KR102316051B1 - Optical device having reduced trap states density on surface of quantum dot and method for manufacutring the same - Google Patents

Abstract

Embodiments include a substrate; one or more electrodes formed on the substrate; and a quantum dot layer electrically connected to the electrode, wherein a surface of the quantum dot layer has been subjected to oxidation treatment and a method of manufacturing the same.

Description

Optical device having a quantum dot surface with reduced trap level density, and method for manufacturing the same

Examples are colloidal It relates to a technique for controlling the density of trap states on the surface of a quantum dot made of a semiconductor crystal material, and more particularly, an optical device obtained by using a technique for reducing the density of trap states on the surface of a quantum dot by oxidizing the surface of the quantum dot, and a method for manufacturing the same is about

In the field of electronics, infrared (IR) technology is utilized in various aspects such as communication, material properties and night vision. In particular, recently, semiconductor-based infrared sensor technology is being used for LiDAR sensors in autonomous vehicles and optical networks.

In the past, in devices for outputting infrared rays, group III-V materials having a band gap in the infrared region were mainly used as semiconductor materials. However, group III-V semiconductors have a problem of high cost.

As an alternative to these III-V materials, interest in quantum dots (QDs) is increasing. Quantum dots are nanocrystal semiconductors that have scalable bandgap and solution processing capabilities. In particular, since it is cheaper than group III-V materials, it is being attempted as an alternative to group III-V materials in the field of photoelectron emitters/detectors.

A well-known factor limiting the device performance of quantum dots is the energy level present in the sub-bandgap, referred to as the trap level. Trap levels are sub-bandgap surface levels caused by dangling bonds or unpassivated surface atoms.

The trap state density can be reduced by controlling the oxidation state of the quantum dot surface. As a method of controlling the oxidation state of the surface of a material, there is a surface chemical treatment method using ligand substitution or an oxidizing agent, or a heat treatment method using a furnace.

In the case of applying the surface chemical treatment method, the surface chemical treatment method has a limitation in that an appropriate oxidizing agent must be individually applied to each quantum dot according to the type of quantum dot (PbS, PbSe, CdSe, CdS, CuInSe2, InP, CsPbI3, etc.) have.

On the other hand, when a heat treatment method using a furnace is applied, heat is applied to the quantum dots for several to several tens of minutes due to a slow ramp-up rate, thereby causing diffusion of atoms. Such diffusion of atoms causes changes in the structure of quantum dots, such as necking and sintering of nanocrystals. The quantum dot structure change lowers the device performance of the quantum dot, so it has a limit in that it cannot reach the performance of a photodetector including a III-V group semiconductor such as InGaAs.

Patent Registration Publication No. 10-1117261 (2012.02.09.)

According to one aspect of the present invention, it is an object of the present invention to provide an optical device having a reduced density of trap states on the surface of quantum dots using RTA, and a method for manufacturing the same, so as to be improved over the existing furnace method.

A method of manufacturing an optical device according to an aspect of the present invention includes: forming one or more electrodes on a substrate; forming a quantum dot layer electrically connected to the electrode; and oxidizing the surface of the quantum dot layer to form an oxide film.

In an embodiment, the quantum dot layer may be made of a colloidal semiconductor material.

In one embodiment, the quantum dot layer is a group II-VI compound, group II-V compound, group III-VI compound, group III-V compound, group IV-VI compound, group I-III-VI compound, II- It may consist of a material selected from any one of the group IV-VI compound, the group II-IV-V compound, and combinations thereof.

In an embodiment, the oxidation treatment may be an RTA oxidation treatment.

In an embodiment, the RTA oxidation treatment may oxidize the quantum dot surface so that the crystal structure of the quantum dot layer is not changed due to atomic diffusion.

In an embodiment, the RTA oxidation treatment may be performed in a temperature range of 100 °C or more and less than 170 °C.

An optical device according to another aspect of the present invention includes: a substrate; one or more electrodes formed on the substrate; and a quantum dot layer electrically connected to the electrode. Here, the surface of the quantum dot layer is oxidized.

In an embodiment, the surface of the quantum dot layer may be RTA oxidation-treated.

In an embodiment, the optical device may further include an oxide film formed on the surface of the quantum dot layer.

According to the method for manufacturing an optical device according to an aspect of the present invention, by applying RTA, it is possible to more precisely control the oxidation state of the surface of the quantum dot compared to the case where heat treatment using a furnace is applied without changing the structure of the quantum dot. For this reason, the trap level density can be reduced to the maximum.

As a result, device performance of quantum dots, such as reactivity and detectivity, can be improved, and an optical device having such improved performance can be obtained.

Effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

In order to more clearly explain the technical solutions of the embodiments of the present invention or the prior art, drawings necessary for the description of the embodiments are briefly introduced below. The same reference numbers are used to identify like elements shown in more than one figure. It should be understood that the following drawings are for the purpose of explaining the embodiments of the present specification and not for the purpose of limitation. In addition, some elements to which various modifications such as exaggeration and omission have been applied may be shown in the drawings below for clarity of description.
1 is a diagram illustrating a process of manufacturing an optical device according to an embodiment of the present invention.
2 is a diagram illustrating an electrode formed on a substrate and a pattern connected thereto according to an embodiment of the present invention.
3 is a diagram illustrating a quantum dot thin film formed on a substrate according to an embodiment of the present invention.
4 to 6 are diagrams for comparing the effects of the oxidation treatment method using the RTA and the furnace, according to various embodiments of the present invention.
7 to 9 are diagrams for explaining the temperature in the RTA oxidation process, according to various embodiments of the present invention.

When a part is referred to as being “above” another part, it may be directly on top of the other part, or the other part may be involved in between. In contrast, when a part is said to be "directly above" another part, the other part in between is not involved.

Terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising," as used herein, specifies a particular characteristic, region, integer, step, operation, element and/or component, and includes the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.

Terms indicating a relative space such as “below” and “above” may be used to more easily describe the relationship of one part shown in the drawings to another part. These terms are intended to include other meanings or operations of the device in use with the meanings intended in the drawings. For example, if the device in the figures is turned over, some parts described as being "below" other parts are described as being "above" other parts. Thus, the exemplary term “down” includes both the up and down directions. The device may be rotated 90 degrees or at other angles, and terms denoting relative space are interpreted accordingly.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, they are not interpreted in an ideal or very formal meaning.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily carry out the embodiments of the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

1 is a diagram illustrating a process of manufacturing an optical device according to an embodiment of the present invention.

Referring to FIG. 1 , one or more electrodes 11 are formed on a substrate 10 ( S11 ). The substrate 10 is a component that supports the electrodes and quantum dots included in the optical device. In an embodiment, the substrate 10 may be formed of any one of Si, SiO2, Al2O3, and combinations thereof.

2 is a diagram illustrating an electrode formed on a substrate and a pattern connected thereto according to an embodiment of the present invention.

The electrode 11 is made of a conductive material, and for example, may be made of a material selected from one of ITO, Pt, Cu, Ag, Al, Ti, Au, and combinations thereof.

The electrode 11 is formed to have an arrangement according to the use of the optical element. In addition, as shown in FIG. 2 , when a plurality of electrodes 11 are formed, a conductive pattern connecting the electrodes 11 is further formed on the substrate 10 .

3 is a diagram illustrating a thin film including quantum dots formed on a substrate according to an embodiment of the present invention.

After step S11 , a layer including quantum dots, hereinafter, a quantum dot layer 13 , is formed on the substrate 10 ( S13 ). As shown in FIG. 3 , the quantum dot layer 13 may be formed as a thin film.

A quantum dot is one of semiconductor materials, and is a nanocrystal material having a characteristic that a light absorption wavelength changes according to its size. The optical device of the present invention having quantum dots includes, for example, various quantum dot photodetectors or light emitting devices, such as photo-conductors, photodiodes, and phototransistors. .

In one embodiment, the quantum dot layer 13 may be made of a colloidal semiconductor material. The colloidal semiconductor material forming the nanocrystals is a group II-VI compound, a group II-V compound, a group III-VI compound, a group III-V compound, a group IV-VI compound, a group I-III-VI compound, and a group II- and a substance selected from the group consisting of a group IV-VI compound, a group II-IV-V compound, and combinations thereof. For example, colloidal semiconductor materials are ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN. , GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, TlSb, PbS, PbSe, PbTe, and combinations thereof.

The quantum dot layer 13 may be formed on the substrate 10 by coating, for example, using a spin coater, but is not limited thereto.

The oxidation state is adjusted to reduce the density of trap states on the surface of the quantum dot layer 13 (S15). In some embodiments, by oxidation treatment, the optical element 1 has an oxide film formed on the surface of the quantum dot layer.

The device performance of an optical device depends on the transport of carriers (including holes and electrons). For good device performance, these carriers must be transported unimpeded to the electrode. Trap states are energy states existing in a sub-band gap capable of trapping carriers of the quantum dot layer 13 traveling toward the electrode. If there are many trap levels, the carriers cannot reach the electrode because the energy of the carriers is lost as thermal energy or the like. Therefore, in order to improve the device performance of quantum dots, it is necessary to reduce the density of trap states. Controlling the oxidation state of the quantum dot surface can further reduce the density of trap states. Even when the quantum dot surface is oxidized too much, the trap state density is not minimized, and when the quantum dot surface is reduced too much, the trap state density is not minimized. Depending on the material constituting the quantum dot, the density of the trap state is further reduced when the oxidation state is appropriately controlled.

In one embodiment, the quantum dot surface is oxidized by RTA (Rapid Thermal Annealing) to control the oxidation state of the quantum dot surface (S15). After the step (S15), the trap level density decreases than before oxidation.

Quantum dots have a very large surface area to volume ratio, so when a surface modification process is performed, the characteristics of the quantum dot surface are greatly changed.

Oxidation treatment using a furnace takes about 30 minutes for temperature increase. When using a furnace, it is difficult to precisely control the oxidation state by heat treatment of the quantum dot surface through short and precise time control. In addition, in order to suppress a crystal structure change due to atomic diffusion, heat treatment at a high temperature (for example, 135 degrees or more) is limited in the oxidation treatment using a furnace.

On the other hand, RTA (rapid thermal annealing) oxidizes the quantum dot surface by rapidly increasing the temperature compared to oxidation treatment using a furnace. For example, oxidation treatment using RTA takes several seconds (eg, 10 seconds or less) of temperature increase time, and it is possible to precisely control the oxidation state by heat treatment for a desired time at a higher temperature.

As such, when the oxidation state of the surface of the quantum dot is treated with RTA, the crystal structure change of the quantum dot, a problem that occurs when the oxidation state of the surface of the quantum dot is treated with a furnace, does not occur. This RTA oxidation treatment is different from the heat treatment for the purpose of increasing the crystal quality during the layer crystallization process.

4 to 6 are diagrams for comparing the effects of the oxidation treatment method using the RTA and the furnace, according to various embodiments of the present invention.

4 is a graph showing the oxidation state of the surface of the quantum dot that is not oxidized and the oxidation state of the surface of the quantum dot that has been oxidized in a furnace at 100 °C, obtained through XPS measurement.

The area indicated by the arrow in FIG. 4 is a problem area that occurs due to excessive oxidation of the surface when oxidation treatment is performed with a furnace. Despite the heat treatment at 100 °C in an electric furnace, there is a problem in that many regions with excessive oxidation are generated.

On the other hand, in the case of oxidation treatment with RTA, the generation of the problem region of FIG. 4 can be suppressed. As shown in [Table 1] below, the lower Pb-O ratio in the case of treatment with RTA than when the oxidation treatment with a furnace indicates that excessive oxidation is suppressed when oxidation treatment with RTA. .

[Table 1]

This suppression of excessive oxidation indicates that the RTA oxidation treatment can obtain quantum dots having better device performance than the furnace oxidation treatment.

5 is a graph showing the specific detectivity (D*, specific detectivity) of quantum dots subjected to RTA oxidation treatment and furnace oxidation treatment at the same temperature (135 °C).

As shown in FIG. 5 , in the case of RTA oxidation treatment, quantum dots having higher specificity and detectability can be obtained.

6 is a graph showing half-width at half-maxima (HWHM) of quantum dots subjected to RTA oxidation treatment and furnace oxidation treatment at the same temperature.

The half-width is a factor related to the quantum confinement effect, which is one of the intrinsic characteristics of quantum dots, and can be used as an index in the first excitation absorption. It indicates that the larger the half width, the worse the quantum confinement effect.

As shown in FIG. 6 , quantum dots having a higher quantum confinement effect can be obtained when the entire RTA oxidation treatment is performed. In particular, it indicates that the quantum confinement effect is deteriorated when the furnace oxidation treatment is performed at the same temperature.

In one embodiment, the RTA may be performed at a temperature greater than or equal to 100 °C and less than 170 °C. In some embodiments, the RTA may be performed at 135°C or higher.

7 to 9 are diagrams for explaining the temperature in the RTA oxidation process, according to various embodiments of the present invention.

The graphs of FIGS. 7 to 9 show: an electrode made of Ti (10 nm)/Au (100 nm) was deposited by e-beam evaporation on a cleaned Si/SiO2 substrate (300 nm); After ligand exchange with TBAI (10 mg/ml) in methanol, spin coating, and washing 3 times with methanol were repeated 10 times to form a 350 nm-thick quantum dot thin film, RTA oxidation treatment or furnace oxidation treatment It is shown using the obtained photo-conductor.

7 is a graph showing the measurement results of infrared (IR) absorption spectra of the PbS quantum dot thin film at various temperatures. After reaching the target temperature, the furnace oxidation treatment was performed in the air for 20 minutes, and the RTA oxidation treatment was performed for 30 seconds after reaching the target temperature.

Compared to the peak width of the experimental example in which the simple quantum dot thin film was coated without oxidation treatment, the peak width of the oxidation-treated experimental example increased at 170° C. when using RTA, and increased at 100° C. when using a furnace. This increase indicates that atomic diffusion occurs in the quantum dot thin film and necking or sintering of the quantum dot thin film proceeds. That is, the degradation of the quantum confinement effect does not start below 170° C. for RTA. In addition, the RTA oxidation treatment does not occur at a temperature of 100° C. or higher (less than 170° C.) at which deterioration of the quantum confinement effect occurs in the furnace oxidation treatment.

8 is a graph showing the reactivity (responsivity) of the quantum dot thin film in the optical power (optical power).

A quantum dot thin film corresponding to a decrease in reactivity compared to a change in optical power has a more sensitive reactivity (ie, high device performance).

As shown in FIG. 8 , the RTA oxidation treatment shows a smaller decrease than the furnace oxidation treatment.

9 is a graph showing the specificity detection degree (D*) of the photoconductor. The specificity detectability (D*), along with the reactivity, depends on the incident light power and the modulation frequency of the light. In the experimental example of RTA-135, it has 1.59 x 10^13 Jones on 95pw, and is the highest specificity detectability (D*) value. In the case of the oxidation treatment for a long time, the gain increases, but the frequency response may decrease, so it is difficult to achieve a high specificity detectability (D*) value in a high frequency region.

In this way, through the RTA oxidation treatment, the surface of the quantum dot is treated at a high temperature for a fast time, so that an optical device with reduced noise, higher detectability, and increased reactivity can be obtained.

Although the present invention as described above has been described with reference to the embodiments shown in the drawings, it will be understood that these are merely exemplary and that various modifications and variations of the embodiments are possible therefrom by those of ordinary skill in the art. However, such modifications should be considered to be within the technical protection scope of the present invention. Accordingly, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

Claims (9)

forming one or more electrodes on a substrate;
forming a quantum dot layer electrically connected to the electrode; and
Comprising the step of oxidizing the surface of the quantum dot layer to form an oxide film,
The oxidation treatment is an optical element manufacturing method, characterized in that RTA (Rapid Thermal Annealing) oxidation treatment.
According to claim 1,
The quantum dot layer,
A method of manufacturing an optical device, characterized in that it consists of a colloidal semiconductor material.
3. The method of claim 2,
The quantum dot layer,
II-VI compound, II-V compound, III-VI compound, III-V compound, IV-VI compound, I-III-VI compound, II-IV-VI compound, II-IV- A method of manufacturing an optical device, comprising a material selected from any one of group V compounds and combinations thereof.
delete According to claim 1,
The RTA oxidation treatment is an optical device manufacturing method, characterized in that the surface of the quantum dot is oxidized so that the crystal structure of the quantum dot layer is not changed due to atomic diffusion.
6. The method of claim 5,
The RTA oxidation treatment, an optical element manufacturing method, characterized in that performed in a temperature range of 100 °C or more and less than 170 °C.
Board;
one or more electrodes formed on the substrate; and
a quantum dot layer electrically connected to the electrode;
The surface of the quantum dot layer is an optical device, characterized in that RTA oxidation treatment.
delete 8. The method of claim 7,
The optical device, characterized in that it further comprises an oxide film formed by RTA oxidation treatment on the surface of the quantum dot layer.

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