JP6037239B2 - Transparent conductive film, apparatus or solar cell using the same, and method for producing transparent conductive film - Google Patents

Description

  The present invention relates to a transparent conductive film, a device or solar cell using the transparent conductive film, and a method for producing a transparent conductive film.

  The transparent conductive film is used for transparent electrodes of liquid crystal display elements, electrode TFTs for display elements such as EL (electroluminescence) elements, and other various light receiving elements. However, on the other hand, improvement in hole mobility of the transparent conductive film is a common problem for all devices having these transparent conductive films.

  Conventionally, as a transparent conductive film, a transparent conductive film made of indium oxide (ITO) containing tin (Sn) and a transparent conductive film made of zinc oxide (ZnO) are known. Particularly recently, a transparent conductive film made of indium oxide to which cerium is added, which has a great effect on improving the hole mobility, has attracted attention (Patent Document 1). In Patent Document 1, the hole mobility, specific resistance, and carrier density when the cerium concentration in the film is changed are investigated, and optimization of the cerium concentration is studied.

International Publication No. 2011/034143

However, Patent Document 1 does not examine the influence of hydrogen inevitably mixed during film growth using a vacuum chamber for industrial use.
Accordingly, an object of the present invention is to provide a transparent conductive film having high hole mobility by appropriately adjusting the concentration of cerium and the partial pressure of a hydrogen source in a growth atmosphere.

In order to achieve the above object, a transparent conductive film according to the present invention is firstly a transparent conductive film having a polycrystalline structure of indium oxide containing hydrogen and a lanthanoid element, and has a hole mobility of 120 cm ^2. / (V · s) or more.

With the above configuration, by setting the hole mobility to 120 cm ² / (V · s) or higher, the influence of grain boundary scattering is reduced, and a transparent conductive film having high hole mobility is obtained.

  The second is a transparent conductive film having a polycrystalline structure of indium oxide, which is arranged so as to fill a space between a number of island-shaped crystals constituting the polycrystalline structure and the island-shaped crystals adjacent to each other. A buffer crystal, and the buffer crystal moves from the first island crystal connected to the buffer crystal toward the second island crystal connected to the buffer crystal via the buffer crystal. It has a crystal structure that continuously changes from the crystal structure of the first island-shaped crystal to the crystal structure of the second island-shaped crystal.

  With the above configuration, the short-range order is maintained in the buffer crystal and at the boundary between the island-shaped crystal and the buffer crystal. For this reason, it is possible to reduce grain boundary scattering received when carriers move from the first island-shaped crystal to the second island-shaped crystal via the buffer crystal. As a result, the carriers have electrical characteristics according to the relationship between the carrier density and the hole mobility mainly due to the influence of ionized impurity scattering, and can have a high hole mobility.

Third, cerium is contained, and the atomic composition percentage is 0.23% or more.
With the above structure, the crystallinity of the transparent conductive film can be increased.

An apparatus according to the present invention includes the above-described transparent conductive film.
With the above configuration, the influence of the grain boundary scattering is reduced, and the device includes a transparent conductive film having a high hole mobility.

The solar cell according to the present invention has the above-described transparent conductive film.
With the above configuration, the effect of the grain boundary scattering is reduced, and a solar cell including a transparent conductive film having high hole mobility is obtained.

A method for producing a transparent conductive film according to the present invention is a method for producing a transparent conductive film having a polycrystalline structure of indium oxide containing hydrogen and a lanthanoid element, wherein the lanthanoid element is cerium, and its atomic composition percentage is the evaporation source a sintered body containing more than 0.23%, and the flow rate of hydrogen gas so that the partial pressure of the hydrogen source is ^{4.2 × 10 -4 Pa~5.4 × 10 -4} Pa And a plurality of island crystals that form the polycrystalline structure and a buffer crystal disposed so as to fill in between the adjacent island crystals, the buffer crystal being the buffer crystal From the first island-shaped crystal connected to the second island-shaped crystal connected to the buffer crystal via the buffer crystal, from the crystal structure of the first island-shaped crystal to the second island-shaped crystal Crystalline Has a crystal structure that varies continuously to crystal structure, the hole mobility is characterized by forming a film to be a 120cm 2 / (V ^· s) or more.

By the above method, the hole mobility can be set to 120 cm ² / (V · s) or more, and the influence of crystal grain boundary scattering can be reduced, and a transparent conductive film having high hole mobility can be manufactured. .

According to the transparent conductive film of the present invention, the hole mobility is 120 cm ² / (V · s) or more, thereby reducing the influence of grain boundary scattering, and a transparent conductive film having high hole mobility. Become.

It is a graph showing the specific resistance of the transparent conductive film which concerns on Example 1, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is data showing the specific resistance of the transparent conductive film which concerns on Example 1, carrier density, and oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on Example 2, carrier density, and the oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is data showing the specific resistance of the transparent conductive film which concerns on Example 2, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on Example 3, carrier density, and the oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is data showing the specific resistance of the transparent conductive film which concerns on Example 3, carrier density, and the oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on the comparative example 1, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing, after annealing). It is data showing the specific resistance of the transparent conductive film which concerns on the comparative example 1, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on the comparative example 2, carrier density, and the oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is the data showing the specific resistance of the transparent conductive film which concerns on the comparative example 2, a carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on the comparative example 3, carrier density, and oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is the data showing the specific resistance of the transparent conductive film which concerns on the comparative example 3, carrier density, and oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on the comparative example 4, a carrier density, and the introduction ratio dependence of oxygen with respect to argon with respect to argon (before annealing and after annealing). It is data showing the specific resistance of the transparent conductive film which concerns on the comparative example 4, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on the comparative example 5, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is data showing the specific resistance of the transparent conductive film which concerns on the comparative example 5, a carrier density, and the oxygen introduction ratio dependence with respect to argon with respect to argon (before annealing and after annealing). It is a graph showing the specific resistance of the transparent conductive film which concerns on the comparative example 6, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is the data showing the specific resistance of the transparent conductive film which concerns on the comparative example 6, carrier density, and the oxygen introduction ratio dependence with respect to argon (before annealing and after annealing). It is a graph showing the relationship between the hole mobility and carrier density of the transparent conductive film which concerns on Example 1 and Comparative Examples 1-4. It is a graph showing the relationship between the hole mobility and carrier density of the transparent conductive film which concerns on Example 2, 3 and Comparative Examples 5 and 6. FIG. 2 is a SEM image of the transparent conductive film according to Example 1 before annealing. 2 is an SEM image after annealing of the transparent conductive film according to Example 1. It is a SEM image after annealing of the transparent conductive film according to Comparative Example 1. It is a SEM image after annealing of the transparent conductive film concerning the comparative example 3. 6 is an SEM image after annealing of a transparent conductive film according to Comparative Example 5. It is a SEM image after annealing of the transparent conductive film concerning the comparative example 6. It is the X-ray-diffraction measurement data after annealing of Example 1, Comparative Example 1, and Comparative Example 3. It is a schematic diagram of the film-forming apparatus for growing the transparent conductive film which concerns on this embodiment.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .

  FIG. 28 is a schematic diagram of a film forming apparatus for growing a transparent conductive film according to this embodiment. A film forming apparatus 100 (HDPE apparatus) according to this embodiment includes a load lock chamber 102, a heating chamber 104, and a film forming chamber 110. Although not shown, a vacuum pump is attached to each chamber.

  The substrate 10 used in the present embodiment has a glass substrate, a polycrystalline silicon substrate, a single crystal silicon substrate, and an upper surface comprising substantially intrinsic i-type amorphous silicon layer and p-type amorphous silicon layer in this order. A single crystal silicon substrate or the like which is a p-type amorphous silicon layer is applied.

The transparent conductive film 12 of this embodiment is grown on the substrate 10 and is a film containing hydrogen (H) and cerium (Ce), the main component of which is indium oxide. The transparent conductive film 12 has a substantially polycrystalline structure, and a crystal structure (or many columnar crystal structures) composed of island crystals and buffer crystals, which will be described later. Also have. Further, the transparent conductive film 12 of the present embodiment is characterized by having a hole mobility of 120 cm ² / (V · s) or more (Example 1, Example 2, Example 3 described later).

  The load lock chamber 102 is provided with a substrate transfer mechanism (not shown) for taking in and out the substrate 10 in a vacuum state. The heating chamber 104 includes a heater 106 that heats the substrate 10.

  A holder (not shown) that supports the substrate 10 is disposed above the film forming chamber 110 so that the surface of the substrate 10 on which the transparent conductive film 12 is grown faces downward. On the other hand, a crucible 112 that houses an evaporation source, introduction pipes 116, 118, 120, and 122 for supplying gas, an arc plasma gun 114, and a mass spectrometer 124 are attached to the lower part of the film forming chamber 110.

Evaporation source to be accommodated in the crucible 112, a sintered body of a powder of _{an In} 2 _{O 3,} or a sintered body of powder of cerium oxide of _{In 2 O 3} (CeO 2) by a predetermined amount mixed. Argon is supplied to the arc plasma gun 114 through the introduction tube 116. Oxygen gas, hydrogen gas, and argon gas are introduced from the introduction pipes 118, 120, and 122, respectively.

  In the film forming apparatus 100, electrons emitted from a cathode built in the arc plasma gun 114 are guided by a magnetic field, and concentratedly irradiated to an evaporation source charged in the crucible 112. Since plasma is formed along this electron flow, the shape of the plasma beam can be controlled by controlling the electron flow with a relatively weak magnetic field. The evaporation source, oxygen gas and hydrogen gas evaporated by electron beam heating are activated in this plasma. A polycrystalline transparent conductive film 12 containing hydrogen is deposited on the lower surface of the substrate 10 in an atmosphere of argon, oxygen, and hydrogen.

  The partial pressure of the hydrogen source in the growth atmosphere of the deposition chamber 110 is monitored by measuring the mass spectrum using the mass spectrometer 124, and the oxygen gas, hydrogen gas, and argon gas from the introduction pipes 118, 120, 122 are monitored. Control the amount of introduction (the opening of the mass flow controller). Note that the pressure during the growth of the transparent conductive film 12 in the film forming chamber 110 is controlled to about 100 Pa.

Here, the partial pressure of the hydrogen source in the growth atmosphere is considered to be proportional to the composition ratio of hydrogen in indium oxide (before annealing) which is the transparent conductive film 12. On the other hand, in a general crystal growth vacuum apparatus including the film forming apparatus 10, a certain amount of moisture or hydrogen included in the outer wall material of the O-ring or chamber or adsorbed on the surface leaks into the growth atmosphere. . For this reason, even if hydrogen gas is not introduced from the introduction pipe 120, the transparent conductive film 12 is necessarily doped with a certain amount of hydrogen. In this embodiment, the partial pressure of the hydrogen source is controlled by setting the hydrogen gas concentration in the process gas (in the growth atmosphere) to 0% to 2.0%, but the partial pressure of the hydrogen source is zero even at 0%. The residual gas partial pressure (4.0 × 10 ⁻⁴ Pa) exists.

  Further, when the transparent conductive film 12 is formed only from the sintered body, the oxygen in the film is depleted. Therefore, the partial pressure of oxygen in the growth atmosphere is increased by the oxygen source introduced from the introduction pipe 120. Thereby, the composition ratio of oxygen in indium oxide which is the transparent conductive film 12 can be increased, and the crystallinity of the transparent conductive film 12 can be increased.

  The inventor of the present application forms the transparent conductive film 12 shown in the following Examples and Comparative Examples, and the resistivity of the transparent conductive film 12 by the four-terminal method, the carrier density by the Hall effect measurement, by the Van der Pauw method. Each hole mobility was measured. As described above, the substrate 10 can be heated by the heater 21 of the heating chamber 102. However, in the following examples and comparative examples, the heating of the substrate 10 before film formation using the heater 21 is performed. Not done.

[Example 1]
Using a sintered body of In ₂ O ₃ powder containing 3 wt% of CeO ₂ powder as an evaporation source and supplying hydrogen gas so that the partial pressure of the hydrogen source is 8.2 × 10 ⁻⁴ Pa, oxygen with respect to argon A series of transparent conductive films 12 were formed by changing the introduction ratio in the range of 7.5% to 15%. Thereafter, each was annealed at 200 ° C. for 30 minutes in the air.
[Example 2]
Similar to Example 1, but different from Example 1 in that a sintered body of In ₂ O ₃ powder containing 2 wt% of CeO ₂ powder was used.
[Example 3]
Similar to Example 1, but different from Example 1 in that a sintered body of In ₂ O ₃ powder containing 1 wt% of CeO ₂ powder was used.
[Comparative Example 1]
Similar to Example 1, but differs from Example 1 in that no hydrogen gas is supplied. However, a hydrogen source having a partial pressure of 4.0 × 10 ⁻⁴ Pa exists as a background of the growth atmosphere.
[Comparative Example 2]
Although it is similar to Example 1, it differs in that hydrogen gas is supplied so that the partial pressure of the hydrogen source is 9.4 × 10 ⁻⁴ Pa.
[Comparative Example 3]
Although it is similar to Example 1, it differs in the point which supplied hydrogen gas so that the partial pressure of a hydrogen source might be 1.0x10 < ^-3 > Pa.
[Comparative Example 4]
Although it is similar to Example 1, it differs in the point which supplied hydrogen gas so that the partial pressure of a hydrogen source might be set to 1.2 * 10 < ^-3 > Pa.
[Comparative Example 5]
Similar to Example 1 but containing no CeO ₂ powder (the content of CeO ₂ powder 0 wt%) differs from the first embodiment in that using a sintered body of _In 2 _{O 3} powder.
[Comparative Example 6]
It is similar to Example 1, except using a sintered body of _In 2 _{O 3} powder containing no CeO ₂ powder, and a hydrogen gas as the partial pressure of the hydrogen source is 1.2 × ¹⁰ -3 Pa It differs from Example 1 in the point which supplied.

1 and 2 show graphs and data showing the dependency of the specific resistance, carrier density, and hole mobility of the transparent conductive film according to Example 1 on the introduction ratio of oxygen to argon (before annealing and after annealing). As shown in FIGS. 1 and 2, in the state before annealing of Example 1, the best value of the hole mobility is 41.2 cm ² / (V · s) (when the oxygen introduction ratio is 15%). Even if it compares with the value shown by patent document 1 of this, it cannot be said that it is favorable.

  However, as shown in FIGS. 1 and 2, the resistivity and carrier density of the transparent conductive film 12 after annealing (post-annealed) are generally lower than that before as-deposited (as-deposited). In particular, the resistivity (Rsitivity) is reduced to a level that is half or slightly lower than half. On the other hand, the hole mobility (Mobility) is increased in each stage as compared with that before annealing. As described above, in the transparent conductive film 12 after annealing, the resistivity and carrier density are lower than those before annealing, and the hole mobility is increased more than before annealing. This also appears in the examples and comparative examples.

In Example 1, the hole mobility is 127 cm ² / (V · s) when the oxygen introduction ratio is 9%, and the maximum value is 145 cm ² / (V · s) when the oxygen introduction ratio is 11%. The ratio is at least 120 cm ² / (V · s) or more in the range of 9% to 15%. In this range, the resistivity maintains a value of 1.99 to 2.64 × 10 ⁻⁴ Ω · cm, and the carrier density has a value of 1.85 to 2.34 × 10 ²⁰ cm ⁻³ . Is maintained.

Note that the hole mobility is 100 cm ² / (V · s) or less when the oxygen introduction ratio is in the range of 7.5% to 8.5%. This is because the lattice defects due to the lack of oxygen are high in density. It exists and this is considered to be the scattering center of the carrier.

  3 and 4 show graphs and data representing the dependency of the specific resistance, carrier density, and hole mobility of the transparent conductive film according to Example 2 on the introduction ratio of oxygen to argon (before annealing and after annealing). 5 and FIG. 6 are graphs and data showing the dependency of the specific resistance, carrier density, and hole mobility of the transparent conductive film 12 according to Example 3 on the introduction ratio of oxygen to argon (before annealing and after annealing). Indicates. Also in Example 2 and Example 3, it cannot be said that it is as good as Example 1 before annealing, but by annealing, all physical quantities are changed to good values.

In Example 2, when the oxygen introduction ratio is in the range of 9.5% to 14%, the hole mobility has a value of 120 cm ² / (V · s) or more, and the maximum value is 13% for the oxygen introduction ratio. At 146 cm ² / (V · s). In this range, the resistivity maintains a value of 2.20 to 2.31 × 10 ⁻⁴ Ω · cm, and the carrier density has a value of 1.99 to 2.20 × 10 ²⁰ cm ⁻³ . Is maintained.

In Example 3, the oxygen introduction ratio ranges from 8.5% to 13%, and the hole mobility has a value of 100 cm ² / (V · s) or more, and the maximum value is 10% for the oxygen introduction ratio. In this case, it is 121 cm ² / (V · s). In this range, the resistivity maintains a value of 3.20 to 3.79 × 10 ⁻⁴ Ω · cm, and the carrier density has a value of 1.56 to 1.80 × 10 ²⁰ cm ⁻³ . Is maintained.

The inventor of the present application said that the composition ratio of cerium is 0.7 at% in the transparent conductive film 12 using a sintered body of In ₂ O ₃ powder containing 3 wt% of CeO ₂ powder as in Example 1 as an evaporation source. We have knowledge. Since the vapor pressure of the material of the evaporation source depends only on the temperature, it is considered that if the amount of cerium of the evaporation source is changed, the composition ratio of Ce in the transparent conductive film 12 is also proportionally changed.

Therefore, the composition ratio (atomic composition percentage) of 12 in the transparent conductive film of Example 2 using the sintered body of In ₂ O ₃ powder containing 2 wt% of CeO ₂ powder as the evaporation source is 0.47 at%, It is considered that the composition ratio of cerium in the transparent conductive film 12 of Example 3 using an In ₂ O ₃ powder sintered body containing 1 wt% of CeO ₂ powder as an evaporation source is 0.23 at%.

FIG. 7 to FIG. 14 are graphs and data showing the dependency of the specific resistance, carrier density, and hole mobility of the transparent conductive films according to Comparative Examples 1 to 4 on the introduction ratio of oxygen to argon (before annealing and after annealing). Indicates. 7 to 14 show ratios when the partial pressure of the hydrogen source is changed when the transparent conductive film 12 is formed by using a sintered body of In ₂ O ₃ powder containing 3 wt% of CeO ₂ powder as an evaporation source. It represents the dependency of resistance, carrier density, and hole mobility on the introduction ratio of oxygen to argon (before annealing and after annealing).

As shown in FIGS. 7 and 8, in Comparative Example 1 (hydrogen source partial pressure: 4.0 × 10 ⁻⁴ Pa), the hole mobility becomes 100 cm ² / (V · s) or less even after annealing. ing. As shown in FIGS. 9 and 10, in Comparative Example 2 (hydrogen source partial pressure: 9.4 × 10 ⁻⁴ Pa), the hole mobility is 120 cm ² / (in the range of oxygen introduction ratio of 9% to 10%. V · s) or more is maintained. Further, even in the oxygen introduction ratio of 11% when the hole mobility is maximum in Example 1, the hole mobility of Comparative Example 2 is 100 cm ² / (V · s).

As shown in FIGS. 11 and 12, in Comparative Example 3 (hydrogen source partial pressure: 1.0 × 10 ⁻³ Pa), the hole mobility is 117 cm ² / max at the maximum when the oxygen introduction ratio is 8.0%. (V · s). However, at an oxygen introduction ratio of 11% when the hole mobility is maximum in Example 1, the hole mobility of Comparative Example 3 is reduced to 58.7 cm ² / (V · s).

As shown in FIGS. 13 and 14, in Comparative Example 4 (hydrogen source partial pressure: 1.2 × 10 ⁻³ Pa), the hole mobility is 107 cm ² / max at the maximum when the oxygen introduction ratio is 8.5%. (V · s). However, the hole mobility of Comparative Example 4 decreases to 51.9 cm ² / (V · s) at an oxygen introduction ratio of 11% when the hole mobility becomes maximum in Example 1.

  15 and 16 show graphs and data representing the dependency of the specific resistance, carrier density, and hole mobility of the transparent conductive film according to Comparative Example 5 on the introduction ratio of oxygen with respect to argon (before annealing and after annealing). 17 and 18 show graphs and data representing the dependency of the specific resistance, carrier density, and hole mobility of the transparent conductive film according to Comparative Example 6 on the introduction ratio of oxygen to argon (before annealing and after annealing). .

15 to 18 show specific resistances when the partial pressure of the hydrogen source is changed in the case where the transparent conductive film 12 is formed using a sintered body of In ₂ O ₃ powder not containing CeO ₂ powder as an evaporation source. Represents the dependency of carrier density and hole mobility on the introduction ratio of oxygen to argon (before annealing and after annealing).

As shown in FIGS. 15 and 16, in Comparative Example 5 (hydrogen source partial pressure: 8.2 × 10 ⁻⁴ Pa), the hole mobility is 107 cm ² / max at the maximum when the oxygen introduction ratio is 8.5%. (V · s). However, the hole mobility in Comparative Example 5 decreases to 51.9 cm ² / (V · s) at an oxygen introduction ratio of 11% when the hole mobility is maximum in Example 1.

As shown in FIGS. 17 and 18, in Comparative Example 6 (hydrogen source partial pressure: 1.2 × 10 ⁻³ Pa), the maximum hole mobility is 124 cm ² / (V when the oxygen introduction ratio is 15%. S), and the hole mobility is maintained at a value of 100 cm ² / (V · s) or more when the oxygen introduction ratio is 9.5% or more.

  In FIG. 19, the graph showing the relationship between the hole mobility and carrier density of the transparent conductive film which concerns on Example 1 and Comparative Examples 1-4 is shown. FIG. 20 is a graph showing the relationship between the hole mobility and the carrier density of the transparent conductive films according to Examples 2 and 3 and Comparative Examples 5 and 6.

19 and 20, the vertical axis represents the hole mobility and the horizontal axis represents the carrier density, and plot data (FIGS. 2, 4, and 6) showing the relationship between the hole mobility and the carrier density in each example and each comparative example. 8, 10, 12, 14, 16, and 18). FIGS. 19 and 20 show a curve μ _I indicating the relationship between hole mobility caused by ionized impurity scattering and carrier density in indium oxide, and hole mobility caused by grain boundary scattering in indium oxide. A curve μ _GB indicating the relationship with the carrier density and a curve μ _IG indicating the relationship between the hole mobility and the carrier density due to both are described.

Here, mu _I can be derived by BHD (Brooks-Herring-Dingle) theory. Further, 1 / μ _IG = 1 / μ _I + 1 / μ _GB . The contribution of neutral impurity scattering in indium oxide to hole mobility is sufficiently smaller than both of the above, and can be ignored.

19, as shown in FIG. 20, plot data of Example 1 are aligned on the line of the mu _I, most of the plot data of Example 2 are arranged on a line of mu _I. Therefore, in Example 1 (cerium composition ratio: 0.7 at%) and Example 2 (cerium composition ratio: 0.47 at%), the influence of grain boundary scattering on the hole mobility is extremely small, and mainly ionized impurities. It can be seen that the influence of scattering is dominant. Example 3 (CE compositional ratio: 0.23at%) plot data, although slightly away from the line of mu _I, partially, because are arranged substantially parallel to the line of mu _I, Example 1 Although not as much as Example 2, it is considered that the influence of grain boundary scattering on the hole mobility is small.

On the other hand, Comparative Example 1 (cerium composition ratio: 0.7%, hydrogen source partial pressure: 4.0 × 10 ⁻⁴ Pa), Comparative Example 3 (cerium composition ratio: 0.7%, hydrogen source partial pressure: 1. 0 × 10 ⁻³ Pa), plot data of Comparative Example 4 (cerium composition ratio: 0.7%, hydrogen source partial pressure: 1.2 × 10 ⁻³ Pa), and Comparative Example 2 (cerium composition ratio: 0. Most of the plot data of 7%, hydrogen source partial pressure: 9.4 × 10 ⁻⁴ Pa) is close to the μ _IG line, so that the hole mobility is not only the influence of ionized impurity scattering but also the grain boundary It turns out that it is influenced by scattering. However, since a part of the plot data of Comparative Example 2 (cerium composition ratio: 0.7%, hydrogen source partial pressure: 9.4 × 10 ⁻⁴ Pa) is arranged on the μ _I line, the oxygen introduction ratio is adjusted. By doing so, it is considered that the influence of grain boundary scattering on the hole mobility can be reduced.

Plot data of Comparative Example 6, although slightly away from the line of mu _I, since aligned substantially parallel to the line of mu _I, the influence of the grain boundary scattering for hole mobility is considered smaller. Plot data of Comparative Example 5, but are aligned substantially parallel to the line of mu _I, as compared with Comparative Example 6, since a significant distance from the line of mu _I, the effect of grain boundary scattering for Hall mobility It is thought that it is larger than Comparative Example 6.

19, in the plot data arranged in the line of mu _I in FIG. 20, the hole mobility has become a 120cm ² / (V · s) or more. As described above, the composition ratio of hydrogen in indium oxide before annealing is considered to be proportional to the partial pressure of the hydrogen source in the growth atmosphere. Therefore, it is almost affected by grain boundary scattering by controlling the cerium composition ratio to 0.23 at% or more and controlling the hydrogen composition ratio (partial pressure of the hydrogen source in the growth atmosphere) within a certain range shown below. The transparent conductive film 12 having hole mobility due to the influence of ionized impurity scattering and having a value of 120 cm ² / (V · s) or more can be formed.

From Example 1 and Comparative Example 2, the partial pressure of the hydrogen source in the growth atmosphere of the transparent conductive film 12 may be set to a range of at least ^{8.2 × 10 -4 Pa~9.4 × 10 -4} Pa . As described above, a hydrogen source having a partial pressure of 4.0 × 10 ⁻⁴ Pa exists as a background in the growth atmosphere. Therefore, the partial pressure of hydrogen gas supplied from the pipe, the flow rate of hydrogen gas so that ^{4.2 × 10 -4 Pa~5.4 × 10 -4} Pa by subtracting the amount of background from the scope of the above Adjust it. Note that the partial pressure of the hydrogen source when forming the transparent conductive film 12 of 120 cm ² / (V · s) or more depends on the pressure of the growth atmosphere, the material of the substrate 10, the temperature of the substrate 10, the plasma density, and the like. Different.

  Next, the relationship between hole mobility and crystal structure is examined. FIG. 21 shows an SEM image of the transparent conductive film 12 according to Example 1 before annealing. 22 to 26 show SEM images after annealing of the transparent conductive films according to Comparative Example 1, Comparative Example 3, Comparative Example 5, and Comparative Example 6, respectively. The samples used for the SEM images in FIGS. 21 to 26 were formed in a uniform manner with the oxygen introduction ratio (11%) when the hole mobility reached the maximum value in Example 1.

As shown in FIG. 21, in SEM (scanning electron microscope) image of Example 1 (cerium composition ratio: 0.7 at%, hydrogen source partial pressure: 8.2 × 10 ⁻⁴ Pa) before annealing, the crystal structure is It is not recognized and is amorphous, and although not shown in the figure, a diffraction peak by X-ray is not recognized. The same applies to comparative examples described later. However, as shown in FIG. 22, in the SEM image of Example 1 after annealing, a large number of island crystals having a particle diameter exceeding 1 μm are formed, and the boundaries between the island crystals are unclear. ing.

As shown in FIG. 23, Comparative Example 1 (cerium composition ratio: 0.7%, hydrogen source partial pressure: 4.0 × 10 ⁻⁴ Pa) is a point where the partial pressure of the hydrogen source is lower than that of Example 1. The only difference is that after annealing, a large number of columnar crystals having a grain boundary with a grain size of about 100 nm are formed.

As shown in FIG. 24, Comparative Example 3 (cerium composition ratio: 0.7%, hydrogen source partial pressure: 1.0 × 10 ⁻³ Pa) is higher in partial pressure of the hydrogen source than in Example 1. The only difference is that after annealing, a region remaining as amorphous and a region grown into a crystal having a grain size of about 6 μm are mixed. In the region grown into crystals, island-like crystals are formed as in Example 1, and the boundaries between the island-like crystals are unclear.

As shown in FIG. 25, Comparative Example 5 (cerium composition ratio: 0%, hydrogen source partial pressure: 8.2 × 10 ⁻⁴ Pa) is different from Example 1 only in that cerium is not doped. However, after annealing, a large number of columnar crystals with a clear grain boundary having a grain size of 1 μm or more are formed.

Comparative Example 6 (cerium composition ratio: 0%, hydrogen source partial pressure: 1.2 × 10 ⁻³ Pa) is different from Example 1 in that cerium is not doped, and the hydrogen source partial pressure is also in Example 1. Higher than. However, as shown in FIG. 26, a large number of island crystals having a particle size of about 1 μm are formed as in Example 1, but the boundaries between the island crystals are unclear.

  The following knowledge is obtained from FIGS. First, cerium has an effect of promoting crystal bonding of indium oxide, and is considered to be a starting point for crystal growth of indium oxide in an amorphous state. Therefore, comparing FIG. 23 (Comparative Example 1) and FIG. 25 (Comparative Example 5), it is considered that the grain boundary grain size in indium oxide decreases as the concentration of cerium increases.

  On the other hand, hydrogen combines with oxygen and indium during film formation to inhibit indium oxide crystal growth and form an indium oxide amorphous. However, by annealing, hydrogen breaks the bond with oxygen and indium and leaves the indium oxide. As a result, oxygen and indium that have broken bonds are bonded and crystallized. However, the higher the concentration of hydrogen in indium oxide before annealing, the higher the amorphousness of indium oxide (the crystallinity decreases). Therefore, it is considered that amorphousness cannot be eliminated even by annealing.

  Therefore, in Comparative Example 1 shown in FIG. 23, since the composition ratio of hydrogen is not so amorphous, it is considered that small columnar crystals (based on cerium) with clear grain boundaries were generated by annealing. It is done. Further, in Example 1 shown in FIG. 22, it is considered that a large number of island crystals were formed because the composition ratio of hydrogen was such that amorphousness was eliminated by annealing. Furthermore, in Comparative Example 3 shown in FIG. 24, since the composition ratio of hydrogen is somewhat difficult to eliminate amorphousness by annealing, the amorphous structure is eliminated and a region where a large number of island crystals are formed and amorphous It is thought that the region as it was was formed.

  In Comparative Example 5 shown in FIG. 25, since the composition ratio of hydrogen is such that cerium does not have much amorphousness in indium oxide without addition, columnar crystals with clear grain boundaries are generated by annealing. It is done. In Example 6 shown in FIG. 26, it is considered that a large number of island-like crystals were formed in the indium oxide to which cerium was not added because the composition ratio of hydrogen was such that amorphousness was eliminated by annealing.

  FIG. 27 shows X-ray diffraction measurement data after annealing in Example 1, Comparative Example 1, and Comparative Example 3. As shown in FIG. 27, for example, when the peak of (222) is compared, Example 1 has the highest intensity, and among these, it can be said that the crystallinity is the highest. On the other hand, in Comparative Example 1, since the grain boundaries are generated at a high density, it is considered that the crystallinity is lower than that of Example 1, and the peak of (222) is smaller than that of Example 1. In Comparative Example 3, island-like crystals similar to those in Example 1 are formed. However, since the amorphous region is large, it is considered that the peak of (222) is smaller than that in Example 1.

Next, the island-like crystals observed in Example 1, Comparative Example 3, and Comparative Example 6 are considered.
As described above, in Example 1, the hole mobility is maintained at a value of 120 cm ² / (V · s) or more when the oxygen introduction ratio is 9% or more, as shown in FIGS. Also as shown in Figure 19, the plot data of Example 1, are arranged on the curve mu _I due to ionized impurity scattering, the Hall mobility can be considered not been little affected grain boundary scatter.

In Comparative Example 6, as shown in FIGS. 17 and 18, the hole mobility is maintained at a value of 100 cm ² / (V · s) or more at an oxygen introduction ratio of 9 or 5% or more. Further, as shown in FIG. 20, plot data of Comparative Example 6 are aligned in close proximity to the curve mu _I due to ionized impurity scattering, believed hole mobility is not much affected by grain boundary scattering .

  As shown in FIGS. 22 and 26, in Example 1 and Comparative Example 6, a large number of island-like crystals are observed, but the boundary has an unclear structure. From the above, in the transparent conductive film according to Example 1 and Comparative Example 6, island-shaped crystals that form a polycrystalline structure, and buffer crystals that are arranged so as to fill between the adjacent island-shaped crystals, It is thought that it has. It is this buffer crystal that forms the unclear boundary of the aforementioned island-like crystals.

  The buffer crystal is considered to be formed as follows. First, in Example 1 and Comparative Example 6, by annealing after film formation, microcrystals serving as seeds of island-like crystals are formed in the form of dots (centered on cerium when cerium is present), and this is the surrounding amorphous portion. To grow. At this time, hydrogen is released from the amorphous portion, and oxygen and indium which are free from bonding due to the separation are bonded, and if cerium is present, this bonding is supported. However, the island-like crystal in the early stage of growth has an ambiguous boundary with the amorphous part, and as the distance from the island-like crystal goes to the amorphous part, the long-range order is gradually lost, only the short-range order remains, and finally the short-range order. The arrangement is gradually lost. Thus, the portion where the crystal structure changes in a gradation is the buffer crystal.

  Then, when the growth of the island-shaped crystal proceeds, the buffer crystal around the first island-shaped crystal and the buffer crystal around the second island-shaped crystal located at a different position from the first island-shaped crystal. Will contact each other, but both have a short-range order, so they mix. However, since the crystal orientations of the first island crystal and the second island crystal are different from each other, the growth of the first island crystal and the second island crystal is completed with the buffer crystal remaining. Become.

  The buffer crystal formed in this way is formed by moving the first island-shaped crystal from the first island-shaped crystal connected to the buffer crystal to the second island-shaped crystal connected to the buffer crystal via the buffer crystal. The crystal structure changes continuously from the crystal structure to the crystal structure of the second island-like crystal.

  When the buffer crystal has the above-described crystal structure, the short-range order is maintained in the buffer crystal and at the boundary between the island-shaped crystal and the buffer crystal. For this reason, it is possible to reduce grain boundary scattering received when carriers move from the first island-shaped crystal to the second island-shaped crystal via the buffer crystal. As a result, the carriers have electrical characteristics according to the relationship between the carrier density and the hole mobility mainly due to the influence of ionized impurity scattering, and can have a high hole mobility. In Comparative Example 3 shown in FIG. 24, island-like crystals are also observed. However, if only this island-like crystal portion is present, it is considered that hole mobility equivalent to that in Example 1 and Comparative Example 6 can be obtained.

  In this embodiment, the case where indium oxide is doped with cerium has been described. However, other lanthanoid elements can also be applied. Further, the transparent conductive film of the present embodiment can be appropriately applied to image display devices such as liquid crystal display devices and organic electroluminescence devices, solar cells such as crystal solar cells, thin film solar cells, and dye-sensitized solar cells, electronic components, and the like. .

  By appropriately adjusting the concentration of cerium and hydrogen, it can be used as a transparent conductive film having high hole mobility, a device or a solar cell using the transparent conductive film, and a method for producing the transparent conductive film.

DESCRIPTION OF SYMBOLS 10 ......... Substrate, 12 ......... Transparent conductive film, 100 ......... Film forming apparatus, 102 ......... Load lock chamber, 104 ......... Heating chamber, 106 ......... Heater, 110 ......... Film formation Chamber, 112 ......... Crucible, 114 ......... Arc plasma gun, 116 ......... Introduction tube, 118 ......... Introduction tube, 120 ......... Introduction tube, 122 ......... Introduction tube, 124 ......... Mass spectrometry apparatus,

Claims (4)

A transparent conductive film having a polycrystalline structure of indium oxide containing hydrogen and a lanthanoid element,
A number of island-like crystals constituting the polycrystalline structure;
Buffer crystals arranged so as to fill between the island crystals adjacent to each other,
The buffer crystal is
From the first island-shaped crystal connected to the buffer crystal to the second island-shaped crystal connected to the buffer crystal via the buffer crystal, the crystal structure of the first island-shaped crystal leads to the second island-shaped crystal. Having a crystal structure that continuously changes to the crystal structure of the island-shaped crystals of
The lanthanoid element is cerium, and its atomic composition percentage is 0.23% or more,
A transparent conductive film having a hole mobility of 120 cm ² / (V · s) or more. An apparatus comprising the transparent conductive film according to claim 1 . A solar cell comprising the transparent conductive film according to claim 1 . A method for producing a transparent conductive film having a polycrystalline structure of indium oxide containing hydrogen and a lanthanoid element,
The lanthanoid element is cerium, and a sintered body having an atomic composition percentage of 0.23% or more is used as an evaporation source, and a partial pressure of the hydrogen source is 4.2 × 10 ⁻⁴ Pa to 5.4 × 10. Adjust the flow rate of hydrogen gas to ^-4 Pa,
A plurality of island crystals forming the polycrystalline structure, and a buffer crystal disposed so as to fill a space between the adjacent island crystals, and the buffer crystal is connected to the buffer crystal. The crystal structure of the second island-shaped crystal from the crystal structure of the first island-shaped crystal as it goes from the first island-shaped crystal to the second island-shaped crystal connected to the buffer crystal via the buffer crystal A method for producing a transparent conductive film, characterized in that the film is formed so as to have a crystal structure that changes continuously to a hole mobility of 120 cm ² / (V · s) or more .

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