JP7232499B2 - Semiconductor device, manufacturing method thereof, and photoelectric conversion device - Google Patents

Description

The present invention relates to a semiconductor device, its manufacturing method, and a photoelectric conversion device.

The highest value of photoelectric conversion efficiency by photoelectric conversion devices such as solar cells has been continuously updated by applying III-V compound semiconductors (such as GaAs). However, due to the high cost of substrates, the range of application of photoelectric conversion devices to which III-V compound semiconductors are applied is limited. Therefore, there is a demand for a technique for forming high-quality III-V group compound semiconductor thin films on inexpensive substrates. Non-Patent Documents 1 and 2 disclose techniques for directly bonding a GaAs film onto a glass substrate.

E.U. Onyegam et al, Sol. Energy Mater. Sol. Cells 111, 206 (2013). J.J.J. Yang et al, J. Appl. Phys. 51, 3794 (1980).

However, the technique of bonding a GaAs film to a substrate such as glass has a high process cost and is difficult to apply to large-area glass substrates, making industrial application difficult. Further, although it is possible to directly form a GaAs film on a glass substrate by a known film formation method, the formed GaAs film does not have the quality applicable to a photoelectric conversion device.

The present invention has been made in view of the above circumstances, and includes a semiconductor film that can be formed at low cost regardless of the size of the substrate and has a quality that can be applied to a photoelectric conversion device. , a semiconductor device, a manufacturing method thereof, and a photoelectric conversion device.

In order to solve the above problems, the present invention employs the following means.

(1) A semiconductor device according to an aspect of the present invention includes an amorphous base material, a base layer formed on one surface of the base material and containing a plurality of first crystal grains containing Ge as a main component; a functional layer formed on the stratum and containing a plurality of second crystal grains having a lattice constant of −2% or more and 2% or less of the first crystal grains, wherein the average grain size of the second crystal grains is 1 μm. That's it.

(2) In the semiconductor device described in (1) above, the second crystal grains may contain GaAs as a main component.

(3) In the semiconductor device described in (1) above, the second crystal grains may contain In, Al, and P as main components.

(4) The semiconductor device according to any one of (1) to (3) may further include a conductive layer between the base material and the underlying layer.

(5) In the semiconductor device according to any one of (1) to (4) above, the substrate is preferably made of an amorphous material.

(6) A method for manufacturing a semiconductor device according to an aspect of the present invention is the method for manufacturing a semiconductor device according to any one of (1) to (5) above, comprising: A step of forming the functional layer on the underlying layer is provided.

(7) In the method for manufacturing a semiconductor device according to (6), before forming the functional layer, a metal layer containing a metal element as a main component and a layer containing Ge as a main component are formed on one surface of the base material. A step of forming a first laminate in which a Ge layer and a Ge layer are laminated in order, heating the first laminate, performing layer exchange between the metal layer and the Ge layer, and using the Ge layer as the underlayer A step of forming a second laminate and a step of removing a layer formed on the Ge layer after the layer exchange may be included.

(8) In the method for manufacturing a semiconductor device according to (7), the first laminate further includes a metal oxide layer containing a metal oxide as a main component between the metal layer and the Ge layer. may have.

(9) A photoelectric conversion device according to an aspect of the present invention includes the semiconductor device according to any one of (1) to (5) above, and an electrode provided on the functional layer.

The semiconductor device of the present invention includes a polycrystalline film containing a plurality of crystal grains containing Ge as a main component on a substrate as an underlying layer. The crystal grains forming the functional layer formed on the underlayer are formed by inheriting the shape of the crystal grains of the underlayer, and have a grain size of 1 μm or more. This grain size is much larger than in the case of forming directly on a base material using existing crystal growth techniques, etc., and realizes a functional layer having high spectral sensitivity. Therefore, the semiconductor device of the present invention includes, as a functional layer, a semiconductor film having quality applicable to a photoelectric conversion device.

Further, in the semiconductor device of the present invention, the base material is amorphous, and the functional layer is formed via the underlying layer made of polycrystalline grains of Ge. Therefore, since the semiconductor device of the present invention does not require application of a bonding technique in its manufacturing process, the semiconductor film constituting the functional layer can be formed on an expensive single-crystal substrate regardless of the size of the substrate. Since no material is used, it can be formed at low cost.

1 is a perspective view of a semiconductor device according to a first embodiment of the invention; FIG. 3A to 3D are perspective views of an object to be processed in the manufacturing process of the semiconductor device of FIG. 1; FIG. 5 is a graph showing Raman spectra of functional layers in the semiconductor devices of Example 1 and Comparative Examples 1 and 2 of the present invention; 4(a) to 4(c) are SEM images showing surface shapes of functional layers in semiconductor devices of Example 1 and Comparative Examples 1 and 2 of the present invention. 4(a) to 4(d) are EBSD images showing distributions of crystal grains forming functional layers in the semiconductor devices of Example 1 and Comparative Examples 1 and 2 of the present invention. 5 is a graph showing the results of spectral sensitivity measurement of solar cells to which the semiconductor devices of Example 1 and Comparative Examples 1 and 2 of the present invention are respectively applied;

DETAILED DESCRIPTION OF THE INVENTION A semiconductor device, a method for manufacturing the same, and a photoelectric conversion device according to embodiments to which the present invention is applied will be described in detail below with reference to the drawings. In addition, in the drawings used in the following explanation, in order to make the features easier to understand, the characteristic portions may be enlarged for convenience, and the dimensional ratios of each component may not necessarily be the same as the actual ones. do not have. Also, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be implemented with appropriate modifications within the scope of the invention.

<First embodiment>
FIG. 1 is a perspective view schematically showing the configuration of a semiconductor device 100 according to one embodiment of the present invention. A semiconductor device 100 mainly includes a substrate 101 , an underlying layer 102 formed on one surface 101 a of the substrate, and a functional layer 103 formed on the underlying layer 102 .

As the base material 101, one made of an inexpensive material such as an amorphous material is used. The base material 101 may have a flat surface on which the base layer 102 and the functional layer 103 can be mounted, and other surfaces may have an uneven structure or a curved surface. Also, the thickness is not limited, and it may be a plate (substrate) or a film (thin film).

The underlayer 102 is a polycrystalline film containing a plurality of first crystal grains 102A whose main component is Ge (germanium) (preferably contains 90% or more). The presence of the underlying layer 102 makes it possible to control the average grain size of the second crystal grains forming the layer (functional layer 103) immediately above. The average grain size of the first crystal grains 102A is preferably 1 μm or more, more preferably 50 μm or more, in consideration of the grain size of the crystal grains formed immediately above. The thickness of the underlying layer 102 is preferably 10 nm to 1 μm.

Functional layer 103 is a polycrystalline film containing a plurality of second crystal grains 103A. The second crystal grains 103A have a lattice constant in a range that facilitates lattice matching with the first crystal grains 102A, ie, -2% or more and 2% or less of the first crystal grains 102A. Since the lattice constant of the second crystal grains 103A is within this range, the layered state in which the strain between the underlying layer 102 and the functional layer 103 is suppressed is maintained. Second crystal grain 103A is preferably 1 μm or more, and more preferably 50 μm or more. Note that the thickness of the functional layer 103 is preferably 500 nm to 5 μm.

The second crystal grains 103A include those mainly composed of III-V group compound semiconductors, specifically those containing GaAs as a main component, such as GaAs, InGaAs, AlGaAs, GaAsP, and GaAsSb. In addition, materials containing In, Al, and P as main components, such as AlAs and InGaP, can be used.

When the underlying layer 102 is a single-crystal film, the functional layer 103 formed thereon is also a single-crystal film, and the two layers are susceptible to cracking due to stress caused by the difference in thermal expansion coefficient. . On the other hand, in the present embodiment, both the underlying layer 102 and the functional layer 103 are polycrystalline films. It has a difficult structure.

A conductive layer may be further provided between the base material 101 and the underlying layer 102 . The material of the conductive layer is preferably an element that does not readily react with Ge forming the underlying layer and that is difficult to diffuse. Examples thereof include ITO, AZO, and TiN. When a conductive layer is provided, an effect of facilitating extraction of photoexcited carriers can be obtained.

2A to 2D are perspective views of an object to be processed in the manufacturing process of the semiconductor device 100. FIG. An example of a method for manufacturing the semiconductor device 100 will be described with reference to FIGS. 2(a) to 2(d).

(First laminate forming step)
First, as shown in FIG. 2(a), a metal layer 104 mainly composed of metal elements such as Al, Au, and Ag, AlOx (x is a real number), GeOx, SiO ₂ and the like is formed on one surface 101a of the substrate. A first laminate 107 is formed by sequentially stacking a metal oxide layer 105 containing a metal oxide element as a main component and an amorphous Ge layer 106 containing Ge as a main component. The formation of the metal layer 104, the metal oxide layer 105, and the Ge layer 106 can be performed using a known film formation method such as a sputtering method, a vapor deposition method, or a chemical vapor deposition (CVD) method. The metal oxide layer 105 can also be formed without using a known film formation method by, for example, once exposing the formed metal layer 104 to the atmosphere before forming the Ge layer. In this embodiment, the case of having the metal oxide layer 105 between the metal layer 104 and the Ge layer 106 is illustrated, but this layer is not an essential configuration as will be described later.

(Second laminate forming step)
Next, the first laminate 107 is subjected to heat treatment at about 50 to 500° C. for about 0.1 to 500 hours. By this heat treatment, Ge atoms forming the amorphous Ge layer 106 are diffused along the crystal grain boundaries and the like in the metal layer 104 . As the heating is continued, the diffusion region of Ge atoms spreads in a direction (in-plane direction) substantially perpendicular to the stacking direction of the metal layer 104 . Then, the metal element in the metal layer 104 is pushed up in a direction away from the substrate 101 by the Ge atoms spreading and diffusing in the in-plane direction.

This phenomenon is considered to occur due to the relationship between the diffusion speed of the Ge atoms forming the Ge layer 106, which is increased by heating, and the crystallization speed of the Ge atoms. That is, when the increased Ge atom diffusion rate exceeds the crystallization rate, the Ge atoms first diffuse into the metal layer 104 and then crystallize.

In this way, the Ge atoms in the Ge layer 106 replace most of the metal elements in the metal layer 104 and crystallize, resulting in layer exchange between the metal layer 104 and the Ge layer 106 . As a result, as shown in FIG. 2(b), a second laminate 107A having a polycrystalline Ge layer 106A as a base layer 102 can be formed. Note that when the Ge layer 106 before the heat treatment is a single crystal film or a polycrystal film, the Ge layer 106 is stable in terms of energy, so the layer exchange is not performed.

The metal oxide layer 105 formed in the first laminate forming step reduces the diffusion rate of the crystal grains of the Ge layer during layer exchange to delay the generation of nuclei, so that the finally formed underlying layer This has the effect of promoting an increase in the grain size of the crystal grains of 102 . The thickness of the metal oxide layer 105 is preferably about 0.110 nm.

In addition, in the first stacked body forming step, if the Ge layer is continuously formed without exposing the formed metal layer to the atmosphere, the metal oxide layer 105 is not formed. However, even in this case, the layer exchange can be carried out, and although not as much as in the case of forming a metal oxide layer, it is possible to form an underlying layer made of crystal grains having a predetermined large grain size. Therefore, the metal oxide layer 105 is not an essential layer in the manufacturing method of this embodiment. Furthermore, in this case, since the metal oxide layer 105 is not formed on the metal layer 104 or the metal layer 104 is not exposed to the atmosphere, the time required for manufacturing can be shortened and the cost can be reduced. production efficiency can be improved.

The thickness of the underlying Ge layer 106A becomes approximately the same as the thickness of the metal layer 104 formed in the first laminate formation step after the layer exchange in the second laminate formation step. Therefore, the thickness of the finally formed underlying layer 102 can be adjusted by the thickness of the metal layer 104 formed in the first laminate forming step. The thickness of the underlying layer 102 is preferably 10 nm or more and 1 μm or less.

(Metal layer removal step)
Next, as shown in FIG. 2(c), on the Ge layer after layer exchange so that the Ge layer (underlying layer 102) that has been moved to the substrate side and re-formed by the layer exchange in the previous step is exposed is exposed. The layers (here, the metal layer 104A and the metal oxide layer 105) formed on the substrate are removed using a known etching method (dry etching, wet etching, etc.) or a known polishing method.

(Functional layer forming step)
Next, a functional layer 103 containing a plurality of second crystal grains 103A is formed on the exposed underlying layer 102 using vapor phase epitaxy (molecular beam epitaxy (MBE), chemical vapor deposition, etc.). do. As the second crystal grains 103A, those having a lattice constant within a range of -2% or more and 2% or less of the first crystal grains 102A are used so as to be easily lattice-matched with the first crystal grains 102A. The semiconductor device 100 of this embodiment can be obtained through the functional layer forming process.

As described above, the semiconductor device 100 according to the present embodiment includes the polycrystalline film containing a plurality of crystal grains mainly composed of Ge as the underlying layer 102 on the substrate 101 . The crystal grains forming the functional layer 103 formed on the underlayer 102 inherit the shape of the crystal grains of the underlayer 102 and have a grain size of 1 μm or more. This grain size is much larger than when it is formed directly on the base material 101 using the existing crystal growth technique or the like, and realizes a functional layer having high spectral sensitivity. Therefore, the semiconductor device 100 of the present embodiment includes, as the functional layer 102, a semiconductor film having quality applicable to a photoelectric conversion device.

Further, in the semiconductor device 100 of the present embodiment, the substrate 101 is amorphous, and the functional layer 102 is formed via the underlying layer 101 made of polycrystalline grains of Ge. Therefore, since the semiconductor device 100 of the present embodiment does not require application of a bonding technique in its manufacturing process, the semiconductor film forming the functional layer 102 can be formed of a single crystal regardless of the size of the substrate 101. Since an expensive base material is not used, it can be formed at a low cost.

Note that the semiconductor device 100 according to this embodiment can be operated as a photoelectric conversion device (element) by providing an electrode on the functional layer 103 . A device in which a p-type semiconductor region and an n-type semiconductor region are formed in the functional layer 103 and electrodes are provided in each of the p-type semiconductor region and the n-type semiconductor region can be operated as a photoelectric conversion device. Examples of photoelectric conversion devices include solar cells and light receiving sensors.

Hereinafter, the effects of the present invention will be made clearer by way of examples. It should be noted that the present invention is not limited to the following examples, and can be modified as appropriate without changing the gist of the invention.

(Example 1)
The semiconductor device 100 according to the above embodiment was manufactured by the following procedure. First, in the first laminate forming step, a metal layer 104 mainly composed of Al, a metal oxide layer 105 mainly composed of AlOx, a metal oxide layer 105 mainly composed of AlOx, and a Then, a Ge layer 106 made of amorphous Ge was formed in order to obtain a first laminate 107 . The thicknesses of the metal layer 104, the metal oxide layer 105, and the Ge layer 106 were set to about 50 nm, about 1 nm, and about 50 nm, respectively.

Next, the first laminate 107 was heat-treated at about 350° C. for about 100 hours to exchange the metal layer 104 and the Ge layer 106 to obtain a second laminate 107A. The Ge layer 106A after the layer exchange was made of crystal grains having a grain size of about 50 μm or more and became a polycrystalline film having a thickness of about 50 nm.

Next, the metal layer 104A and the metal oxide layer 105 after layer exchange were removed by wet etching with diluted hydrofluoric acid (approximately 1.5%) to expose the Ge layer 106A.

Next, on the exposed Ge layer 106A, that is, on the underlying layer 102, a functional layer 103 mainly made of GaAs crystal grains was formed using a molecular beam epitaxy method to obtain the semiconductor device 100 of this embodiment. . The functional layer 103 inherited the shape of the crystal grains on the underlying layer 102, was made of crystal grains with a grain size of about 50 μm or more, and became a polycrystalline film with a thickness of about 500 nm.

(Comparative example 1)
A semiconductor device was manufactured by forming a functional layer directly on a substrate using a molecular beam deposition method . The manufacturing procedure was the same as in Example 1, except that no underlayer was formed.

(Comparative example 2)
A semiconductor device was manufactured by using a Ge(111) single crystal substrate as a base material and directly forming a functional layer thereon by using a molecular beam epitaxy method. The manufacturing procedure was the same as in Example 2, except that the type of base material and the method of forming the functional layer were changed.

3 is a graph showing Raman spectra of functional layers in the semiconductor devices of Example 1 and Comparative Examples 1 and 2. FIG. The horizontal axis of the graph indicates the Raman shift [cm ⁻¹ ], and the vertical axis indicates the spectral intensity. Since the three spectra have peaks at substantially the same positions, it can be seen that the functional layers made of GaAs crystal grains are properly formed in all semiconductor devices.

4A to 4C are SEM images showing surface shapes of functional layers in the semiconductor devices of Example 1 and Comparative Examples 1 and 2, respectively. Since the surfaces of the three functional layers exhibit substantially uniform shapes in the in-plane direction, it can be seen that the functional layers are formed of continuous films in any of the semiconductor devices.

5A to 5C are EBSD images showing the crystal orientation in the thickness direction of crystal grains forming the functional layer in the semiconductor devices of Example 1 and Comparative Examples 1 and 2, respectively. FIG. 5D is an EBSD image showing the in-plane crystal orientation of the crystal grains forming the functional layer of Example 1. FIG.

In FIG. 5A, it can be seen that the crystal grains are preferentially oriented in the (111) orientation. Furthermore, in FIG. 5(d), many crystal grains with large grain sizes (in units of several μm to several tens of μm) are observed. From these results, it can be seen that the functional layer of Example 1 is a polycrystalline film composed of a plurality of crystal grains with large grain sizes. This is because the functional layer of Example 1 is formed on an underlayer of a polycrystalline film composed of a plurality of crystal grains, and the shape of the crystal grains constituting the functional layer is the same as the shape of the crystal grains of the underlayer. It is thought that this is because it has been inherited.

In FIG. 5(b), a plurality of small crystal grains having a grain size of less than 1 μm can be seen, and their identification is difficult. The reason why the grain size of the crystal grains of the functional layer of Comparative Example 2 is smaller than that of Example 1 is considered to be that no underlying layer is interposed between the substrate and the functional layer.

In FIG. 5(c), no grain boundaries between crystal grains are seen, so it can be seen that the functional layer of Comparative Example 1 is a uniform single crystal film. This is because the functional layer of Comparative Example 1 is formed on the single crystal substrate, and the shape of the crystal grains forming the functional layer inherits the shape of the crystal grains of the single crystal substrate. It is considered to be

For the semiconductor devices of Example 1 and Comparative Examples 1 and 2, electrodes were provided on each of the functional layers, and their spectral sensitivities were measured.

Here, the spectral sensitivity is represented by the external quantum efficiency defined as the ratio [%] of the number of electrons generated from the functional layer to the number of photons irradiated to the functional layer per unit time. FIG. 6 is a graph showing the results of spectral sensitivity measurement. The horizontal axis of the graph indicates the wavelength [nm] of light incident on the solar cell, and the vertical axis indicates the external quantum efficiency [%].

The solar cell of Comparative Example 1 obtained almost no spectral sensitivity, while the solar cell of Example 1 obtained a high spectral sensitivity of about 90% when 2 V was applied. This is probably because the functional layer responsible for photoelectric conversion in Example 1 is composed of crystal grains having larger grain sizes than the functional layer in Comparative Example 1.

Moreover, in the solar cell of Example 1, although an amorphous substrate was used as the base material, a higher spectral sensitivity than the solar cell of Comparative Example 2 using a single crystal substrate was obtained. I understand. This result indicates that a solar cell with sufficient spectral sensitivity can be realized at low cost without using an expensive single crystal substrate.

DESCRIPTION OF SYMBOLS 100... Semiconductor device 101... Base material 101a... One surface of base material 102... Underlying layer 102A... First crystal grains 103... Functional layer 103A... Second crystal grains 104, 104A... Metal layer 105... Metal oxide layers 106, 106A... Ge layer 107... First laminate 107A... Second laminate

Claims (10)

an amorphous substrate;
a base layer formed on one surface of the base material and containing a plurality of first crystal grains containing Ge as a main component;
a functional layer formed on the underlayer and containing a plurality of second crystal grains having a lattice constant of −2% or more and 2% or less of the first crystal grains;
The underlayer has a thickness of 1 μm or less,
A semiconductor device , wherein the thickness of the functional layer is 5 μm or less, and the average grain size of the second crystal grains is 50 μm or more. an amorphous substrate;
a base layer formed on one surface of the base material and containing a plurality of first crystal grains containing Ge as a main component;
a functional layer formed on the underlayer and containing a plurality of second crystal grains having a lattice constant of −2% or more and 2% or less of the first crystal grains;
The underlayer has a thickness of 1 μm or less,
The average particle size of the second crystal grains is 1 μm or more,
A semiconductor device, wherein the grain size of the second crystal grains is 10 times or more the thickness of the functional layer. 3. The semiconductor device according to claim 1, wherein said second crystal grain contains GaAs as a main component. 3. The semiconductor device according to claim 1 , wherein said second crystal grain contains at least one of In, Al and P as a main component. 5. The semiconductor device according to claim 1 , further comprising a conductive layer between said base material and said underlying layer. 6. The semiconductor device according to claim 1, wherein said base material is made of an amorphous material. A method for manufacturing a semiconductor device according to any one of claims 1 to 6 ,
A method of manufacturing a semiconductor device, comprising: forming the functional layer on the underlying layer by using a vapor phase epitaxy method. Before forming the functional layer,
a step of forming a first laminate in which a metal layer containing a metal element as a main component and a Ge layer containing Ge as a main component are laminated in order on one surface of the substrate;
a step of heating the first laminate to perform layer exchange between the metal layer and the Ge layer to form a second laminate with the Ge layer as the underlying layer;
8. The method of manufacturing a semiconductor device according to claim 7 , further comprising removing a layer formed on said Ge layer after said layer exchange. 9. The method of manufacturing a semiconductor device according to claim 8 , wherein the first laminate further includes a metal oxide layer containing a metal oxide as a main component between the metal layer and the Ge layer. . A semiconductor device according to any one of claims 1 to 6 ;
and an electrode provided on the functional layer.

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