JP7527768B2 - Phototransistors and Electronic Devices - Google Patents

Description

This disclosure relates to a phototransistor using quantum dots and an electronic device equipped with such a phototransistor.

An example of a phototransistor (optical transistor) using quantum dots is disclosed in Non-Patent Document 1. In the phototransistor in Non-Patent Document 1, a quantum dot layer is disposed on an organic semiconductor layer using DPP-DTT, and a drain current (photocurrent) flows in the organic semiconductor layer.

Zou et al., Adv. Optical Mater. (2018)1800324

However, in such phototransistors, there is generally a demand for improving the device characteristics. It is desirable to provide a phototransistor capable of improving the device characteristics, and an electronic device equipped with such a phototransistor.

A phototransistor according to an embodiment of the present disclosure includes a semiconductor substrate having a gate electrode, an insulating film formed on the semiconductor substrate, a source electrode and a drain electrode spaced apart from each other on the insulating film, a quantum dot layer disposed between the source electrode and the drain electrode and serving as a path for a drain current as a photocurrent flowing between the source electrode and the drain electrode, and a self-assembled monolayer disposed between the insulating film and the quantum dot layer and between the source electrode and the drain electrode. The quantum dot layer has a plurality of quantum dots of a core-shell type and conductive ions dispersed among the plurality of quantum dots. The core-shell quantum dot has a core made of a semiconductor material, a shell that covers the periphery of the core and is made of a semiconductor material, and a ligand that covers the periphery of the shell and is made of an insulating material. In addition, when the drain current flowing through the quantum dot layer in a bright state in which the quantum dot layer is irradiated with a predetermined light is Id(L), and the drain current flowing through the quantum dot layer in a dark state in which the quantum dot layer is not irradiated with a predetermined light is Id(D), the value of (the above Id(L)/the above Id(D)) is greater than ¹⁰ .

An electronic device according to one embodiment of the present disclosure includes one or more phototransistors according to one embodiment of the present disclosure.

In the phototransistor and electronic device according to an embodiment of the present disclosure, a quantum dot layer that serves as a path for a photocurrent (drain current) is provided with a plurality of core-shell type quantum dots having the above-mentioned core, shell, and ligand , and conductive ions dispersed among the plurality of quantum dots. As a result, in a bright state where light is irradiated, the mobility of electrons is significantly increased compared to a dark state where light is not irradiated, and the difference in the photocurrent value between the bright state and the dark state is also significantly increased. In addition, since the value of (Id(L)/Id(D)) is greater than 10 ⁵ , the characteristics of the device (phototransistor) are actually improved.

In a phototransistor according to one embodiment of the present disclosure, the thickness of the quantum dot layer may be set to, for example, a value in the range of 22 nm or more and 175 nm or less. In this case, the difference in the photocurrent value between the bright state and the dark state is particularly increased, and the device characteristics are further improved. In this case, the thickness of the quantum dot layer may be set to, for example, 75 nm. In this case, the difference in the photocurrent value between the bright state and the dark state is maximized, and the device characteristics are further improved.

In the core-shell quantum dot, the core is made of, for example, CdSe, the shell is made of, for example, CdS , the ligand is made of, for example, thiocyanate, and the conductive ion is, for example, Cd ion (Cd ²⁺ ).

According to the phototransistor and electronic device according to one embodiment of the present disclosure, the quantum dot layer, which serves as the path of the photocurrent (drain current), is provided with multiple core-shell type quantum dots and conductive ions dispersed among the multiple quantum dots, so that the difference in photocurrent value between the bright state and the dark state can be significantly increased. This makes it possible to improve the characteristics of the device (phototransistor).

1 is a perspective view illustrating a schematic example of an overall configuration of a phototransistor according to an embodiment of the present disclosure; 2 is a schematic diagram illustrating a detailed configuration example of the quantum dot illustrated in FIG. 1 . 2 is a flow chart showing an example of a method for forming the quantum dot layer shown in FIG. 1 in the order of steps. 1A and 1B are schematic diagrams for explaining an example of the operation of a phototransistor in a dark state and a light state. 1A and 1B are schematic diagrams illustrating an example of characteristics of a phototransistor in a dark state and a light state. FIG. 13 is a diagram illustrating an example of characteristics of a phototransistor according to an embodiment of the present disclosure. FIG. 13 is a diagram illustrating another example of characteristics of a phototransistor according to an embodiment of the present disclosure. FIG. 13 is a diagram illustrating another example of characteristics of a phototransistor according to an embodiment of the present disclosure. FIG. 13 is a diagram illustrating another example of characteristics of a phototransistor according to an embodiment of the present disclosure.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The description will be made in the following order.
1. Embodiment (Example of the configuration of a phototransistor using core-shell type quantum dots)
2. Application examples (applications of phototransistors to electronic devices)
3. Modifications

1. Preferred embodiment
[Overall configuration of phototransistor]
1 is a schematic perspective view illustrating an example of the overall configuration of a phototransistor (phototransistor 1) according to an embodiment of the present disclosure. The phototransistor 1 is a field effect transistor (FET) capable of detecting light in a predetermined wavelength range, as will be described in detail later.

As shown in FIG. 1, the phototransistor 1 includes a semiconductor substrate 10 having a gate electrode 11, an insulating film 12, a self-assembled monolayer 13, a quantum dot layer 14, and a pair of electrodes 15a and 15b.

(Semiconductor substrate 10, gate electrode 11)
The semiconductor substrate 10 is a substrate using various semiconductors. An example of such a semiconductor substrate 10 is an n-type Si (silicon) substrate.

As described above, in the example of FIG. 1, the gate electrode 11 is provided on the semiconductor substrate 10 and functions as a back gate electrode. However, the gate electrode 11 is not limited to such a back gate electrode and may have other structures. As shown in FIG. 1, a predetermined gate voltage Vg is applied to such a gate electrode 11 between the ground (and the electrode 15a as a source electrode, which will be described later).

(Insulating film 12, self-assembled monolayer 13)
1, the insulating film 12 is formed on the semiconductor substrate 10. The insulating film 12 is made of an insulating material such as _SiO2 (silicon dioxide), and the thickness of the insulating film 12 is, for example, about 500 nm.

As shown in FIG. 1, the self-assembled monolayer 13 is formed in the region between the electrodes 15a and 15b on the insulating film 12. This self-assembled monolayer 13 is a film called a SAM (Self-Assembled Monolayer), and is designed to reconstruct the surface of the semiconductor substrate 10, which is, for example, a Si substrate. Such a self-assembled monolayer 13 is made of materials such as n-octadecylphosphonic acid, bis(trimethylsilyl)amine, and 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and the thickness of the self-assembled monolayer 13 is, for example, about 10 nm.

(Quantum dot layer 14)
1, the quantum dot layer 14 is formed in a region between the electrodes 15a and 15b on the self-assembled monolayer 13. The quantum dot layer 14 is a layer that serves as a path (current path) of a drain current Id as a photocurrent that flows between the electrodes 15a and 15b (a source electrode and a drain electrode, which will be described later in detail). The thickness d of the quantum dot layer 14 is, for example, within a range of 22 nm to 175 nm (22 nm≦d≦175 nm), which will be described later in detail.

Such a quantum dot layer 14 has a plurality of quantum dots 141 and a plurality of conductive ions 142, as shown in FIG.

The quantum dots 141 are dispersed in the quantum dot layer 14 and are configured in a core-shell structure, which will be described later. A detailed configuration example of such quantum dots 141 will be described later (Figure 2).

1, the conductive ions 142 are dispersed among the multiple quantum dots 141. Examples of the conductive ions 142 include metal ions such as cadmium ions (Cd ²⁺ ).

(Electrodes 15a, 15b)
1, the electrodes 15a and 15b are disposed on the insulating film 12 at a distance from each other so as to sandwich the self-assembled monolayer 13 and the quantum dot layer 14 therebetween. In the example of FIG. The electrode 15a is connected to the ground, and a predetermined drain voltage Vds is applied between the electrodes 15a and 15b. In other words, in the example of FIG. 1, the electrode 15a is a source electrode. and the electrode 15b functions as a drain electrode.

Each of these electrodes 15a and 15b is made of, for example, various metal materials, and an example is an electrode with a two-layer structure of Au (gold) and Cr (chromium). In this case, the thickness of the Au layer and the Cr layer is, for example, (Au/Cr) = (17 nm/3 nm).

Note that electrode 15a corresponds to a specific example of a "source electrode" in this disclosure, and electrode 15b corresponds to a specific example of a "drain electrode" in this disclosure.

[Detailed configuration of quantum dot 141]
Next, a detailed configuration example of the quantum dots 141 (and the quantum dot layer 14) will be described with reference to FIGS.

Figures 2(A) and 2(B) are schematic diagrams showing examples of the detailed configuration of quantum dot 141.

As shown in FIG. 2A, the quantum dot 141 is a core-shell quantum dot, and has a core 21, a shell 22, and a ligand 23.

As shown in FIG. 2A, the core 21 is a spherical portion located in the center of the quantum dot 141. The core 21 is made of, for example, various semiconductor materials, one example of which is the compound semiconductor CdSe (cadmium selenide).

As shown in FIG. 2A, the shell 22 is a film-like portion that surrounds the core 21. The shell 22 is also made of various semiconductor materials, such as the compound semiconductor CdS (cadmium sulfide).

As shown in FIG. 2(A), the ligand 23 is disposed so as to cover the periphery of the shell 22. The ligand 23 is made of, for example, various insulating materials, one example of which is thiocyanate (S-C≡N).

The energy levels corresponding to the positions of the core 21, shell 22, and ligand 23 in such a quantum dot 141 are, for example, as shown in Figures 2(B) and 2(C). That is, the energy level of the shell 22 is higher than the energy level of the core 21, and the energy level of the ligand 23 is higher than the energy level of the shell 22. In other words, a so-called quantum well structure is realized in this quantum dot 141.

[Method of forming quantum dot layer 14]
Here, the quantum dot layer 14 having such core-shell type quantum dots 141 and the above-mentioned conductive ions 142 can be formed, for example, as shown in Fig. 3. Fig. 3(A) to Fig. 3(C) are flow charts showing an example of a method for forming the quantum dot layer 14 in the order of steps.

First, as shown in FIG. 3(A), a quantum dot film is formed in which quantum dots 141 having the aforementioned core-shell structure (core 21, shell 22, and ligand 23) are dispersed.

Next, as shown in FIG. 3B, the quantum dot film thus formed is subjected to a ligand exchange process. This narrows the distance between the quantum dots 141 in the quantum dot film.

Next, as shown in FIG. 3(C), the quantum dot film is subjected to a predetermined surface modification and filling process, thereby adding the conductive ions 142 described above to the quantum dot film.

Then, as indicated by the dashed arrows in FIG. 3, the formation steps in FIG. 3(A) to FIG. 3(C) are repeated as appropriate. This completes the quantum dot layer 14 shown in FIG. 1 and FIG. 2.

[Actions, actions and effects]
Next, the operation, function and effects of the phototransistor 1 of the present embodiment will be described in detail with reference to FIGS. 4 to 9 in addition to FIGS. 1 to 3.

A. Operation
Fig. 4 is a schematic diagram showing an example of the operation of the phototransistor 1 of the present embodiment in a dark state and a light state. Fig. 5 is a schematic diagram showing an example of the characteristics of the phototransistor (an example of the corresponding relationship between the gate voltage Vg and the drain current Id) in a dark state and a light state. Fig. 5(A) and Fig. 5(B) each show an example of the characteristics of a general phototransistor, and Fig. 5(C) shows an example of the characteristics of the phototransistor 1 of the present embodiment.

First, in the dark state shown in FIG. 4A, the phototransistor 1 is not irradiated with a specific light (irradiation light Lin) described later. Therefore, in this dark state, the electrons e cannot overcome a specific energy barrier (such as an energy gap in a quantum well structure) in the semiconductor layer (quantum dot layer 14) in the phototransistor 1 (see arrow P11). As a result, in this dark state, the drain current Id as a photocurrent does not flow between the source electrode and drain electrode (between electrodes 15a and 15b) in the phototransistor 1.

On the other hand, in the bright state shown in FIG. 4B, external illumination light (incident light) Lin is irradiated onto the phototransistor 1. Therefore, in this dark state, electrons e are excited in the semiconductor layer (quantum dot layer 14) in the phototransistor 1 by the light energy of the illumination light Lin (see arrow P12), and the excited electrons e are able to overcome the energy barrier described above (see arrow P13). As a result, in this bright state, a drain current Id flows as a photocurrent between the source electrode and drain electrode (between electrodes 15a and 15b) in the phototransistor 1.

Then, by detecting the change in the photocurrent (drain current Id) between the dark state and the light state (the difference between the on and off states of the photocurrent), it becomes possible to use the phototransistor 1 of this embodiment as an optical sensor, for example.

Incidentally, the phototransistor 1 of this embodiment may have, for example, the following structure. That is, the wavelength range of light detectable by this phototransistor 1 (the above-mentioned irradiated light L in ) may be selectively set according to the energy level structure in the quantum dot layer 14 described above (see FIG. 2(B) and FIG. 2(C)). Specifically, for example, when irradiated light L in a wavelength region on the long wavelength side (infrared region or red region) is to be detectable, it is necessary to set the energy gap in the quantum dot layer 14 relatively small. On the other hand, when irradiated light L in a wavelength region on the short wavelength side (such as ultraviolet region or blue region) is to be detectable, the energy gap in the quantum dot layer 14 may be set relatively large.

In the characteristic example (of a typical phototransistor) shown in FIG. 5(A), the above-mentioned dark state characteristic G11 and the above-mentioned bright state characteristic G12 are as follows. That is, in the characteristics G11 and G12, when the gate voltage Vg is equal to or greater than the threshold voltages Vth11 and Vth12, respectively, the drain current Id increases significantly as the gate voltage Vg increases. Also, in the example of FIG. 5(A), when switching from the dark state (characteristic G11) to the bright state (characteristic G12) (see dashed arrow P21), the drain current Id increases almost uniformly.

In the characteristic example shown in FIG. 5(B) (an example of a phototransistor using a high-mobility semiconductor), the characteristic G21 in the dark state and the characteristic G22 in the bright state are as follows. That is, in this case, when the gate voltage Vg is equal to or greater than the threshold voltages Vth21 and Vth22 in the characteristics G21 and G22, respectively, the drain current Id increases significantly with the increase in the gate voltage Vg. Also, in the example of FIG. 5(B), when the dark state (characteristic G21) is switched to the bright state (characteristic G22) (see the dashed arrow P22), the drain current Id increases almost uniformly. However, in the example of FIG. 5(B), since a high-mobility semiconductor is used as described above, the slope of the drain current Id in the cases of Vg≧Vth21 and Vg≧Vth22 is steeper than in the example of FIG. 5(A).

On the other hand, in the characteristic example shown in FIG. 5(C) (an example of the phototransistor 1 of this embodiment), the characteristic G31 in the dark state and the characteristic G32 in the bright state are as follows. That is, first, in the characteristic G32 in the bright state, as in the cases of FIG. 5(A) and FIG. 5(B), when the gate voltage Vg becomes equal to or greater than the threshold voltage Vth32, the drain current Id increases significantly in response to an increase in the gate voltage Vg. In contrast, in the characteristic G31 in the dark state, the drain current Id is almost constant (≒0) regardless of the change in the gate voltage Vg. This is because, for example, the threshold voltage in the dark state is significantly higher than the threshold voltage Vth32 in the bright state. In other words, in the example of FIG. 5(C), it can be said that the drain current Id is very unlikely to flow in the dark state. Therefore, in the example of FIG. 5(C), when switching from the dark state (characteristic G31) to the bright state (characteristic G32) (see dashed arrow P23), the increase in drain current Id becomes much larger than in the examples of FIG. 5(A) and FIG. 5(B), especially in the voltage range where the gate voltage Vg is relatively high.

Considering the above, when considering the photoresponse of the phototransistor (the amount of change in the photocurrent (drain current Id) between the dark and light states), it can be said that among the examples of Figures 5(A) to 5(C) above, the example of Figure 5(C) is the most ideal example of photoresponse. This is because, as mentioned above, in the example of Figure 5(C), the difference in the photocurrent value (the value of the drain current Id) between the light and dark states of the phototransistor is the largest.

Incidentally, in conventional phototransistors using quantum dots, as in the phototransistor of Non-Patent Document 1 mentioned above, the drain current flows as a photocurrent not in the quantum dot layer but in another semiconductor layer (such as an organic semiconductor layer). In such conventional phototransistors, the characteristics are as shown in Figure 5(A) or Figure 5(B) above, for example, and the device (phototransistor) characteristics (photoresponse) are insufficient.

(B. Actions and Effects)
In contrast to this, the phototransistor 1 of the present embodiment focuses on the fact that, among quantum dots, core-shell quantum dots are particularly difficult for current to flow through (for example, the threshold voltage shows a very high value as shown by the characteristic G31 in FIG. 5C described above), and is configured as follows: That is, unlike the conventional phototransistor described above, the quantum dot layer 14 using core-shell quantum dots 141 is set as a path through which the drain current Id, which serves as a photocurrent, flows, and conductive ions 142 that can become a current path in the quantum dot layer 14 are dispersed and arranged in this quantum dot layer 14.

Specifically, in this phototransistor 1, as shown in Figures 1 and 2, the quantum dot layer 14, which serves as the path of the photocurrent (drain current Id), is provided with a number of core-shell type quantum dots 141 and conductive ions 142 dispersed among the quantum dots 141.

As a result, in the phototransistor 1, for example, as described in detail below, in the bright state where the quantum dot layer 14 is irradiated with the irradiation light Lin, the mobility μ of the electrons e is significantly increased compared to the dark state where the quantum dot layer 14 is not irradiated with the irradiation light Lin. As a result, in this phototransistor 1, the difference in the photocurrent value (the value of the drain current Id) between the bright state and the dark state is also significantly increased compared to the case of a conventional phototransistor (for example, see the example of Figure 5 (C) described above).

(Example)
Various examples of characteristics of the phototransistor 1 according to the embodiment of the present invention will now be described in detail with reference to FIGS.

6 shows an example of the correspondence relationship between the gate voltage Vg and the drain current Id in the phototransistor 1 when the quantum dot layer 14 has a thickness d=175 nm, and an example of the correspondence relationship between the drain voltage Vds and the drain current Id. Note that the characteristic example for "No Cd ²⁺ " shown in Fig. 6 corresponds to a comparative example in which cadmium ions (Cd ²⁺ ), which are an example of the conductive ions 142 described above, are not dispersed in the quantum dot layer.

In the characteristic example shown in FIG. 6, in the comparative example in which the conductive ions 142 are not dispersed in the quantum dot layer, it can be seen that the drain current Id hardly flows even when the gate voltage Vg and drain voltage Vds are set relatively high. This is presumably because, as described above, current flows very little in the core-shell type quantum dots 141, and the conductive ions 142 that can be a current path in the quantum dot layer are not dispersed. In contrast, in the example in which the conductive ions 142 are dispersed in the quantum dot layer 14, it can be seen that a relatively large drain current Id flows even when the gate voltage Vg and drain voltage Vds are low compared to the comparative example. This is presumably because, unlike the comparative example, the conductive ions 142 that can be a current path in the quantum dot layer 14 are dispersed in the quantum dot layer 14.

Figure 7 shows an example of the characteristics of the phototransistor 1 in the dark and bright states described above (an example of the corresponding relationship between the gate voltage Vg and the drain current Id). Specifically, Figures 7(A), 7(B), and 7(C) show such example characteristics when the quantum dot layer 14 has a film thickness d of about 22 nm, about 75 nm, and about 175 nm (see 22 nm≦d≦175 nm, which is an example of the range of film thickness d described above). Note that all of Figures 7(A) to 7(C) show an example of the characteristics when the drain voltage Vds=15 V, and ultraviolet light (UV light) is used as an example of the irradiated light Lin in the bright state.

In all of the characteristic examples shown in Figures 7(A) to 7(C), like the example in Figure 5(C) described above, the drain current Id is ≈ 0 in the dark state, and the difference in the photocurrent value (the value of the drain current Id) between the bright state and the dark state is very large. It can also be seen that as the value of the film thickness d of the quantum dot layer 14 increases (in the order of Figures 7(A) to 7(C)), the value of the drain current Id in the bright state also gradually increases.

Figure 8 (A) shows an example of the relationship between the film thickness d of the quantum dot layer 14 and the drain current Id(L) in the bright state (when the gate voltage Vg = 0 V and the drain voltage Vds = 15 V). Also, Figure 8 (B) shows an example of the relationship between the film thickness d of the quantum dot layer 14 and the mobility μ(L) of the electron e in the bright state and the mobility μ(D) of the electron e in the dark state.

In the characteristic example shown in FIG. 8(A), it can be seen that the value of the drain current Id(L) as the photocurrent in the bright state increases almost linearly as the thickness d of the quantum dot layer 14 increases. In addition, in the characteristic example shown in FIG. 8(B), when comparing the mobility μ(D) of the electron e in the dark state with the mobility μ(L) of the electron e in the bright state, it can be seen that the mobility μ of the electron e increases significantly (by about several tens of times) by switching from the dark state to the bright state. Furthermore, in the characteristic example of FIG. 8(B), it can be seen that both the mobility μ(D) and μ(L) of the electron e increase as the thickness d of the quantum dot layer 14 increases, and the rate of increase is particularly large in the mobility μ(L) of the electron e in the bright state.

9 shows an example of the relationship between the gate voltage Vg and the ratio (=Id(L)/Id(D)) of the drain current Id(L) in the bright state to the drain current Id(D) in the dark state, for each of the thicknesses d of the quantum dot layer 14 of about 22 nm, about 75 nm, and about 175 nm. Note that the dashed line G101 in FIG. 9 shows the maximum value ((Id(L)/Id(D)≈8× ¹⁰⁴ ) in a phototransistor using conventional quantum dots as a reference example (see Chen et al., Adv. Mater. 2017).

9, it can be seen that the value of (Id(L)/Id(D)) in the phototransistor 1 is greater than 10 ⁵ and exceeds the value in the above-mentioned reference example (≈8×10 ⁴ ) when the quantum dot layer 14 has a thickness d of about 22 nm and about 75 nm. In other words, it was confirmed that there are cases in this embodiment where (Id(L)/Id(D))>10 ⁵ .

As described above, in this embodiment, the quantum dot layer 14, which serves as the path of the photocurrent (drain current Id), is provided with a plurality of core-shell type quantum dots 141 and conductive ions 142 dispersed among these quantum dots 141, so that the difference in photocurrent value between the bright state and the dark state can be significantly increased. Therefore, in this embodiment, it is possible to improve the characteristics (photoresponse) of the device (phototransistor 1).

In addition, in this embodiment, if the wavelength range of the light (illumination light L in ) detectable by the phototransistor 1 is selectively set according to the energy level structure in the quantum dot layer 14, the following occurs. That is, the wavelength range of the illumination light L in detectable by the phototransistor 1 can be arbitrarily adjusted according to such an energy level structure. As a result, it is possible to improve the convenience of using the phototransistor 1.

Furthermore, in this embodiment, when the film thickness d of the quantum dot layer 14 is set to a value within the range of 22 nm or more and 175 nm or less, the difference in the photocurrent value between the bright state and the dark state can be particularly increased, and the characteristics of the phototransistor 1 can be further improved. In this case, particularly, when the film thickness d of the quantum dot layer 14 is set to 75 nm, the difference in the photocurrent value between the bright state and the dark state is maximized, and the characteristics of the phototransistor 1 can be further improved.

In addition, in this embodiment, when the value of (Id(L)/Id(D)) is set to be greater than 10 ⁵ with respect to the drain current Id(L) in the bright state and the drain current Id(D) in the dark state, it is possible to actually improve the characteristics of the phototransistor 1.

2. Application Examples
Next, an example of application of the phototransistor 1 described in the above embodiment to an electronic device will be described.

The phototransistor 1 described in the above embodiment can be applied to various electronic devices. In other words, one or more phototransistors 1 can be built into such various electronic devices.

Specific examples of such electronic devices include imaging devices (such as high-sensitivity cameras), motion sensors that use infrared light (such as automatic doors), ultraviolet sensors in the ultraviolet range, and illuminance sensors that automatically control the brightness of monitors on smartphones, etc.

3. Modifications
Although the technology of the present disclosure has been described above by giving embodiments and application examples, the technology is not limited to these embodiments and the like, and various modifications are possible.

For example, the configuration (shape, arrangement, number, material, etc.) of each component described in the above embodiment is not limited, and other shapes, arrangements, numbers, materials, etc. may be used. In addition, the numerical examples and characteristic examples of the phototransistor 1 are not limited to those described in the above embodiment, and other numerical examples and characteristic examples may be used.

In addition, in the above embodiment, a specific method for forming the quantum dot layer 14 has been described, but the method is not limited to the method described in the above embodiment, and the quantum dot layer 14 may be formed using other methods.

Furthermore, with this technology, it is possible to apply the contents described so far in any combination.

The effects described in this specification are merely examples and are not limiting, and other effects may also be present.

1...phototransistor, 10...semiconductor substrate, 11...gate electrode, 12...insulating film, 13...self-assembled monolayer, 14...quantum dot layer, 141...quantum dot, 142...conductive ion, 15a, 15b...electrodes, 21...core, 22...shell, 23...ligand, Vg...gate voltage, Vds...drain voltage, Id, Id(L), Id(D)...drain current (photocurrent), e...electrons, Lin...irradiated light, Vth11, Vth12, Vth21, Vth22, Vth32...threshold voltage, d...film thickness, μ(L), μ(D)...mobility.

Claims (5)

a semiconductor substrate having a gate electrode;
an insulating film formed on the semiconductor substrate;
a source electrode and a drain electrode spaced apart from each other on the insulating film;
a quantum dot layer disposed between the source electrode and the drain electrode and serving as a path for a drain current as a photocurrent flowing between the source electrode and the drain electrode;
a self-assembled monolayer disposed between the source electrode and the drain electrode, between the insulating film and the quantum dot layer;
The quantum dot layer is
A plurality of quantum dots having a core-shell structure;
and conductive ions dispersed among the quantum dots;
The core-shell quantum dots are
A core made of a semiconductor material;
a shell surrounding the core and made of a semiconductor material;
a ligand that covers the shell and is made of an insulating material;
It has
The drain current flowing through the quantum dot layer in a bright state in which the quantum dot layer is irradiated with a predetermined light is defined as Id(L),
When the drain current flowing through the quantum dot layer in a dark state in which the quantum dot layer is not irradiated with the predetermined light is Id(D),
A phototransistor in which the value of (Id(L)/Id(D)) is greater than 10 ⁵ . The phototransistor according to claim 1 , wherein the quantum dot layer has a thickness within a range of 22 nm to 175 nm. The phototransistor according to claim 2 , wherein the quantum dot layer has a thickness of 75 nm. In the core-shell quantum dot, the core is made of CdSe, the shell is made of CdS, and the ligand is made of thiocyanate;
4. The phototransistor according to claim 1, wherein the conductive ions are Cd ions (Cd ²⁺ ). one or more phototransistors;
The phototransistor is
a semiconductor substrate having a gate electrode;
an insulating film formed on the semiconductor substrate;
a source electrode and a drain electrode spaced apart from each other on the insulating film;
a quantum dot layer disposed between the source electrode and the drain electrode and serving as a path for a drain current as a photocurrent flowing between the source electrode and the drain electrode;
a self-assembled monolayer disposed between the source electrode and the drain electrode, between the insulating film and the quantum dot layer;
The quantum dot layer is
A plurality of quantum dots having a core-shell structure;
and conductive ions dispersed among the quantum dots;
The core-shell quantum dots are
A core made of a semiconductor material;
a shell surrounding the core and made of a semiconductor material;
a ligand that covers the shell and is made of an insulating material;
It has
The drain current flowing through the quantum dot layer in a bright state in which the quantum dot layer is irradiated with a predetermined light is defined as Id(L),
When the drain current flowing through the quantum dot layer in a dark state in which the quantum dot layer is not irradiated with the predetermined light is Id(D),
An electronic device in which the value of (Id(L)/Id(D)) is greater than 10 ⁵ .

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