JPH0377382A - Solar battery cell - Google Patents

Abstract

PURPOSE:To prevent the conversion efficiency from decreasing and eliminate the difficulties in accurate control of etching by forming a semiconductor layer of the first conductivity type, which is the same conductivity type as a substrate separated by a semiconductor layer of the second conductivity type which is the opposite conductivity type to the substrate, forming a protective diode on the first-conductivity-type semiconductor layer, and forming a solar battery functional part on the remainder of the surface of the substrate. CONSTITUTION:A multilayer solar battery functional part 200 comprises an n-type high impurity GaAs layer 201 made on the principal surface 101 of a substrate, a GaAs/AlGaAs multilayer lattice commensurate layer 202, an n-type GaAs layer 203, a p-type GaAs layer 204, and a p-type AlGaAs layer 205 to prevent electrons generated in the p-type GaAs layer 204 from extincting by surface recombination. A protective diode 300 comprises layers 301-305 made of the same materials as the layers 201-205 of the solar battery functional part 200 respectively. A positive (surface) electrode 401 to connect the layer 204 and a layer 106, a conductor layer 402 to connect the p-type AlGaAs layer 305 of the protective diode 300 and the substrate 100, and a negative (rear) electrode 403 are formed.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a solar battery cell made of a compound semiconductor, which is used as a solar battery cell, particularly in a solar power generation device in which a plurality of solar battery cells are connected in series. It is.

(Prior Art) A solar battery cell is basically a diode side-end semiconductor device having one pn junction inside. Since the generated voltage of such solar cells (hereinafter abbreviated as "cells") is relatively low, they actually receive 9! When constructing an electric device, it is common to connect a plurality of cells in series so that the sum of the individual generated voltages becomes a desired cutting voltage.

It is also well known to connect a plurality of such series bodies in parallel to obtain a desired output current.

In a photovoltaic power generation device like the one described in L, if some of the cells connected in series are in the shadow of something during operation (the incident light disappears), this shadow occurs. Since the cell does not generate electricity and works to block the current, the output of the power generation device is significantly reduced. Furthermore, when a cell is viewed as a diode, the total generated voltage of other cells connected in series or the reverse direction voltage is applied to the darkened cell, so if the reverse direction 1iJi (reverse breakdown voltage and Voltage Daiba)
If a small damage occurs, a destructive phenomenon will occur, and the subsequent function as a colon battery cell will be significantly reduced or completely destroyed.

There are two ways to prevent this. The first method is to increase the reverse breakdown voltage of the cell, and this can be achieved by reducing the impurity concentration in the base layer of the cell. However, in general, the p-n junction of a solar cell needs to be shallow, and in particular, in U'DI cells, the depth of the junction is 0.3 to 0.5 gm or more to increase short wavelength sensitivity. The impurity concentration required to obtain a reverse breakdown voltage of several white volts (for example, 1013 to 14aLoIls/cl
13) It is actually extremely difficult to create a pn junction using a diffusion method for the base layer. Furthermore, it is difficult to obtain the desired low impurity concentration through crystal growth, and generally speaking, there is a limit to increasing the reverse resistance of the cell, making it particularly unsuitable for use in high-voltage power generation devices.

The second method is to connect a protection diode in parallel with the series-connected body with opposite polarity for each range that does not exceed the sum of the generated voltages of individual cells connected in series or the reverse breakdown voltage of one cell. That's true. This method of using anti-parallel protection diodes is a practical method, and connecting protection diodes to a series connection of many cells requires space for a protection tie-out. others,
This increases the time required for manufacturing, leading to an increase in cost, and also has disadvantages such as lowering the reliability of the device due to an increase in the number of parts. This is a big problem, especially in the case of writing devices that require high reliability.In order to solve the disadvantage of 6L, instead of using an individual diode as a protection diode, an anti-parallel It was considered to form a connected protection diode. For example, JP-A-57-184255, JP-A-57-184255,
A compound semiconductor (GaAs) solar cell based on such a concept is disclosed in Japanese Patent No. 204180 and the like. In order to incorporate a protection diode into a cell, it is generally necessary to electrically separate the n(p) type layer of the solar cell and the M(p) type layer of the protection diode. In the cell described in the publication, two solar cells (i.e., p-n junction element) are formed by separating Ti into a semi-insulating substrate made of materials such as GaA and S, and one of them is separated into Ti. The solar cell function part and the other part are used as protection diodes.

[Invention or problem to be solved]

In the 1-type thick gS'' Wi and Ike cells that form protection diodes connected in antiparallel in the same cell, the substrate is semi-insulating, so the side opposite to the light-receiving surface of the solar cell functional part It is not possible to provide the n(p) electrode on the back side of the substrate.Therefore, it is unavoidable to expose a part of the n(p) type layer of the functional part that is formed in contact with the substrate surface to the light receiving surface side (i.e. (remove the p (n) type layer, etc. that is present in -L),
Is there a Ha(P)'ili pole formed in the exposed part?
In this case, the internal series resistance of the solar cell increases due to the lateral resistance of the n(p) type layer, resulting in a low conversion efficiency. Furthermore, by forming an n(p) electrode on a part of the light-receiving surface, the right-handed light-receiving area is reduced, and the conversion efficiency is further reduced. In addition, in order to expose 7 parts of the n (p) type layer to the light receiving surface side for electrode formation, mup (
n) The etching depth must be strictly controlled during selective removal of the p(n)-type layer and the n(p)-type layer.
When the shaped layers are made of the same material, precise control of the etching depth is extremely difficult.

This starter I has a structure that can solve the problems mentioned in L, such as a decrease in conversion efficiency and difficulty in controlling the heavy etching process, and can be manufactured using a relatively simple process. The purpose is to provide a commercially efficient solar cell.

[Means to solve the problem]

In order to achieve the second object, the solar cell of the present invention has a semiconductor substrate having a first conductivity type. ! A semiconductor layer of the same first conductivity type as the substrate separated by a semiconductor layer of the second conductivity type opposite to the substrate is formed on a part of the surface portion on the side of the battery functional part type X&, and the semiconductor layer of the first conductivity type A protection diode is formed in the layer portion, and a solar cell functional portion is formed in the remaining substrate surface portion. Furthermore, the sun? forming a positive (front) electrode of the solar cell so as to electrically connect the surface semiconductor layer of the pond functional part and the first conductivity type semiconductor layer portion separated from the substrate by the second conductivity type semiconductor layer; , a conductor is provided to electrically connect the surface semiconductor layer of the protection diode and the substrate, and a negative (back surface) 'ilt pole of the solar cell is provided on the back surface of the substrate.

[Effect]

Is this invention thick? Ii! Since the cell uses a semiconductor substrate, it is possible to provide both electrodes for the battery member on the front and back sides of the substrate. There is no need to expose the rn(p) type layer of the functional section that is in contact with the substrate to the light-receiving surface side. Therefore, an undesired reduction in conversion efficiency can be avoided without significantly sacrificing the light-receiving area for electrode formation, and without adding to the internal series resistance due to the lateral resistance of the n (p) type layer. It can be avoided. Furthermore, since there is no need for selective etching to expose the n(p) type layer mentioned above for electrode formation, there is no need to worry about precise control of such etching during manufacturing, and the manufacturing process can be simplified. can reduce manufacturing costs.

〔Example〕

Next, a detailed description will be given with reference to examples.

FIG. 1 is a sectional view showing the structure of a first embodiment of a solar cell according to the present invention. The solar cell shown in this figure has a GaAs protection diode made of GaAs.
/Si solar cell, in the figure, (100) is the first
and second upper surfaces (101) and (102) to the right of n-type S
i board, (200) is the 1-1- of this board (LGO)
: Solar cell functional part formed on the surface (101), (:
10O) is a consignment diode. Solar cell function part (2
[)0) is an n-type highly impurity glue GaAs layer (201) provided on the main surface (1,01) of the substrate, GaAs/
Case f matching layer (202) consisting of a multilayer structure of AUGaAs
, n-type GaAs layer (20:I), P-type GaAs
It consists of a multilayer structure of a layer (204) and a p-type AUGaAsi3 (205) that serves to prevent electrons generated in the p-type GaAsW (204) from disappearing due to surface recombination. The protection diode (300) is composed of fi (301) to (305) made of the same material as each layer (200 to (205)) of the solar cell functional section (200) described below. Main surface (1 (It)
p-type 3iM formed including a part of p-type Si! (106) is p-type Si! (105) is formed with the main surface within the boundary, (1,08) is silicon nitride (SiJ<)
The final membrane (401) is the positive (front) 1r1 pole that connects the scrap (2011) and the layer (100).

(402) is the P type AUGa of the protection diode (300)
A conductor layer (403) connecting the As layer (305) and the substrate (100) is a negative (A-side) electrode.

Next, a method for manufacturing the solar cell shown in FIG. 1 will be explained with reference to cross-sectional views of each step in FIG. 2.

First, 11
Form a thermal oxide film (10:l) at 00°C to 1200°C,
A part of the oxide film (10:1) on the first main surface (+01) is removed by a well-known photoetching method to open a window (104) and form a required selective diffusion mask (FIG. 2A). Next, this substrate was coated with B, H, (diborane) approximately 1.5%, 0
2 (oxygen) in an N2 (nitrogen) atmosphere containing approximately 0.5% 3
B (104) is deposited into the substrate through the window (104) by performing a penetration heat treatment at 1200°C for several hours.
boron) is diffused to form a p-type layer (1,05).

Subsequently, a selective diffusion mask (not shown) with a smaller window within the window (+04) is formed and 'PH3 (phosphine)
A deposit treatment similar to that described above was performed at approximately 1000°C in an N2 (nitrogen) atmosphere containing approximately 2% and 02 (oxygen) and approximately 1% O2 (oxygen), and a penetration treatment was further performed as described above.
(phosphorus) is diffused to form an n-type layer (+06) (FIG. 2B).

” The formation of the two-legged p-type layer and n-type layer may be performed by ion implantation instead of diffusion. In that case, a photoresist mask on a thermal oxide film (10:l) is used as a mask. However, the p-type layer is, for example, BF.

(boron trifluoride) as a P-type impurity source, and in the case of an n-type layer, for example, AS113 (arsine) or P
It is formed by implanting As or P at an energy of 50 to 100 KeV using li3 (phosphine) as an n-type impurity source.

Next, the oxide film (103) on the surface (1,01) side of the substrate (100) is removed using a common etching solution such as hydrofluoric acid or ammonium fluoride aqueous solution, and the main surface is In order to form a p-n junction (206) that functions as a GaAs solar cell, Takoba MO-CVD is used.
・N-type high impurity GaAs layer (201), lattice matching scrap (202),
n-type GaAs layer (203), p-type GaAsW (20
4) and p-type AAGaAs (205) are sequentially grown to form a superimposed layer.

In this case, GaAsW is formed using (CI+,)lIGa (trimethyl gallium) with 11□ as a carrier gas.
and ASH3 (arsine) were introduced into a reactor maintained at approximately 800°C, and in the case of an n-type layer, (C
2+15) Zn in the form of 2211 (diethylzinc), p
In the case of a shaped layer, Se (selenium) is added as an impurity in the form of H and Se (hydrogen selenide). In addition, the formation of the AUGaAs layer is as follows: L, (Ctl*): +Ga and 8s1
1. (C113), A, and Q (trimethyl aluminum) gases are added thereto, and the same procedure as above is carried out. In case of p-type layer)! Add 2 Se.

The layer (202) includes 3 to 1 AUGaAs/GaAs layer.
It is normal to form by laminating 111'9.

Next, the p-n junction part (between the substrate and the layer (105) and between the layers (105) and (1,06)) and the part including the p-type layer (ios) on the surface of the Si substrate (100) is The above gas phase 1i1: Nagai (201) to (205) in
For example, it is removed by a well-known selective etching method using an aqueous solution of hydrofluoric acid or nitric acid as an etching solution, and the solar cell function part (200) and the protective tie-out part ('+00) are separated and independent (Fig. 2C). ). In the figure, each layer constituting the protection diode (300) has a solar cell function section (20
0) corresponding to each Pil+ (201) to (205), (old), (302), (:103),
(304) and (305) are attached.

Solar cell function part (200) and protection tie auto (300)
Instead of separating the parts using the etching method as described above,
When forming the heavily open layers (201,) to (205), a growth inhibiting layer such as a silicon oxide film or a silicon nitride film is provided on the portion of the substrate surface corresponding to the portion to be etched and removed, thereby improving the solar cell function. It is also possible to grow the protective diode section and the protection diode section separately from the beginning.

Next, a silicon nitride (si3N4) film (1,08
) (Fig. 2D). The silicon nitride film is made using N2 (nitrogen) as a carrier gas and Nl+3 (ammonia) as a carrier gas.
It can be formed by a CVD method at about 800° C. using gas and SiH4 or 5ilL2CQa (silane) gas. Next, at a predetermined location on the front side of the L mark, that is, (1.09), (+, I[)), which is indicated by a pair of broken lines in the figure.
The silicon nitride film at the locations (111) and (1,12) and the AUGaAs film at the (112) location are removed by photo-etching. The silicon nitride film can be removed by plasma etching using carbon fluorine butts using a photoresist as a mask. Furthermore, ANGaAsW can be etched with an aqueous solution of hydrofluoric acid or nitric acid. Next, an electrode metal layer (401) is applied to the protective tie (300) and the solar cell function section (200) by means of sorrel or vapor deposition.
(402) and (404) are formed (Fig. 1). The positive electrode (401) of the solar cell is a p-type GaAs layer (204).
) and the n-type layer (106), the electrode (402) of the protection diode (:100) is connected to the p-type AUGaAs element (
:105) and the exposed first main surface of the substrate (100). Note that the oxide film (103) on the back surface (102) of the substrate (100) is also removed, and the metal layer is completed by forming a negative electrode (403).
T? I), the above positive electrode 1 (401) and the electrode (4[1
2) is at least the p-n junction portion on the surface of the Si substrate, n
The portion including the p-type layer (106) and the p-type layer (105) and the surface portion of the protection diode (300) are formed so as to be substantially completely covered to block the incidence of light. The metal layer for the electrode is, for example, for the n-type layer a, and C is Au-G.
For other parts, a multi-layer consisting of an e-Ni alloy layer and A and G layers, and a multi-layer of Ti and AgW are suitable.

FIG. 3 is a cross-section IA of the second embodiment of the solar cell according to the present invention. In addition, the 11A to 4th drawings show cross-sectional views at various points in the pickling process.
Parts that are the same as or equivalent to each part of the side path shown in 1-slope are given the same reference numerals.

The solar cell shown in FIG.
It is structurally the same as the cell shown in FIG. 1, except that the cell 300) is formed in the Si substrate (100). That is, the first
In the cell shown, either the protection diode (300) or the p-type FFe
n-type layer (1,0) separated from the rest of the substrate by (1,05)
6) GaAs and ARGaA layered on surface 1;
In contrast, in FIG. 3, an n-type layer (+06) and a p-type layer (1,07) formed on the surface of this n-type layer (106) It differs in that it is configured as a tie auto. Substrate (Ion),
GaAsA9 (
201), (201), (200 and lattice-ordered layer (2
02), the ANGaAsW (205), the silicon nitride film (108), and the electrodes (401) and (401) are all the same as those in FIG.

The cell of this embodiment can be manufactured by almost the same process as the cell shown in FIG. 1, except for some parts. That is, 1. First, an n-type Si substrate (+, OO) is prepared as in the 4th fMA, a Si thermal oxide film (l[13) is formed on its amphiboid surface, and a window (+04) is opened (FIG. 4A). Next, the window (l
B (boron) is diffused from (14) to p-type layer 4 (+
05) is formed, and p (phosphorus) is further diffused into this p-type layer to form an n-type layer (106). The steps up to this point are the same as those described for FIGS. 2A and 2H. Subsequently, a p-type layer (1,07) is formed in the n-type layer (106) (FIG. 4B). The formation of the p-type layer (+07) is the formation of the p-type layer (+07).
1, 05), or increase the deposition temperature a little higher, for example by about 1.
The temperature shall be 100°C.

Next, in order to remove the silicon oxide WJ (10:l) on the light-receiving surface side, that is, the eleventh surface (101) side, and form a p-n junction (206) that functions as a solar cell on that surface. , n-type highly impurity GaAsFF9 (201), lattice alignment layer (202), n-type layer aA, s layer (203)
), P-type layer aAs history (204) and p-type AUG
Make aAsR (205) sequentially J&long to make them violent. Next, at least the p-n junction portion and the p-type layer (1,[+5) on the surface of the Si substrate (1,00), nJ
f4i elbow (io6), the L-marked open layer on a predetermined portion including the p-type layer (107) is removed by etching, and -1
Form the solar cell micrometer (200) and protection diode (:1QO) part with separated oil on J: (Figure 4C)
, the above-mentioned modified layer forming step and separation step of both functional parts are performed in the second step.
This is the same process as described in connection with Figure C.

Next, as shown in the fourth diagram, the first soil surface (101
Silicon nitride Wi (108) is formed as an antireflection film and an insulating film for metal wiring on the entire surface of the ,
, After removing the silicon nitride and ARGaAs layers at locations (1,11) and (1,12), the protection diode (
Electrode metal layers (401), (402), and (404) are formed on the portion 300) and the required portions of the solar cell functional portion (200). The positive electrode (401) is made of p-type GaAsW (204
) and the n-type layer (106), and connect the protective tie (:
The electrode (402) of I[10] connects the p-type layer (1117) and the exposed first main surface of the substrate (I[lO), and the inner electrode connects at least the p-n junction portion of the substrate surface, n J of type layer (1,06) and p type layer (+05), (107)
: Formed so as to substantially completely cover the area and block the incidence of light. In addition, the oxide film (l[
1:l) is also removed and a metal layer is provided to form a negative electrode (40:l) (FIG. 3).

(Effects of the Invention) The solar cell of the present invention having a horizontal structure as shown in the two-legged mount 1 and the second embodiment has a solar cell function section (20 ports) when the light receiving surface receives light. p-type GaAsW: (2
04) and the n-type aAs layer (203), a photovoltaic force is generated between the #11 electrode (401) and the negative electrode (403).
It operates as a battery with negative value. -Blade protection diode 1'
(3[)0) is the electrode (402) and the n-type layer (106)
and electrode (401) to measure solar cell Ja function 2
00), so in a solar power generation system where many such cells are connected in series, if some of the cells are in the dark, the voltage from other cells will be affected by this protection. The tie auto is forward-biased to conduct, which serves to prevent reverse destruction of the shaded cells and to bypass the current, thereby reducing the reduction in conversion efficiency of the device. In addition, since the protection diode is connected in antiparallel to the solar cell function section, the power generation function is performed in the opposite direction to the original power generation direction of the device, or each electrode or the protection diode and its surrounding Since the entire light-receiving surface side of the -n junction is shielded from light by m, the power generation capability in the reverse direction does not adversely affect the power generation performance of the solar cell functional section.

In addition to the effects listed in L, the cell of this invention has the following effects:
There is the following effect.

(1) By using a conductive semiconductor material instead of an insulating or semi-insulating material for the substrate, it is possible to provide positive and negative picture electrodes on the light-receiving surface side and back side of the substrate, respectively, and together with the picture electrode. Compared to the conventional type provided on the light-receiving surface side, the effective light-receiving area can be increased and the conversion efficiency can be improved accordingly.

(2) By providing the negative electrode on the back side of the substrate, there is no need to expose a part of the n(p) type layer of the solar cell functional part to the light-receiving surface side and provide a negative electrode there. This eliminates the reduction in conversion efficiency due to the lateral resistance of the exposed n(p) type layer.

(3) Since the connection between the positive electrode and the external conductor can be made at the electrode part on the n (p) type layer of the substrate (the part (404) in Figs. 1 and 3), the above connection can be made. Therefore, it is possible to avoid the risk of damaging the p-n junction of the solar cell functional part due to the heat generated during parallel gap welding.

(rn(p) of the solar cell functional part to form a zero negative electrode)
) Since there is no need to expose a part of the p (n) type layer, there is no need for a selective removal operation of the p (n) type layer covering the part, that is, a difficult etching process in which the depth must be precisely controlled.

(5) The separation method for microscopic measurement of protective tie-back solar cells using p-n junctions in the substrate can be realized relatively easily in terms of process, and other steps are also simple6 (6 ) The structure in which the protective diode or solar cell functional part is incorporated into the cell of m-) and the manufacturing of (4) and (5) above] Due to the reasons related to the second step, the solar cell, and therefore the solar power generation device. The cost of production can be reduced.

Note that this invention has been explained using a so-called p-on-n type GaA, s cell (GaAs/Si solar cell) with Si as the substrate, or as two embodiments. In addition, compound semiconductors such as Ge or GaAs.

It goes without saying that various modifications can be made, such as using not only GaAs but also other compound semiconductor materials such as Yr+P# for the active part and diode of the battery, or adopting a straddle-on p-type configuration.

[Brief explanation of drawings]

1 [N is a cross-sectional view showing the structure of an embodiment of the solar cell according to the present invention, and FIG. 3 is a sectional view showing the structure of a second embodiment of the solar cell according to the present invention; FIG. FIG. 3 is a cross-sectional view for explaining the outline of each manufacturing process. 100... Semiconductor having the first conductivity type 7. (Board (
n-type Si substrate), 101... semiconductor substrate (n-type Si
102... second main surface of semiconductor substrate (n-type Si substrate), 200... solar cell functional section. 300...protective diode, 105...second conductivity type layer (p-type layer), 106...first conductivity type layer (n-type layer), 107...second conductivity type layer , 201, :
lO+...First conductivity type first compound semiconductor layer (n
type layer aAs layer), 2+12.302... lattice matching layer, 203, :103... second conductivity type
Compound semiconductor layer (n-type layer aAs layer), 204.304
...Second conductivity type compound semiconductor layer (p-type layer aA
s layer), 205, 305... second conductivity type compound semiconductor MCp type AUGaAs layer), 401--
--Positive electrode, 402... Electrode of protection diode, 4
03...Cathode electrode. Agent Dai Iwa Masu Yuaki 1 Diagram 2 Diagram A Column 2 Diagram B Reading 2 Diagram C Mulberry 2 Leap D Ko 3 Diagram

Claims (3)

[Claims] (1) A semiconductor substrate of a first conductivity type having first and second main surfaces facing each other, and a first layer of a second conductivity type extending into the substrate from a portion of the first main surface of the substrate. , a second layer of a first conductivity type formed including the first main surface within the boundary of the first layer, and a first layer formed on the first main surface separated from the first layer. A first compound semiconductor layer of a conductivity type and a second compound semiconductor layer of a second conductivity type formed on the first compound semiconductor layer.
a solar cell functional part including a compound semiconductor layer; and the first compound semiconductor layer.
a diode portion formed within the boundary of the conductive type second layer;
The second compound semiconductor layer has a positive electrode and a negative electrode provided on a second main surface of the substrate, and the second compound semiconductor layer is connected to the diode portion by the positive electrode through the second layer of the first conductivity type. A solar cell comprising a first conductivity type region connected to the substrate, and a second conductivity type region of the diode portion connected to the substrate. (2) Claim in which the diode portion is constituted by a laminate of a compound semiconductor layer of a first conductivity type and a compound semiconductor layer of a second conductivity type, which are formed on the second layer of the first conductivity type. (
1) The solar cell according to item 1). (3) The diode portion according to claim (1), wherein the diode portion is formed by the second layer of the first conductivity type and the third layer of the second conductivity type formed within the second layer. solar cell.