Cu2O semiconductor, method for manufacturing the same, and semiconductor device

Abstract

To provide a novel Cu2O semiconductor capable of controlling hole concentration within a specific range. [Solution] The Cu2O semiconductor that solves the above problem is doped with Se and / or S, and has a hole concentration of 1.0 × 10⁻¹⁶ 15 cm -3 The above 3.0 × 10 20 cm -3 The following applies:

Description

Technical Field

[0001] The present invention relates to a Cu2O semiconductor, a method for manufacturing the same, and a manufacturing apparatus for a semiconductor device.

Background Art

[0002] Conventionally, Cu2O (copper(I) oxide) has been known as a semiconductor material, and its use as a p-type semiconductor for various semiconductor devices has been studied. For example, it is expected to use a Cu2O semiconductor layer as a p-type semiconductor layer of a light absorption layer of a solar cell, or as a back surface field layer (BSF layer) that connects the light absorption layer and the transparent electrode of a solar cell. However, in order to use these layers, control of the carrier concentration is necessary, but the doping technology for Cu2O semiconductors and the method for controlling the carrier concentration have not yet been established.

[0003] For doping of a semiconductor, it is common to use an element having a valence different from that of the constituent atoms of the host compound. For example, in a GaAs semiconductor, Ga (+3) of group 13, which is a constituent atom thereof, is replaced with Zn (+2) of group 12 to form a p-type semiconductor, or replaced with Si (+4) of group 14 to form an n-type semiconductor. On the other hand, regarding the Cu2O semiconductor, it has been reported in Non-Patent Documents 1 and 2 that O (-2) of group 16, which is a constituent atom thereof, is replaced with N (-3) of group 15 to form a p-type semiconductor.

[0004] On the other hand, p-type semiconductors in which monovalent Cu (+1) of a Cu2O semiconductor is replaced with an alkali metal of group 1 (for example, Na, etc.) have been reported in Non-Patent Documents 3 and 4. Although Cu (+1) and an alkali metal (+1) are formally of the same valence, holes are considered to be generated due to complex defects.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Literature

[0006]

Non-Patent Literature 1

Non-Patent Literature 2

Non-Patent Literature 3

Non-Patent Literature 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, when using a Cu2O semiconductor for a solar cell or the like, control of its carrier concentration is very important. For example, when using a Cu2O semiconductor as a p-type light absorption layer, it is preferable to set the hole concentration to about 10 , ,

[0008] cm -3 ~10 17 cm -3 Furthermore, when using a Cu2O semiconductor as the BSF layer of a solar cell, it is preferable to set the hole concentration to 10 18 cm -3 ~10 19 cm -3 In addition, for use as a transparent conductive film of a solar cell, it is desirable to have a hole concentration of about 10 20 cm -3 However, in the N-doped Cu2O semiconductor, only control of the hole concentration to about 10 15 cm -3 ~10 16 cm -3 has been reported (for example, Non-Patent Document 1). At such a hole concentration, it is difficult to use the Cu2O semiconductor as the light absorption layer or BSF layer of a solar cell. On the other hand, in the alkali metal-doped Cu2O semiconductor, it has been reported that the hole concentration becomes on the order of 10 17 cm -3 However, the study on the control range and control method of the hole concentration is insufficient, and there is a demand for providing a Cu2O semiconductor having a higher hole concentration and a Cu2O semiconductor with controlled hole concentration.

[0009] The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a novel Cu2O semiconductor capable of controlling the hole concentration within a specific range, a method for manufacturing the same, and a semiconductor device including the same.

Means for Solving the Problems

[0010] ​​​​The present invention provides the following Cu2O semiconductor. [1] Doped with Se and / or S, and with a hole concentration of 1.0 × 10 15 cm -3 The above 3.0 × 10 20 cm -3 The following is a Cu2O semiconductor.

[0011] The present invention provides a method for manufacturing a Cu2O semiconductor as described below. [2] A method for producing a Cu2O semiconductor as described in [1] above, comprising the step of forming a Cu2O film in the presence of Se and / or S by molecular beam epitaxy or sputtering.

[0012] This invention provides the following semiconductor devices. [3] A semiconductor device containing the Cu2O semiconductor described in [1] above. [4] The semiconductor device according to [3], wherein the semiconductor device is selected from the group consisting of a solar cell, a thin-film transistor, a semiconductor light-emitting element, and a power device. [Effects of the Invention]

[0013] The present invention provides a novel Cu2O semiconductor capable of controlling the hole concentration within a specific range, a method for manufacturing the same, and a semiconductor device containing the same. [Brief explanation of the drawing]

[0014] [Figure 1] This graph shows the relationship between the temperature of the Cu2Se Knudsen cell and the hole concentration of the obtained Cu2O semiconductor when producing a Cu2O semiconductor by molecular epitaxy in an embodiment of the present invention. [Modes for carrying out the invention]

[0015] 1. Cu2O semiconductor and method for manufacturing the same The present invention relates to a material doped with Se and / or S, and having a hole concentration of 1.0 × 10⁻⁶15 cm -3 The above 3.0 × 10 20 cm -3 The following concerns a novel Cu2O semiconductor.

[0016] As mentioned above, conventional methods of doping Cu2O with various elements have been reported, but in reality, these methods have not yielded Cu2O semiconductors with hole concentrations controlled within the desired range. In response to this, the present inventors conducted diligent research and found that doping Cu2O with Se or S allows for a control of the hole concentration to 10 15 cm -3 From the table 20 cm -3 We discovered that it is possible to control the unit down to the base level.

[0017] The reason is not entirely clear, but it can be considered as follows. For example, when Cu2O is doped with Se, it is thought that Se replaces the O in the Cu2O crystal. This is because the only anion in Cu2O is O, and furthermore, Se is a group 16 element like O and has the same valence (-2). On the other hand, substitution by a congener element does not result in a change in valence. Therefore, congener elements are not usually expected to function as acceptors that supply holes or donors that supply electrons. However, as shown in the examples described later, when Se is added, the hole concentration increases in proportion to the amount added, and the hole concentration is increased to 10 20 cm -3 It is also possible to increase the concentration to a certain level. In other words, when Se is added, a phenomenon occurs that cannot be explained by simple O substitution.

[0018] Here, it has been reported that the hole concentration increases with the addition of Na in the same Cu2O (see Non-Patent Documents 3 and 4 above). Na, like Cu, is valent to +1. Therefore, even if Cu is substituted, it cannot be expected to function as a donor or acceptor. On the other hand, an increase in hole concentration actually occurs with the addition. The reason for this is thought to be that Na, which has a larger ionic radius than Cu, does not actually substitute for the Cu site but occupies an interatomic position, and with the same Na configuration, two pairs of Cu vacancies are formed, and this combination is thought to function as an acceptor.

[0019] It is believed that a similar phenomenon occurs within Cu2O when se is added. Specifically, within the Cu2O crystal, se, which has a larger ionic radius than oxygen, does not displace oxygen but occupies interatomic positions. As a result, two pairs of Cu vacancies are formed, and these function as acceptors. However, the effect is significantly higher when se is added compared to when alkali metals such as sodium are added, and as in this application, the hole concentration can be increased to 1.0 × 10⁻⁶. 15 cm -3 The above 3.0 × 10 20 cm -3 The following controllability is expected. Note that while the examples described later show results for Se, similar effects are expected to be obtained with S, which has a larger ionic radius than O. However, since the O vacancies created by the introduction of Se and S are donor defects, many aspects of the phenomenon of increased hole concentration remain unclear. The increase in hole concentration is thought to be due to the introduction of composite defects with Cu vacancies, which are the most readily formed intrinsic defects in Cu2O and also function as acceptors, but a theoretical understanding of this remains a challenge for future research.

[0020] In the Cu2O semiconductor of the present invention, it is sufficient that at least one of Se and S is doped, or both may be doped. The amount of Se and S doping is appropriately selected according to the desired hole concentration, and the hole concentration is 1.0 × 10⁻⁶ 15 cm -3 The above 3.0 × 10 20 cm -3 The following is not particularly limited, as long as it is possible to do so.

[0021] Furthermore, the hole concentration of the Cu2O semiconductor of the present invention is 1.0 × 10⁻⁶. 15 cm -3 The above 3.0 × 10 20 cm -3The hole concentration only needs to be controlled within the following range, and is appropriately selected depending on the application of the Cu2O semiconductor. The hole concentration of the Cu2O semiconductor can be adjusted by the amount of Se or S doping during the manufacturing of the Cu2O semiconductor. In this invention, the hole concentration of the Cu2O semiconductor is a value determined by Hall measurement, and in particular, a value determined by AC Hall measurement, which has high measurement accuracy. Furthermore, the conductivity type can also be determined by AC Hall measurement. The AC Hall measurement was performed at room temperature using an alternating magnetic field with a maximum magnetic field of 0.4 T.

[0022] Furthermore, the shape of the Cu2O semiconductor of the present invention is not particularly limited, but when the Cu2O semiconductor is used in a semiconductor device, it is formed in layers on electrodes or various semiconductor layers. When the Cu2O semiconductor is in layer form, its thickness is appropriately selected according to the application and performance. For example, when used as a light absorption layer in a solar cell, a layer made of Cu2O semiconductor of about 2 to 5 μm is likely to function as a p-type semiconductor layer. When used as a BSF layer in a solar cell, an effect can be expected at about 10 nm. When used as a transparent conductive layer, an effect can be expected at about 20 to 300 nm.

[0023] The method for manufacturing the Cu2O semiconductor described above is not particularly limited, but it can be manufactured by, for example, forming a Cu2O film in the presence of Se and / or S using molecular beam epitaxy, metal-organic vapor deposition, or sputtering.

[0024] For example, when fabricating the Cu2O semiconductor using molecular beam epitaxy (MBE), the molecular beam epitaxy apparatus used is the same as that of known epitaxy apparatuses. For example, when fabricating a Cu2O semiconductor on a substrate, the molecular beam epitaxy apparatus only needs to include a vacuum chamber and vacuum evacuation system for generating an ultra-high vacuum, a stage for holding and heating the substrate within the vacuum chamber, a Knudsen cell for irradiating each raw material, and a plasma cell for supplying oxygen radicals.

[0025] When fabricating Cu2O semiconductors, a Cu molecular beam is irradiated onto a substrate held on a stage from a Cu Knudsen cell, and O radicals are simultaneously emitted from an O plasma cell. In addition, Se (or S) doping is possible by simultaneously emitting Se molecules (or S molecular beams) from a Se-source Knudsen cell (or S-source Knudsen cell). For example, Cu2Se can be used as the Se source. The amount of Se molecular beam emitted can be adjusted by the temperature of the Se-source Knudsen cell. When doping with S, for example, Cu2S can be used as the S source, and in this case as well, the amount of S molecular beam emitted can be adjusted by the temperature of the S-source Knudsen cell.

[0026] Due to the various properties of the Cu2O matrix, high-temperature film deposition is desirable. However, when used as a solar cell, for example, film deposition is required below the glass strain point temperature. For example, when using high-strain point glass, film deposition is required at approximately 650°C or below. However, film deposition at 550°C or above is preferable. Also, the vacuum in the vacuum chamber during standby should be ultra-high vacuum (1 × 10⁻⁶). -7 It is preferable to set the temperature to Pa or less. Furthermore, the temperature of the Knudsen cell for the Se source is appropriately selected depending on the type of Se source, but when Cu2Se is used as the Se source, adjusting the temperature to a range of 1100°C to 1200°C makes it easier to obtain a Cu2O semiconductor with the above-mentioned hole concentration. However, the temperature of the Knudsen cell for the Se source and S source is not limited to the above temperature range as it depends on the weight of the source and the shape of the apparatus.

[0027] On the other hand, when manufacturing the Cu2O semiconductor by sputtering, equipment similar to known reactive sputtering equipment can be used, for example, a magnetron sputtering apparatus. When manufacturing the Cu2O semiconductor by reactive sputtering, for example, a target containing copper, Se, S, etc., is prepared, and the Cu2O semiconductor can be deposited by sputtering it in an oxygen and argon atmosphere. The amount of Se and / or S doping can be adjusted by the amount of Se and S in the target. Furthermore, Cu2O semiconductors can also be manufactured by non-reactive sputtering methods. In that case, a compound with a composition close to that of the desired compound (Cu2O semiconductor) is selected as the sputtering target. Then, a target with Se and S added to the compound, or a different target containing Se and S, is prepared, and sputtering is performed in an argon atmosphere (and a small amount of oxygen supply), making it possible to deposit a Cu2O semiconductor doped with the desired Se and / or S.

[0028] 2. Semiconductor devices The Cu2O semiconductor mentioned above has a hole concentration of 1.0 × 10⁻⁶. 15 cm -3 The above 3.0 × 10 20 cm -3 The following range allows for easy control of the hole concentration depending on the application. Therefore, this Cu2O semiconductor can be used as a semiconductor layer in various semiconductor devices. Specific examples of its use in semiconductor devices include the light absorption layer, back-side electrolytic (BSF) layer, and transparent conductive film layer in solar cells, the p-type semiconductor layer in thin-film transistors (TFTs), the p-type semiconductor layer in semiconductor light-emitting devices, and the p-type heterolayer and guard ring layer in power devices.

[0029] For example, in the light-absorbing layer of a solar cell, a higher carrier concentration (hole concentration) results in a higher open-circuit voltage, offering a direct advantage in controlling the carrier concentration. On the other hand, this high carrier concentration reduces the width of the depletion layer on the p-type (light-absorbing layer) side of the pn junction. Therefore, the light-absorbing layer of a solar cell should have a hole concentration of 1 × 10⁻¹⁶.16 cm -3 ~5×10 17 cm -3 It is preferable to use a Cu2O semiconductor that is controlled to a certain extent.

[0030] On the other hand, the BSF layer of a solar cell is a layer that reduces the contact resistance between the light-absorbing layer and the transparent electrode layer, thereby improving the curve factor of the solar cell. In such a solar cell, the hole concentration in the BSF layer is set to 1 × 10⁻¹⁶. 18 cm -3 ~1 × 10 19 cm -3 It is preferable to use a Cu2O semiconductor that is controlled to a certain extent. Also, when used as a transparent conductive film, 10 20 cm -3 The use of Cu2O semiconductors is preferred. [Examples]

[0031] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited in any way thereto.

[0032] 1. Formation of Cu2O semiconductor An alkali-free glass substrate was prepared and fixed to the stage inside the vacuum chamber of the molecular beam epitaxy apparatus. The substrate temperature was set to 550°C and the pressure to 1 × 10⁻⁶. -2 The pressure was set to Pa or less. Then, a Cu molecular beam was irradiated from a Knudsen cell, which is the Cu source of the molecular beam epitaxy apparatus, O radicals were irradiated from an O plasma cell, and a Cu2Se molecular beam was irradiated from a Se source using Cu2Se as the Se source to form a Se-doped Cu2O semiconductor layer. The amount of Cu supplied during Cu2O semiconductor layer formation was adjusted by controlling the temperature of the Knudsen cell in the Cu source gun. The amount of O supplied was controlled by controlling the amount of oxygen introduced into the apparatus. Furthermore, copper selenide (Cu2Se) was used as the Se source, and its supply was controlled by controlling the temperature of the Knudsen cell filled with Cu2Se source. Using this method, Cu2O semiconductor layers were fabricated by varying the heating temperature of a Knudsen cell containing Cu2Se from 1100°C to 1200°C.

[0033] 2. Measurement of carrier concentration (hole concentration) For each Cu2O semiconductor layer obtained above, the carrier concentration and conduction type (electron conduction or hole conduction) were evaluated by AC Hall measurement. The conditions for the AC Hall measurement were as follows. (Measurement conditions) Hall measurement device: ResiTest8300 manufactured by Toyo Technica Co., Ltd. Measurement temperature: room temperature Maximum magnetic field: 0.4T (AC magnetic field)

[0034] 3. Discussion The AC Hall measurement results showed that the conduction type of the Se-doped Cu2O semiconductors was p-type (hole conduction). Furthermore, there was a correlation between the heating temperature of the Cu2Se Knudsen cell during Cu2O semiconductor layer formation and the carrier concentration (hole concentration) of the resulting Cu2O semiconductor. These results are shown in Figure 1.

[0035] As shown in Figure 1, when the heating temperature of Cu2Se is 1100°C to 1165°C, that is, when the amount of Se supplied in the molecular beam epitaxy apparatus is low, the hole concentration is approximately 2 × 10⁻⁶ 15 cm -3 ~3×10 16 cm -3 Therefore, the Cu2O semiconductor layer had a relatively low hole concentration. In contrast, when the heating temperature of Cu2Se exceeds 1165°C, that is, when the amount of Se supplied is high, the hole concentration is approximately 1 × 10⁻⁶. 17 cm -3 ~3×10 20 cm -3 It increased to 10. From these results, it can be seen that with Se-doped Cu2O semiconductors, the hole concentration can be increased by 10 depending on the amount of Se doping. 15 cm -3 From the table 20 cm -3 It can be said that control is possible down to the level of the unit. [Industrial applicability]

[0036] According to the present invention, a novel Cu2O semiconductor capable of controlling the hole concentration within a specific range, a method for manufacturing the same, and a semiconductor device containing the same can be obtained. This Cu2O semiconductor is extremely useful in various industrial fields, including the solar cell field.

Claims

1. Se and / or S are doped, and Hole concentration is 1.0 × 10⁻⁶ １５ cm －３ The above 3.0 x 10 ２０ cm －３ The following is: Cu ２ O semiconductor.

2. The Cu according to claim 1 ２ A method for manufacturing semiconductors, By molecular beam epitaxy or sputtering, in the presence of Se and / or S, Cu ２ Includes a step of forming an O film, Cu ２ A method for manufacturing semiconductors.

3. Cu according to claim 1 ２ comprising an O semiconductor Semiconductor devices.

4. The semiconductor device is selected from the group consisting of solar cells, thin-film transistors, semiconductor light-emitting elements, and power devices. The semiconductor device according to claim 3.

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