invention has been described with respect to a GaAs solar cell, similar effects can be obtained with devices using other compound semiconductors.

〔The invention's effect〕

As described above, in the GaAs solar cell on the Si substrate according to the present invention, the welding assembly location of the p electrode and the welding assembly location of the n electrode are formed outside the GaAs solar cell itself. External connector can be connected without causing damage or deterioration of characteristics, and not only can it be put into practical use, but the connector itself can also be connected by using the p and n electrodes protruding to the outside as the connector itself. It is possible to reduce the assembly cost and increase the cell filling rate when modularizing by connecting multiple cells because there is no need for a process to perform, and when considering it as a module in the power generation system, from the module of the same size, This has the effect of increasing the efficiency of the solar cell module by obtaining more power.

Furthermore, since the p and n electrodes that are traveling to the outside have a stress relief structure, there is an effect that a highly reliable cell connection point can be obtained when further modularized.

[Brief description of drawings]

FIG. 1 is a sectional perspective view of a compound semiconductor photoelectric conversion device on a Si substrate according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are assemblies of a conventional GaAs solar cell on a Si substrate to an n-electrode. And FIG. 3 is a view showing the situation of assembly in the case of one embodiment of the present invention, FIG. 3 is a plan view of a compound semiconductor photoelectric conversion device on a Si substrate according to one example of another embodiment of the present invention, and FIG. The figure is a cross-sectional view of a conventional GaAs solar cell on a Si substrate. 1 is a Si substrate, 2 is n-type GaAs, 2'is n-type GaAs as a solar cell active layer, 3 is GaAs / AlGaAs superlattice, 4 is p-type GaA
s, 5 is p-type AlGaAs, 6 is an antireflection film, 7 is a p-electrode, 7a
Is a p grid electrode portion, 7b is a p bus electrode welded portion, 8 is an n electrode, 8a is an n electrode on the second main surface, 8b is an n bus electrode welded portion,
9 is a side surface insulating film, 10 is a second main surface insulating film, and 11 is the Si of the present invention.
GaAs solar cells on a substrate, 14 is a welding table, 15 is a welding head, and 51 is a conventional GaAs solar cell on a Si substrate. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

(57) [Claims] 1. A Si substrate of the first conductivity type and a first Si substrate
And a second conductivity type III-V compound semiconductor layer formed on the first conductivity type III-V group compound semiconductor layer. In the photoelectric conversion element having, the second conductivity type electrode is connected to the second conductivity type III-V group compound semiconductor layer, and a part of the second conductivity type electrode is connected via an insulating film.
A first conductive type electrode is formed on the second main surface of the Si substrate in the same plane as the second main surface and not on the second main surface, and the first conductivity type electrode is formed on the second main surface of the Si substrate; Part of the second main surface is on the same plane as the second main surface
A compound semiconductor photoelectric conversion device on a Si substrate, wherein the compound semiconductor photoelectric conversion device is stretched and formed on a portion that is not on the main surface. 2. A compound semiconductor photoelectric conversion on a Si substrate according to claim 1, wherein a stress relief structure is provided on portions of the first conductivity type electrode and the second conductivity type electrode that are not on the second main surface. element.