Semiconductor photoelectric conversion device

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvement in or relating to a semiconductor photoelectric conversion device which has a conductive substrate or a first conductive layer formed on a suitable substrate, a non-single-crystal semiconductor laminate member formed on the conductive substrate or the first conductive layer, including at least one I-type non-single-crystal semiconductor layer and having formed therein at least one PI, NI, PIN or NIP junction, and a second conductive layer formed on the non-single-crystal semiconductor laminate member.
2. Description of the Prior Art
Heretofore there have been proposed a variety of semiconductor photoelectric conversion devices of the type that has a conductive substrate or a first conductive layer formed on a suitable substrate, a non-single-crystal semiconductor laminate member formed on the conductive substrate or the first conductive layer, including at least one I-type non-single-crystal semiconductor layer and having formed therein at least one PI, NI, PIN OR NIP junction, and a second conductive layer formed on the non-single-crystal semiconductor laminate member.
In the semiconductor photoelectric conversion device of such a structure, the I-type non-single-crystal semiconductor layer has a function of generating photo carriers corresponding to the incidence thereon of light. The I-type non-single-crystal semiconductor layer contains hydrogen or a halogen as a recombination center neutralizer, by which are neutralized recombination centers which would otherwise exist in large quantities since the I-type non-single-crystal semiconductor layer is formed of a non-single-crystal semiconductor. This prevents that photo carriers created in the I-type non-single-crystal semiconductor layer are lost by their recombination.
The conventional semiconductor photoelectric conversion devices of this kind have a photoelectric conversion efficiency as low as 8% or less.
As a result of various experiments, the present inventor has found that one of the reasons for such a low photoelectric conversion efficiency of the conventional photoelectric conversion devices is that in the case where the I-type non-single-crystal semiconductor layer of the non-single-crystal semiconductor laminate member having the function of creating photo carriers is inevitably formed to contain oxygen as an impurity, the oxygen content is as high as 10.sup.20 atoms/cm.sup.3 or more.
Further, the present inventor has found that another reason for such a low photoelectric conversion efficiency is that when the I-type non-single-crystal semiconductor layer is inevitably formed to contain carbon as an impurity, the carbon content is as high as 10.sup.20 atoms/cm.sup.3 or more.
Besides, the present inventor has found that another reason for such a low photoelectric conversion efficiency is that when the I-type non-single-crystal semiconductor layer is formed to contain phosphorus, the phosphorus content as an impurity is as high as 5.times.10.sup.16 atoms/cm.sup.3 or more.
Moreover, the present inventor has found that when the oxygen content in the I-type non-single-crystal semiconductor layer is as high as 10.sup.20 atoms/cm.sup.3 or more, the semiconductor photoelectric conversion device provides such a low photoelectric conversion efficiency as 8% or less is for the following reason:
In the case where the I-type non-single-crystal semiconductor layer contains oxygen in as high a concentration as 10.sup.20 atoms/cm.sup.3 or more, a large number of clusters of oxygen are formed in the I-type non-single-crystal semiconductor layer and these clusters of oxygen serve as recombination centers of photo carriers.
Accordingly, when the oxygen content is high as mentioned above, the I-type non-single-crystal semiconductor layer contains a number of recombination centers of photo carriers which are not neutralized by a recombination center neutralizer. Consequently, photo carriers which are generated by the incidence of light in the I-type non-single-crystal semiconductor layer are recombined with the recombination centers, resulting in a great loss of the photo carriers.
Further, the I-type non-single-crystal semiconductor layer, when containing oxygen, generates dangling bonds of oxygen, which serve as doner centers. In the case where the I-type non-single-crystal semiconductor layer contains oxygen in such a high concentration as 10.sup.20 atoms/ cm.sup.3 or more, it contains many dangling bonds of oxygen acting as doner centers. In this case, the center level of the energy band in the widthwise direction thereof in the I-type non-single-crystal semiconductor layer relatively greatly deviates further to the valence band than the Fermi level. Accordingly, the efficiency of generating photo carriers based on incident light in the I-type non-single-crystal semiconductor layer is very low. Further, the diffusion length of holes of the photo carriers in the I-type non-single-crystal semiconductor layer is short. This leads to low photoconductivity and very high dark conductivity of the I-type non-single-crystal semiconductor layer.
Moreover, when the I-type non-single-crystal semiconductor layer contains oxygen, the oxygen is combined with the material forming the layer. For instance, when the layer is formed of silicon, it has a combination expressed by Si--O--Si. Accordingly, when the oxygen content is as high as 10.sup.20 atoms/cm.sup.3 or more, the layer contains the combination of the material forming the layer and the oxygen in large quantities.
On the other hand, the combination of the material forming the I-type non-single-crystal semiconductor layer and the oxygen contained therein is decomposed by the irradiation of light to create in the layer dangling bonds of the material forming it and dangling bonds of the oxygen.
Accordingly, in the case where the I-type non-single-crystal semiconductor layer contains oxygen in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more, the dangling bonds of the material forming the layer and the dangling bonds of oxygen, which are generated in the layer, greatly increase by the irradiation of light. In such as case, the dangling bonds of the material forming the layer act as recombination centers of the photo carriers, the loss of the photo carriers generated in the layer increases. When the dangling bonds of oxygen increase, the center level of the energy band in the widthwise direction thereof, which has greatly deviated further to the valence band than the Fermi level, greatly deviates to the side of the valence band correspondingly, resulting in marked reduction of the photo carrier generating efficiency of the I-type non-single-crystal semiconductor layer. Also the diffusion length of holes of the photo carriers in the I-type non-single-crystal semiconductor layer is further reduced, markedly lowering the photoconductivity and raising the dark conductivity of the layer.
In such a state that the photocarrier generating efficiency and the photoconductivity of the I-type non-single-crystal semiconductor layer have thus been lowered and the loss of the photo carriers in the layer and the dark conductivity of the layer have thus been increased, if the layer is heated, the dangling bonds of the material forming the layer and the dangling bonds of oxygen, generated in large quantities in the layer, are partly recombined with each other to re-form the combination of the material forming the layer and oxygen. As a result, the dangling bonds of the material forming the layer and the amount of oxygen decrease. In the I-type non-single-crystal semiconductor layer, however, the dangling bonds of the material forming the layer and the dangling bonds of oxygen still remain in large quantities. Consequently, the photo carrier generating efficiency and the photoconductivity of the I-type non-single-crystal semiconductor layer are very low to impose a loss on the photo carriers in the layer, and the dark conductivity of the layer is extremely high. In addition, the values of the photo carrier generating efficiency, the photoconductivity, the loss of photo carriers and the dark conductivity of the I-type non-single-crystal semiconductor layer largely differ before and after irradiation by light and after heating.
The above is the reason found by the present inventor for which the photoelectric conversion efficiency of the conventional semiconductor photoelectric conversion device is as low as 8% or less when the I-type non-single-crystal semiconductor layer contains oxygen in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more.
Further, the present inventor has found that when the I-type non-single-crystal semiconductor layer contains carbon in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more, the photoelectric conversion efficiency of the conventional semiconductor photoelectric conversion device is as low as 8% or less for the following reason:
When the I-type non-single-crystal semiconductor layer contains carbon in such a high concentration as 10.sup.20 atoms/ cm.sup.3 as referred to previously, the layer forms therein a number of clusters of carbon. The clusters of carbon act as combination centers of photo carriers as is the case with the clusters of oxygen. Accordingly, when the I-type non-single-crystal semiconductor layer contains carbon in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more, a great loss is imposed on the carriers that are created in the layer on the basis of the incidence thereon of light.
The above is the reason found by the present inventor for which the photoelectric conversion efficiency of the conventional semiconductor photoelectric conversion device is 8% or less when the I-type non-single-crystal semiconductor layer contains carbon in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more.
Moreover, the present invention has found that when the I-type non-single-crystal semiconductor layer contains phosphorus in such a high concentration as 5.times.10.sup.16 atoms/ cm.sup.3 or more, the photoelectric conversion efficiency of the conventional semiconductor photoelectric conversion device is as low as 8% or less for the following reason:
In the case where the phosphorus content in the I-type-non-single-crystal semiconductor layer is as high as 5.times.10.sup.16 atoms/cm.sup.3 or more, the center level of the energy band in the widthwise direction thereof in the I-type layer relatively greatly deviates to the side of the valence band further than the Fermi level as in the case of the layer containing oxygen in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more. Accordingly, the photocarrier generating efficiency of the I-type non-single-crystal semiconductor layer is very low. Further, the diffusion length of holes of the photo carriers generated in the layer is short, and hence the photoconductivity of the layer is low and its dark conductivity is very high.
The above is the reason found by the present inventor for which the photoelectric conversion efficiency of the conventional semiconductor photoelectric conversion device is as low as 8% or less when the phosphorus content is higher than 5.times.10.sup.16 atoms/cm.sup.3.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a novel semiconductor photoelectric conversion device which is provided with a conductive substrate or a first conductive layer formed on a suitable substrate, a non-single-crystal semiconductor laminate member formed on the conductive substrate or the first conductive layer, including at least one I-type non-single-crystal semiconductor layer and having formed therein at least one PI, NI, PIN or NIP junction, and a second conductive layer formed on the non-single-crystal semiconductor laminate member and which is far higher in photoelectric conversion efficiency than conventional semiconductor photoelectric conversion devices of the abovesaid construction.
In accordance with an aspect of the present invention, even if the I-type non-single-crystal semiconductor layer of the non-single-crystal semiconductor laminate member which has the function of generating photo carriers is inevitably formed to contain oxygen as an impurity, the oxygen content is as low as 5.times.10.sup.18 atoms/cm.sup.3 or less.
In accordance with another aspect of the present invention, even if the I-type non-single-crystal semiconductor layer of the non-single-crystal semiconductor laminate member is inevitably formed to contain carbon as an impurity, the carbon content is as low as 4.times.10.sup.18 atoms/ cm.sup.3 or less.
In accordance with another aspect of the present invention, even if the I-type non-single-crystal semiconductor layer of the non-single-crystal semiconductor laminate member is inevitably formed to contain phosphorus as an impurity, the phosphorus content is as low as 5.times.10.sup.15 atoms/cm.sup.3 or less.
Therefore, the semiconductor photoelectric conversion device of the present invention has a far higher photoelectric conversion efficiency than the conventional semiconductor photoelectric conversion devices of this kind.
The reason for which the photoelectric conversion efficiency in the case of the oxygen content being 5.times.10.sup.18 atoms/cm.sup.3 or less is far higher than the photoelectric conversion efficiency in the case of the oxygen content being 10.sup.20 atoms/cm.sup.3 or more as described previously in connection with the prior art, is the following reason confirmed by the present inventor for the first time.
When the oxygen content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.18 atoms/cm.sup.3 or less, there is formed in the layer substantially nor or a very small number of clusters of oxygen which act as recombination centers of photo carriers. Accordingly, the I-type-non-single-crystal semiconductor layer has substantially no or a very small number of recombination centers of photo carriers based on oxygen. Consequently, substantially no or a very small amount of loss is imposed on the photo carriers that are created in the I-type non-single-crystal semiconductor layer.
When the oxygen content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.18 atoms/cm.sup.3 or less, the number of dangling bonds of oxygen contained in the layer is very small, even if they are contained. Accordingly, the center level of the energy band in the widthwise direction of the I-type non-single-crystal semiconductor layer hardly deviates from the Fermi level and even if it deviates, the amount of deviation is very small. Consequently, the photo carrier generating efficiency and the photoconductivity of the layer are far higher than those obtainable with the conventional semiconductor photoelectric conversion device in which the oxygen content of the I-type non-single-crystal semiconductor layer is 10.sup.20 atoms/cm.sup.3 or more, and the dark conductivity of the layer is far lower than in the case of the prior art device.
Further, when the oxygen content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.18 atom/cm.sup.3 or less, even if the layer contains combinations of the material forming the layer and the oxygen, the number of such combinations is very small. Accordingly, dangling bonds of the material forming the layer and oxygen are not substantially formed by the light irradiation of the semiconductor photoelectric conversion device and, even if they are formed, their number is very small. Further, even if the device is heated, the dangling bonds of the material forming the layer and the dangling bonds of oxygen do not increase. The photo carrier generating efficiency, the photo conductivity and the dark conductivity of the layer do not substantially differ before and after irradiation by light and after heating.
The above is the reason for which when the oxygen content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.18 atoms/cm.sup.3 or less, the semiconductor photoelectric conversion device of the present invention exhibits a far higher photoelectric conversion efficiency than the conventional semiconductor photoelectric conversion device in which the oxygen content of the I-type non-single-crystal semiconductor layer is 10.sup.20 atoms/cm.sup.3 or more.
The reason for which the photoelectric conversion efficiency in the case of the carbon content being 4.times.10.sup.18 atoms/cm.sup.3 or less is far higher than the photoelectric conversion efficiency in the case of the carbon content being 10.sup.20 atoms/cm.sup.3 or more as described previously in respect to the prior art, is the following reason confirmed by the present inventor for the first time.
When the carbon content of the I-type non-single-crystal semiconductor layer is 4.times.10.sup.18 atoms/cm.sup.3 or less, there is formed in the layer substantially little, if any, clusters of carbon which act as recombination centers of photo carriers. Accordingly, the I-type non-single-crystal semiconductor layer has substantially little, if any, combination centers of photo carriers based on carbon. Consequently, substantially little, if any, loss is imposed on the photo carriers that are created in the I-type non-single-crystal semiconductor layer.
The above is the reason for which when the carbon content of the I-type non-single-crystal semiconductor layer is 4.times.10.sup.18 or less, the semiconductor photoelectric conversion device of the present invention exhibits a far higher photoelectric conversion efficiency than does the conventional semiconductor photoelectric conversion device in which the carbon content of the I-type non-single-crystal semiconductor layer is 10.sup.20 atoms/cm.sup.3 or more.
Besides, the reason for which the photoelectric conversion efficiency in the case of the phosphorus content being 5.times.10.sup.15 atoms/cm.sup.3 or less is far higher than the photoelectric conversion efficiency in the case of the phosphorus content being 5.times.10.sup.16 atoms/cm.sup.3 or more as referred to previously with respect to the prior art, is the following reason similarly confirmed by the present inventor for the first time.
When the phosphorus content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.15 atoms/cm.sup.3 or less, even if the layer contains dangling bonds of phosphorus, their number is very small. Accordingly, the center level of the energy band in the widthwise direction of the I-type non-single-crystal semiconductor layer scarcely deviates from the Fermi level and even if it deviates, the amount of deviation is very small. Consequently, the photo carrier generating efficiency and the photoconductivity of the layer are far higher than those obtainable with the conventional semiconductor photoelectric conversion device in which the phosphorus content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.16 atoms/cm.sup.3 or more, and the dark conductivity of the layer is far lower than in the case of the prior art device.
The above is the reason for which when the phosphorus content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.15 atoms/cm.sup.3 or less, the semiconductor photoelectric conversion device of the present invention exhibits a far higher photoelectric conversion efficiency than does the conventional semiconductor photoelectric conversion device in which the phosphorus content of the I-type non-single-crystal semiconductor layer is 5.times.10.sup.16 atoms/cm.sup.3 or more.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are schematic cross-sectional views respectively illustrating first and second embodiments of a semiconductor photoelectric conversion device to which the present invention is applicable.
FIG. 3 is a graph showing the relationships of the photoconductivity and dark conductivity of an I-type non-single-crystal semiconductor layer of a non-single-crystal semiconductor laminate member and the oxygen content of the layer in the semiconductor photoelectric conversion devices of FIGS. 1 and 2;
FIG. 4 is a graph showing the relationships of the photoconductivity and dark conductivity of the I-type non-single-crystal semiconductor layer of the non-single-crystal semiconductor laminate member and the carbon content of the layer in the semiconductor photoelectric conversion devices of FIGS. 1 and 2;
FIG. 5 is a graph showing the relationships of the photoconductivity and dark conductivity of the I-type non-single-crystal semiconductor layer of the non-single-crystal semiconductor laminate and the phosphorus content of the layer in the semiconductor photoelectric conversion devices of FIGS. 1 and 2;
FIG. 6 is a graph showing the relationships of the photoelectric conversion efficiency, a short-circuiting current and a curve factor of the semiconductor photoelectric conversion devices of FIGS. 1 and 2 to the oxygen content of the I-type non-single-crystal semiconductor layer;
FIG. 7 is a graph showing the relationships of the photoelectric conversion efficiency, a short-circuiting current and a curve factor of the semiconductor photoelectric conversion devices of FIGS. 1 and 2 to the carbon content of the I-type non-single-crystal semiconductor layer;
FIG. 8 is a graph showing the relationships of the photoelectric conversion efficiency, a short-circuiting current and a curve factor of the semiconductor photoelectric conversion devices of FIGS. 1 and 2 to the phosphorus content of the I-type non-single-crystal semiconductor layer; and
FIGS. 9 and 10 are graphs showing the relationships of the normalized photoelectric conversion efficiency of the semiconductor photoelectric conversion devices of FIGS. 1 and 2 to the wavelengths of light before and after the irradiation of the devices by light and after their heating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 and 2 illustrate first and second embodiments of the semiconductor photoelectric conversion device to which the present invention is applicable.
The embodiment of the semiconductor photoelectric conversion device of FIG. 1 to which the present invention is applicable has such a construction as follows:
A light transparent conductive layer 2 as of a tin oxide is formed, for example, by vacuum deposition on an insulating and light transparent substrate 1 as of glass.
On the light transparent conductive layer 2 is formed a non-single-crystal semiconductor laminate member 3. The non-single-crystal semiconductor laminate member 3 is formed by a sequential lamination of, for instance, a P-type non-single-crystal semiconductor layer 4, an I-type non-single-crystal semiconductor layer 5 containing hydrogen or a halogen as a recombination center neutralizer, and an N-type non-single-crystal semiconductor layer 6. Accordingly, the non-single-crystal semiconductor laminate member 3 has one I-type non-single-crystal semiconductor layer 5 and has formed therein one PIN junction. In this case, the P-type non-single-crystal semiconductor layer 4 is formed of silicon (Si), Si.sub.x C.sub.1-x (0<x<1, where x=0.8, for instance), germanium (Ge) or the like, and the layer 4 is, for instance, 100 .ANG. thick. When the P-type non-single-crystal semiconductor layer 4 is formed of silicon or Si.sub.x C.sub.1-x, the I-type non-single-crystal semiconductor layer 5 is formed of silicon or Si.sub.x Ge.sub.1-x, and when the layer 4 is formed of Ge, the layer 5 is formed of Ge. The layer has a thickness of, for example, 0.5 .mu.m. Further, when the I-type non-single-crystal semiconductor layer 5 is formed of silicon or Si.sub.x Ge.sub.1-x , the N-type non-single-crystal semiconductor layer 6 is formed of silicon or Si.sub.x C.sub.1-x (x=0.9, for example), and when the layer 5 is formed of germanium or Si.sub.x Ge.sub.1-x, the layer 6 is formed of germanium or Si.sub.x Ge.sub.1-x. The N-type non-single crystal semiconductor layer 6 is, for example, 200 .ANG. in thickness.
The non-single-crystal semiconductor layers 4, 5 and 6 making up the non-single-crystal semiconductor laminate member 3 are successively formed by a CVD method which does not employ a glow discharge, or a plasma CVD method which employs a glow discharge.
On the non-single-crystal semiconductor laminate member 3 is formed, for example, by vacuum deposition a reflective conductive layer 7 as of aluminum.
The above is a description of the structure of the first embodiment of the semiconductor photoelectric conversion device to which the present invention is applicable.
The second embodiment of the semiconductor photoelectric conversion device of FIG. 2 to which the present invention is applicable has such a construction as follows:
On a reflective conductive substrate 11 as of stainless steel is formed the non-single-crystal semiconductor laminate member 3 as is the case with the semiconductor photoelectric conversion device shown in FIG. 1.
The non-single-crystal semiconductor laminate member 3 is formed by a sequential lamination of the P-type non-single-crystal semiconductor layer 4, the I-type non-single-crystal semiconductor layer 5 containing hydrogen or a halogen as a recombination center neutralizer and the P-type non-single-crystal semiconductor layer 6 as is the case with the non-single-crystal semiconductor laminate member 3 in FIG. 1. Accordingly, the non-single-crystal semiconductor laminate member 3 has one I-type non-single-crystal semiconductor layer 5 and has formed therein one PIN junction as is the case with the non-single-crystal semiconductor laminate member 3 in FIG. 1. The non-single-crystal semiconductor layer 4, 5 and 6 are also formed by such a CDV method as mentioned above.
On the non-single-crystal semiconductor laminate member 3 is formed, for instance, by vacuum deposition a light transparent conductive layer 12 as of indium oxide containing a tin oxide, which corresponds to the conductive layer 2 in FIG. 1.
Further, a conductive layer 13 for external connection use is formed on the conductive layer 3.
The above is a description of the structure of the second embodiment of the semiconductor photoelectric conversion device to which the present invention is applicable.
The first and second embodiments of FIGS. 1 and 2 are apparently identical in construction with known semiconductor photoelectric conversion devices.
With the structure of the semiconductor photoelectric conversion device shown in FIG. 1, when light 8 impinges on the device from the outside of the substrate 1, it reaches the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 to create therein photo carriers. Accordingly, if a load is connected across the light transparent conductive layer 2 and the reflective conductive layer 7, power is supplied to the load. With the structure of the semiconductor photoelectric conversion device of FIG. 2, the light 8 incident on the light transparent conductive layer 12 reaches the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 to generate therein photocarriers as is the case of the device shown in FIG. 1. Accordingly, if a load is connected across the reflective conductive substrate 11 and the light transparent conductive layer 12, power is supplied to the load.
When the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 is formed of silicon by the CVD method using, for example, silane (SiH.sub.4) gas as a semiconductor material gas, it inevitably contains oxygen, carbon and phosphorus.
The reason is that it is extremely difficult to remove oxygen, carbon and phosphorus from the silane gas when it is prepared.
Incidentally, commercially available silane gas of 99.99% purity usually contains oxygen about 0.1 ppm in the form of a simple substance (O.sub.2) and about 3 ppm in the form of water (H.sub.2 O), carbon about 5 ppm in the form of methane (CH.sub.4) and about 0.1 ppm in the form of ethane (C.sub.2 H.sub.6), ethylene (C.sub.2 H.sub.4), propane (C.sub.3 H.sub.8) and propylene (C.sub.3 H.sub.6) and phosphorus about 0.1 ppm in the form of phosphine (PH.sub.3).
Further, when the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 is formed of germanium by the CVD method using, for example, german (GeH.sub.4) gas as the semiconductor material gas, the layer 5 inevitably contains oxygen, carbon and phosphorus because it is extremely difficult in practice to remove them from the german gas when it is prepared.
Moreover, the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 is formed of Si.sub.x Ge.sub.1-x by the CVD method using, as the semiconductor material gas, a mixture of silane and german gases, the layer 5 inevitably contains oxygen, carbon and phosphorus because it is extremely difficult, in practice, to prepare the silane and german gases with substantially no oxygen, carbon and phosphorus contents.
In the conventional photoelectric device similar to those of FIGS. 1 and 2, the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 contains oxygen in a high concentration exceeding 10.sub.20 atoms/cm.sup.3, carbon in a high concentration exceeding 10.sup.20 atoms/cm.sup.3 or phosphorus in a high concentration exceeding 5.times.10.sup.16 atoms/cm.sup.3.
In contrast thereto, according to the present invention, even if the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 inevitably contains oxygen, the oxygen content is only 5.times.10.sup.18 atoms/cm.sup.3 or less.
The I-type non-single-crystal semiconductor layer 5 with such a small oxygen content can be formed by using, as the semiconductor material gas in the case of forming the layer of silicon through the CVD method as mentioned above, a silane gas which is obtained by passing a raw silane gas of high purity through a passage in which is placed a molecular sieve having a mesh diameter of 2.7 to 4.65 .ANG. or zeolite having a pore diameter of the same size so that the oxygen content of the silane gas may be reduced to substantially zero or negligibly small.
The reason for which such a silane gas with practically no or a negligibly small amount of oxygen can be obtained from the raw silane gas through using the molecular sieve or zeolite, is as follows: The effective molecular diameter of the silane is larger than 4.65.ANG. and when oxygen is contained in the form of O.sub.2 and H.sub.2 O in the raw silane gas as referred to perviously, their molecular diameters are 2.7 to 4.65 .ANG., so that the silane cannot pass through the meshes of the molecular sieve or the pores of the zeolite and hence is not adsorbed on the molecular sieve or zeolite, whereas the oxygen and water contained in the raw silane gas pass through the meshes of the molecular sieve or the pores of the zeolite and are effectively adsorbed thereon.
The oxygen content of such a silane gas can be further reduced by passing it through a passage in which a deoxidizing agent is placed. By using thus obtained silane gas, the oxygen content of the I-type non-single-crystal semiconductor layer 5 can be further reduced.
Further, according to the present invention, even if the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 inevitably contains carbon, the carbon content is only 4.times.10.sup.18 atoms/cm.sup.3 or less.
The I-type non-single-crystal semiconductor layer 5 with such a small carbon content can be formed by using, as the semiconductor material gas in the case of forming the layer of silicon through the CVD method as mentioned above, a silane gas which is obtained by passing a raw silane gas of high purity through a passage in which is placed a molecular sieve having a mesh diameter of 2.7 to 4.65 .ANG. or zeolite having a pore diameter of the same size so that the carbon content of the silane gas may be reduced to substantially zero or negligibly small.
The reason for which such a silane gas with practically no or a negligibly small amount of carbon can be obtained from the raw silane gas through using the molecular sieve or zeolite, is as follows: The effective molecular diameter of the silane is larger than 4.65 .ANG. and when carbon is contained in the form of ethane, ethylene, propane and propylene in the raw silane gas as referred to previously, their molecular diameters are 2.7 to 4.65 .ANG., so that the ethane, ethylene, propane and propylene contained in the raw silane gas pass through the meshes of the molecular sieve or the pores of the zeolite and are effectively adsorbed thereon.
Further, according to the present invention, even if the I-type non-single-crystal semiconductor layer 5 of the non-single-crystal semiconductor laminate member 3 inevitably contains phosphorus, the phosphorus content is only 5.times.10.sup.15 atoms/cm.sup.3 or less.
The I-type non-single-crystal semiconductor layer 5 with such a small phosphorus content can be formed by using, as the semiconductor material gas in the case of forming the layer of silicon through the CVD method as mentioned above, a silane gas which is obtained by passing a raw silane gas of high purity through a passage in which is placed a molecular sieve having a mesh diameter of 4.5 .ANG. or zeolite having a pore diameter of the same size so that the phosphorus content of the silane gas may be reduced to substantially zero or negligibly small.
The reason for which such a silane gas with practically nor or a negligibly small amount of phosphorus can be obtained from the raw silane gas through using the molecular sieve or zeolite, is as follows: the effective molecular diameter of the silane is larger than 4.8 .ANG.. and when phosphorus is contained in the form of phosphine in the raw silane gas as referred to previously, its molecular diameter is 4.5 .ANG., so that the phosphine contained in the raw silane gas passes through the meshes of the molecular sieve or the pores of the zeolite and is effectively adsorbed thereon.
The above is a description of embodiments of the semiconductor photoelectric conversion device of the present invention.
According to the present invention, the I-type non-single-crystal semiconductor layer 5 contains oxygen in such a low concentration as 5.times.10.sup.18 atoms/cm.sup.3 or less, carbon in such a low concentration as 4.times.10.sup.18 atoms/cm.sup.3 or less and phosphorus in such a low concentration as 5.times.10.sup.15 atoms/cm.sup.3 or less.
Therefore, according to the embodiments of the present invention shown in FIGS. 1 and 2, the photoconductivity of the I-type non-single-crystal semiconductor layer 5 is higher than that of the I-type non-single-crystal semiconductor layer of the conventional photoelectric conversion device which contains oxygen in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more, carbon in such a high concentration as 10.sup.20 atoms/cm.sup.3 or more and phosphorus in such a high concentration as 5.times.10.sup.16 atoms/cm.sup.3 or more.
FIGS. 3 to 5 show this.
That is, in the case where the carbon content and the phosphorus content of the I-type non-single-crystal semiconductor layer 5 are 3.times.10.sup.20 and 5.times.10.sup.16 atoms/cm.sup.3, respectively, the photoconductivity (.OMEGA.cm).sup.-1 of the layer 5 relative to the oxygen content (atom/cm.sup.3) thereof is such as indicated by a curve C-1A in FIG. 3. In the case where the carbon content and the phosphorus content of the layer 5 are 4.times.10.sup.18 and 5.times.10.sup.15 atoms/cm.sub.3, respectively, the photoconductivity of the layer 5 relative to the oxygen content thereof is such as indicated by a curve C-1B in FIG. 3.
In the case where the photoconductivity of the layer 5 is such as indicated by a point C-1A' on the curve C-1A in FIG. 3, when the layer 5 contains oxygen in the concentration at the point C-1A', the dark conductivity (.OMEGA.cm).sup.-1 of the layer 5 is such as indicated by a point D-1A' in FIG. 3. In the case where the photoconductivity of the layer 5 is such as indicated by a point C-1B' on the curve C-1B in FIG. 3, when the layer 5 contains oxygen in the concentration at the point C-1B', the dark conductivity of the layer 5 is such as indicated by a point D-1B' in FIG. 3.
Further, in the case where the oxygen content and the phosphorus content of the I-type non-single-crystal semiconductor layer 5 are 1.times.10.sup.20 and 5.times.10.sup.16 atoms/cm.sup.3, respectively, the photoconductivity of the layer 5 relative to the carbon content thereof is such as indicated by a curve C-2A in FIG. 4. In the case where the oxygen content and the phosphorus content of the layer 5 are 3.times.10.sup.17 and 5.times.10.sup.15 atoms/cm.sup.3, respectively, the photoconductivity of the layer 5 relative to the carbon content thereof is such as indicated by a curve C-2B in FIG. 4.
In the case where the photoconductivity of the layer 5 is such as indicated by a point C-2A' on the curve C-2A in FIG. 4, when the layer 5 contains carbon in the concentration at the point C-2A', the dark conductivity of the layer 5 is such as indicated by a point D-2A' in FIG. 4. In the case where the photoconductivity of the layer 5 is such as indicated by a point C-2B' on the curve C-2B in FIG. 4, when the layer 5 contains carbon in the concentration at the point C-2B', the dark conductivity of the layer 5 is such as indicated by a point D-2B' in FIG. 4.
Moreover, in the case where the oxygen and carbon contents of the I-type non-single-crystal semiconductor layer 5 are both 2.times.10.sup.20 atoms/cm.sup.3, the photoconductivity and the dark conductivity of the layer 5 in the case of its phosphorus content being 5.times.10.sup.16 atoms/cm.sup.3 is such as indicated by points C-3A' and D-3A' in FIG. 5, respectively. In the case where the oxygen content and the carbon content of the layer 5 are 5.times.10.sup.18 and 4.times.10.sup.18 atoms/cm.sup.3, respectively, the photoconductivity and the dark conductivity of the layer 5 relative to the phosphorus content thereof are such as indicated by curves C-3B and D-3B in FIG. 5, respectively.
As will be appreciated from the above, according to to the present invention, the I-type non-single-crystal semiconductor layer 5 has a far higher photoconductivity than does the I-type non-single-crystal semiconductor layer of the conventional semiconductor photoelectric conversion device.
Further, according to the present invention, one of the reasons for the high photoconductivity of the I-type non-single-crystal semiconductor layer is that the photoelectric conversion efficiency, the short-circuit current and the curve factor((short-circuit current x open voltage)/maximum power) of the semiconductor photoelectric conversion device of the present invention are far higher than those of the conventional semiconductor photoelectric conversion device.
FIGS. 6 to 8 show this.
That is, when the photoconductivity of the I-type non-single-crystal semiconductor layer 5 is such as indicated by the curve C-1B in FIG. 3, the photoelectric conversion efficiency (%), the short-circuit current (A/cm.sup.2) and the curve factor of the semiconductor photoelectric conversion device relative to the oxygen content (atom/cm.sup.3) of the layer 5 are such as indicated by curves E-1B, S-1B and F-2B in FIG. 6, respectively.
When the photoconductivity of the I-type non-single-crystal semiconductor layer 5 is such as indicated by the curve C-2B in FIG. 4, the photoelectric conversion efficiency, the short-circuit current and the curve factor relative to the carbon content of the layer 5 are such as indicated by curves E-2B, S-2B and F-2B in FIG. 7, respectively.
Further, when the photoconductivity of the I-type non-single-crystal semiconductor layer 5 is such as indicated by the curve C-3B in FIG. 5, the photoelectric conversion efficiency, the short-circuit current and the curve factor of the semiconductor photoelectric conversion device relative to the phosphorus content of the layer 5 are such as indicated by E-3B, S-3B and F-3B in FIG. 8, respectively. In this case, the oxygen and carbon contents of the layer 5 are 10.sup.3 times the phosphorus content thereof.
Thus, according to the present invention, the photoelectric conversion efficiency, the short-circuit current and the curve factor of the semiconductor photoelectric conversion device can be increased far higher than those obtainable with the prior art semiconductor photoelectric conversion device.
Moreover, according to the semiconductor photoelectric conversion device of the present invention, its photoelectric conversion efficiency is hardly affected by irradiation by light and, even by heating after the light irradiation, the photoelectric conversion efficiency undergoes no appreciable changes.
FIG. 9 and 10 show this.
That is, when the photoconductivity of the I-type non-single-crystal semiconductor layer 5 is obtained as indicated by the point C-1A' in FIG. 3, the photoelectric conversion efficiency (normalized with maximum photoelectric conversion efficiency being 1) for the wavelength (mm) of incident light is such as indicated by a curve E-4A in FIG. 9 before irradiation by light and, after the irradiation by light, it becomes such as indicated by a curve E-5A in FIG. 9 and, by heating at 150.degree. C. for two hours after the irradiation by light, the photoconductivity becomes such as indicated by a curve E-6A in FIG. 9.
When the photoconductivity of the I-type non-single-crystal semiconductor layer 5 is such as indicated by the point C-1B' in FIG. 3, the photoelectric conversion efficiency (normalized as mentioned above) for the wavelength of incident light is such as indicated by a curve E-4B in FIG. 10 and after irradiation light under the same condition as that in the case of the curve E-5A in FIG. 9 being obtained, the photoelectric conversion efficiency becomes such as indicated by a curve E-5B in FIG. 10 and, by heating under the same condition as mentioned above after the irradiation by light, the photoelectric conversion efficiency becomes such as indicated by a curve E-6B in FIG. 10.
As will be appreciated from the above, according to the present invention, the photoelectric conversion efficiency hardly changes and it remains substantially unchanged even if heating is carried out after the irradiation by light. While the present invention has been described as being applied to the semiconductor photoelectric conversion device in which the non-single-crystal semiconductor laminate member has a PIN or NIP type structure and, accordingly, it has formed therein one PIN or NIP junction, the present invention is also applicable to such a semiconductor photoelectric conversion device in which the non-single-crystal semiconductor laminate member has an NI, PI, NIN or PIP type structure and, accordingly, it has formed therein at least one NI, PI, NIN or PIP junction.
Also the present invention is applicable to semiconductor photoelectric conversion device of the type in which the non-single-crystal semiconductor laminate member has, for example, an NIPIN or PINIP type structure and, accordingly, it has formed therein at least one PIN and NIP junction.
It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

Number	Date	Country	Kind
57-146561	Aug 1982	JPX
57-182546	Oct 1982	JPX

Number	Name	Date
4064521	Carlson	Dec 1977
4109271	Pankove	Aug 1978
4239554	Yamazaki	Dec 1980

Semiconductor photoelectric conversion device

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